75myway

Hey Guys and Gals,

Whats the max HP a Qjet can handle?

7T1vette

Around 400, I believe. It will provide 750 cfm...800 with mods.

rcread

Around 550 or so, at the flywheel.

427Hotrod

There are folks running in the 9's in the 1/4 mile in full bodied cars in class racing. Making a lot more than 550 HP.

Would they go even faster with a *real* carb? Sure....but the Q-Jet does a pretty amazing job when set up right.

JIM

baxsom

Too bad there are only like 5 people in the world that really know how to do that.

jb78L-82

Agreed. The Qjet is a very good carb IF you can get it to run right. The potential is there BUT as stated many times by more than a few folks, its design is over complicated for what it needs to do, it is difficult to custom tune for different applications, is difficult to rebuild due to its design (see my first statment), and its performance will quickly degrade with time and miles. There is a reason that there are sooo many aftermarket carbs offered as Qjet replacements-there are sooo many problems from owners with Qjets!

straub18045

wow a loaded question. it will handle whatever you throw at it. no several engines runnin over 600 hp no prob with them. mine rated at 500 hp. no problems, perfect actually.BUT you need someone who knows what they are doing or disasters will happen

Sigforty

They can be built to handle all power levels. There are a few tricks to make them better and the rods and jets can be changed. As 427hotrod said they can be run into the 9s. There are quite a few super stock cars that run q-jets due to class limitations. The problem is you have to pay for one to be setup right and the setup is a skill most people these days except for a few still have.

MotorHead

I suppose in Super Stock classes where they have to run "original" engine parts you have some guys in the 9's but generally you will see Holleys and Demons on the motors no matter what class at the race track and more fuel injection now too.

It is very true regarding tuning these carbs, the guys that know how to really tune any carb are getting scarce, like really scarce.

Any bubba knows hows how to change jetting and few other things but those that actually know how to setup a carb completely and actually know how it works are almost non existent these days

TopGunn

Not entirely true. Buy this book and do it yourself, get an education and have fun in the process.

MotorHead

I have found books on tuning a Holley / Demon carb and what they usually boil down to is the just the easy stuff and use lines like" Changing HS air bleeds is best kept for an experienced carb technician"

So they explain how to fix and tune one to a certain point and beyond that they say not to mess with it. I never bought any of the books because I leafed through them and I can see they aren't going in much deeper than the basics.

I can't comment of the Quadrajet book above, it could be quite helpful

TERRY CLARK

What engines did Chevorlet put Holleys on instead of Q-Jets? Was it because the Q-Jets were too small ? ZL1s, L88s,LT1s & 302s?

straub18045

i have the book above and it is in depth i think well worth the money, and good book for reference

SteveG75

Chevrolet went to Holley on the performance engines for several reasons.
- Image. Holley had that performance image.
- Racers. Racers used Holleys and wanted Holleys.

Sigforty

True, from people I know who have sent in carbs to Cliff they do one hell of a job as well as wrote that book. lol

7t9l82

the q jet has gotten a somewhat deserved bad rap. that said a properly set up Holley will out perform any other. mixture distribution kills a q jet on a drag car. but as has been said it is a good street Carb IF set up properly. GM used it on low level performance cars because it was CHEAP!

straub18045

i mean this with all due respect.

SteveG75

A Holley works good at two throttle settings, idle and WOT. The Q-Jet is a much more sophisticated carb that satisfied power and emissions requirements and was much more expensive to manufacture.

GM tested and designed hundreds of Q-Jet rod and jet combos for different vehicles. The main circuit has an adjustable power piston that varies mixture based on load. The secondaries are mechanically operated with an adjustable air door that sense load and delivers just what the engine needs.

Holleys are simple and cheap. Q-Jets were expensive and sophisticated.

7T1vette

jb78L-82

I had the Qjet on my 78 L-82 from 1978-1986 at which time I switched to the Holley 4175 650 CFM spreadbore. The holley idled better, cruised perfectly, has been stone reliable, and felt more powerful at WOT. The Holley also was certainly as fuel efficient as the Qjet BUT it probably could not meet the emissions of the OEM Qjet. 9 years experience with the original Qjet and 24 years with the Holley-Real world experience. No hypothetical here!