carburator sizing cfms????

68dustin · Dec 2, 2008

carburetor sizing cfms????

ok, i know ive heard a 302 is good enough with a 600 to 650 size carburator. The question is: if your running a 750 tunned correctly on a 302 where are you losing? power wise & performance.... other than you wasted extra money on a bigger carb. Please answer my question if you can because i cant find much on the cons of running a little bigger carburator. thanks

:SNSign:

SoCalCruising · Dec 2, 2008

The main thing is throttle response, esp. at lower RPMs, and ease of tuning. I ran a Carb shop 750 DP for a while, then replaced it with a 650 HP series DP. Throttle response was snappier and fuel consumption went down. It is VERY unlikely that their will be any difference in power (up top) with the 750 on a 302.

68dustin · Dec 2, 2008

thanks..i was just wondering because i have a 750 and i like it way better than the 650 had before. other than gas mileage like you said, the 750 had more power and better et's at the track.

rbohm · Dec 2, 2008

dustin, it really depends on what you are doing with the car as to what carb cfm you want to use. for racing at the strip, or on tracks with long straights, you will pick up a bit of top end power, but at the expense of low end throttle response. it also depends on how your engine is built as well. there are also times where a larger carb will actually gain low end power over a smaller carb. it all depends on the combination, and that includes the drive train as well.

10secgoal · Dec 3, 2008

I had a 750 on my 302 also. It did everything better at the track.60ft, mph. A 750 can get as good MPG as a 650 if tuned correctly.

68dustin · Dec 3, 2008

its kinda nice hearing from other people they got the same idea. Everyone trys to beat it in me and preach saying a 750 is way too big and you only need a 600. i dont give a flying fu*k if a 600 is all i need, but my car isnt a daily driver & far from a gas saver. Im going for power not a stock powerless mustang...... :Track:

1968notchback · Dec 3, 2008

68dustin said:
its kinda nice hearing from other people they got the same idea. Everyone trys to beat it in me and preach saying a 750 is way too big and you only need a 600. i dont give a flying fu*k if a 600 is all i need, but my car isnt a daily driver & far from a gas saver. Im going for power not a stock powerless mustang...... :Track:

If you have already made up your mind that you need a 750, then why did you even post the question?

I suggest using a 1250 cfm. Or what about TWO Holley 1250 Dominators! You can help send up the oil company stock prices.

There, feel better?

woodsnake · Dec 3, 2008

There are some good threads about carbs/cfm ratings over on S B F Techdotcom.

If you aren't concerned about mileage, and have some decent heads,
Run the 750!!

68dustin · Dec 3, 2008

1968notchback said:
If you have already made up your mind that you need a 750, then why did you even post the question?

I suggest using a 1250 cfm. Or what about TWO Holley 1250 Dominators! You can help send up the oil company stock prices.

There, feel better?

its not that i have my mind set on the 750. in fact i have both carbs. i have a new 750 on the car and a new 650 off the car. i have tryed both, and as of right now the 750 out performs the 650. i am trying to see what other people think between the two carbs on a small block since ive looked and cant find any info. If you read any book or talk to 99% of people and you say you have a 750 on a small block they laugh and say "thats way to big". oh and by the way, i will be glad to run up some oil prices with my 3 old schools gross poluting the world & making the climate a little warmer...

rbohm · Dec 3, 2008

i say use the carb that works best for your application. my 289, when it finally gets built, will use a 480cfm autolite carb because it will be a street engine, and will need to actually get some decent fuel economy.

if a 750 gives you the best results for what you want, then go with it.

D.Hearne · Dec 3, 2008

68dustin said:
its not that i have my mind set on the 750. in fact i have both carbs. i have a new 750 on the car and a new 650 off the car. i have tryed both, and as of right now the 750 out performs the 650. i am trying to see what other people think between the two carbs on a small block since ive looked and cant find any info. If you read any book or talk to 99% of people and you say you have a 750 on a small block they laugh and say "thats way to big". oh and by the way, i will be glad to run up some oil prices with my 3 old schools gross poluting the world & making the climate a little warmer...

I'll put in my 2 cents here. Not knowing what you've got in the build, the 650 is plenty of carb for a 302. You MIGHT gain a teeny-tiny bit on the top end with a 750, but only on the top. This only applies if the 750 is a vacuum sec carb. If it's a double pumper, the 750 is definately too big, you WILL loose power on the bottom to mid range. If you managed to make gains on the bottom end,(with a DP750) it's only because the lost bottom end performance has affected the traction and bettered the bottom end due to the tires not breaking loose because of the carb being too big on the bottom end. And if you really want my advice, you need more than one carb , something like a 2x4 or sixpack in place of a single four.

68dustin · Dec 3, 2008

D.Hearne said:
I'll put in my 2 cents here. Not knowing what you've got in the build, the 650 is plenty of carb for a 302. You MIGHT gain a teeny-tiny bit on the top end with a 750, but only on the top. This only applies if the 750 is a vacuum sec carb. If it's a double pumper, the 750 is definately too big, you WILL loose power on the bottom to mid range. If you managed to make gains on the bottom end,(with a DP750) it's only because the lost bottom end performance has affected the traction and bettered the bottom end due to the tires not breaking loose because of the carb being too big on the bottom end. And if you really want my advice, you need more than one carb , something like a 2x4 or sixpack in place of a single four.

i like the six pack idea...those look so tight.... oh by the way my build is: 68 mustang and is 2900 lbs. i got a 302 bored 30 over, air gap dual plane intake, 4:11 gears, t-5 5speed, trick flow twisted wedge heads, holley 750 carb double pumper dual feed, decent size cam....cant remember specs of the top of my head, all msd ignition, holley fuel system, shorty headers, 2-1/2" exhaust dumped at axles..

carburator sizing cfms????

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