I have two carbs. I think one is Rochester Quadra Jet and I think the other is a Carter Quadra Jet. How can I find out exactly what kind of carbs I have and what the specs are like the cfm's and so on.

 

Is there a # stamped on it or anything that I can use to identify it?

 

Every carb has a number, on the driver's side, immediately above the secondary throttle linkage. It starts out with either 702, 704, 1705, or 1708. Beyond that, there are an enormous variety of other features about them that you can look at; whether it's electronically controlled or not, what kind of choke (divorced, integral, or electric), how the fuel line hooks up (not all of those will work on all engines), etc. etc.

CFM is meaningless on a Q-jet. It's the wrong question to ask. It's enough to say that it's enough but it's not too much. The ultimate flow capacity of a Q-jet is somewhere around 750 CFM depending on how it's measured, except for ones that came on smaller engines, which have a tab that keeps the secondary air valve from opening all the way, which limits the CFM to about 630. You'd never even notice that in about 99% of all installations, and even them only at WOT. It has no effect whatsoever on gas mileage, driveability, or any of those things, that you associate with "CFM ratings".

It's not like an aftermarket carb where they change the size of the bores; on Q-Jets they're all the same (with a tiny handful of exceptions you're not likely to ever encounter). Most other "specs" are the same way; there aren't any.

Rochester is the fuel systems division of GM. They contracted out manufacturing of alot of Q-Jets to Carter. This makes no difference whatsoever; number for number, they are identical. So you don't need to worry about parts interchange or that sort of thing.

These carbs are ordered by the various car divisions to highly detailed specs, to match specific applications. Every carb number is tailored to the individual requirements of the car it came on; car weight, emissions requirements, engine size, camshaft, etc. etc. They are not very easy to customize in many cases. Post your numbers and maybe somebody can identify them; but even if we can't, who knws? they might be great, or they might be junk.

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"So many Mustangs, so little time..."
ICON Motorsports

[This message has been edited by RB83L69 (edited September 10, 2001).]

 

Thanks for the info. I will post the #'s tonight or tomorrow. I have a SBC 355 Weiand duel plane intake, 1.94 76cc heads, the largest recommended cam for stock torque converter (cant remember exact #'s but I will look for them tonight), and running 2.5 inch duel exhaust with crossover pipe. All in front of a TH350 trans and 3.55:1 possi rear end. Just courious when carb I should run with this setup. The one on there now seems fine but since I have the other I was just wondering with would be better. I will get the #'s and post them soon. Thanks again

 

Carter Q-jets have a "made by Carter" (or something like that) on the side of the bowl. Carter used slightly different metal than rochester but I can't tell you if it was better or not.

I would look for a carb and distributor from an L82 'vette. The L82 cam had a 450/460 lift and appropriate duration and as a result the advance curve and off idle jetting would be closer to what you will need.

Many years ago I built a 350/327 for my chevelle. It was a real dog until I got the right carb and distributor. I tried a BBC q-jet and while it worked great wide open it just never drove that well. I changed jets, metering rods and power springs but finally gave up. I think the off idle circuit just couldn't be modified enough to handle a smaller engine. I got a rebuilt carb and distributor with the right codes and with a bit of tuning got it to where I wanted it.

Good luck & cheers,

 

The car this motor is in is a 79 Corvette and I have the stock carb off that motor which is now out of the car. It is not the L82 motor though. It is the L42 or something like that rated at 190 hp instead of 225 like the L82. The carb I am running is a Q Jet off a motor that was in a old v6 converted to v8 third gen camaro I bought a while back and the engine was blown. So *** only know what that carb came off of. Then motor I am running now is out of a 72 malibu or something that I had bored .40 over and rebuild myself. I will check the #'s tonight and post them by tomorrow. Thanks again.

 

Ok got the specs!

Carb #1 is on the car right now is and the #'s are 7044502 BM 2363 This carb I pulled off a blown motor and dont know if any jetting or setting have been changed but seem to do a pretty good job with this engine.

Carb #2 is a stock carb off my 79 vette 350cid motor that I pulled out of the car to put the motor I built in. The #'s are 17059216 CMA 0939 this carb should be stock and not tampered with.

My Cam Specs are the following:
Cam Lift int .295 exh .310
Valve Lift int .443 exh .465
Lobe CTRS int 100 exh 124
Lash Hot Hyd.
Adv Dur int 280 exh 290
.050 Dur int 214 exh 224
Adv timing BTC 39 ABC 61 BBC 88 ATC 22
.050 Timing BTC 7 ABC 27 BBC 56 ATC -12

The rest of my setup I posted in a earlier post in this topic. I am also running a Edelbrock 50-75-100hp adjustable plate N2O kit. So far I have tried 50 and now 75. I normaly try and shift around 5500rpm but it does occationally see 6000rpm because the rpm do pick up pretty quick on the juice!

The current carb seems to do pretty well throughout the whole rmp range. It used to suck either down low or up high in the rpm range depending on the timing but I later found out I had the vaccum advanced hooked up to the wrong port. Now that is straightened out it runs a lot better all around.

My question is which of these carbs would I be better off with my setup. For any of you cam guru's, how is my cam grind for this setup? My friend wanted me to go with a milder one but the guy doing my machine work when I was rebuilding my block said to go bigger so this is what I ended up with. Also what could I do to either one of these carbs to possibly make my car perform better.

Thanks again and sorry for the long winded post

 

Ok,
Carb # 1 comes out to be off a nondescript '74 350 V8 (definitely out of a chevy) w/auto and california emmisions.

Carb # 2 comes out to be off of the '79 L48 corvette engine with auto... 49 states legal

Both carbs are very similar, I would say the '79 carb will work slightly better, but you may not see a noticeable difference...

 

Just don't exhange primary RODS between the 2 carbs. 70-series and 170-series carbs have different primary rods.

Primary jets and secondary rods are interchangable, however.

 

Thanks for all the input!
Any more suggestions on which carb to use? Would that that modification to help open up the secondary butterflys work with either one of these carbs and would it benifit my setup? If so, how do I make that modification?