Thread: Carburetor Size??

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quadrajets have theee worst secondary metering system on the planet which consist of a set of what I call 'piss tubes' and what others call spray bars.
The primarys are so tiny, which house large [compared to the primary venturi size] boosters which together give great low end/milage but offer lil cfm in relation to the secondarys huge flow..which only strengthens the argument for why the heck couldn't they of come up with something better than 'piss tubes' and no boosters..

If it wasn't for stock class/fast class rules they would have all been recycled by now, and rightfully so.
A thermoquad is better piece, and I still would not recommend it for what you are doing because it is to a ventilated dinosaur bone.

nothing meters as well as a square bore.
Yes you are able to more fine tune the cruise with metering rods.. but in the end you'll short power wise with spread bore.

How big a carb you can get away with [without sacrificing low end] will directly relate to tune/compression.
The cam already gives us a power band or rpm, so now it's a usage requirement.

How much initial timing do you run for right now?

750-830 annular square bore.

spread bore carbs have poor wot metering.

quadrajets have sewer pipes for secondarys, if it weren't for class rules they be recycled.

Originally Posted by kens383stroker

I have a 383 stroker, aluminum heads 64cc, aluminum roller rockers, 557 cam ( not sure of duration) Looking for a good 750 carb for it. Thanks

Bye bye throttle response

A good formula is (displacement x rpm)/3,456. This formula assumes 100% volumetric efficiency (VE). A strong street motor will usually be around 85% VE, a race motor may be close to 100%. Take the results from the formula x your approximate VE. For example, if you plan to turn your 383 6,000 r.pm., and it's a street motor, 383 x 6000/3456 = 664.73 x .85 = 556.19 cfm air flow, so a 600 should work well.

This is what I have used in the past. Is this not a good formula?

Originally Posted by 1wild&crazyguy

750-830 annular square bore.

spread bore carbs have poor wot metering.

quadrajets have sewer pipes for secondarys, if it weren't for class rules they be recycled.

I agree with Wild . Q-Jet's work ok on Stock to Mild Street Engines . And they have a Nice Rolling Punch to them . But they are Problematic in many ways and way over Price-ed . You never hear the true negative Side to them small front to Large rear barrels . I have worked on the Very First Q-Jet Models and the Computer one's and Know how to Mod them if I have to use one . I have one on My SB Chevy Pick up . It work's ok it has some of the normal Q-Jet Problems . I am saving for a Edelbrock Performer carb to replace it And them what you call sewer pipes a Lot of the Time fall out into the secondary fuel well . I have had some fun with Q-Jets but they ain't what Folks try and make them up to be .