quadrajet carburetor.

[stevef]

Not sure if your looking to also drive it on the street but if you want a good race Q-Jet, i would call Leon Miranian 1-518-793-7933. Hes located in New York. Ive been as fast as 10.80 with one of his Q-Jets.

[Ron Golden]

Jeff,
I didn't know about the 450 cfm rating. Just goes to show, one is never too old to learn something new.

Ron

[My427stang]

How do you guys that run them in some of the fast cars get around the small float bowl?

I was under the assumption at some point there is a fuel feed issue, or is it a wive's tale if you have enough volume to the carb?

[stevef]

i run #8 line from the pump to the carb, and have good race fuel pump. the fuel pressure gauge barely budges going down the track.

[Keith Morganstein]

How do you guys that run them in some of the fast cars get around the small float bowl?

I was under the assumption at some point there is a fuel feed issue, or is it a wive's tale if you have enough volume to the carb?

I don't really consider the Q-jet for all out race, though it can be used that way.

I like it for street/strip because it has good primary fuel metering, and very adjustable secondary action. The small primary can have good economy and be very responsive. I believe you would consider it a 5 circuit carb.

If you use a good fuel supply system, get rid of the inlet fitting filter and use a higher flow needle and seat (there are a couple styles) you should have enough fuel for most any street driven small block.

Funny, but at this point I don't even have a carb on anything I'm driving. I just gave my last good Q-jet away.

[panic]

decrease spring tension on the secondary air valve opening. That's where a lot of the bogging, etc. stems from.

I've had good luck loosening the secondary spring wind-up and relying on the dash-pot to cover the transient; drill the little bleed hole out a few thou at a time if needed. This is a delicate balance, because the secondary rod height is a function of air valve rotation, so you want to be sure it's doing what you want for metering as well as covering any stumbles. You may have to try several hangars vs. tension even with the same rod pair.

[Cogburn]

I haven't done any q-jets for footbraking. The ones I have done were for mud drags and they were made to just slam the throttle wide open on the light.

With footbraking it seems there might be a vacuum problem and the dashpot that normally controls the opening rate of the secondary air valve will be ineffective.

Adjusting the air valve spring to work without the dashpot might be a little tricky.

[jeff swisher]

I am going to get it for this post
on my car that i ran the Q jet on i removed the dashpot that controlled the secondary air valve ..Bent a little known rod to make it a mechanical secondary and set the wind up spring on the light side,,That little 355 would take all the air you could feed it and quick Never a bog

Then my my uncle saw my handi work He wanted to put it all back together and tune it with the dashpot and the drillbit tricks I let him tweak and tune for about 5 hours ,Then he gave up and admitted that i had the best tune on it ,,And he had never seen one that would run better without the dashpot ..Except mine...

[crazyman]

I wonder how a feedback Qjet would work if you jetted it correctly with the metering solenoid closed, then set up an adjustable pulsewidth box to open it up when running E85. Set the box at the right AFR, and it should be good at any rpm.

One could almost have a selectable secondary fuel system. In theory, it would work best for a street driven dual tank pickup truck. One tank for gas, one tank for E85 with the pulsewidth box wired into the tank selector switch.

[MadBill]

Holley used to offer two such systems for their OEM-replacement style carbs. They called them "Mile Dial" and 1/4 Mile Dial" as I recall. The first allowed leaning out the cruise mixture for economy via a dash-mounted control box knob that adjusted the solenoid duty cycle. The second did the same for WOT mixture.

[ZEROMAN91]

There was a guy named val headworth that had a real good rep for doing quads, he did one for a guys duallie and really picked it up both mileage and performance.

[esahc]

What is the best Q-Jet to find for a performance street application? I noticed that the Q-Jets on the late '70s Cadillacs, Buicks, and Pontiacs are always missing when I go scouring through the wrecking yards.

Mercury marine aka mercruiser as well as outboard marine corperation aka omc both used quadrajets well into the 1990's. Boats are typicly ran at solid state with much less throttle fluxuation than a street car, as a result of this you tend to find better cores on a marine engine. The only real difference is the float bowl vents on marine carbs have a stub to dump fuel into the primaries should you have a stuck float or similar over abundance of fuel, they have to do this to meet coast guard spec, other than that they are the same casting, all jets etc interchange. Now days with everything going to efi the marine carbs are cheap at marine salvage yards. You can often find awesome deals on take off from shops that speciualize in efi conversions pretty cheap too!

A gentleman in an earlier post referred to a 450 cfm quadrajet in a buick..... alot of the 4.3 mercs used this carb as well, but some also used a 500 cfm version if i remember correctly, alot of the early 4.3 gm and 3.8 gm engined cars had the small quadrajet too.

As others have said if set up properly they make a pretty damned good street/strip carb. They usually will offer far better part throttle responce/ fuel econemy than a comparabley sized holley if set up properly. They got a much undeserved bad rap back in the day and still do now. Basicly due to their complexity and the fact that they are a very tunable and somewhat complex carb. Jets, metering rods etc arent as readily availible at parts stores as the holley parts are but are readily availible from places like carb parts wharehouse and others, the parts are cheap and typicly ship within 24 hours. Get the hp book as others have suggested, even if you buy a carb already set up and pay someone to tune it for you the read alone is well worth the money, that and most autozones will have it and other rochester carb tutorial books on the shelf. Once familiar with their strengths,weaknesses and quirks you will most likely find it much easier to dial in than a holley, I know I have always been able to make a quadrajet work well and have never had any real luck in tuning the holley, but then again i grew up messing with big block oldsmobiles and pontiacs and didnt have alot of money, always wanted a holley but worked with what i had. By the time i could buy a holley I wanted the quadrajet back lol, ive even ran a few of them on ford small blocks! it was worth it just to see my fellow gearhead high school buddies scratch their heads

[AUTOMAN]

Buick 800CFM from '75-'78 with APT and side fed fuel(ala chevy)
Some had APT and altitude needles along with 2 prim. needles.

QJet freak and I made them run good!

Sec. pre-load is key, along wih sec. fuel squirt-instantly.
Redrill sec. fuel ports from above to below air valve. Plug original holes.

Sec. fuel accel "pump" before the air valve opened!

cliff

[gnicholson]

Those late model v6qjets were the same size as the v8 carbs they just restricted the secondary. The best book on qjets was the original doug roe book . He was a Rochester engineer. The factory tuning on the pre 71 carbs are the best but they all can be tuned

[Monzsta]

I've ran the gambit with carbs. I tried my damndest to get Hollys, Carters, and all the variants to run nice. I always went back to the trusty Q-Jet. I found them to be the easiest to tune, and stubbornly reliable. Secondary adjustments are so easy I had a couple sets of hangers and custom ground needles. I always hated Hollys and having to crack a sideways fuel bowl on a hot manifold never gave me a good feeling.

You absolutely need to have a good fuel supply due to the small fuel bowl but they are almost impervious to G force loading and the needle and seat can take some decent pressure without flooding the carb.