So what do you think about having my Q-Jet rebuilt (by Lars)?
Would it be a good choice for that engine?

OK, now I see that we are dealing with a fairly serious engine. It may be worth going with a bigger carb. It will run with your 600 for now, if cash is short, you can get a 750 later, if you wish. Also, yeah, you won't go wrong sending your Q-jet off to Lars, but You'll need a new intake manifold, if you're running a squarebore now. You can get a Performer RPM with the spreadbore flange.

Scott

OK....I guess for now I'll run the 600cfm and make a decision whether to get a 750 or re-use the Q-jet.....

The Q-Jet will perform well with some mods......it would have to be fattened up considerably....but it will flow well......

Only problem is that most manifolds out there anymore that flows well enough at that power level is a square bore flange....

I recommend a 3310 Holley or Quick Fuel equivalent.....

Jebby

http://www.summitracing.com/parts/ed...FctcMgodVGsAIA

You can bolt a square bore carb to this manifold using a very inexpensive adapter, while you decide what carb you want to go with in the long run. Decide now whether you will use a spread or square bore carb, and order your intake manifold accordingly. You can use a square carb on a spread flange, using an adapter plate, without giving up much, but the other way around (spread bore carb on a square bore flange) doesn't work so well.

Scott

A 383 with a max of about 6200 rpm will work fine with a 600 cfm. I have explained in the past here on the forum how to jet EDL carbs. Because the manual gives such poor choices with like 6% changes. You have to be able to think about what a rod and jet is actually doing. The jet has an area of flow and the stepped rod blocks the jets flow depending on its diameter. you just have to do the math with an online area calculator. Advise of just changing the jets up two sizes is just wrong.

It will work fine but be down on power upstairs......
A 750 is closer to optimal jetting out of the box for a 430 horse motor....
Those 383's will have about 11-13 in of vacuum at idle....if you run an Edelbock....you need to change step up springs to a light one...

I agree....the manual choices are limited.....I use a mic for the rods....and some fuzzy logic.....
The jets on the primary require the lid to be removed.....the jets on the 750 are closer......
I have put many 750's on many 425-450 horse small blocks and the Edelbrock works fine with a rod and step up spring change.....

The 3310 Holley is almost spot on out of the box....@11-13 inches of vacuum.....

Jebby

If you go to an online carb CFM to cubic inch calculator. A 383 with a 6200 rpm redline and 85% VE is something like 589 CFM

Also for those of you who don't know The NASCAR restricted motor races are only 500CFM. I've actually driven a GT1 Vette 496 ci with a 500 cfm NASCAR carb and it was a TQ monster and I was shifting at over 6000 rpm. All of these are 700 some HP motors. So the big carb on small motors like a 383 just don't wash with me.

I actually had a race car years ago with a holley 450 cfm four barrel It was in a 358 ci paved circle track late model sportman class

Well, for sure I'm going to start off with my 1406 600cfm and break in the engine and see how I like it

BTW, here is the new engine!
It arrived black

Looks better in chevy orange don't ya think? !!!!

I understand the calc and it is a good reference.....but every hi-performance engine runs a carb that is about 25% bigger than the calc states for a number of reasons.....too long in tooth to get into here....

Good idea...run the 600 because you have it.....see what you think...

Jebby

Yes, and the fact that vacuum secondary carbs limit over carburation compared to their double pumper counter parts. Also single planes and double plane intakes withe a partialy cut divider require less CFM than a true dual plane

Just FYI.....when you put an unrestricted carb on a new NASCAR engine....it picks up some 250 horsepower!!!!!

Looks like your manifold is square and spread bore compatible.....

Jebby