View Full Version : Carb sizing OK?

10-14-2007, 07:42 AM
I have an Edelbrock 850 cfm Q-Jet carb I plan on putting on a fairly heavy built 383 for my '67 Camaro.
I'm concerned somewhat that this carb is going to be a too much for my 383. (The projected HP is 470-480).

Using the traditional carb-sizing formula dictates a carb no bigger than 700 to 750 cfm. However, I contacted the good folks at Edelbrock and they said that one of the benefits of the Q-Jet (and also the reason it has so many moving parts) is that the secondaries stay out of the picture unless the engine demands the extra airflow -- and that I shouldn't have any problems.

I'd appreciate any advice from you all on this -- particularly if you have a Q-Jet setup or otherwise have insights.

Thanks very much.

10-14-2007, 02:24 PM
Nothing wrong with Qjets and as for the Qjet secondaries learn how to adjust the air valve.
I set them tight and then loosen up a little at a time till you can feel nothing but a strong pull all the way up to redline.
Most people wrongly think you need a buh-wahhhh from it and this means theairvalve is opening too soon most likely.
also I found that you also need to make sure you have asmuch initial and centrifical in as the engine can use without spark knock and still pull good, and in as fast as the engine can handle it.
Then hook up vacuum advance to manifold vacuum, as it is for mileage and srivability and it goes away as the engine is trying to make best power.
You will also have to dial in your idle speed and mixture twice, pnce with out Vac advance and then idle it down and reset it again.
Oh and the Qjet might need a dose of either Sunoco Ultra 94 ,if you have it available or get a 20 gall treatment bottle of Techron by Chevron fuel injector cleaner periodicly as the Qjet sometimes will pick up a few contaminates and start idling funny, this is because the idle circuits ar of a finer tuning quality over say a holley.
Good Luck

10-14-2007, 05:58 PM
Thanks for the info!

Do you think an 850 cfm Q-Jet carb will be too much for a built 383?