[Will]

Hey guys,

After reading KS Circuitguy's questions about his recent NOS pass with a 150 shot, thought I'd ask what special considerations I have to think about when running the same 150 shot with a Q-jet?

Here's the combo (if it ever gets finished):
440 cubes (428 crank/455 block), Ross dished pistons (9.7:1 CR), 1-5/8" headers for now, Street Dominator intake, mild solid roller with 1.7 rockers (234/244 duration, .580" lift), and a Q-jet that's been built specifically for this combo with fast opening secondaries.

Ignition is an HEI with Crane HI-6 and PS91 coil and I'll be adding a Crane timing module to take out 6 degrees of advance when the nitrous is on.

Fuel delivered via a Mallory Comp140 pump and 1/2" lines to a Mallory regulator mounted at the front of the engine, with 3/8" lines from the regulator to the carb and fuel solenoid.

Since it's an open plenum intake with a spreadbore vac. secondary Q-jet, is there anything special I need to be worried about, or should look for?

Thanks!
-Will

[Will]

Hey guys,

After reading KS Circuitguy's questions about his recent NOS pass with a 150 shot, thought I'd ask what special considerations I have to think about when running the same 150 shot with a Q-jet?

Here's the combo (if it ever gets finished):
440 cubes (428 crank/455 block), Ross dished pistons (9.7:1 CR), 1-5/8" headers for now, Street Dominator intake, mild solid roller with 1.7 rockers (234/244 duration, .580" lift), and a Q-jet that's been built specifically for this combo with fast opening secondaries.

Ignition is an HEI with Crane HI-6 and PS91 coil and I'll be adding a Crane timing module to take out 6 degrees of advance when the nitrous is on.

Fuel delivered via a Mallory Comp140 pump and 1/2" lines to a Mallory regulator mounted at the front of the engine, with 3/8" lines from the regulator to the carb and fuel solenoid.

Since it's an open plenum intake with a spreadbore vac. secondary Q-jet, is there anything special I need to be worried about, or should look for?

Thanks!
-Will

[Brian Baker]

Will,

Nothing to look for, really. You've got your bases covered. Only thing I can think of is to check the baseplate screws on the Q-Jet. If yours is equipped with a center screw, it's a good idea to pull it out and loctite it (don't want it to work loose and drop into the intake).

You'll be needing a weaker spring under the power piston holding the primary rods, but the shop prepping the carb should already know this. A yellow spring will work well, since you'll be hard pressed to pul more than 11" of vacuum at idle with that cam and a single plane intake.

My fuel delivery system is similar to yours. I drilled a hole in the bottom of the stock tank, welded a bung to it for mounting hardware. I'm running 1/2" line from tank, through filter, to pump (Mallory 140 pump and filter) and forward to regulator (Mallory). From regulator to carb and N2O solenoid I'm running 3/8" line. There is no bypass back to the tank. When I'm just running the motor, I typically keep the fuel pressure down to 5-psi, but I step it up to 7.5-psi when running the nitrous. Much more than 7.5 though and the engine begins to idle rough (I guess because the pressure is blowing the needle off the seat and trying to flood the carb).

I've only sprayed it 6 times, but have had no problems related to fuel starvation thus far on a 150-HP shot. To date, the best times have been:
12.78 @ 106MPH, 1.81 60 ft. (motor)
11.91 @ 115MPH, 1.75 60 ft. (n2o)

I spray it at WOT on launch. It has a major bog when the n2o kicks in, which unloads the suspension and then causes violent tirespin when it comes on again. I installed a purge valve, which has helped some, but the bog is still there (need to work the bugs out).

[Gach]

Will, my opinion get a Holley, with a 4 corner idler. Although the Q-jet is a good street crab, it will not give you the best performance with that nice little roller cam. The Holley intake is perfect for what your doing, but the Holley crab will work much better with Nitrous, no vacum secondaries.
The idling circuit on a Q-jet, gets very touchy with a roller. The big advantge is with the Holley you can square the crab, which is always a problem with a Q-jet, hence the brog. Grantee to run 2 tenths better then a Q-jet, and be allot more street able, and tunable

[This message has been edited by Gach (edited 03-23-2001).]

[PONTIAC DUDE]

Crab.....brog.....Help.. I'm on the floor. Gach, you do that on purpose. LOL. I love it.
Later, buddy.
BTW: The Q-suck will work OK. but the "bog" can kill an engine leaving on NOS. Lean as the secondaries open allowing in more air then fuel. If you spray after launch, then I don't see a problem. Have run Q-sucks up to 175hp with no problems, after that your on your own.

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NOS is like American Express.....You don't leave home without it.
http://www.angelfire.com/fl4/pontiacdude428

[Gach]

Dude, I knew you would get it, can't stop laughing ( Q-suck's ) is that anything like the Wenz-slow heads...LOL

[Brian Baker]

So then, can my bawg (bawlg? bog?) be attributable to the fact I'm running the Q-Jet? No bog at all when launching at WOT on the motor, just when the N2O kicks in at WOT. I didn't think it was the Q-Jet, as the secondary airflap doesn't open right away when launching from WOT. I do plan to step up to a Holley later this summer, however. Experimenting with the alcohol Holley last year on the street leaves me to believe the Q-Jet is severly restricting airflow.

[carbking]

Nitrous is not my field, so just tossing out a question. Has anyone tried this with a large two barrel so the secondary opening doesn't get in the way???

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Good carburetion is fuelish hot air.

[Gach]

Actually we use Q-jets for cams with flat lobes, then your assured to get enough fuel.

[Will]

You guys are too much!

Thanks for all the advice, much appreciated!

Gach, I'd run a Holley, but then my Ram Air aircleaner wouldn't fit. Even though the Q-suck might not be optimum for racing, you said it best when you said it's a good street crab. Since my car will mainly be a street slug that gets bracket raced a few weekends each summer, I don't think a couple of tenths is going to bother me much.

The guy who's building my Q-jet knows how to make them idle with big cams and how to get the secondaries open quick. He's built them for Super Stock applications. At least, he says he does!

The engine's about a month away from completion. Seems I say that about every month, but the last hurdles were finally cleared today that could have stalled it again. Pistons & rods were shuffled around for most consistent deck height and the endplay checked out, so all that's left to do is deck the block, install cam bearings, tap the oil galley plugs, set the ring gaps, then assemble and measure for pushrod length. Since the only work on it gets done Sundays, that means about 4 more weeks, including ordering the pushrods.

Oh, and I fudged the lift numbers on the cam. It's only .545 after subtracting lash.

[PONTIAC DUDE]

The NOS can't be causing the BAWG, as it creates it's own atmosphere. You could put a blockoff plate over the manifold and run on NOS system itself. Your adding gas and N2O. Timing? Distribution? Spray pattern?

------------------
NOS is like American Express.....You don't leave home without it.
http://www.angelfire.com/fl4/pontiacdude428

[Gach]

How about this info were getting from Pontiac Dude, about running nitrous, were damn lucky to have him on this board. How long would it take to figure all this stuff out, he's been there. Of course I'm only saying that because I'm going to the bottle, so I have to butter him up....LOL.

Will, for years I was a Q-jet man, and when some one would say Get a Holley, I would give them examples of many Super Stock guys running super fast with Q-Jet's, never realizing they had no choice. What I've found is budget dictates, what you run, there has to be a limit some were. The 64 Goat still has a Q-jet, and last time out he ran 11.80's, pump gas 400 motor.

That's going to be one hell of a street motor, real good combination, it'll make your old motor seems like Ma's grocey getter.