biggus

Now that it's getting to be swap meet season is there any such thing as a Qjet cfm chart or list somewhere? Almost bought a real nice one, the guy really didn't know and I didn't. What cfm were they? Seems like I heard one time anywhere from 500 to 800.

Bozang1

I was questioning this the other day myself. Couldn't find any black and white answers but after all of my reading it seems to me that there were 750's and 800's. Your car gets what it needs whether it's 500 or 650 or ??? That's the beauty of the Qjet. I'm thinking I'll be keeping mine. I'd like to hear others thoughts though

Octania

youtube videos "how to tell 750 vs 800 CFM"

Exact stamped # means diff between $5 parts carb and $5000 OAI carb.

And beware of restamps.

Google a rare number such as 7028254 and "carb" for some decoding sites

Fun71

This is correct, two versions that are either 750 or 800 CFM.

Marx3

if you are looking for Qjets that are the most suitable for rebuilding and modifying, you should look for units were the ID number starts with 170xxxxx that has the fuel inlet pointing forward.
Those units will almost always be large cfm units for BOP. ( btw the 800 cfm unit is known to actually flow 849 cfm )

joe_padavano

The smallest Qjets were 750. Further restriction of flow was done by limiting the secondary air valve opening angle, as was done on the 307 motors.

Octania

"Further restriction of flow was done by limiting the secondary air valve opening angle, as was done on the 307 motors. "

That's enough for you, little buddy!
No more air or fuel!

BlackGold

Well, at the RPM most Olds 307s spin, the secondary air valve isn't stopping air flow so much as increasing its velocity, making the carb work better. But maybe you spin your 307s faster than that.


Back to the original post:
Since essentially all Quadrajets are capable of flowing 750 cfm, there are much more important considerations in choosing one. There are basic differences between, say, Olds and Pontiac and Chevy, and Rochester also made many improvements over the years. Pick up either Doug Roe's or Cliff Ruggle's book to learn more.

can66

hi guys,the qjet you want are numbered 17057--- or 17059---.these are 1976 to 1978 carbs that have the part throttle adj.i have 2 of these carbs that i plan t install on a '66 425.and you should read CLIFF RUGGLES's book on the same.qjets are good carbs,just gotta learn them a little and they will serve you well.

Marx3

that's an understatement :-) Learn the how's and the why's and the Qjet is an EXCELLENT carb :-) Cliff Ruggles claims he can make an engine run like it's fuelinjected and that is no exaggeration. Using his tricks work that way every time :-)

can66

hi,thanks and the 2 carbs i have is 1 is from a '77 z28 with about 60000 miles on it and the other one is a '78 z28,carbs were made about 8 months from each other!!.i am also using a 02 sensor in the pass. side exh. manifold to tune this sucker to the nth degree..

Marx3

Beware! those late 70's Chevy carb's are usually the type with large main air bleeds, big jets and very big rods to lean them out completely. They can be difficult to tune.