Great thread OP, and not trying to hijack, but thought this relevant...... I've got a square bore intake and want to run the unmolested spread bore QJet taken from my 80'. I should be OK with hood clearance as I will be fitting the L88 hood. I guess the question I have is what kind of effect does an adapter have on performance, and might I be better off just buying a Holly HP carb instead given the cost to rebuild the Qjet, buy the spacer, etc? It's going on a fresh, moderately built 383 with a 2004R and 3.54's out back. Just a street car.

 

Which intake are you running? If there's a spread bore equivalent, I'd go with that. The GM 10185063 intake is a very nice piece. (ZZ4 intake)

Spread bore adapters do hurt power a little bit.

For a street car, the QJ is gonna come out on top so I'd try to run one if at all possible.

Luckily the performer RPM is still available in spread bore which is a great intake.

 

Ok

Let me preface this by saying that every piece of your fuel system matters!!!

The achilles heel of the Q-Jet is it's small fuel bowl, it out paces any other design in every other area because of it tuneability (great idle circuit design)

For daily driver the stock stuff is ok BUT, if you run your rig over 4500 rpm regular there is a significant advantage to working on your fuel delivery system. I won't go into that now,we'll save that for another time.


The Skinny on the stuff I have tested personally.

1. I have seen no HP loss, the results I have seen were to the contrary (not to be contrary, sorry)


Adapter
Go buy the Mr. Gasket Square bore to spread bore adapter


http://www.summitracing.com/parts/mrg-1932/media/images

with some conservative hand blending will get you about another 3 horsepower over stock,the key here is conservative.

Just so you know though, unless you're a pretty good shoe you will not feel 20 hp (most didn't) unless you are wringing the innards out of your stuff. The daily driver will never feel it.

Air filter housing

I have tested most all of the designs and the best design for the dollar is the one made by MR. Gasket for the Q-Jets (complete metal bottom) not the one with the plastic extension piece, forgive me I do not remember the P/N (its been a couple of years)

Gasket

First, It matters

Run the thick open plenum gasket (factory style)



Lastly never overtighten your Quadrajet it will warp and ruin the body


One Last thing

Stick with a 14" x 4" air filter element if it will fit under the hood (I cannot remember it's been a while since I sold my C3)

if you deviate from this in either direction it's a detriment to performance and personally I do not like the filter top elements I think they are dirt sifters and the stuff ends up in your engine.

Finally grease all of the filter contact surfaces when you put your filter on. you should never get more than a very light dusting if any on the inlet of your carbs venturi inlet.


My Two cents, Jimbo

 

I've generally just tightened my q-jet with a nut driver. Will it warp under nut driver torque?

 

Nope unless you have a superman grip you are in good shape...


Good Job, Jim

 

Since there seems to be a dire shortage of opinions here I absolutely must offer mine...

To all those who say nothing runs better than a well-tuned QJet, y'all are absolutely right. But getting a carb as complicated and mysterious as the Quadrajet to run properly and reliably on a 'custom'application can be a difficult trick if you're not an expert. Unlike a Holley, the QJet wasn't really designed for repeated disassembly and reassembly, it was essentially created to be put together once, bolted onto whatever engine it belonged on and run until it went to the crusher.

That said, it does have some neat features that make it very different from a garden-variety Holley 4150/4160-series carb...1)It is essentially a variable-cfm design, so you can conceivably take it off of a 327 and bolt it onto a 454, and it will run fairly well on either one. 2)It is small, which can be important in limited-hood-clearance situations a la C3 Vette. 3)Its spread-bore design makes it great for economy, as long as you can resist the temptation to stick your foot in it. Its downsides are (again) difficulty in tuning, fiddly choke mechanism, limited bowl capacity, and very easily-warped airhorn. Oh...it's UGLY too.

As for the Holley, they have idle calibrations that are tailored to their cfm ratings, so putting a 750 on your small block isn't likely to work very well. It will run, but likely won't respond to idle mixture adjustments. Best carb for a 350 would either be a 650 or 670 cfm. You generally give up a bit of economy with a Holley, but once you've got the right-size unit on your car they are very easily tunable-set the float levels, get the right power valve in there, dial in the main jets, and you're good to go. The biggest negative with a Holley is that they tend to run into hood clearance issues on C3's. The best thing?

They LOOK cool...

 

Hey Shark Racer, I'm running a Pro Comp 2025 Dual-Plane Crosswind Intake (the more I look at it the less likely I think I am to fit this under even my L88 hood)


Jimboscarbs and Birdsmith, thanks for the info and links, very helpful!!

 

i'm full race, 383 to 7,000 RPM..... i run a mighty demon 750 annular, picked up 15+hp over my holley... on the Dyno....

and yes... it runs PERFECT, and I will never part with it...

that being said... I think the Q is a great carb for just about any other situation. Other than smoking Mustangs!!!

 

Just jumping in on the Qjet with adapter subject. I have Vortec heads on my 383 and the only Edel RPM airgap manifold available is a square bore. I'm using an adapter like jimbo shows, with no massaging, with a dropbase air cleaner and a 3 inch filter. This barely fits under the stock 77 hood using a flat nut instead of a wingnut (its that close). It runs good with great street manners.

 

you are correct with your engine setup I would guess you are in the 500 Hp range???, unless you did fuel delivery system work from front to back the Q-Jet would not suit you. As far as fuel baffling I think it would be ok, I built a ton of Q-Jets for circle track racing and never had slosh of spill over problems

I am curious though what size fuel supply line and what pump are you running?

also were the gains you saw across the board? average HP and TQ numbers increased?


Jimbo

 

I have had that setup on several engines, the only detriment you will see is the 3" filter. However, unless you are wringing every last ounce out of it you wont notice it.

The only reason I mentioned it I had tested all of that stuff back to back when I was putting together a customer guide for the stuff I sold.

I did it so I could talk apples to apples when someone called.
I will have to dig it up and post it on here.

The funny thing was ( racers are all the same) I would ask customers before I built their carb "is your camshaft and heads legal"? (class racing) the reply was always ya ya my stuff is legal.

Carburetor delivered
phone rings, uh hey man this carburetor stumbles when I first pick up the gas...

Reply: are you running legal heads and camshaft???

Long pause, Tic toc

uh,well no

Reply, I would laugh and tell them that was the first thing I asked you before I built your carburetor...

I would then laugh again and tell'em don't worry, do this this and this your all set.

Jimbo

 

yea... last Dyno was 460hp at the rear wheels... 440tq

I am running the stock fuel lines... never gave any though about changing them.... and a stock pump... i have seen the pressure from it while on the dyno, and wot i still have 4-5psi....

 

is the 4-5 PSI you are seeing on the dyno

or at the end of the straight away?

it makes a difference


Best Regards, Jim

 

just WOT on the dyno.... i have a fuel rail gauge.

 

Based on personal experience with other set ups ( I have not tested the same exact set up you are running)

I would make this same check while under straight line acceleration to the maximum intended RPM you regularly run.

The reason I say this is the pump you are running (Positive displacement) is way more efficient at pushing fuel than pulling fuel.

your test has been a static only test (sitting still)

The effects on fuel under acceleration play a part in your fuel systems ability to deliver an ample fuel supply.

you may be ok because of the size of the fuel bowls on you carburetor and the length of the straightaways you race on and the time you are on the wood. If all of this is in your favor you may be ok.

I would check it in any event you may be surprised

Also are you running a stock ignition???

 

how would you test this? a fuel gauge inside? that is the only way i would know off hand


Ignition:

Accell HV coil and distributor, Accell module, MSD multi spark discharge system with rev limiter set to 7K rpm, Mallory 8.5 wires, accell shorty plugs....

 

Please never put it inside unless you put an isolater in line with it.

That is not a bad answer if you want a permanent setup for your track car either( be sure to get any air out of the line if you use one).

or

I would run something temporary, you could pick up a steel braided line route it where you can see it while driving and put a decent gauge on it, most fuel logs have a provision for a secondary gauge.

Remember the range you are measuring, to be master of the obvious, don't use a 0-100 psi gauge to measure fuel pressure 0-15 psi or less would be prefect.

As for you ignition, you are good to go in m opinion, the reason I asked is the stock HEI is a great invention, but it was invented to get average joe anywhere but down the race track.

Hope this helps, Jimbo

 

I installed a supercharger on my jeep jk and installed a fuel gauge on the A-pillar as fuel pressure is very important with a supercharger... The point I guess is it has a remote sending unit in the fuel line with a remote electric gauge. Works great.

 

I come from the circle track world, so that is where my recommendation is centered from.

I had also looked at some data loggers before I sent the pic of the isolater.

I wanted to tell you also, it looks like you do autocross or something of the sort.

The data loggers used in Kart racing, never really made a big translation into big cars (I used them when I raced Karts with my boys) the also have a transponder so you can keep up with lap times, I would check them out, money well spent for the competitive guy.

Its been awhile since I have looked at them
here is a link to one for automotive use. http://www.mmautoperformance.com/inn...FWhyQgod-zAApA

Also if you want to really go fast on the cheap (relatively) get into Kart racing, I raced at the Nationals at Tunica a few years back, it was the first year they ran the unlimited outlaw series karts there. I must say I went fast enough with no roll cage to get spooked and that does not happen easily.

Oh and the auto cross thing if they are not sniffing tires...

you should be doping your tires too, you just think you are putting down good lap times now...

Doped Tires = like being on rails


Best Regards, Jimbo

 

I hope he also has very snug belts and a Kirkey seat

(...mmm - gummy tires..lol , they'll pick up every rock in the pits too)