Q-jet experts , couple questions
 

What is the minimum clearance you can run from air cleaner base to hood/air cleaner lid?

Not running a choke so is there any advantage removing the tower a'la Holley?

How about epoxy work around the top rim?

Any simple/cheap tricks for improving flow on the primary side?

Oh, it's for a bracket car so the "rules" don't apply.


Thanks

Re: Q-jet experts , couple questions
 

Just wire the choke open goes just as fast, we use a flow thru lid goes just as fast as nothing.
some castings are larger on the primary side eg 454 motorhome
Thanx Trevor
re air cleaner lid k/n style yes. re dime a dozen I buy my Quadrajets by the pound :) and I think that other co. is bankrupt....again

Re: Q-jet experts , couple questions
 

Trevor,

The choke blade,rod etc all have been removed and mounting holes filled.

Are you talking about K&N style lid?

Re: Q-jet experts , couple questions
 

One of the air cleaner bases with the really big radius will help direct air flow. I don't know that the K&N lid helps that much. It may or may not, depending on the area around the carburetor, and only experimenting will tell you.

You need an inch or so at least between the hood and the vent tube. The Q-Jet is a very sophisticated fuel metering device, and air flow around the bowl vents and the feeds/bleeds is critical, excessive turbulence or a lack of clearance around them can upset the circuits.

The Doug Roe book on Q-Jets is one of the best sources for Q-Jet information and tips. No Q-Jet racer should be without a copy of his own.

Re: Q-jet experts , couple questions
 

"Oh, it's for a bracket car so the "rules" don't apply."

Why run a Q-jet when Holley carbs are a dime a doz. and simpler to tune.

Re: Q-jet experts , couple questions
 

I was wondering the same thing, Bob.


No, you can't remove the tower on a Q jet without making a mess out of it.

Re: Q-jet experts , couple questions
 

Holley simpler to tune? If you call up Mike Beachy and get the hanger adjusting tool he makes, you can tune the carb with simply changing the hanger once you get close with metering rods and jets. I dont see how you can get any simpler than that?

Power? I have been on at least 6 different dynos. A 800 to 850 Holley loses power on our SSers every time. That includes the expensive flowed boosters and all. The only carb that has ever out HPed the Q-jet is the 1150 with all the max tuned flow boosters and venturi. That was only 7HP.

Why do we use the Holley then? For measurements only with the Super Flow air bonnet. It screws with the vent tubes and the secondary air horn. We have found to relocate the air flow mechanism and relocate it as far away from the carb as possible, then making a custom Q-jet carb bonnet helps. The secondary air horn still doesnt like it.

Re: Q-jet experts , couple questions
 

Lynn its a bracket car, they dont look at the same things we do, it would still be cheaper to run a holley.

Re: Q-jet experts , couple questions
 

I have bracket guys running Q-jets and the love them. You dont have th carry a bucket full of jets and gaskets everywhere you go. You can get away with substandard fuel delivery with a Holley due to the larger fuel bowls and inlets, but otherwise the Q-jet is pretty damn cheap.

I spent a lot of time with the Q-jet guys in Rochester, NY. You guys wouldnt believe the technology of a Q-jet. They still state that the Q-jet was the closest carb to actual fuel injection ever made.

Re: Q-jet experts , couple questions
 

For the record, I wasn't advocating a Holley carb for anything, unless the user's application required a bunch more CFM.
I doubt that's the case here.
More specifically, I'd rather see him cobble and hack up a Holley, rather than a good Q- Jet.

Re: Q-jet experts , couple questions
 

Thanks, so far, I think?

I guess I have to tell he "rest" of the story. I have been running with A Holley.

Trying something different, a set of Q-jets on a old Offy intake.

The carbs are Buick bases, Chevy bodys and Pontiac tops so alot of the cobbling had been done. ;)

I dug around my library and low and behold, found Roe's book circa '81.

Giving myself a refresher.

I will keep them away from the bridgeport for now.

Oh Lynn, they are sitting on a Pontiac!

Re: Q-jet experts , couple questions
 

I have put a 750 holley on a few stock elim cars just to see how fast they could REALLY go.......granted, a high dollar q-jet will perform just as well but who wants to spend the bucks ?

Re: Q-jet experts , couple questions
 

Neil:

How dare you be rational? Only true engineers know how to cross the dyno finish line first.

hahaha...!

Hope all's well in r-e-a-l h.p. land.

c-ya

Re: Q-jet experts , couple questions
 

Lynn,
What is the ideal fuel pressure to have for the Q-Jet ?
What is the best S.B. Chevy performance intake manifold to use and modify ?

Glenn

Re: Q-jet experts , couple questions
 

"Rational" or not :rolleyes:, I am going to use the Q-jets.

I would appreciate if we stayed on topic, not Holley vs..........

The fuel system is up to par, all Mallory components, proper size line to and from (return), good wiring etc etc. Fuel is steady and feeds 630 hp just fine.

The present pump is a 140 but have a back up 250 if it is needed.

Re: Q-jet experts , couple questions
 

If you are changing from a Holley to a q-jet you will need a better fuel system. The mallory 140 pump probably will not do the job. The 250 with a 1/2 inch line is the minimum.

Re: Q-jet experts , couple questions
 

Greg, I am going from a (single)Holley to 2 Qjets.

Do 2 Qjets hold similar volume of fuel as 1 dominator with standard bowls (no extensions)?

Do you think the 250 is still needed?

I am kinda type "A" with fuel and wiring.

Here is the present system:

8 Gallon cell with dual #8 outlets from the sump,(2) #8 mesh filters to a Y with #8 inlets to a #10 out direct to the pump, #8 line to the front mounted paper filter,#8 fitting dirct to the regulator, dual #8 outlet lines to the carb, the return is also #8.

There is only 1 90 degree fitting (full flow) and it is on the high side before the regulator.

The cell and pump are mounted in the trunk,high. If I remove the lines up front at the carb, fuel will gravity feed!

Re: Q-jet experts , couple questions
 

You only need more fuel if you are going faster
Thanx Trevor

Re: Q-jet experts , couple questions
 

I don't know. I've never heard anyone try to run 2 q-jets.

Re: Q-jet experts , couple questions
 

Two Q-Jets do not hold as much fuel as a single 4150 or 4160 Holley, never mind a Dominator.

To run Q-Jets, you need serious volume, without high pressure. Often you'll find you can't even run 7 psi with the 0.130" needle and seat.

Re: Q-jet experts , couple questions
 

tj310, faster would be nice but if can stay where I am (10 flat @131mph) I would be happy. Maybe be dreaming but unless you try.........

Greg, this manifold and carb combo has worked on a 12 second car with great results. The intake has "some work" to even out distribution so the plugs are very uniform in color after a run.

Alan, do you like the Mallory 250 vs the 140 with the system listed above or do I have 40 feet of #10 line in my future?

Re: Q-jet experts , couple questions
 

Q-jets are the most finicky and sensitive carbs I've ever fooled with. They can be made to run extremely fast but the can also get screwed up for no apparent reason. I would definitely go with the bigger pump. Personally I have had nothing but trouble from Mallory fuel pumps and regulators, but I do have a couple of friends who run the 250 pump and it seems to be okay.

Re: Q-jet experts , couple questions
 

Like Greg, I'm not a fan of the Mallory pumps. In fact, I'm not a Mallory fan at all, fuel or ignition. I don't like Holley or Barry Grant, either. For fuel pumps, it's next to impossible to beat Magna Fuel or Aeromotive. And yes, I'd run -10 line, and I'd probably run a bypass style fuel log with a -8 return.

Re: Q-jet experts , couple questions
 

Redlight,
I have been running a Q-Jet on my bracket '57 Chevy for a few years now and I love it. It's a legal # 17056228 Chevy 400 smog carb. I ran the car for many years with a well worked 850 holley. The car also had a fiberglass hood with a snorkel scoop and an air box sealed to the hood. I put the stock hood and hinges back on the car because I like the super stock look. At the same time I switched to the Q-jet so unfortunately it is not a fair comparison.
Although it doesn't look like it in the picture the carb sits so high that the vent tube is almost touching the hood. The car is consistently .04 quicker in the 60' but is about .05 sec. and 1 mph slower in the 1/4 mile.
Basicly the car picked up down low but doesn't run as hard on the big end which is because of no fresh air (scoop).
The car is more consistant and runs great so I say go for it. Like the others have said give it plenty of fuel volume and try one mod at a time & see what it does on the track.
Keep me posted as I want to build another one and try some (not class legal) mods including switching to E85.

Regards,
David

Re: Q-jet experts , couple questions
 

Somebody say Quadrajets? Not my car, this is(was?) sitting in a 67 Olds...recent experiment called Quadrajet Madness. I seem to recall video of the car running at a show...instant throttle responce....never heard if it ran down the 1/4...