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looking for a Quadrajet

buffblazer

buffblazer

1/2 ton status
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after reading the carb poll, i want a quadrajet, now i was looking at summit rebuilt ones but all the ones i have found are 750cfm and even thought my 350 in my 86 k5 is built up a little i still think its gonna be over carbed

so where do i find a quadrajet new for my 350?
 
As trashy as it sounds, go to pick your part, 1/2 off days all the time. I bought one that looks like a relatively recent rebuild for $25 off of a Caddy and threw it on my truck without touching it. It ran a hell of a lot better than my Summit/Edelbrock rebuilt I threw on there a fewe years ago. Just look for one that looks relatively decent, and check the throttle shaft bores, that is where they get a lot of air leaks. I also bought a couple more from the junkyard over the years for other cars, including my Firebird. It ran better than the Demon that I have on there now!
 
There are only two Quadrajets sizes ever made...750CFM and 795. (or 800 depending on who you ask)

So no, you won't be overcarbed with a Q-jet. Stick with the 750 though, theoretically better throttle response.
 
Although the body is rated for 750CFM, actual rating varies with the size of primary jets and metering rods as well as the secondary rod and hanger size and a variety of other things. That is why GM was able to use the Q'-jet on virtually every size of V-8 they ever built. In reality, it's a variable-cfm carb, which is one of the reasons it's the most efficient and capable carb out there.
 
Only way to change CFM is to change the passage size, no?

They meter fuel based on demand, but that's essentially every carb out there. My understanding (I've dealt with nothing but Q-jets) is that Q-jets are the best "all around" carb because of all the design features in one package...small primaries, big secondaries, central float/float bowl, etc.

I know where you are going though...there is an almost infinite number of combinations of all the fuel metering parts of a Q-jet. Enough to keep you busy for years playing with them. :) Luckily, since the Q-jet IS such a great carb, it is very adaptable. This is why you don't see people playing with rods, jets, hangars, power piston springs, etc. that often...there isn't much need. You could certainly get better performance by doing so, but the returns are usually pretty miniscule if the carb isn't way off (like a carb off a 305 on a 454) so most people don't mess with it.
 
If you want a new Q-Jet the only place to get one is Edelbrock. They have some old stock they are selling :http://store.edelbrock.com/edelbrockcarbsq-jetapplicationcarbs.aspx.
Those are the only ones that I know of. Every other Q- Jet sold is rebuilt.

BTW The CFM on Q-Jets is not controlled by metering rods, hangars, or Jets. They meeter fuel flow Not air flow.
The amount (CFM) of air delivered to the engine is controlled entirely by the air valve and the throttle plates.
The air valve uses a combination of engine vacuum and spring tension to meeter the correct air volume for the engine.
The air valve also controls the fuel to the secondaries. The secondary metering rods are connected to the air valve. The more the air valve opens the higher the metering rods are lifted allowing more fuel to flow.
That is why the Q-Jet is a one size fits all carb. It will only deliver as much air as the engine needs. It does not matter if it is a 283 or a 454. When properly tuned and jetted. The Q- jet wont deliver too much CFM or fuel for the engine.
Q-Jets are also the best carb made for offroad use.
 
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