FUEL INJECTION CALIBRATION
Calibrating a fuel injection unit is similar to selecting the right jets,
power valve, and accelerator pump cam for a Holley carburetor.
||The blackened horizontal screw on the left is the Economy Stop;
the screw on the right is the Power Stop.
Calibration means positioning the enrichment lever stops so that the
unit has the best nozzle fuel pressures for efficient combustion. The
two stops have an extremely wide range of adjustment. They can be set
to provide nozzle fuel pressures that are much higher or lower than GM
recommended pressures. The "economy" stop position controls
the fuel pressure at steady cruising speeds. Under acceleration, the enrichment
lever moves to the "power" stop to control the nozzle fuel pressure.
The enrichment lever will stay on the power stop as long as the car is
under hard acceleration.
One common misconception is that stop positions can be set on a workbench
by using a vacuum gauge plumbed to the enrichment diaphragm. Actually,
the only way to determine the proper stop positions is to measure the
nozzle fuel pressure OR gauge the air / fuel ratio with an accurate exhaust
gas analyzer. Both of these methods require the FI unit to be installed
on a running engine. Once the stop positions are set, you then use a vacuum
gauge to set the length of the enrichment diaphragm rod. The rod length
controls when the enrichment lever travels from the economy stop to the
power stop. This is similar to setting the timing of the accelerator pump
shot on a carburetor.
The calibration will affect the settings of the other adjustable features
on your fuel injection. In other words, you must properly calibrate a
unit before you set the idle mixture, choke position, etc.
These are the other adjustable features that allow each Rochester FI
unit to be custom tuned to work properly with a particular cam grind and
- Idle speed (idle speed screw)
- Idle fuel mixture (idle mixture screw)
- Fast idle speed (fast idle speed screw)
- Cold enrichment / choke fuel mixture (bakelite cover / choke butterfly
- Timing of enrichment lever movement (enrichment diaphragm rod length)
INSTALLATION, START-UP, AND MAINTENANCE
It's important to use top quality parts in your ignition system. I recommend installing a new Delco plug wire set. I never use those "properly dated" reproduction plug wires because of their tendency to misfire under load. I prefer to use new ignition coils rather than 40 - 50 year old GM originals. You can buy new plug wires and coils from K&B Special Products near Atlanta. Their phone number is (770) 777-1031. The K&B Delco coils fit in original Corvette coil brackets and work properly with a stock low-resistance ballast resister. An excellent spark plug available today for injected Corvettes is the Autolite #295. This plug is a non-resister design equivalent to the discontinued AC 46.
You can easily break the mounting ears on the 1963 - '65 plenum feet
by over-tightening. Do not apply more than 5 ft-lbs. of torque to the
hold-down nuts when installing the plenum on the adapter manifold.
When replacing the '63 - '65 plenum cover seal, use a soft rubber reproduction
version. Do not use a rigid seal like those installed by GM. A hard seal
will not conform to the shape of the plenum and can cause the cover to
crack when it is fastened down.
||This is a Piston Stop Tool made from an old spark plug and hardware
Use black RTV silicone sealer on the engine block at the ends of the adapter manifold rather than the pre-formed rubber or cork seals that come in intake manifold gasket sets. This reduces the risk of cracking the corners of the manifold. Tighten the manifold-to-head bolts to no more than 25 ft-lbs. I usually tighten the front bolt on each side to 5 ft-lbs. less than the others. Also, use silicone sealer around the water jacket openings in the cylinder heads where they mate to the adapter manifold.
Confirm that that the Top Dead Center mark on the harmonic balancer is
properly matched to the "0" on the timing chain cover scale.
Chevrolet offered high performance small block balancers with the timing
mark in several different locations over the years. You can check the
location of your TDC balancer mark by using a piston stop tool.
If your distributor has a vacuum advance canister, it should be disconnected while setting the timing. You should make sure the total amount of mechanical advance is 36 degrees at high rpm. You'll probably find that 8 degrees of initial advance will give you 36 degrees total in a '57 FI distributor. The '58 - '65 distributor initial timing when using either the Duntov "097" cam or the later "30-30" cam should be 12 - 16 degrees.
If you're installing a 7017380 series unit, remember to plug the purple
wire into the micro-switch. It also plugs into the ignition harness just
above the windshield wiper motor. If you forget to install this wire,
the engine will not start.
Check to make certain the throttle butterfly is fully open when the accelerator
pedal is pressed to the floor. The accelerator linkage rod length is adjustable.
Make sure the bellcrank return spring is strong enough to fully close
the throttle butterfly every time. Some reproduction pull-back springs
are too weak to work properly.
If a quick first time start-up is important to you, pre-fill the fuel
bowl through the top vent before installing the unit. You will have to
remove the top fuel meter bracket and screen first in order to do this.
Modern gasoline has a relatively low boiling point compared to gas sold
during the sixties. If you experience a rough idle due to percolation
(gas boiling in the distribution spider), use undiluted racing gas instead
of pump gas. Racing gas has a 50% boil-off temperature over 210 degrees.
Aviation gas won't fix a percolation problem. It has about the same 50%
boil-off temperature as pump gas, which is often as low as 150 degrees.
Blends of racing gas with pump gas don't seem to help either.
After the engine has warmed up, hold the accelerator pedal at least 3/4
to the floor while turning the key to start. This prevents flooding.
Always start and drive your injected car at least once a month. Keep
fresh gas in the tank. Pump gasoline has a shelf life of about one year.
Racing gas has stabilizers that allow it to last much longer.
If your unit has a cranking signal valve, assume it will be the next
FI part to fail. The primary symptom of CSV failure is an excessively
rich fuel mixture.
Always carry a spare gear pump drive cable with you. You may never need
one, but if you do break a drive cable on the road, your engine will not
run until you replace it.
SHIPPING A FUEL INJECTION UNIT
||U-Haul Moving Centers sell cardboard boxes in several large sizes.
Rough handling by a parcel delivery service can do more damage to your FI unit in 2 seconds than you will cause by driving it hard for thirty years. The best way to protect your FI system is to "double box" it yourself before shipping. Double boxing is not difficult or expensive; it just takes some additional time.
First, empty all the gas from the fuel meter by turning your unit on its side. Then pack the unit inside a cardboard box that fits fairly close around it on all sides. Ship the plenum mounted on the adapter manifold. A good box for this is sold by U-Haul Rental Centers. This box is 22" x 15" x 12", and U-Haul calls it a "Legal Tote Box". Fill the open spaces inside this box with bubble wrap or wadded up paper so your FI unit can't move around. Do not put any Styrofoam packing peanuts inside the box with the unit.
Next, place the distributor (less cap) inside its own tightly fitting cardboard box. It's very easy for the iron and steel distributor parts to nick and scratch the aluminum parts of your unit if you don't put the distributor in its own box.
Now place the distributor and FI unit boxes inside a large box that will hold them both. The U-Haul size appropriate for this is 24" x 24" x 18". It's called an "Extra Large Box". The two inner boxes should fit inside the outside box with at least an inch of open space on each side. Fill the open spaces between the inner boxes and outer box with Styrofoam packing peanuts.
Packing supplies such as cardboard boxes, bubble wrap, and packing peanuts are sold at almost all FedEx Office stores as well as U-Haul Moving Centers.
Personally, I prefer to use FedEx Ground. I've never had to file a damage claim with them, and their delivery times are usually no more than 3 or 4 days from anywhere in the continental U.S.
If you're shipping an FI unit to me, please use my residence address: Jerry Bramlett, 151 Levert Ave., Mobile, AL, 36607.
ROAD TESTING VS. STATIONARY TEST ENGINES
For many years I used a stationary Corvette engine on a test stand to
calibrate fuel injection units. While I was always able to calibrate units
to GM specifications using this set-up, some running problems didn't show
their symptoms at all while the unit was being tested.
||Always use an air cleaner when calibrating or testing an FI system.
Without any air cleaner, the fuel mixture will be about 10% leaner
than with an air cleaner.
I decided several years ago that stationary testing wasn't good enough
for my customers. No FI owner wants to be turned into a test monkey by
his mechanic. I needed to be certain that I had found and corrected all
running problems before I shipped an FI system back to its owner.
An engine must be under a heavy load to fully test the performance of
the FI system. For example, on an unloaded stationary engine an FI pump
with excessive gear clearance will provide enough fuel to rev the engine
to 5,000 rpm. However, in a 3000 pound Corvette test car, a pump with
loose gears will cause the engine to fall on its face when you floor the
accelerator pedal. There really isn't a practical way to simulate every
effect of car acceleration on the FI system other than to install it on a
Corvette and drive it hard.
My testing program includes driving every FI system I repair under real-world
conditions. I also use an instrumented chassis dynamometer to check the air/fuel
ratios of each unit under acceleration and cruising loads. To handle this testing
I maintain three Corvettes set up to receive customer units and distributors. Two
are 1963 convertibles. The third test car is a '57 model.
I keep my own FI adapter manifolds installed on these test cars. That
way I can quickly install and remove the customer's unit and distributor
without draining any engine coolant. My road testing includes some cold
engine operation as well as some steady speed cruising after warm-up.
The toughest test of any unit is hard acceleration through at least three
gears, and I perform this test at least twice.
I've learned a lot through my road testing program. I doubt I would have
ever encountered some of the FI problems I've had to solve if I had just
kept using that stationary engine test stand.
COLD ENRICHMENT / CHOKE DESIGN PROBLEMS
Let's face it… GM never did get the cold enrichment system design quite right for the '57 - '65 Corvette fuel injection units. They did come close with the '63 - '65 hot air choke design, but even that one needs help to work properly.
The design of the '57 - '61 cold enrichment mechanism was an evolving bad joke. It worked as well as a broken clock; it would be right occasionally, but not very often. Its biggest problem was the on-or-off way it richened the A/F mixture.
||This is a '58 - '61 cold enrichment housing with the bakelite
cover assembly removed. The piston on the left cuts off vacuum to
the enrichment diaphragm when it is fully extended. The larger piston
on the right sends a vacuum signal boost to the main diaphragm when
it is depressed.
The cold enrichment came on and went away in one distinct, rather than many gradual, steps. Initially no vacuum would be sent to the fuel meter enrichment diaphragm. This kept the lever parked on the power stop during the first minute of operation. The result was a super-rich mixture until the enrichment lever was allowed to swing over to the economy stop.
This system used an electric heat coil to control activation. This coil usually cooled off much faster than the engine block. When an owner would re-start his car after letting it sit only 20 - 30 minutes, the cold enrichment system would be activated although the warm engine didn't really need an over-rich mixture.
The first true "choke" type FI cold enrichment system was introduced
in 1962. It featured a butterfly plate in the air meter controlled by
an electrically heated coil. While it did come on and go away in a gradual
motion, it was problematic too. The coil still cooled off faster than
the engine. A new problem was introduced as well. The steel butterfly
plate was installed on a relatively flexible aluminum shaft. That shaft
passed through four (count-'em) four holes in the pot metal venturi cone.
Over many heating / cooling cycles the pot metal cone would warp. This
would throw the four shaft holes out of alignment, causing the butterfly
shaft to bind.
Chevrolet finally went to an exhaust heat controlled choke in 1963. This
made the choke activation more a function of true engine heat. The steel
choke butterfly was still installed on an aluminum shaft. In this design
it passed though "only" three holes in the pot metal venturi
cone. However, the shaft would still bind due to changing dimensions after
many heating cycles. A new problem was the over-rich mixture caused by
the butterfly being too restrictive to air flow when the choke was fully
I believe GM tried to correct the '63 - '65 choke over-rich problem by
selling an "FI Choke Modification Kit" at their parts counters.
The kit included a choke pull-off piston to be installed in the choke
housing, a more aggressive fast idle cam, and a weaker bimetallic spring
on a new choke cover. This kit is best remembered for introducing a new
problem. Engine manifold vacuum would move the pull-off piston down when
the engine was running. This piston motion would hold the choke butterfly
open against the closing force of the bimetallic spring until the spring
warmed up. However, carbon / dirt would build up in the piston bore and
eventually cause the piston to stick.
There's really not much you can do to improve the operation of the '57
- '61 FI cold enrichment systems. I'll admit they will work adequately
to get you down the road when the engine is cold. You'll just have to
tolerate the over-rich mixture they produce initially.
You can make several simple improvements to the '62 - '65 choke systems.
First, you can align-bore the choke shaft holes in the venturi cone slightly
over-size. This will allow the aluminum butterfly shaft to rotate freely
again. I would also recommend buying a reproduction butterfly plate and
cutting a large window in it. This will effectively lean out the mixture
when the butterfly is closed without having to endure the hassles caused
by installing a sticking pull-off piston in the choke housing.
MODERN PUMP GAS ISN'T GOOD ENOUGH
Until November, 2011, I used pump premium gasoline for all my road testing and calibration work. Occasionally I'd get a bad tankful at some station and have to replace it with a different brand, but that happened only once or twice a year. Unfortunately, I consider those years the "good ol' days". Today the pump premium sold here in Mobile is unacceptable for use in Rochester injected Corvettes. Now I use undiluted racing gas exclusively in my test cars.
||On a '57 - '62 unit, make sure there is an air gap between the
top of the spider hub and the bottom surface of the plenum.
Modern pump gas can cause FI running problems throughout the RPM range. You're probably familiar with the poor idle caused by percolation (boiling) of pump gasoline in the distribution spider. You may not have heard about the problems it causes during cruising and at high rpm though. Those problems are a little tougher to detect.
It took four hours on the chassis dyno for me to understand the Air / Fuel ratio differences between running modern pump gas and true racing gas. I was in shock by the end of that test session. I found that pump gas burns much leaner at idle (below 1,000 rpm) and high rpm (above 4,000 rpm) during hot weather than racing gas. Oddly, pump gas burns richer than racing gas at legal cruising speeds (30 to 70 mph). This means that although your car will run on pump gas, it won't run its best. In the summer your idle will be rough after the engine is fully warm, and you'll foul spark plugs more frequently while cruising. This also means sustained engine operation (many minutes) at very high rpm (above 5,000 rpm) with pump gas could burn a hole in a piston or a head gasket on a hot day.
Here's my opinion why modern pump gas doesn't calibrate properly in old Rochester FI units. Gasoline is a mixture of many components. These components have different physical characteristics. Some are "light ends", and vaporize at relatively low temperatures at atmospheric pressure. This fact isn't apparent when you see the published vapor pressure of gasoline because it's an average for the entire mixture.
At idle, the distribution spider is only pressurized to 0.25 pounds per square inch. This is very near atmospheric pressure. A significant portion of modern pump gasoline will vaporize inside a hot spider hub at such a low pressure. This causes the Air / Fuel mixture at the nozzles to go lean. It may not be lean enough for your seat-of-the-pants gauge to detect, but I can certainly see it going lean using the dynamometer control panel instrumentation.
The high speed lean-out is caused by a similar, but different, vaporization problem. All pumps need a certain amount of feed pressure on the suction side to maintain liquid flow at the design pumping rate. If this feed pressure (called "Net Positive Suction Head") is less than required by the pump design, the incoming liquid will partially vaporize into bubbles. It's called "pump suction cavitation" when this happens. Bottom line: a pump that doesn't have enough Net Positive Suction Head will not flow as much liquid as it should.
The amount of Net Positive Suction Head is determined by the height of the liquid feeding the pump suction side and the physical properties of that liquid at pumping temperature. Hot modern pump gasoline less than 3" high in the fuel bowl doesn't provide squat for NPSH. I can see exactly when gear pump cavitation starts while watching the dyno control panel. On a hot day, it can occur as low as 4,000 rpm under full acceleration load. It only gets worse as the rpm's climb. By 5,000 rpm, cavitation can cause a mixture as lean as 18:1. That's lean enough under load to hurt some engine parts if you don't take your foot out of it.
Pump gas burning richer than racing gas while cruising is not a big shock to me. After all, octane rating is often indirectly related to volatility. Because it is more volatile, I believe modern pump gas burns more efficiently than racing gas at relatively low engine compression ratios. Running slightly rich while cruising won't cause any major problem. It may foul spark plugs a little sooner than running the right A/F ratio, however.
You can run 100LL Aviation gasoline, but it won't help much. Those special gasoline additives sold at auto parts stores don't have any significant effect either. Neither does the additive sold at swap meets that is 99% kerosene. I've tried the thick, one-piece, plenum to baseplate gasket too. It was no help. Insulating the gas line from the engine fuel pump to the FI fuel meter makes things worse.
The best course is to just run 100% racing gas. I use the VP brand with a 110 octane rating, but other brands of racing gas would probably work just as well. I tried cutting it 50% with pump premium to save money, but the running problems were still there.
CLIFF'S VERSION: Your FI unit will start and cruise on modern pump gas, it just won't idle consistently at 800 rpm or perform its best in hot weather unless you run racing gas. This is due to pump gas boiling in the spider. I know of no FI modification or fuel additive that will completely prevent pump gas boiling at very low nozzle pressures during hot weather.
'63 - '65 SPIDER DESIGN PROBLEMS
I believe GM was very aware of the spider percolation problem in early
Rochester FI units. They tried several fixes to eliminate the problem.
The first was to isolate the spider from the heat radiating upward from
the adapter manifold. In 1957 and most of 1958 fuel injected Corvettes
were fitted from the assembly line with a thick, one-piece cardboard gasket
/ heat shield between the plenum and the adapter manifold. This proved
ineffective, so the large gasket wasn't used on later units. The next
cure they tried did have some positive effect on the idle percolation
problem, but it also introduced a new problem that wasn't apparent for
||These are the parts inside a 1963 - 1965 spider center hub. If
that tiny, weak spring ever loses its tension or gets gummed up, the
spider will perform poorly.
In 1963 the gas feed circuit to the distribution spider was made into
a loop. Instead of getting gas that had been through the spill valve,
the spider now received only some of the gas from the gear pump while
it was on its way to the spill valve. This new design circulated more
of the relatively cool gasoline from the fuel meter through the spider
hub. I think that's why the '63 - '65 FI units don't have as bad an idle
percolation problem as the pre-'63 units.
The down side of this spider feed loop arrangement is its effect on the
spider hub design. The anti-siphon needle valve was gravity operated from
1957 through 1962. In 1963 though, gravity could not be used. The spider
hub had been inverted to make more room for the fuel supply loop. This
made the hub needle valve "upside-down". A tiny spring had to
be installed below the needle valve to shut it when the engine was turned
off. This new spring-loaded needle valve design had an unintended effect:
it provided a variable resistance to gas flow into the spider. The more
the spring was compressed by gasoline flow, the more backpressure it produced.
The previous gravity-operated needle valve had a constant amount of backpressure
essentially equal to the weight of the needle valve.
I believe this variable resistance of the spider hub spring was properly
considered in the engineering design of the '63 - '65 FI units. However,
the manufacturer of these tiny springs probably didn't have good quality
control. I believe that many spiders were assembled with springs that
had significantly different spring rates than what GM specified. I believe
this because about 30% of the '63 - '65 spiders that I check flunk one
of my driving tests.
I call this my "freefall-to-idle" test. It works like this.
[WARNING: Do not try this in your driveway.] After warming up the engine,
I stand on the accelerator pedal through three gears. I then suddenly
take my foot off the accelerator pedal and disengage the clutch at the
same time. This allows the engine speed to freefall from about 5,500 rpm
to an 800 rpm idle without any resistance from the drivetrain. At this
point the FI system has been running full rich for about ten seconds.
It has fully compressed the spider hub needle valve spring during that
period. Now the FI system has to immediately create a much leaner mixture.
The spring has to extend to the precise location necessary to support
an idle. Evidently that's a hard test for an imperfect spider to pass.
If the spring is defective, the resulting idle mixture will immediately
be too rich or too lean and the engine will die.
CRANKING SIGNAL VALVE STARTING PROBLEMS
Almost all fuel injected Corvettes with starting problems are equipped
with Cranking Signal Valves. The CSV is an ingenious device that just
doesnt work very reliably in the real world. It is designed to pass
about 1 water of manifold (plenum) vacuum to the main diaphragm
to make an FI unit squirt gas from its nozzles during engine cranking.
When the engine starts and the plenum vacuum jumps above 19" water
(1.4" mercury), the CSV is supposed to shut tight. Well, that was
the original theory anyway. Early FI Corvette owners quickly found that
the CSV could suddenly fail with no warning. However, it almost always
failed partially open. This allowed too much plenum vacuum to the main
diaphragm, making the FI unit run very rich. Once a CSV failed you could
still start the engine, but it would run so rich it wouldnt idle
||If your Corvette won't cold-start immediately after a three second
blast of ether, then the problem isn't in the fuel injection unit.
A Corvette engine with the 097 "Duntov" camshaft can make as
much as 22" water vacuum in the plenum while cranking IF the throttle
is fully shut and the Cranking Signal Valve is not bleeding off any vacuum
to the main diaphragm. However, these aren't normal cold starting conditions
for FI engines. Usually the throttle is partially open because of the
fast idle cam position. Also, the Cranking Signal Valve is letting some
of the plenum vacuum go to the main diaphragm. Under typical cold start
conditions for FI engines, the plenum vacuum varies in rapid pulses between
4" and 7" of water. This lower-than-optimum plenum vacuum is
actually a good thing. If the plenum vacuum was over 14" water, the
Cranking Signal Valve would be essentially shut and should not pass enough
vacuum to make the FI unit squirt any fuel from the nozzles.
You're probably wondering how much vacuum is required at the main diaphragm
for an FI unit to shoot a steady stream of fuel from the nozzles at cranking
speed (150 - 200 rpm). The answer may surprise you; it certainly did me
when I tested two units to find out. Only .5" to .7" water vacuum
is needed at the main diaphragm during cranking to generate a good fuel
stream at all nozzles. That's not very much vacuum. Engine manifold (plenum)
vacuum is normally measured in inches of mercury. One inch of mercury
vacuum equals 13.6 inches of water vacuum. This means that plenum vacuum
during a normal cold start is less than .5" mercury, and that only
about .07" mercury vacuum is passed by the CSV to the main diaphragm.
My tests of Cranking Signal Valves were also a little surprising to me.
I found that the plenum vacuum passed by these valves is extremely low.
Under normal cold engine cranking conditions (rapidly pulsing 4"
- 7" water plenum vacuum), most good cranking signal valves will
pass about 1" water vacuum. The dozen CSV valves I tested passed
the highest vacuum to the main diaphragm when the plenum vacuum (at the
threaded CSV nipple) was only 2" water. Above that plenum vacuum
level, the vacuum passed by the CSV went down quite rapidly. Most good
CSV's stop passing any significant vacuum at about 14" water plenum
I believe these are the leading causes of CSV equipped FI engines failing
to start quickly when cold:
- A low gas level in the fuel meter bowl.
- A tiny vacuum leak at the main diaphragm or in the signal tubing
connections above it.
- Too much liquid gas in the cylinders (liquid gasoline won't explode,
it has to vaporize first).
- A spill valve that is not fully seated (causing it to sit low in
the fuel meter casting).
- A very slow engine cranking speed (not generating enough plenum vacuum).
- Too much plenum vacuum during cranking (shutting the CSV).
HOMEMADE FUEL INJECTION TOOLS
Over the years I've constructed four special tools to help me work on
fuel injected Corvette engines. None of them are high tech, but they still
save me a lot of time.
- Tool #4: Oil Seal Installer
This tool is a long bolt with several nuts and washers for pulling a
distributor mainshaft oil seal into place. The large nut acts as a slip
collar to protect the top of the distributor while the bolt and small
nut are turned with wrenches.
I'm often asked if a Rochester injection system will work properly on
a highly modified small block. The key to the answer is the camshaft used.
That's because a Rochester FI system uses engine rpm, plenum manifold
vacuum, and air meter venturi vacuum levels to determine how much gas
to squirt from the nozzles. The injection unit doesn't know what displacement
engine is sitting under it. The injection doesn't really care about the
compression ratio either. However, the unit does know and care
how hard the engine is sucking on the manifold runners at all running
speeds. And, the engine vacuum / rpm curve is primarily determined by
the profile of the cam lobes.
It's possible to redesign the axle link, spill valve, enrichment lever,
and idle vacuum signal systems to work with a very radical aftermarket
camshaft. Well, at least it's possible in theory. It's certainly not practical
though, and I'm not about to attempt to do it for a customer. It makes
much more sense to me to confine engine modifications to installing better
flowing cylinder heads and a using a larger displacement block. I would
definitely install a mild camshaft with a near-stock profile if I was
going to use Rochester fuel injection. By mild, I mean a cam that produces
at least a steady 12 inches of mercury vacuum in the plenum at an 850
rpm idle speed.
Chevrolet used two different high performance camshafts with Rochester
fuel injection on the assembly line. The first of these cams, used in
'57 through '61 283 engines, was the "Duntov" or "097"
solid lifter design. This same cam was also used in the '62 - '63 327
fuel injected Corvette engines. I know through my own testing that the
097 cam will produce 13 to 14 inches of vacuum at an 800 rpm idle IF the
lash is set at .012" on the intake and .018" on the exhaust valves.
Chevrolet used a much more radical cam in the '64 - '65 327 fuel injected
engines. This cam is known as the "30-30" or 375hp solid lifter
cam. This cam usually produces about 12 inches of steady vacuum at 850
rpm if the lash is set at .030" and .030". I say "usually"
because some modern aftermarket versions of this cam require more lash
than .030/.030" to reach this level of vacuum. Some brands need as
much as.035" lash on both intake and exhaust valves to make acceptable
vacuum at low engine speeds. I suggest you buy a Federal Mogul / Speed
Pro copy of the 30-30 cam to avoid using larger lash settings. Their copy
of the 30-30 cam is sold under their part number CS-118R. Their copy of
the 097 cam is sold under part number CS-113R.
These two cams aren't the only grinds that will work with Rochester FI.
The old 327/350hp hydraulic cam will work just fine too. So will the 1970
- '72 LT-1 solid lifter cam. There are probably many more acceptable cams
that I haven't ever tried. Just remember to check the plenum (manifold)
vacuum level at an 850 rpm idle speed to determine if your cam is making
enough vacuum to use Rochester injection. If you come up with less than
12 inches, then you're going to have a drivability problem that will be
extremely hard to ignore around town. Out on the freeway it won't make
a significant difference in driving sensation. So, if you insisted on
using a radical cam in an injected engine, I guess you could just keep
the revs over 3,000 all the time. Yeah.....now THAT'S the ticket for a
relaxing cruise around town!
CHEVROLET FUEL INJECTION DISTRIBUTORS
Over the nine model years that Chevrolet offered Rochester fuel injection,
they assembled 12.5 different V-8 distributor designs to drive the fuel
meter gear pumps. The extra "half design" was a slightly modified
service distributor that bore the same part number as the 1111070 assembly
line distributor. All of these distributor designs will work with any
Rochester '57 - '65 small block Chevrolet FI system. However, some of
the designs had features that make them less than perfect for today's
This information was compiled with the help of Don Baker. I consider
Don the leading expert on Rochester FI distributors. His machining skills
are unmatched. When I encounter a distributor that needs more repair than
I can provide, I send it to Don. You can contact him in Sandwich, Illinois,
at (815) 498-9522.
- 1110889 -- This dual point distributor was the first design used
with the 283 horsepower fuel injected Corvette engines in 1957. It had
no vacuum advance mechanism or tach drive coupling. It's weak point is
the unsealed bearing that was used at the top of the mainshaft. Chevrolet
received owner complaints about oil-fouled points shortly after it hit
the streets. Their solution was to replace the 889 with a new distributor,
the 1110905. It's very difficult to find an 889 FI distributor in use
today. I doubt any 889's were installed on the assembly line after December,
1956. Also, many 889's installed in 1956 were quickly replaced with 905
distributors during 1957 while under warranty.
- 1110905 -- The 905 distributor was identical to the 889 with two
exceptions. It had a larger drain hole to take the oil away from the upper
gear chamber, and it had a sealed upper mainshaft bearing. It still had
dual points that were not externally adjustable, no vacuum advance, no
tach drive, and a two piece main body that allowed advance adjustments
without rotating the distributor base at the manifold. The 905 distributor
design was used in almost all of the 1957 model year 283 hp engines.
- 1110906 -- The 906 was the first FI distributor designed for use
with an automatic transmission. It was installed during the 1957 model
year only. It had single points that were not externally adjustable, and
it had no provision for tach drive. It also had a vacuum advance mechanism
with a hexagonal canister (stamped 125) and a threaded vacuum hose connection.
The 906 upper housing looked very similar to that of the 905. However,
the 906 upper housing was about 1/4" taller to accommodate a slot
for the vacuum advance canister. This taller housing required a taller
distributor mainshaft. The 906 point cam was also different from the 905
version. It used a slightly different rotor orientation for the single
set of points. Beware of those who offer a 906 that has been "converted
to 905 specs". This conversion can certainly be done, but proper
a conversion requires much more than filling the advance canister slot
with Bondo and installing a mounting plate for dual points.
- 1110908 -- The 908 design was the first FI distributor to have
a mechanical tach drive coupling. The cable end design (required to mate
with the distributor tach drive cross-shaft) was round with a "tang"
or ridge projecting from the side. Except for the tach drive, the 908
distributor was very similar to the 905 design. It had dual points that
weren't externally adjustable, and no vacuum advance. Many believe that
the 908 was first installed on the 1957 "air box" 283hp Corvettes
to drive their steering column mounted tachs. I believe that most 908
distributors were installed on early 1958 Corvettes with the 290 hp injected
- 1110914 -- This distributor was used in 1958 through 1961 solid
lifter FI engines. It had externally adjustable dual points, a tach drive
coupling, and no provisions for vacuum advance. The mainshaft top cam
(or "football") was stamped with the number 42. The points cam
was stamped 122. The mechanical advance weights were each stamped 37,
and most of these weights had an "extra" small hole in their
heavy ends. The upper housing of the 914 distributor used a much smaller
diameter clamp (than previous FI distributors) to hold it tight against
the lower housing. This smaller clamp design was used for all later FI
distributors. Beginning with the 914 model, all FI distributor lower housings
had a removable square data plate which allowed quick inspection of the
cross-shaft drive gear while the distributor was mounted in the engine.
- 1110915 -- This distributor was used in all the 1958 through 1961
FI engines with hydraulic cams. It had externally adjustable single points,
vacuum advance canister #134, and no provision for a tach drive. In place
of the tach drive coupling was a hex-head plug. This distributor was the
only FI design with a manual oiling tube projecting from the side of the
main housing. This tube provided oil through cotton wicking to lube the
upper housing vertical hub surface. The mainshaft top cam was stamped
73. The points cam was stamped 726 or 728. The distributor weights were
unmarked and were the same as those used in passenger cars.
- 1110990 -- This dual point distributor was used only in very early
1962 model FI engines. It had no vacuum advance, and the points were externally
adjustable. The mainshaft cam was stamped 54. The points cam was stamped
722. The advance weights were stamped 37, and most had the heavy end holes
- 1111011 -- This distributor was used in all of the later 1962
FI engines. It was identical to the 990 distributor design (dual points,
mainshaft cam #54, advance weights #37) except it sometimes used a points
cam stamped 724.
- 1111022 -- This distributor was used in all 1963 FI engines. It
was identical to the 011 (mainshaft cam #54, advance weights #37, points
cam #724) except for these three features: the 022 used single points,
it had a felt wick in a plastic stand for oiling the point cam, and it
had a vacuum advance mechanism. The advance canister was stamped 201 15.
The canister had the modern conical shape with a smooth nipple for the
hose connection. This canister required a relatively high amount of vacuum
for full advance. The hose from the canister was attached to a "ported"
connection on the air meter that did not provide vacuum at idle.
- 1111063 -- This distributor was used with the 7017375R series
FI systems that were installed in early 1964 model injected Corvettes.
It was identical to the 022 model (single points, vacuum advance, felt
wick for point cam, mainshaft cam #54, advance weights #37, point cam
#724) except for the advance canister used. The 063 advance canister was
a low-vacuum design stamped 236 16. The hose from it was attached to a
full-time vacuum connection on the plenum.
- 1111064 -- This distributor was the only model installed with
the '64 - '65 FI transister ignition system. It used the following parts:
advance canister 236 16, mainshaft cam #03, un-numbered advance weights
with a hole in the heavy end, and magnet rotating cam #736 (or possibly
#540 or #542). The cap used with this distributor still had the little
sliding door for external access to adjust points.
- 1111070 -- This distributor was used with most, and possibly all,
'64 and '65 7017380 series injection units. The assembly line version
had a 236 16 vacuum canister, a felt wick for the point cam, mainshaft
cam #03, point cam #732, and un-numbered advance weights with a hole on
the heavy end. Sometime after fuel injection was dropped as a production
option, the service versions of this distributor were changed slightly.
The felt wick for oiling the point cam was changed to a foam donut on
a plastic stand. Also, the point cam was changed to a number 536 and the
mainshaft cam became an 03W or had no stamped number at all. Most of the
distributor weights used in the service distributors lacked the extra
holes in the heavy end.
THE SHOCKING TRUTH ABOUT CALIBRATION ACCURACY!
||Click to enlarge scanned sheet.
Chevrolet first printed "Form 1514C, Fuel Injection Specifications"
in July of 1965 to document tuning info for all the FI model series from 1957
through 1965. Fuel injection mechanics have been using this one page data sheet
as their primary reference source for calibration settings ever since. At first
glance it seems to have all the data needed to calibrate a Rochester fuel injection
system installed on a stock Corvette engine. Well, except that a lot of the stop
settings listed are nonsense.
Frankly, I have no idea how most of the recommended nozzle pressures listed on
that sheet were determined. I've never seen a GM or Rochester chart showing the
nozzle orifice sizes originally installed in the 19 different FI model series. I
think having such a chart is essential to understanding why the author of Form 1514C
thought the calibration pressures he listed were appropriate. I've found through my
own hot testing that some of those listed set pressures just don't work well.
Engine displacement, compression ratio, camshaft grind, and engine load pretty
much determine the nozzle discharge volume needed at any particular rpm. Then, once
you pick a nozzle orifice size, it's a relatively straight-forward calculation to
determine how much fuel pressure at the nozzle inlet is optimum for each enrichment
lever stop setting. So.... why did the author of Form 1514C list so many different
stop settings for different unit series that were installed on nearly identical 283
engines with nearly identical nozzle sizes? It doesn't make any sense that a '57
7014520 series FI with Q nozzles should have stop settings about 50% higher than a
'58 7014900R unit with Q nozzles when they are both mounted on 283 engines with
the 097 Duntov cam.
My biggest objection to GM's "nozzle pressure" calibration method is
that it doesn't produce consistent air / fuel ratios from unit to unit. I believe
this is the result of two quality control (or engineering design) issues that Rochester
never addressed. Most importantly, I suspect the fuel meter gear pumps produced by
Rochester NEVER had identical performance curves, even when they were new. Now that
they have about fifty years of wear on them, I think the output of each pump varies
considerably. Also, consider this: the nozzle orifice discs were manufactured from
very thin stainless steel. These discs "take a set" when first subjected
to high gasoline pressure on one side. They inelasticly deform, in other words, and
that uniquely affects the shape, volume, and pressure of the fuel spray coming from
I've found that the only way to ensure correct air / fuel ratios is to calibrate
every unit on a hot engine using a chassis dynamometer. I've been doing this with
each unit I have restored since 2008. After I have the unit running well enough to
pass all my road tests, I rent a local chassis dyno to perform instrumented testing. The dynamometer computer display allows me to watch the air / fuel ratio in
real time as I fully accelerate and also as I cruise with a road resistance load. I
then adjust the stops until I can generate a computer print-out proving proper calibration.
A side benefit of this calibration method is that I can usually compensate for a slightly
worn gear pump and even some non-stock nozzle sizes.
I'll never again trust GM's "nozzle pressure" method to determine calibration
stop settings. It's just not accurate enough to satisfy me.
FI PROBLEMS IN THE IGNITION SYSTEM
When a phone caller asks me to diagnose a problem in his FI unit, I always give him the same initial advice: "First, don't take the unit apart". I say that because many fuel injection problems are actually in the ignition system. There's usually something significant that must be addressed beyond replacing the points, rotor, cap, and condenser with new parts.
Even after fifty years, the distributor cross-shaft gears and mainshaft bushings seldom have much wear IF the oil feed tubing has never been disconnected. But many times a past owner will have plugged the oil feed line while he ran an FI distributor with a carburetor. This is a serious mistake. The distributor needs that lubrication even when it's not powering the gear pump. Without the extra oil, the gears can wear out in the center of the teeth. You can tell if the gears are still good by looking at them. If the teeth are the same thickness throughout their length, then they're full strength. A shiny face is okay. However, if they're noticeably thinner in the middle, they should be replaced.
If so equipped, you must make sure the vacuum advance is still working and that it has the correct specs for your model year. The hexagonal '57 - '61 vacuum canister is no longer available new, but Standard Products still sells B22 canisters for '63 distributors and B28 canisters for the '64 - '65 distributors. By the way, these new canisters don't come with a rubber bushing to limit the amount of advance. You have to provide that yourself.
The contact points must have high tension springs to avoid point bounce at engine speeds over 5,000 rpm. I normally install Standard "Blue Streak" ignition parts. Standard has consolidated some part numbers over the years, but the good numbers used to be DR2336XP for '57 dual-point distributors, and DR2270XP for the later models. You'll have to cut off the lubrication wick on one set of the DR2270XP points to install them in a '58 - '62 dual-point distributor. I do that with a Dremel tool cut-off wheel.
I've found that some '58 - '65 FI distributors are worn in a way that makes the point dwell change at high rpm. This can be an issue if the dwell drops by more than 5 degrees. This problem could be due to up-and-down movement of the point cam on the mainshaft, or it might happen because of a warped lower housing... I just don't know. The only sure cure is replacing the points with an electronic spark trigger. I normally use the M & H single-wire design because I think it's very durable. The Pertronix set-ups work fine too... well, right up until the time they don't work at all. Take your pick.
Having the right coil and ballast resister is important too. But you shouldn't trust the part number to tell you if the coil is right. For years, one vendor in particular has sold genuine Delco coils with the right numbers but the wrong resistance across the primary windings. Evidently he's been taking old Delco coils from God-Knows-What vehicles and putting new metal skins over the bottom can. Check the electrical resistance across the small terminals on top of the coil. Your ohm meter should read 2.0 to 2.3 ohms when the coil is cold. If the resistance is much less than that, you're going to burn your points by passing too much current through them. If it's much more, you're going to have a high speed misfire because of a weak spark. The same test can be used for the ballast resister. It should have 0.3 to 0.6 ohms of resistance when cold.
Here's what I think of reproduction plug wires from Chicago and modern AC spark plugs: they suck. If you have those repro plug wires because they "look correct" with the fake dates, please use them for shows only. Eventually they will cause misfiring at high speeds. The same goes for AC resister type spark plugs. Since AC no longer makes a non-resister design, I suggest you use Autolite #295 plugs. Those plugs are equivalent to the old AC 46 heat range.
The mechanical advance curve is determined by the length of the slot in the point cam, the thickness of the bushing on the limit pin, the strength of the springs on top, and the mass of the weights that stretch the springs. I seldom receive a distributor with all those parts working properly. Some of them have usually been exchanged for aftermarket parts that don't fit or work right. In fact, most of the original factory advance springs don't work right either. They allow the mechanical advance to start below idle speed. That gives you an erratic idle speed as the engine hunts for a stable amount of spark advance.
I'm not going to list all the weird distributor aberrations I've come across. It would just depress you. It seems that all Delco fuel injection distributors were owned by Gyro Gearloose at one time, and Gyro "improved" them to the point of not running right. My advice is simply this: make sure your distributor is working properly before you even think about tearing down your fuel injection. You'll probably find at least some of the problems I routinely encounter.
MAKING A '57 FI UNIT RUN RIGHT
The most difficult challenge in the Rochester repair world is getting a 4360, 4520, 4800, 4960, or 7300 FI system to work properly. It's only been in the last few years that I've become confident these units can be made to run right. To get them to that level, you must make several modifications to the original designs, install perfect reproduction parts, and ensure every single component functions flawlessly. You Do-It-Ur-Selfers have now been warned.
You won't have much of a problem getting strong full-throttle acceleration. That's easy to do. It's creating the right air/fuel ratio at low cruising speeds, getting a consistent and smooth idle speed, and starting easily when cold that will have you pulling your hair out with a '57 unit. Here's why.
All '57 FI units were built with sand-cast fuel bowls. These bowls are very prone to "gumming up" with gas deposits, and they are extremely difficult to clean thoroughly. Gas varnish and corrosion sometimes hides between the steel spill valve sleeve and its aluminum casting bore. I haven't found a sure way to remove and re-install this sleeve without scarring the bore. And once the bore is scarred, you darn sure can't drill it oversize without also making some custom spill and fuel valve parts.
The spill and fuel valves in sand-cast bowls must have extremely close fits in their bores to work properly. A .001" side clearance is a relatively loose fit, and a .003" clearance is completely unacceptable. However, both the spill and fuel valve pistons must move very freely in their bores. So freely, in fact, that they will fall out from their own weight when placed in the dry sleeve while you're test-fitting them. This means you must carefully polish the sides without removing much material at all. Good luck with that.
The original axle links Rochester installed in the sand-cast bowls were very durable. It's not uncommon to find them still being used fifty years after the units were first assembled. But durable is not everything an axle link in a '57 unit needs to be. It must also be heavily counter-balanced to consistently return the spill valve to the exact position necessary for a proper idle mixture. I've found that Frank Antonicelli's newest reproduction axle link design works better than any GM or other reproduction axle link in a sand-cast fuel meter. Its counterweight is much heavier than that of a Rochester '57 axle link. That's why I think Frank's design works so well.
The main diaphragms GM put in their service "rebuild kits" were very good. Although the last batch of these diaphragms was made in 1975, most emerge in usable condition when found in NOS kits today. But the world is rapidly running out of NOS GM FI rebuild kits. Most of us have to make do with new reproduction diaphragms for our repair work. Here's what you should look for in a repro main diaphragm for a '57 FI unit: a high formed "hump" in the fabric around the magnesium center disc. Some of the modern repro diaphragms have almost no "hump". If you use one of the flat repro diaphragms in your '57 FI unit, you may not have enough sensitivity in your idle mixture screw to get a reliable idle speed. It could also limit the richness of your mixture under full acceleration.
The very first Rochester production design was the 7014360 FI series. These FI systems were such absolute turds that most were replaced by Chevy dealers before the '57 model year was over. They can be salvaged these days, however, if you modify them to function more like the 4520 series design. You must replace the one-piece nozzles with a good set of two-piece nozzles, install a single spider design from a '58 - '62 series, fill the off-idle boost port with epoxy, seal the upper bearing on the distributor mainshaft, install a '58 - '63 enrichment diaphragm spring, and eliminate the Coasting Shut-Off system in the fuel meter. Actually, Chevrolet introduced all of these improvements as running changes in later FI design series.
The second FI series installed during the '57 model year was the 7014520. This system was far from perfect, but it was a great improvement over the 4360 design. It used a single spider, had two-piece nozzles with internal screens, didn't have a CSO system, and came with an upper bearing seal in the distributor. But, it still had an enrichment diaphragm spring that was too short, a poor cold enrichment system, and the unnecessary off-idle boost port.
For the 4520 design, Rochester also modified the 4360 cold enrichment system. They changed it in two ways, both of them making it worse. The cold enrichment housing now had an internal "pull-off" piston that leaned out the A/F ratio on start-up. That's exactly when the fuel mixture needs to be super rich. Also, they sent plenum vacuum to the enrichment diaphragm immediately on cold start-up. That's why a 4520 unit will usually die right after the first start in cold weather. There's no way to keep the enrichment lever on the power stop for the first 30 seconds of running.
There isn't an easy fix for the 4520 "choke" deficiencies. You can eliminate the pull-off piston, but you can't make the enrichment lever stay on the power stop without installing a modified choke housing. And sure enough, that's what Rochester did when they came out with the 7014800 series FI design. The 4800 cold enrichment housing has no pull-off piston and does have a valve keeping vacuum from going to the enrichment diaphragm initially.
But back to the 4520 design flaws... Rochester hadn't yet figured out that the off-idle boost port (in the air meter bore) made low-speed cruise mixtures too rich. In fact, they increased the size of that detrimental boost port when they introduced the 4520 design! The port diameter was double the size used in the 4360 series! You absolutely must close this huge port or you'll have low-speed cruising air / fuel ratios as rich as full acceleration A/F ratios! You WILL have some prematurely fouled spark plugs if you don't plug this boost port.
By the time the 4800 FI series was introduced in mid-1957, Rochester was starting to see the problems caused by the off-idle boost port. They went back to a boost port size smaller than in the 4360 units. However, it still should be plugged to lean out the air / fuel mixtures while cruising at low speeds. As I explained above, Rochester improved the 4520 cold enrichment design for the 4800 series by removing the pull-off piston and installing a valve to keep the enrichment lever on the power stop initially.
The late-'57 7014960 and '59 7017300 series were based on left over 7014800 parts. Therefore the modifications necessary to make them run properly are exactly the same as those for the 4800.
The fine-tuning of 4360 through 4960 units can only be done on a properly running engine. For example, it's impossible to guess the right size for the restriction orifice inside the brass tee above the main diaphragm while on a workbench. You have to set the initial spark timing, run the unit until its fully warm, calibrate it under load, and then test its return-to-idle characteristics. If the engine sometimes dies rather than settle at a 750 rpm idle speed, then you may have too small an orifice in the tee. But maybe not.. it could also be a sticking spill valve, a plenum base vacuum leak, or an excessively lean idle mixture screw adjustment.
After making all these improvements, you'll still have to solve the same problems found in all Rochester FI units: the lack of an anti-siphon electric solenoid, the need for a closely matched set of stock nozzles, the necessity of having an efficient gear pump, etc. However, I'm guessing those ordinary issues will be a lot easier to deal with than solving the special '57 problems I've discussed in this write-up.
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