Top end RPMs have a great deal to do with carb sizing. A 750 isn't too big if you are running over 7,000 RPMs. I am running a 650 Speed Demon Double Pumper with my stick car, you might want to run a vacuum secondary carb with you slushbox. A 650 should get the big end a little sooner.

 

The improvement in carb and intake manifold design has made the "formula" obsolete for quite some time now relative to optimizing performance.

If all you're doing is picking a carb for a grocery getter, the formula will be adequate. But a modified/high performance engine will not realize it's peak potential with that method.

Here are a couple of links with good info:

http://carcraft.com/techarticles/56919/

http://www.pro-system.com/pjames011900.html

http://www.popularhotrodding.com/tech/0503phr_carburetor_tech_terminology/

 

I always had good luck with a modified 3310 Holley with the Torker and F4B manifolds and iron heads. What rear gear and tire radius are you running? Trans brake?

With the torker, I found the combination to be sensitive to the height/profile of the plenum divider, more so than to the thickness of the carb spacer. Be sure to experiment.

Nice numbers for a stock suspension rig. Good show.

Pat

 

Hi,

The rear end ratio is 5-something, the tire is 26 inch, no trans-brake.

The motor "feels" done @6000+. It could be the dual plane manifold, or the carb.

I've got three different carbs available the 600 vac (actually 2), a 650 mech, and a 750 mech.

I've been considering a 4 hole 1 inch spacer, and maybe annular boosters for the 750.

 

What dual plane intake is it?

 

Hi,

It's the Power Plus+, PO installed.

John

 

In a fairly recent issue of Popular Hotrodding, they had a great article by David Vizard on this subject. To gloss over it quickly a point to concider is manifold design. When you have a dual plane manifold, basically you're dividing the carb in half and as a intake valve opens, it only has access to half the carb. With a single plane the intake valve has access to all four venturiis. Basically Dave Vizard said a dual plane manifold would like more carburation then a single plane. For what it's worth, I read an article several years ago about porting intake manifolds. The maniold they used was the old Torker with the twisted carb. What they found was that the old Torker didn't have enough port volume to match todays heads and would be a restriction.

 

If we're talking about the edelbrock torker II manifold here, EVERYTHING I'veread concerning that manifold is that it is junk. What tranny are you running with those gears? Thats some crazy gear you got goin there its not too much is it?

 

Hi,

It's an old Torker 289. I checker with the PO, it's a 4.56 ratio. Sorry for the confusion.

John