I've known for quite a while that GM put the Quadrajet on small ci engines, but the larger of the two models? This makes me rethink what I know about carbs. Oh yes, one little detail I neglected: It was turbo'd.

I picked this up at a swap meet for $10 and am curious. The primaries, and I checked the oem listings to confirm, were 67 jets and 45 metering rods. Common is a thirty thousandths diff. from jet to rod. On 301 trans am's they ran 72 jets with 52 rods, again with the 800 cfm model.

Now that I have a AFR gauge I'm tempted to take another whack at the QJ. But I realize that in a QJ is not like working with other carbs. There is the added factor of idle and main air bleed restrictions. Adding that little bit of tuning is like adding a little to the circumference of a circle. By doing so you can double the area, double the work and difficulty of tuning a QJ.

It just seemed an interesting carb to throw into the forum mix.

 

Well, the next best thing to having a lab for testing (like the auto makers) is having people like you and AB doing some real-world testing/experimenting and posting the results.

 

I just uncovered an interesting bit of info that has eluded me for years: The cfm of the primary side of the two Quadrajet models.

It seems the 750 cfm models range around 180 cfm on the primaries.

The 800 cfm models range around 210 cfm.

That makes the larger of two flows 33% less than the primaries of a 600 cfm 4v square bore. Of course I have seen square bores that had smaller primary than secondary venturi.

How interesting that a 350 sbc can spend 99% percent of its driving life on 180 cfm. Wonders never cease.

 

Quite a few V6 boat engines came with 4v carbs. I've been curious about the I6 Pontiac that came with a 4v as to what size was used.

 

Another tidbit I recently learned is that Quadrajets came oem on several model FORDS!

"Boom!" That was the sound of illusions of ford blue and chevy orange bursting. Reality is that so many part found on GM and Ford alike, Dana, Borg/warner tranmissions and many other parts, Holley, Saginaw, etc., sell their parts to anyone with a check, regardless of color.

 

It is a bit baffling as to what all a Q-jet carb could found in, even when limiting it to GM factory applications. I once saw a GM car with a V6 that had a QJ on top, but there was an EGR plate under the carb, which only had holes for the primaries. The Plate made the QJ work like a 2 bbl, since there was no way the secondaries could ever operate.

There are (or were) many parts manufacturers that sold stuff to all 3 of the major US automakers (4 if you look back to when AMC still existed). Some of these manufacturers were owned by 1 of these "big 3", either in whole or part. One example of this, is the NP435 and NP transfer cases. These could be found in Ford, GM, dodge, and jeep brands, yet New Process Gear was wholey owned by Chrysler from about the WW2 timeframe.

 

I guess if you had seen it twice on cars owned by different people, then you could be certain it was not placed there by some questionable mechanic. Rochester has a 2v version of the QJ, so why would GM install an oem plate to block half of a QJ's intake? Did they think no one would notice? Very interesting. I would be quicker to blame it on some po or mechanic than on GM.

 

Considering the car was only 2-3 years old at the time, I highly doubt it was modified in any way.
There has never been any rhyme or reason as to how GM built things. Look at their current list of recalls, mostly over stuff they knew about before vehicles ever went into production, but they built them anyways.........

 

Good point! That is crazy, and interesting. You hadn't been drinking when said Quadrajet appeared, had you? Joke. Ha ha.

 

I rounded all my QJ goodies and wrote an ebook about the beast. Imagine that.