question about carb size

LayZ

Veteran Member
Jun 9, 1999
1,857
NJ. US
Marv D said:
Here try this...

No one has bothered to ask what Cu In motor, what RPM your turning it o, if VE is along the lines of a stock motor or a well scienced out race motor.

With no information you can make guesses all day long, and never be wrong.

http://www.wallaceracing.com/intakecfm.php

The calc is cool, but how do I figure out the VE? they are 781 heads but again can't say if there was any work done to them.

OK so what does it mean when you hook up the vaccum gauge to the vaccum port under the carb, it reads 20 at idle and when I WOT, it goes all over the place? That normal?
 
Last edited:

muscl car

Veteran Member
Lifetime Gold Member
Jul 8, 2001
23,894
Gallatin Tennessee
LayZ said:
The calc is cool, but how do I figure out the VE? they are 781 heads but again can't say if there was any work done to them.

OK so what does it mean when you hook up the vaccum gauge to the vaccum port under the carb, it reads 20 at idle and when I WOT, it goes all over the place? That normal?

Weak valve springs !!
 

Coadster32

Veteran Member
Lifetime Gold Member
Oct 2, 2013
2,336
Milford,CT
Marv D said:
Here try this...

No one has bothered to ask what Cu In motor, what RPM your turning it o, if VE is along the lines of a stock motor or a well scienced out race motor.

With no information you can make guesses all day long, and never be wrong.


(Guess you didn't read posts 7 and 8.)

There are plenty of CFM calculators out there. it really comes down to the high end rpm that he wants to accomodate.
 

450bench

Veteran Member
Feb 25, 2002
3,672
memphis, tn-shelby
If it's a street car, how many times is the thing going to see max rpm? Maybe 1 percent of the time? If the 700 runs good, run it and leave it alone.
If your going to do a bunch of street racing or take it to the track some, get a used 850 vacuum secondary or 850 dp and try it out.
Quick comment, I ran a 4778 700 on a fairly strong square port 427 a bunch of years ago. Ran a best of something like 11.90 on the rare occasion I went to the track and ran great on the street. Goofed around with a bigger carb and struggled to get it dialed in for the street. I know I got into the 11.80s but certainly wasn't worth the trouble when it mattered most, driving it.
 

APEowner

Veteran Member
Dec 9, 2013
646
Albuquerque, NM
Based on what little you know abut the engine I'd say that the 700 is fine. You may be giving up a bit on the top end but you should have better drive-ability. Again, too small of a carb will not make the car run badly, it'll just limit power at high RPMs. Too large of a carb can make a car run badly.
 

LayZ

Veteran Member
Jun 9, 1999
1,857
NJ. US
Ok i was just concerned about the rear squirters indicating that i was restricting it. Just seemed odd that the backs where so high. I figured that it was too small a carb to handle the volume of air going in, so the higher squirter was making it work.

LOL on that note if anyone ever needs squirters from .25 to .38 let me know i have a ton of them!

I messed around with cams too and the red with the .40 squirter and high flow screw seemed to work.
 

vegas1974z28

Moderator
Staff member
Lifetime Gold Member
Jan 10, 2002
4,686
Las Vegas,NV
LayZ said:
Ideally I'm looking for 600HP would like to keep it oval port maybe switch out the manifold for a square port have it port matched run something like this: http://iskycams.com/cart/index.php?main_page=product_info&products_id=182
and if possible keep the RPM range lower for street use. May be pipe dreaming but if your going to ask, i'll tell ya.

I have 650 hp on a 496...I use a 1050 dominator....and it is NO WHERE near street friendly.
 




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