As some of you know i have been working on modifying a stock rochester fuel injection setup for my vintage road race car. i am working on sencing signal linearity and nozzel disc size right now. I called a gentleman that set up a 62 FI unit to run with a GMC blower setup. I was currious how he worked out fuel delivery rates with the blower setup. We had a nice long talk and as always i learned a lot. It seems like really smart people(myself excluded) love to play with fuel injection. As part of the conversation he mentioned that he believes 5 early FI cars were built by GM to test the use of a GM blower mated to a Rochester FI setup.He has some componenets and a photo of an air box race car with a belt driven GM blower. Does anyone know about these cars ? He said a John Camden was a young engineer at GM that did some of the early work. Have any of you heard or seen any of these cars? These were not cars that a private person retrofitted but rather GM testing cars that were raced. i thought if anyone in the world would know someone on this board would. Jerry
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Re: Early Fuel Injection with GM blower
Forget the GM Blower - go to McCullough. -
Re: Early Fuel Injection with GM blower
Jerry, sorry I can't help, but I did drag race (late 60's) small blocks with GMC blowers, but with Hilborn injectors. I will be watching you post for and information that you may find. Good Luck on your research.Comment
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Re: Early Fuel Injection with GM blower
although i've got no knowledge of any blown rochester GM experiments back in the 50's, i tend to agree with loren. if one were to mount a rochester unit atop a 471, 671 or a 871 detroit diesel puffer, hood scoop would be a couple inches above the top of the windshield frame. not so with a mccullough.mikeComment
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Re: Early Fuel Injection with GM blower
If you blow into a carburetor (or the Rochester FI system), you have to figure out a way to increase fuel flow in proportion to the inlet air DENSITY.
Probably some kind of two stage power valve would work, but density does not increase as fast as pressure due to heating of the compressed charge, but if boost is not too high, pressure enrichment can probably keep the A/F ratio in the proper ballpark.
The Avanti Paxton supercharged engine blew into an AFB, but I don't know how they handled boost enrichment.
Remember, carburetors and the Rochester FI system meter fuel on the basis of air volume flow and can't correct for changes in density. That's why they run richer with increasing altitude and need a supplemental enrichment system in a supercharged blow-through application.
DukeComment
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Re: Early Fuel Injection with GM blower
Could I be right to envision a roots type GM blower w/o a plenum, but with the air meter mounted to the top of the blower housing and the fuel components on the sides? (I think I saw something like this in some old GM internal publication).
Stu FoxComment
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Re: Early Fuel Injection with GM blower
I agree with Duke, the trick is to have a relatively constant boost so the the volume measured is at a predictable density and then match the fuel injector nozzel disks to match air flow. Also the injectors need to be before boost to prevent plumbing problems with a presurized plenum.
There is a good article about how one person did this with a very nice proffesional installation. its at ;
www.corvetteshopsandiego.com/1958-corvette-supercharger-build.html
I don't want to debate the merits of one supecharger system versus another, I was just trying to see if this vast resevoir of knowledge knew of any of these 5 early corvettes with factory(GM) superchargers on them. Has anyone seen one of these cars?Comment
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Re: Early Fuel Injection with GM blower
Interesting, Jim therre is also the BOCar vintage race car that used a chevy 283 with Rochester FI and a GM blower mounted in front of the engine driven off the front of the engine. this kept a low hood profile and worked great. i saw one run at Road America . It was a rocket!Comment
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Re: Early Fuel Injection with GM blower
If your "source" has a picture, why not print it? There are WOs that deal with the purchase of McCullough/Paxton superchargers.....Comment
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Re: Early Fuel Injection with GM blower
The picture shown in Jerry's link is exactly the blower installation that I was referring to that I saw many years ago in a GM internal pub, or one closely resembling it. Exact same arrangement, i.e. no plenum, rather mounts directly to the lower manifold. Guess my mind isn't failing me after all.
Stu FoxComment
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Re: Early Fuel Injection with GM blower
Your mind is good Stu. There are several GM internal photos of this type of setup and other configurations using a GM blower in the Ken Kayser publication.Comment
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Re: Early Fuel Injection with GM blower
There is some interesting information in these charts. Look at the Duntov cam and .398" lift cam (most likely the '57 to '66 base engine cam) charts. Both use as a baselines what are probably a 283 HP FI and a 220 HP base engine. Compare the peak power and torque to the advertised ratings.
Mike McCagh's engine was tested to the same SAE gross lab dyno standards as these engines, so the results are directly comparable.
Mike's engine made 364 lb-ft peak torque and about the same top end power as the supercharged Duntov cam engine, but at lower revs.
These tests were probably done with production line heads. I don't think Chevrolet understood at the time the dramatic increase in port flow coefficient and power head massaging could produce.
Head work, increased stroke, and a better tuned camshaft would have been a much easier way to achieve equal or better output than a supercharger.
DukeComment
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Re: Early Fuel Injection with GM blower
Jerry,
A while back (late 70's or early 80's) at Bloomington a seller (Terry Mc?) had one of those setups for sale. It looked complete with distrubtor and base plate. No idea where it is now. I have pictures somewhere at home. If I remember right the Rochester air meter sat on the left side of a 4-71 GM blower, fuel meter on the right side. Over the weekend I will see if I can find pics. BillComment
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