If I put a carberator on my engine that is quite a bit too large for the motor, what will be the outcome? Will the engine not run or will it just run rather poorly? I have a 750 edelbrock I bought for my 408, how will that do on a hot 302?
Good question. I don't have the answer unfortunately, but I have a similar problem. I have an A code motor with all the bolt on Cobra stuff (i.e intake, tri-y's) I want to install. Additionally, I have the Holley 715 cfm Lemans (GT-350) carb I would like to install. I know that for street duty, this is WAY too much carb for the motor. But the car isn't my daily driver, and I like the period correctness of all the parts in combination. Of course I want the car to run well too. Am I going to need to stuff a hotter cam in there just to get the motor to run well with that carb? It would really break my heart to have to do that! /forums/images/icons/wink.gif /forums/images/icons/wink.gif
The problem will be with the engine running poorly unless its wide open. A large carb on a small motor does not have enough air velocity through the carb for good metering of the fuel. Off idle is especially difficult to get right, although it can be done. Spreadbores use smaller primaries to keep the velocity up, and can be spec'ed with higher cfm carbs without loosing the velocity in the primaries.
For an example of how well a large carb works on a 302, just ask Ford, as they stuffed a 780 on top of the Boss 302. Oh wait, my car stumbles off idle . . .
While it is true that too large a venturi will enhance a low speed bog on a small engine, this is more predominent on a spread bore than a square bore which is predominently used on Fords. Here's what I calc given the following...
Max RPM: 6,000 (since it's "Hot")
CFM: 472 + I allow an additional 20% of flow for ignition, headers, etc. which makes the max CFM 566.
So you have an overfill of about 25%
Reduce your fuel jets about 12.5%, the accellorator pump should be a 50cc unit should be fine, and that should put you within about 2 jets of being on the money!
Now i don't have a spec book in front on me, and it's been too many years for me to remember but, the 650 & 750 Holley's which are of the same series share components, alhough I don't think you'll have to, worst case scenerio, you may end up purchasing a metering block for the 650 to really fine tune it with ease.