Performance carburetor

[mike561]

Im looking to get a new performance carb in the future, whats the best type to go with and not hurt gas mileage but still gain performance???

[silicon212]

Stick with the one you have.

That way, your computer system continues to work and you get the most out of your engine while still saving gas.

[mike561]

stick with the q-jet? what im wondering in general will i gain any h/p with a better carb?

[silicon212]

No. Carbureting an engine is an artwork - too many people don't do this right and wind up overcarbureting an engine. While a 750-scfm carb would do good on a 350 running at 7K RPM, it is too much for the same engine at driving speeds. Your 305 would do good with no larger than a 600-scfm carb. Now here is the thing - if you demanded high-RPM power from the 305 (being completely hypothetical here - a 305 isn't exactly a powerhouse), that 600 would run out of air at high RPM and engine performance would suffer. If you put a larger carb on it, venturi speeds will be too low and the carburetor will not properly mix the air and fuel - causing other problems.

A Q-jet is, for practical purposes, a variable-venturi carb, providing the proper airflow in all engine RPM ranges - it delivers what your engine needs at any range. If your engine demands 600 SCFM airflow at 2200 RPM, the Q-jet delivers that - but the Q-jet can flow up to 780 SCFM for almost any street-strip need.

If you feel you need to run a 'performance carb', then you will also need to replace the distributor on your engine with one which uses mechanical advance (vacuum and centrifugal). You then lose the power advantage of an aggressive, computer optimized spark curve.

The 350 that is in my car now has about 286k miles on it since its 1993 reuild. 220k of that mileage was spent under the hood of a 1975 Grand Am. The carb I used on it was a Carter AFB 600. It was a great carb for its application, but the E4ME Qjet on the engine now (as well as what you have) is just as good in city driving, giving higher top-end (it's not wheezing at higher RPM like the Carter was), and better economy as well.

[mike561]

ok just wanted to clear that up, i remember hearing that you'd have to rewire a few things too

[PeteA216]

I agree with silicon, although I did actually have great luck converting my engine to pre-ECM it is a lot of work and in your case may be more trouble than it's worth. Doing so requires a lot of tuning and know how. I did get a nice power gain, but fuel economy suffered a bit. If you still want to get a performance carb while leaving your ECM and fuel economy intact Holley does offer a performace carburetor that has the TPS and Fuel Mixture solenoid exactly as a stock Q-Jet does. It is big $$$ though.

[wafrederick]

Stay away from Holley for a carburetor,a pain in the butt to set up.Edelbrock makes the best carburetors and are the same as q-jet,are set to put in with no tweeking at all

[mike561]

yeah i had either a edelbrock or holley in mind...

[silicon212]

Originally Posted by wafrederick

Stay away from Holley for a carburetor,a pain in the butt to set up.Edelbrock makes the best carburetors and are the same as q-jet,are set to put in with no tweeking at all

Edelbrock makes two different carburetor lines. One is the aforementioned Quadrajet - it's not a knockoff either as Edelbrock now owns the licensing and tooling for the Q-jet. The other is a rebadged Carter AFB.

The AFB is an excellent carburetor for non-computer cars - I much prefer them over Holley carbs. Easier to setup, less trouble-prone. In fact, my AFB (Carter/FM and not Edelbrock) didn't need a rebuild until it had piled on about 175,000 miles!

I still think the Q-jet E4MC/E4ME electronic carb is best for a computer car.

[silicon212]

One other thing -

If you live in an area where your vehicle is subject to emission/smog inspection, you will have a much easier time with the Q-jet. As great as the engine ran with the AFB, getting it through smog here in Arizona was a beyotch. Same engine with same cam, heads, valves, intake, etc - and it will run on the IM147 test dyno for 15 seconds before the computer passes it (the IM147 is supposed to be 147 seconds on the dyno), first time, with electronic control and the aforementioned E4ME.

[mike561]

We dont have emmissions testing here in fl so im not concerned about that. what if i were to get a 2 barrel edelbrock carb (if they exist) would that be better to gain power but without hurting gas milage as well? btw this car is also my daily driver, hence why its gotta be fair on gas still.

[PeteA216]

A 2BBL even if you can find one made by Edelbrock will possibly give you better gas mileage, but will also significantly reduce the engine's peak power output. Honestly, you're probably better off sticking with what you've got, like Silicon always tries to say; an ECM will make an engine run at it's peak for both economy and power output. If you want some more power, and keep, if not improve mileage, then TBI or MPI is probably the way to go, however it's pretty involved.

[mike561]

I just figured that since im getting a k & n filter why not get a carb to go with it, i plan on having the exhaust redone too from the headers all the way back. what kind of power gain should i expect from that? i want flowmasters, with the dual pipes out the back.

[silicon212]

A two barrel will have lower city performance, and lower highway economy, than the Qjet will.

[bobss396]

I agree with sticking with the Q-Jet. If you can get a good deal on a new or remanufactured one, that's the way to go.

The knockoffs are also very good. I had one years back that was made by Carter and it was excellent and provided lots of power to a small block that I has with 202 heads and a mild cam.

Bob