I've been wondering for a while now, how exactly does a Rochester MFI work? Obviously being sold in street-driven Corvettes it must be a heck of a lot more streetable than a Hilborn or an Enderle, so what makes it more streetable? Does it have some kind of vacuum fuel metering? I can't find much info on it just searching.
Taken from wikipedia: Chevrolet introduced a mechanical fuel injection option, made by General Motors' Rochester Products division, for its 283 V8 engine in 1956 (1957 US model year). This system directed the inducted engine air across a "spoon shaped" plunger that moved in proportion to the air volume. The plunger connected to the fuel metering system which mechanically dispensed fuel to the cylinders via distribution tubes. This system was not a "pulse" or intermittent injection, but rather a constant flow system, metering fuel to all cylinders simultaneously from a central "spider" of injection lines. The fuel meter adjusted the amount of flow according to engine speed and load, and included a fuel reservoir, which was similar to a carburetor's float chamber. Just a quick copy and paste
Does it have some kind of vacuum fuel metering? Your on the right track. There were two diaphragms which controlled fuel flow. The main diaphragm was controlled by total airflow through the air meter. There was an enrichment diaphragm controlled by manifold vacumn. The two diaphrams worked through links to a lever with an adjustable fulcrum to control fuel to the distribution lines. They really are not that complicated but dealers rarely if ever had any mechanics trained to work on them. When something went wrong they would just replace them with a carburator setup.
The plenum and an idle circuite were the main things that made it more streetable. That is the reason that you could run a flying toilet when they were popular on the street was the plenum. It works as a buffer. There is a modern mechanical injection, not traditional by any means but mechanical called a Bill Mitchel Injectorater that is fully streetable and the biggest reason is that it has a plenum and an idle circuite.
Well thanks for all the info, helped a lot! Believe it or not there's one sitting on a small block Chevy in my High School's auto shop. Unfortunately we don't have auto classes any more. I've been trying a while now to figure out who I'd go to to take that thing off their hands... the engine's junk, it was used as a cutaway, but the injection is all intact except for the cover on top of the doghouse. It's a shame such a nice machine was butchered to teach a few kids who for the most part were only looking for extra credits. I was one of the few there legitimately to learn.. not to ramble, but I think most people in our hobby (not sure if I'm quite qualified to say that yet) would be surprised how few high school kids are into the classics anymore.
If it has the removable cover it's a late model unit. Worth putting some serious money in to get it running. I would love to have it, but know what it's worth and just got back from a swap meet..... Dennis D
Yeah, I'd love to have it, too. Chances are some time in the not-so-distant future they'll sell all the left over parts and engines in the shop, and if I know about it I'll be there looking for that SBC. Not sure what I'll do with it if I get it, though.. sure I could get a junkyard 350 and put it on, but I think it would be a cool adaptation to a different engine, like a nailhead or something.
This is a great explanation of the basics of the Rochester Mechanical Fuel Injection..... http://chevy.oldcarmanualproject.com/fuelinjection/fi01.htm
You think so? I'd have to agree, it would look cool, although on the other hand I would really like to have a Rochester fuel injected car to show off, especially a Bel Air fuelie! I really wonder myself if it was a factory Corvette engine that got cut up or if it was actually made as a cutaway by GM. I assume if it were the latter it would be more valuable.
Although in that case I could possibly buy a Rochester MFI off ebay to use, then keep the cutaway in the shop to match. That way I can go and show people how it works, or even open the thing up and see for myself, get some firsthand knowledge on the subject.
great post i never knew how they worked, i did know they had a loe of trouble with the 57 pontiac F.I.
Racers adapting the plenum chamber or the dog house as they were often called was the origin of the the tunnel ram manifold. The design of todays pro stock intake manifolds has it roots in the design of the Rochester F.I. from the fifties.
Here is mine on just finished 32 Roadster. Had the unit since 1974 and ran on another car for years. There is a lot of FI information on this guy's site <CITE>www.jerrybramlett.net</CITE>
The Jalopy Journal
