QJet Size for my 5.7

[Bizeeb65]

Hey guys... quick question. I am getting a qjet from a 454 and I intend on putting it on my 350. The carb is off a running engine, and I can pretty much take care of everything on the install but there is one thing I am wondering about. Will I have to rejet the qjet to work with my 350? Are the primaries or secondaries going to dump too much fuel due to the current setup for a 454? Any and all suggestions welcome fellas.

[b454rat]

Someone told me that there were only two sizes of Q-jets, don't know the CFMs, but IIRC around 670, and a bigger one that was on the 472 and 500 Caddy's. Someone will correct me if I'm wrong.

[mountain4x4]

Originally Posted by b454rat

Someone told me that there were only two sizes of Q-jets, don't know the CFMs, but IIRC around 670, and a bigger one that was on the 472 and 500 Caddy's. Someone will correct me if I'm wrong.

I think theyre 750 and 800 cfm. The 800s were on trucks. I'd recommend tuning it with a w/b o2 sensor on a dyno if possible, or buy one from someone who will set it up for your motor. I'm not sure if the ones on 454s were tuned differently from sbcs, but most likely they were. A good carb shop will tell you approx what jet sizes you'd need. They are easy to work with...

[custommccannix]

sbc came out with 750cfms except on 3/4 tons and bbc came with 800cfms. yes you will need to change your float level, metering rods, main jets, and needle valves. if you can take it somewhere it would be best. my own personal preference is to put 650cfm edelbrock carbs on my sbc as long as it is under 500 horses. good luck.

[positrack@earthlink.]

Originally Posted by mountain4x4

I think theyre 750 and 800 cfm. The 800s were on trucks.

x2

The 750s were for cars, the 800s for trucks according to everything I've read. Jet has them listed that way. The size difference is in the primaries, I believe the secondaries are all the same size. I can't remember the exact dimentions of the two differently sized primary bores, but if you look around, you might come across it. The calibration is different between BBs and SBs. Possibly different between displacements and years as well, but I'm not sure on that. If you don't know much about carb tuning, you'd probably be best to take it somewhere to get recalibrated. But then again, if you're brave and just want to dive in, the best understanding comes from 1st hand experience (and misery ). Get a manual/high-performance tuning and modification guide and see what you can do with it.