I am about to put a 79 corvette carb on my 84 firebird and I want to know how feasable the 800 CFM max will be, is it too much ?? I also want to know if there is a way to lower it to 700 or so and what kind of tool would I need to evaluate the actual amount flowing in?

Am I putting up too many posts?

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[This message has been edited by ChillPhatCat (edited August 15, 2001).]

 

Humm, all the carb guys must be out sick today...

I doubt a '79 Vette q-jet would actually flow 800 cfm, but even if it did, the beauty of the q-jet is that it will adjust itself to work with smaller demand (i.e., smaller engine). Just tune the secondaries with rods/hanger and AV adjustment.

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are'nt the stock qjets off our camaros able to flow 700 cfm with a bit of modding?

 

But I have a firebird... not a camaro J/K (about the difference)

How much does the q-jet on 350 CID third/second gens flow?

[This message has been edited by ChillPhatCat (edited August 18, 2001).]

 

I think the qjets on the 3rdgens flow something a little less than 600cfm stock, but can flow 750cfm with some work.

 

The Q-Jet came with two different size primary venturis. I know the 850 CFM had the bigger primaries. But most all Q-Jets had their CFM ratings limited by how far the secondary air valve was permitted to open.

There is a tang on the passenger's side that sticks out and limits how far it will open. Cut that off or bend it so the air valve top can open completely.

Personally, I would have rather looked for a Q-Jet whose carb number started with 704**** or 702****. Your 1979 carb probably has something like 1709****. Those "170" Q-Jets have wide taper primary metering rods calibrated for EGR. EGR really muddies the part throttle response but disconnecting it will bring on lean detonation because of the wide taper. I haven't seen too many performance narrow taper primary metering rods for the 170 Q-Jets. The older "70" Q-Jets can accept the older narrow taper metering rods, thereby allowing you to enjoy the linear response of a non-EGR engine and no pinging.

All is not lost however! You probably have the aneroid altitude compensator on your Q-Jet. It's on the right front corner under a cone shaped thing. Pry the dust cap out and turn the adjusting screw about a half to 3/4 turn counterclockwise. This will richen up the main metering circuit and slightly reduce the effect of those wide taper primary metering rods.

I'd still keep my eye open for a pre-EGR 70-series Q-Jet though!

 

It's fine. It's a Q-Jet. It has an air valve, that won't open any farther than the engine can suck it open; it's self-regulating.

OBTW that carb will have a number starting with 1705; its rods & jets interchange with all the older ones. Like the other post said though, a pre-emissions Q-Jet is a whole lot better of a basis for a fast car than that one; those cars were such pigs.... I remember how much fun it was smoking them all by multiple car lengths with my L69 car when I got it, which was about a 15 sec flat car.... that 79 Vette was probably rated at 180 HP tops, the L69 was rated at 190 out of a 305, in a 300 lb lighter car. That should give you a good idea of how pitiful a late 70s 350 Vette was.

If you're ever looking around in a boneyard at old Q-Jets, the one to get is 7029202, it's off of a 69 or 70 350 with double-hump heads. You find them alot in Impalas and especially station wagons.

The correct tool for calibrating a carb is a track. You can do a good bit of work with a vacuum gauge, a speedo or tach, a stopwatch, and the readily available butt dyno.

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