Thread: Quadrajet carb - why???

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This is more for education and curiosity, but ya never know.

I cut my eye teeth on Holley carbs as my performance choice - from 3 barrels, tri power Fords, 750 and 780 CFM 3310's but I'm now am using Edelbrock Performers and really do like their ease of tunability. After reading some posts here and elsewhere, I'm interested in what folks have to say about the Quadrajet. And why. The Eddy's perform well, but in the age of $3.50+/- 93 octane gasoline, is there a better choice, like that Q-jet for day in and out cruising with only a stomp of the gas pedal to have lots of performance. My chief complaints with the Edelbrocks have been ease of starting after sitting for a couple weeks and very rich idle and low end. Yes, I know that the idle and low end richness can be somewhat corrected with jet and rod changes as well as other adjustments. I've done a lot of that, but it's still a bit too rich.

Then of course, what can be used to correctly fit the Q-jet on a, for instance, a Performer RPM manifold? These intakes have a carb base design for the Holley as well as the Performer carbs - the carb side long oval holes are too small at least for the rear. Adapters will tend to choke down the flow and actually add a venturi effect.

What kind of performance gains would I expect to feel (this is seat-of-pants) vs say a 600cfm Edelbrock? Gas mileage? Guestimates of course accepted

OK guys, food for thought and discussion. I'm nowhere ready to spend the several hundreds of dollars to convert. And if I do, and for some more bucks it might just be the FAST injection, but that's grist for another discussion.

the qjet will get you no millage as far as i know. i run 390 holleys on mild sbc for the street. once tuned they offer great response and good millage.

Coming out of the marine industry, I have a lot of experience with the Q Jet. The vast majority of Inboard/ Outboard and straight Inboard engines built by Mercruiser, Volvo Penta, PleasureCraft, and OMC, to name a few, came off the assembly line with them. They were used on everything from 4.3's to 454's.

The Q Jet is one of the most misunderstood carbs out there, and are actually very good in design and performance. The concept is that you have these two very small primarys that you run on for economy, but when you need more speed you kick in the huge secondaries. I've had a lot of boats with them, and have always marked my throttle with a line at the point where the secondaries were just starting to open. If I kept my throttle below that line the fuel economy was fantastic (I had a 27 foot cruiser that only drank 6 gph) but if you went beyond that mark it started to drink fuel like there was no tomorrow.

Lots of big GM cars came stock with them too, like 472/500 Caddies, 455 Olds, and similar Pontiacs. The racing crowd has never done much with them, why, I am not sure. But lots of street engines have had them on over the years.

Don

If you notice RPM style intakes do not have a Spread bore/Quadrajet base it is because it would not be useful in terms of flow,the small primaries need smaller ports to function properly and keep velocity up.You might look at the Edelbrock Performer Air-Gap #2601 which has a multi-fit base.One manifold that is overlooked since they don't advertise is the Offenhauser Dual-Port which has isolated runners for primary and secondaries check out their catolog at Exceter Auto online and read up on it,by speeding up velocity at lower speeds they are more fuel efficent when the larger primaries open the velocity picks up the incoming extra fuel along for the ride.The Spread bore manifolds are better suited for this than the square bore intakes.I have ran these with a Holley 650 Cfm Spreadbore carb that replaces the Quadrajet and was very satisfied with performance and mileage.If a quadrajet is in good shape it may be OK but tuning it and finding parts not too EZ.

don's right on the money. my problem was not being able to keep the secondaries closed and them big suckers can destroy millage quick. had a friend who was an ace on them but sadly he passed. not too many out there that can get them right any more. to be honest had i not already had an intake i was going to run a 2 barrel on my shop truck. the 390 and the 450 holley's work really good for small street motors.

arn't Q-Jets just Rochester 2 Jets with 2 extra larger barrels? messed with Q-Jets but never 2- Jets

anyway, they can provide good economy if you keep your foot out of it.. but once the secondaries opens up, that howl just sounds so cool..

Ahh - now we're getting into the meat a bit.

What Jeff pointed out about the manifold is one of my concerns if I were to decide to try one. That's why my question was about adapters. Unfortunately, that Edelbrock #2601, - it wont work on my SB Ford and they don't make one either.

As far as howl - gotta love that sound and even my Performer will once both levels of the secondary open. Of course, any fuel economy ----but by then, who cares when the music is playing from under the hood

They do make an adapter to use a holley on a quadrajet manifold. I used one to put a quadrajet on my 460 dually after I got tired of trying to make the stock Holley work right. I just flipped the adapter over and seems I may have drilled some holes or such, but it did work and that Old dually ran better with the quadrajet than it ever did with the factory Holley.

Originally Posted by IC2

Ahh - now we're getting into the meat a bit.

What Jeff pointed out about the manifold is one of my concerns if I were to decide to try one. That's why my question was about adapters. Unfortunately, that Edelbrock #2601, - it wont work on my SB Ford and they don't make one either.

As far as howl - gotta love that sound and even my Performer will once both levels of the secondary open. Of course, any fuel economy ----but by then, who cares when the music is playing from under the hood

Now you are playing my song! (being a Ford guy myself) the Dual-Port Offy intake does come available with a Spread Bore base for an SBF,back in the mid 70's I sold some of those along with a Holley Economaster carb(450 CFM Quadrajet replacement) and Crower Mileage Maker Cam(still available) and had reports of 25+ MPG in Mustangs and Fairlanes and Falcons.

As to the adapter plate idea, it has been done more times than we will probably ever know, and the ones I have known about have not reported any ill effects from the small intake base holes, and some even said their car ran a bit better; and they loved the boot they got when the jumped on it. If you know someone who can tune one right, get yourself an adapter plate and turn it upside down and give a Q-Jet a try, you might be surprised; it might take a little modding to the plate, but I can't truly say.

I have run Q-Jets on all of my GM engines since my '68 SS396 (ran low 12's on either a Q-Jet or a Holley), up through the late eighties, I have one on the 350 in my '59, and they are excellent runners when they are tuned right; even "rough tuned" they will run pretty well. All of my work trucks had them, and I could get in the high teens on the 400s on long highway hauls, loaded; unloaded, they would often push into the low twenties. Best I ever got was in our '70 Kingswood Estate wagon with a 383 and an RV cam and Q-Jet; the run from Orange County to Flagstaff averaged 22 mpg over the 500 mile run - the car weighed 4800+/- unloaded, and we were going camping so it was loaded to the max. Like has been said, if you can stay out of the secondaries, they will reward you in one way, and when you pop the secs open, they reward you in another; the push is amazing, but the mileage goes down the hole, so to speak.

Edelbrock does make a Performer RPM specifically for spread-bore applications on SBC - the 7104. $175 at Summit, JEGS, and others..

PERFORMER RPM Q-JET (1500-6500 rpm)
Designed for 1955-86 262-400 c.i.d. Chevy V8s for spread-bore (Q-Jet) or square-bore carbs. Delivers maximum power and a broad torque curve for high-performance street. Carb pad will accept square-bore carbs without adapters. Performer RPM Q-Jet has same provisions as #7101

Originally Posted by glennsexton

Edelbrock does make a Performer RPM specifically for spread-bore applications on SBC - the 7104. $175 at Summit, JEGS, and others..

PERFORMER RPM Q-JET (1500-6500 rpm)
Designed for 1955-86 262-400 c.i.d. Chevy V8s for spread-bore (Q-Jet) or square-bore carbs. Delivers maximum power and a broad torque curve for high-performance street. Carb pad will accept square-bore carbs without adapters. Performer RPM Q-Jet has same provisions as #7101

You are correct - but what I said is that they don't make one for my SB Ford, and that the one Jeff referenced wouldn't work on that Ford engine

Over the years on my trucks I have had several combos---with the Q jet on my 84 chev 454 about the best we could do on milage was 6 mpg---On Fords 460 with the 780 vacume Holleys around 9 mph and with the 850 double pumpers could get 11-12---all this was when pulling 5 wheel trailers on long road trips--the 850 dp worked best because we had lot more available BEFORE the seconaries cracked open

You're right about the big blocks, Jerry; all of my good mileage was with small block engines, regardless of the cu-in - they all were excellent if you kept out of the secondaries. Now, the 396 and 454s, well, they just got from six to twelve, pretty much whether you were going up or down, or empty or loaded; hitching a trailer on really sucked the mileage down, though.

Get "Cliff Ruggles" book on quadrajets. He is the Guru for Quads. He also rebuilds them and sells everything to repair and rebuild them. Call him at ..1-740-397-2921 and he will tell you everything you need to know about Quads. Google "Cliff Ruggles" to find his website.

Jack.