what is the cfm of the stock High Output quadrojet i have on my 83 z28?

I was once told that the Quadrajet was rated 590 cfm, but I'm not sure how accurate that is. I do know that there was a difference in the rating some how so if you were getting an aftermarket carb you would need to go either higher or lower (can't remember which). I'll end up putting a 600 or a 650 cfm on my 5.0L H.O. if I can't fix my QJ...

I'm pretty sure the LG4 Q's were 600cfm, but the L69 ones were 650cfm.

thanks for the info but im ditchin the quadrojet and gettin a holly 650 ive decided


thanks anyway

I think all QJets are rated at about 750 cfm.

I thought they were 780CFM.
I can't remember where I read it though.
4ME4 <- does that sound right? That's what used to be on my 81 Z-28.


Ron

Closer to 795 cfm. The non-HO versions sometimes had an AV opening stop that would keep the flow lower, but that wasn't used on HO engines. Assuming it's the factory carb, that is. FWIW, my '86 LG4 carb opened fully.

These q-jets are big enough to feed a healthy 383 or 406. If you're thinking your 305 is low on power because you need a bigger carb than your q-jet, you need to change your thinking.

Designation should be either M4ME (mechanical) or E4MC (CC).

Isn't it just how far the computer opens it... or are there mechanical stops in place... it wouldn't make sense to make different sized carbs... also, If I remember correctly, there were bigger jets on the L69 carbs... The reason going aftermarket may add power is that they aren't computer controlled for the most part and thus you are actually controlling fuel deliverey.

The computer doesn't have anything to do with how far the carb opens up. The secondary air valve is what is limited to reduce the flow, and that is mechanical.

Technically, the "jets" are the same in all q-jets (secondaries, anyway), and the computer again has nothing to do with that. The secondary mixture is tuned via rods and hanger, and those were (sometimes) different between L69 and LG4. In non-computer controlled q-jets, the primaries had replaceable jets and rods, but in CC carbs, they are all the same, and THAT is what the computer controls.

White, why are you "ditchin" the q-jet? Do you understand all you'll affect by doing so? If you go with the Holley, you need to replace the distributor as well, since the computer controls the distributor and without the signal from the carb, it'll go into a wimpy default mode. If you have automatic tranny, your TCC lockup won't be automatic anymore for the same reason.

Ahh... gotcha... anyhow, I would recommend trying to get the Q-jet to work with you... I probably wouldn't have done more than replace the intake if the previous owner hadn't done the non-CC conversion already... it makes inspection a little trickier and it is hard to get the same mileage as the Q-jet... one thing that i wouldn't mind is 24 MPG vs my 17... There are plenty of things you can do with the stock carb... there's a tech article on here about them.

-CPC

The rods were different on the L69 carb.

Yup, and for $5 you can make them the same. Damon's tech article on the QJet is worth its weight in gold pressed latinum to anyone who actually wants to get some performce out of their QJet.

i've e-mail the question to the fellows at edelbrock and they told me the cfm rating is 795, the difference is the jet and rod size, that's it.
Fernando.