Rochester Carb
 

How can I tell how big my carb is? It is a Rochester Quadrajet. I want to get a Edelbrock/Holley 650 CFM carb but i want to make sure that I'm not going down in size.

There should be numbers on the side somewhere. Google them.

750 or 850 cfm.

So would getting a 650 cfm edelbrock or holley carb be a stupid thing to do to get more power?

Stay away from Edelbrock carbs.

Unless the engine is built, the Q-jet is plenty of carb for you. No need to swap it. You'll also get better mileage with the Q-jet. If you look at it, you'll notice that it has much smaller primaries than secondaries, which means when you are driving around town at part throttle, you are using less air and fuel.

- Justin

The one I am getting is a Holley Carb. 650 Cfm and I'm getting it for free as well as headers for free. would going down in size be better power since its a better product or is better to leave the rochester on?

Look into that Q-jet book I sent you the link for, there are ways to optomise the preformance of the carb but playing with jetting and meetering rods. Of course the CFM's will not change if you know what your doing you can make a carb run real sweet or real ****** depending on your ability level. Ive had my share of trial and error in my day but you learn quick

The headers will definitely be nice, but it's up to you what you wanna do with the carb. You most likely won't notice much difference if the Holley is setup for your combo, since you really don't need all the air that the Q-jet can provide. I don't know your exact combo, but I'm pretty sure I remember you saying that it was a fairly mild combo.

- Justin

Its pretty much mild, I'm just thinking I'm better of with a holley than a q-jet

is it a spread bore holly?

Now that's the question of the day! Good call.

yeah... fu*k those adaptor plates.

:wink:

I jsut know its a holley, and I also am not changing it jsut to change it bonzo, I want to get more power, and my carbs choke is not working correctly. plus, its FREE.

Q-jet choke problems are almost always the bimetal spring on the side - like $10.

I'm busting rocks, good luck.

If it's a square bore Holley and you have a spread bore manifold, it won't fit right unless you use an adaptor- which is a total hack ass band-aid.

Q-Jets are very underrated. I'd run a Q-Jet over a Holley 650 vacuum-secondary.

go to auto zone, pick up a haynes or chilton manual on Q jets. tells you every single thing about them, in ever model ever made. they are very underrated....theres nothing wrong with a nice running Qjet. theres a reason pontiac, buick, and olds kept running them for 30+yrs. holleys were just better marketed and popular.

Good advice- I'd take it one step further and pick up HPBook's "Rochester Quadrajet" and work with that as well.

the easy way to find out how much carb your car needs is to use the air flow formula.

(CID x Peak RPM x VE) / 3456 = CFM Draw of your engine.

going one size up from the airflow demanded by the engine is a good way to apply the results.

you will find that GM, like most manufacturers, oversized carbs from the factory. it is jsut an easy production line way to avoid minor tuning issues as the extra air flow made them more forgiving.

i was talking to the orginal poster.....but anyway.....

I know. I was recommending that he get the Rochester manual in a roundabout way :wink:

They make non CC q jets right? If so would the gas milage be about the same with the CC qjet?

How are there tunability? I want to be able to drive my car and not suck down gas! How much better milage would I see with a q jet, verses a demon?

WF:

Yes, there are non computer-controlled Q-Jets. The pre-74 models are probaly the best to use IMO. I'm not sure about mileage, but personally I feel that you could get better mileage out of a non-computer controlled Q-Jet since the cc ones were rather primitive. They are harder to tune than Holleys and Demons (which is why most people dump Q-Jets and call them Quadrabogs, Quadradoorstops, etc.) but when they are tuned correctly they work awesome. You drive around on the small primaries for economy but you have huge secondaries when you need them.

However, as much as I like the Q-Jet, I will be running a big Holley on my car, and all the other classics I work on have Holleys/Demons as well. They are just that much easier to tune, and parts are much easier to find.

Do a search on NastyZ under the username "Damon" regarding Q-Jets. Damon is a Q-Jet guru.

Thanks alot man, I never understood why everyone bashes q jets, my lg4 had so much more top end then my buddys L89 with more mods then I did. I shot damon a pm, asking him, I can tune a non computer controlled carb simular to work with my combo.

raftermeng, you can have my old qjet for $5

pre 74 for non-computer controlled? my 78 doesnt have anything close to a computer in or on it. even has a clock with actual minute and hour hands.