Another carburetor question , I have a 1978 L82 manual trans. 350 cu
motor with mild cam , headers, dual plane intake . Wanting to put a 750cfm holley double pumper . Can anyone tell me if this is too much carbuetor . Presently running a Q-jet from factory cfm ? Thanks for any input.

 

Are you using the 882 OEM heads? What's wrong with the factory Q-jet which is actually rated at about 700 CFM?

I have had a Holley 650 CFM 4175 vacuum secondary carb on my stock L-82 4 speed for 25 years now. Runs great.

Just curious-what cam are you running? I am thinking of having my 882 heads rebuilt with some minor porting etc (want to keep it original-I know there are MUCH better heads but...)and installing a voodoo 262/268 cam with a felpro 1094 head gasket. With stock L-82 internals, McJacks shorties and dual 2.5's, the car produced 233 RWHP with a weak #6 cylinder-thus the cylinder head rebuild possibly) Thanx.

 

Your Q-Jet is a much better carb and can flow 750 cfm. It's also much more efficient during normal driving (better 'cruising' mileage) AND is self-regulating to match flow requirements to whatever engine it is installed.

Just rebuild what you have and stick it back on the engine.

 

JB 78L82

I dont know what size cam I have since I bought car with cam in it already , Reason for considering holley 750 dp is that I have good torque and take off power but in second gear I seem to loose torque and gradually pick up speed . Thinking maybe I need larger carb. I have original double hump heads

 

Your existing carb is already 750 cfm. Bigger is not better nor is switching to a Holley.

 

you probably got too much carb...a 600 or 650 is plenty for what you got.

 

The hard part with a QJ is getting it set up. Once you've figured that out, you're golden and will have the best street induction setup you can get short of EFI.

 

i agree, for years i have had a strong dislike for the quadrajet, recently i rebuilt one and put it back on my L-82 re jetted an d adjusted and it works as well as any of them. i think a 750 double pumper would be o.k. i also think for a modified 350 a 600 is too marginal, for a pickup that is stock a 600 is o.k. but why put a carb smaller than the factory installs on it. let the attacks begin.

 

A 600CFM carb is pretty good for a mild 350, and if the stock QJ has really been beat on (stripped fuel filter, warped airhorn, bent throttle shaft or whatever) for some it will be better to just get a new carb.

That said, you can still pick up another QJ for great prices...

 

Q-JET is king when built correctly don't ditch it

 

I am sorry that I no longer have my OEM Qjet-lent it to a friend in 1983 for his Trans AM built 400 and never saw it again-don't ask-more for originality than anything else. As others have stated, IF you can get the qjet to run right and keep it that way, the Qjet is pretty good. However, the the holley 4175 650 Q jet replacement on my mild L-82 4 speed today (since 1983 on the L-82), has run flawlessly all these years and rebuilt about 1.5 years ago by me. The engine is totally stock internals with no pollution control, 2.5 duals, Shorty headers, 1.5 comp cams roller tipped rockers, the Holley 4175 etc-dynoed 233 RWHP recently with a weak #6 cylinder. The Holley 4175 makes good power, idles better than the Qjet, easy to rebuild and tune, better cold start and hot characteristics than the my Qjet, and it make good smooth power throughout the rev range. The mileage was slightly better with the Qjet versus the 4175-and I mean slightly-nothing significant. If mileage is a concern, much more drastic measures are needed such as a 5/6 speed conversion-that will improve your mileage greatly-not using a Qjet versus a Holley 4175 on a car with 3.70 gears and a 4 speed, as an example.

I would keep the Qjet if you can and try to get it to run correctly, otherwise the 4175 is not a bad replacement. In my opinion, the Qjet is overly complicated for what it is capable of doing and at its core is just a carb not FI.

 

I too was a Quadrajet "hater" back in the day due to my lack of knowledge of them. I have always used Holleys because of the ease of tuning them. I recently have changed my opinion after reading up on the Qjet and seeing posts here on the forum. I recently had my Qjet rebuilt by a knowledgeable tuner that I found here on the forum. My car really runs great now.

My suggestion would be to use your money to have the Qjet rebuilt. I think that you will be happier overall.

 

Holley street avenger 670 is perfect.

I am not a fan of the qjet. Too many annoying problems.

 

Don't underestimate the fact that the Q-Jet is self-regulating!!! A Q-Jet can NEVER be "too much carb" for any engine on which it is placed. The primaries are relatively small and very efficient; plus, their transition between 'idle', 'off-idle', and 'cruising' modes is the best of any carburetor ever made. And, the secondaries only open up as far as the engine requires.

If you don't understand the operation and design of the Q-Jet, you can't really appreciate its capabilities.

Bottom line: All carburetors can be tuned to perform equally well at the WOT condition. There is NO advantage of one carb over another with a full-throttle setting...if they have been properly tuned. But, there is no other carb that is better at idle and transistion, or for economy, than the Quadra-Jet (assuming that you actually need a 4-bbl. carb).

Ditch it for a 'simpler' carb if you want. If you decide to do that, send the Q-Jet to me.

 

i was a qjet hater back in the day and only ran holleys but now i looked into the qjet more and learned lots about them and read cliffs book and talked to him about setting up the carb and damn what a difference good gas mileage and power i really like the qjet now and wont part with it

 

I agree with you about 95% of the way... with exception to your comments on full throttle. Square bore carburetors do a bit better in that regard, to the tune of a very small amount of horsepower, say half a percent.

But even knowing that, I will stick with a Q-Jet for the rest of the reasons you enumerated, I too believe that there is no better carb for a car that sees the streets. The amount of control you have over varying conditions is phenomenal (and also why they're so overwhelming at first.) It's the closest thing to EFI you'll find short of EFI.

 

You are correct and I agree with you for all practical purposes WOT is the same, but I gotta say this only because I built Q-jets for stock class racing, I dynoed everything I sent out the door.

On more than one occasion I back to back tested my stuff against Professionally built Holley's and the Q-jet will cover them every time within its CFM limitation. It does takes allot of work to do it but it will do it none the less and the instructions to do it are not in any book I have read, and I have read every carburetor book I could get my hands on.

For those that don't know, buy a good carburetor you will never be disappointed in your purchase it is one of the best HP per dollar purchases you can make. In defense of this ask any racer if he will ever sale a good carburetor (not likely) it will go in a bag on the shelf full of WD-40.

For racing stuff never buy a carburetor that has not been dyno tested

For those of you who have more time than money go get Cliff Ruggles book and rebuild it your self. you will not be disappointed (follow the recipe in the back of the book for what you are building).

As far as Holley's go the best out of the box carburetors for the money when I quit working on carbs were the HP series Holley's, run back to back against professionally built stuff they were not far off the mark.

My two cents,Jim

 

I can back up everything Jim says, and I've had exactly the same dyno results (some of which I've published here on this Forum). I can also back up his comments on the HP-series, especially the new "Ultra" series HP for street use.
Lars

 

what i would like to see is more intakes made to fit the quadrajet.an edelbrock r.p.m air gap with a spread bore flange would be nice, to use one now a 1" adapter is needed and we know what that does to hood clearance. I'm not a fan of "adapters" of any type , although i am a believer in carb spacers. so we are very limited in intake choices. so when i get the air gap manifold i will also be buying a holley h.p.

 

the hp are great carbs very very adjustable

On older holleys some circuits arent thats why I think many hate them. If youre engine was outside a certain parameter it could be hard to tune just right.

I do like the Qjets they are a "smarter" carb. I just dont know how to work on them.