I have a rochester off a '79 auto corvette on my '84 corvette.
not happy with the carbs performance and am trying to find the cfm's on the stock '79 vette carb so I can get an equal holley.
any help
Harry

 

i believe it's 750cfm, and i'm glad you saw the light

i call them quadrajunk's for a reason...

you might also wanna take a look at demon carbs...i hear nothing but good things about them

 

If the QJ is rebuilt correctly and an anti-leak kit is installed, it can be a great performing carb. And it will likely give you noticeably better mileage than an equivelant Holley. It's actually quite a simple carb to rebuild.

 

I agree with Corvette Kid, I had a Quadrajet on my 1980, 355 C.I. that put out 375 HP, and after I rebuilt it, I didn't have any problems. I believe the actual flow was in the 635 CFM range. I had a friend that worked at Rochester Products here in Rochester N.Y., so he was able to get me metering rods, hangers, and jets right off the assembly line. One big problem is usually the float, which begins to absorb gas as it ages, then creates all kinds of problems. Switching to a brass float was the first thing, the second was, when, or if, you elect to rebuild it, remove the plugs in the front part of the carb at the base. These are the idle mixture screws which are set at the factory, and it will give you more latitude when setting it up. The hardest thing I had was setting the choke, but found an interesting tool that used a magnet and hooked to the butterflies so I was able to set that up with no problem also. As mentioned above, they will give you better gas mileage because the primaries are smaller than the secondaries, so if you aren't getting a shoe shine from the fan belt, it should give you better numbers. Hope this helps!!

 

750 CFM should be plenty for a 350. Too many people over carb the motor and it could hurt performance.

Bigger is not always better. The carb has to be consistent with the rest of the motor. The intake, heads, valves, cam, and exhaust.

So I don't think it's the size that's the problem, but the operation.

 

 

Yep! Q-Jets are probably one of the best carbs ever produced, and they had a long time to refine it. They are either 750 or 800 CFM; easy to tell looking into the venturi. I got the 800 unit I rebuilt and modded off, of all things, an '80 Olds Royale 307 ci. It's currently on a lightly modded '76 400ci SBC sitting on an engine stand. I removed it from my '86 GP after a kid in a *** PU slammed into me on the I-state. It worked very well. Yes, I do like torque!

The size is not as critical with Q-Jets because the secondaries operate on demand airflow. A good book to get on these carbs is "Rochester Carburetors" by Doug Roe, from HP Books, Berkly Publishing Group, ISBN 0-89586-301-4. It's well worth the $17. It has sections on HP mods and tuning that any reasonably competent mechanic can do. I figure I'll put the fully rebuilt 400 in my '89 'vette (assuming I ever find it) after I get tired of fooling with the TPI electronics and go stark raving retro!

I'm no expert on Hollys or other "HP" carbs but I think they lose a lot of driveability and mileage by being too simple and they cost way too much for all they are. Compared to a Q-Jet, most are downright "kiddy carbs". Unfortunatly, I've seen Q-jets disappearing from most normal junkyards 'cause the cars they were on are getting crushed. Still see a few at swapmeets, $20 usually.

 

"Compared to a Q-Jet, most are downright "kiddy carbs".

For the average mechanic ,bigger jet= richer;smaller = leaner (Holley) was all they wanted to know.
Metering rods / hangers / jets made Q-jets too complicated so they got a bad name; familar story when things aren't understood.
Plenty of past stock class record holders running Q-jets.

 

I have twin 350s in my boat..with professionally rebuilt Marine QJs,
they're great for a boat with their small primaries (fuel economy) and the large secondaries (for power), would I ever put them on a vette..no, I prefer the simplicity of Holleys for that. I've rebuilt QJs and Holleys in the past and the Holleys with external float adjustment etc. are much easier for me!

 

If it is the 17059211/SM, 17059210/AUTO carb it is a 800 cfm Q-jets. I had a bad experience one year at the US Nationals for having one on my 79 A body. It was suppose to be the 17059203/SM, 17059202/AUTO 735 cfm model. The Q-jets are a great carb like many of these guys suggest.