What size carb?

-
L

LImopar

Active Member
Joined
Mar 20, 2006
Messages
39
Reaction score
0
Location
Ronkonkoma New York
I have a 72 318, stock bore, edelbrock performer cam, edelbrock performer intake manifold, 302 heads with mild porting, stock exhaust manifolds, 3:55 sure grip. Right now I have a Holley 650 carb on it. Is this too much carb for the motor. If it is what size carb should I look into. I was thinking maybe an Edelbrock 600 or trying the Summit 600 that just came out.

I will be building a mildly worked up 340 in the future. If I take the Holley 650 off the 318 do you think I would be able to use it on a 340 with some mild work done to it, or would it be too small.
 
Keep the Holley, it will cover all the bases you have now and for later.

Build dependent on the 340, the 650 will be fine.
 
^ What he said.

Is your Holley 650 a Spreadbore or SquareBore?..the easy way to tell is the Secondaries have larger Venturi's on a Spreadbore....squarebores have the same size venturi's on all corners.

650cfm is fine for up to a 450hp small block...although above 450 crank hp, your gonna need more fuel/air...and a 750 would be desirable then.
 
there is a good formula for this

(engine displscement (c.i.d.) X max rpm) / 3456 = ideal carb cfm

**example
360 X 6500 / 3456 = 677.08
this formula gives you a good base line to start then you can estimate for larger cams heads ect. this formula assumes 100% volumetric efficiency where we probably only see about 80%V.E. in street engines, so in mild street apps. use only 80% of your total and round up to the next whole cfm number in this case it would be 550-600
 
I find that formula not to be so good. Needs work/adjustments.
 
ken hensley told me that one .he said that herb mcandliss told him years ago i dont really know for sure if it is accurate for all engines but i think i saw it in a summit catalog a while back too i have always had luck just throwing a 600 on mild engines and a 750 on hotter engines and tuning them from there
 
That equation is a decent deal to find a baseline.

But why does my 360 that only needs a 750, according to the equation, run much better with a 950 or 1050 on it??? Hmmmmm!

A 600 carb is a decent choice for the OP's current engine, IMHO. On a manual trans car you can get away with more carb. I run nothing short of Holley 750's on 340's, manual or auto cars.
 
I read once somewhere a long time ago that if you attach a vacum gauge to the intake manifold and it does not go to zero at full throttle((not just stabbing the throttle but full throttle under a load) you are under carburated. I've never seen anything quick and simple for overcarburated.
 
Thanks for all the input guys. I guess I will keep the 650 on this build and try to tune it. When the 340 is built I will probably get a 750. Thanks again for all the help.
 
You must log in or register to reply here.
-

Back
Top