1960s era GM Constant-Flow Mechanical Fuel Injection

[tangel]

Good afternoon all,
I was curious if anyone had any notes or information on modifying the 57-65 GM/Rochester Mechanical Fuel Injection systems. Reason for my asking is I am getting involved in Vintage Racing 60's era corvettes and intend to run the systems on the race cars. I know there were a number of master's theses written on various experiments examining the performance and emissions capabilities of modified units. Unfortunately I am certain all of the work is probably older than SAE's searchable database (obviously couldn't find anything there). Thanks for the help!

 

[evelrod]

As far as vintage racing goes...The idea is to leave it as it was raced in the 60's. Laughable concept? Yup! As I race VARA it would seem that all the Chebby engines were conceived in the 80's (or later)!!! I know my '61 Vette (in '61/'62) would not turn 9000+ rpm...at least not more than once!

I do recall seeing several articles in Hot Rod about mods to 1st and 2nd gen Rochester units...Long time back but with photo layout for the challenged. You might, therefore, ck into the Peterson Publishing "How To" and "Engine" books.

Rod

 

[patprimmer]

Go to HRE.com

Jim Harvey there might have some info on Rochester MFI.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[evelrod]

I don't know where you are located but you might also check with Dick Guldstrand (racer friend and a really nice, helpful guy) at Guldstrand Motorsports (Burbank, I believe) If he does not know, no one does!

I also recall the Vic Edelbrock Jr's dad did some mods to the units back in the day...You might check with them. I think Vic races a fuelie in vintage.

Rod

 

[Metalguy]

I ran a 1965 Vette FI for years. One problem was the larger rubber diaphram would harden very fast. That caused the thing to run lean, esp. at idle. I buy a new one and it would run fine for a month or so.

Gold is for the mistress - silver for the maid
Copper for the craftsman cunning in his trade.
"Good!" said the Baron, sitting in his hall
But iron - cold iron is the master of them all.
Rudyard Kipling

 

[MikeHalloran]

The Rochester FI hit production around 1958. When first introduced, the metering system was serviced only as a (very expensive) unit.

By 1960, they had a field calibration technique worked out, using an electric drill to drive the flex cable that ran the fuel pump (normally driven from the distributor)... while catching the fuel dispensed from the loose manifold in a baking pan or something similar. Outdoors recommended, given the proximity of vaporized fuel and an ignition source.

It's covered in the 1960 Helm manual for Chevy passenger cars (all of them), in enough detail to help you understand how it works and what to do when it doesn't work.

I'm told it works very much like WW2 aircraft FI, except for the aspirating nozzles, which mean you have to keep the engine real clean.



Mike Halloran
Pembroke Pines, FL, USA

 

[dicer]

As far as performance mods, it is going to be the same as anyother fuel system. It will need to put out what ever the HP requirements of the engine are. (BSFC) It may mean modifying the injectors and the metering unit, as well as increasing air flow through the plenum and velocity stacks, ports etc. What do your rules allow? Kind of a shame to goof up an old Rochester FI unit though, they are pretty rare and expensive now. I bought one for $60.00 in 1971, and would see them all the time for $150. boy did I goof up. I would think spacing out and maybe a design change on the venturi cone would help, but then you'll loose some of the signal. Too bad there aren't some after market parts so you don't have to goof up original stuff.

 

[bentwings2]

I ran a 57 Chev 4 spd with the Rochester FI 283 hp in drag racing back in the very early '60's. It was one of only a few that GM made for the sedans as a NASCAR rule.

The first thing is to get some manuals and specifications. I had at one time a copy of virtually everything written about the things. Like a dummy I loaned the stuff to a friend and never got it back.

Clean is the word. There are some very small nozzles and tubes that just will not tolerate any dirt. A 2 micron fuel filter would be a must. Next it needs to be adjust to stock specs. If you are off a bit, it just isn't going to run very well. Remember this thing is mechanical and measures air flow mechanically so parts that move must move smoothly with absolutely no binding or sticking.

All rubber hoses need to be the right size and cannot leak. The slightest vacuum leak and you are dead.

The high pressure fuel pump drive cable was a real weak part and I always had half a dozen on hand as they were hard to get even back then. Today there are heavy duty or improved ones available. I don't have a supplier, sorry but I have talked to guys that run these in the streetrod groups and they still carry a spare.

The spill plunger needs to be adjusted carefully or the diaphram can be ruined. There are some fine threads here.

There were 2 or 3 sets of nozzles available. The ones off the 315 hp Vette were the ones to have as I recall. (dimmly)

Also be careful of using a 'ram air' system as the air flow signals can be disrupted.

I found that making the distributor run reliably to 7000 rpm (engine) was very important. Today that should not be hard unless you have to run points and condenser. Convert it to a dual point at least. The motor would go past that but rapidly lost power so I stayed at 6800 as a max shift point. I also ran with out a vac advance for drag racing and had full advance in by about 2600-2700 rpm. The 283 liked a lot of advance back then so 38 deg total worked well.

Once I got it set up, it ran very well, made a lot of hp and was a lot less trouble than the clutch, transmission, axels, drive shaft and rear end.

 

[tangel]

Thanks for the replies so far. I am in full agreement with your concerns of "ruining" a good original unit.
One of my design constraints is no permanent modifications to the unit. Fortunately, the car we will be running is a '65, and these later units have a removable top from the plenum. Current plan is to fabricate a custom plenum top and connect two original air-meters to this custom top. (Very similar to the Gulf racecars of the 60's). We will be using a 327ci with heavily ported period-correct cylinder heads. Aiming for approx 6800-7000 rpm peak power to maximize the inlet manifold runner's tuning effects. The ignition will be from a period Joe Hunt Magneto on the GM distributor.
My understanding is the current reproduction nozzles for the units are fairly high in quality (~2% flow variance), which removes one of the largest obstacles. Hopefully the original gear pump and fuel distribution lines produce sufficient fuel flow to supply the 327.

I have a copy of the SAE paper authored by GM Engineers John Dolza, et al which does an outstanding job explaining much of the theory behind the operation of the unit. However, the paper does not give any quantitative data.

I mainly hoped someone might have some information stashed away regarding modifications to the fuel delivery system and correlating the vacuum signal of a modified unit. I am especially curious regarding modifications to the "spill plunger" (also a reproduction part) to increase fuel flow. I realize no matter what I am looking at a number of hours with A/F measurement equipment to get the curve right - but it would be easier with a baseline to start from.
Thanks again

 

[patdaly]

Dumb question, I know you say no permanent modifications, but is there anywhere in the rulebooks that say it must remain mechanical FI?

I am sure a talented person could convert it to EFI without showing, and the cubic money you save would more than offset the purchase price of the Rochester unit.

But then, that would be outside of the spirit of competition.

 

[Metalguy]

Bill Thomas of CA used to make/supply? an early style spill plunger that was supposed to work better than the later one. I bought one and couldn't get it to work at all. Sold it to a friend who installed it in his FI unit with no changes and it ran fine. Never figured it out.

I hated the way it would run lean after the diaphram hardened a bit. The final straw was when metal disc/plug on the HP pump bowl fell out and spilled gas all over the engine. I was running along ~70 on the NY Thruway, and somehow it didn't fireball. Found the plug on the valve cover. Shoved it back in, drove home and installed a 4 barrel. Car ran much better. Traded the FI (chromed '65 unit) for a Paxton blower.

Gold is for the mistress - silver for the maid
Copper for the craftsman cunning in his trade.
"Good!" said the Baron, sitting in his hall
But iron - cold iron is the master of them all.
Rudyard Kipling