I KNOW!!!! :lol: :lol: :lol: :lol:

Be realistic a 650cfm is more air than that set up is going to flow.
If you punch these numbers in a cfm calculator you get 550-650 cfms being a street engine.

carb size
 

hey kwk you may be right and you may be wrong. he didnt giv e his rpm operating range, which i am guessing should be around 6500. if thats is the case and you use the standard cfm formula of rpms x cu. in. divided by 3456 then you come up with the cfm of 700 cfm. i would go with a 700 as first choice and 750 as second choice. the 650 cfm is really too small of a carb for this engine. being a 383 and a healthy cam it really could use the 750 cfm. just my opinion chevy art

10.25 compression, low flow heads, and he wants a it to clearly idle and not load up. A dyno would show that the engine would make no more power at 6500 than 5000.

Read his other post. 91 octane.

Save your carb money

650cfm

ok this is comin from someone who has a very similar 383
the difference between 650 and 750 was night and day
deffinately go with the 750 ul like it much better

I find that hard to believe.....unless you were talking removing the 750 and putting on the 650. I had a set of those heads on a 10 to 1 406 years ago in a street car.I bought a 700 DP brand new..It came staock with a 30 cc pump on the front and a 50cc on the secondaries...It would fall on it's face if you smashed it from an idle...I later got a good deal on a 650 DP and put it on with no other changes.The car came alive big time...



That engine combo would be more fun to drive with the smaller carb


The only argument that makes sense for the 750(in my opinion) would be that you would have the bigger carb later on when you updated the engine with better heads...

That's because the 830 was too big.

in a street car too small is way better than too large.

Just my opinion but I agree with kwkracing. Those heads are going to be finished at a relatively low rpm.

well as hard to believe as it may be i had a 650 vac secondary and a 670 vac secondary, and it woke up drastically when i put the 750 dp on it, all i had to do was put a lil bit smaller squirter in the front

No wonder.... You can not put a vacum secondary carb on a engine that pulls little to no vacume and expect it to perform properly.

his and my cams are not tht big
the motor makes plenty of vacum even at idle

Ive always gotten better performance out of a double pumper vs a vacuum secondary carb no matter what size the carb is.