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Old 04-09-2013, 11:22 PM
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trashed my summit 600cfm

i installed a brand new summit 600cfm 4bbl carb on my 302 ford awhile back,I was very pleased with its performance,But not too long ago it began giving me headaches,the idle mixture screws backing out,not staying in,floats wont stay adjusted..the secondaries wont close all the way,and fuel leaking by..i did all the checks,and it seemed everything was okay once i re-adjusted everything.But thats the trouble..it will not stay that way..constant tinkering.So i said screw it and bought 3 awesome rebuild kits for autolite 4100 carburetors.I have 6 cores that were in various conditions,instead of rebuilding them i thougt buy a new summit.Anyways from 6 carburetors i came up with 3 good ones,all 600cfm.Im currently at 17-18mpg plugs look good,and the damned thing is reliable! i was told i cant run a 600cfm carb on a stock 302 all sorts of things would happen..anything from dirty sparkplugs to causing the earth to shift from its orbit..nobody was right.I rebuilt the carb,put it on the 302 and the truck is running better than it has for a long time.Now i just picked up 3 of the smaller autolite 4100's.i will rebuild those and see what they do on my daughters 65 falcon wagon 302/c-4

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Old 04-10-2013, 02:31 AM
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I would have thought 600cfm would be perfect for a 302. Did ya send the other carby back to summit? I would...



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Old 04-10-2013, 06:42 AM
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I've run 600 cfm Holleys, mostly 0-1850's and Edelbrock 1405/6 carbs on about everything from 302cid to 460 Fords with great success. Is it REALLY too big, probably but both are very tunable with fairly small primaries for low rpm operation and pretty big secondaries for WOT.

The 'usual' formula for carb size:

CID x RPM divided by 3456 x VE (volumetric efficiency)
An example:

302 x 5000 / 3456 x .80 =
1510000 / 2765 =
548 cfm is the optimum carb size. Rounded up is 600cfm which is perfect

3456 is a standard design constant
.80 or 80% is a good engine's effiency
5-5500 rpm is about all a 302 in good shape will do without at least some minor head and exhaust work

I'm running a 600 Edelbrock on my well warmed over 5.0:
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Old 04-10-2013, 10:58 AM
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I agree with you that a 600cfm is a bit too big for a stock 302,But i have run the plain-jane holley 600s' with no real issues,other than it ran a bit rich,but that can be tweaked a bit.I was trying to avoid using another Holley on the truck and i wasnt certain that the old autolites i have would be any good..so i got what i thought would be close to an autolite..it was good for awhile.I called summit they said they wont make good on it. But anyways,the 40+yr old autolite has proven to be the better carburetor.I should have rebuilt them in the first place,i never had a problem after rebuilding one,reliable,easy to adjust and STAYS adjusted.Im going to do a pair of the 1.08 venturi autolites next,then try it out on the truck..i would have done thse first..but i didnt have any at the time i needed the truck
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