[Z Code 400]

Anybody running one of these on the street????

[Sporter]

Close enough.

http://forums.maxperformanceinc.com/...d.php?t=614379


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[Z Code 400]

I remember a Turbo V6 Buick once that had a remote-mounted Q-Jet...Robert

[Goatracer1]

I have been using a Procharger on my GTO for about 10 years now with great results. Only problem in all that time is once had to replace bearings in the tensioner. They were a common parts store item.

[Goatracer1]

Sorry didnt see the part about Quadajet. I use a Holley but you could use a Q-jet if you use an air box or find a way to seal the accellerator pump shaft.

[Cliff R]

The q-jet will work fine with a blow thru set-up. Keep in mind that there are quite a few different style of airhorns, some have no venting inside the air cleaner housing seal, others have several places to vent.

The direct airbleeds exposed to the incoming air stream also become a factor with blow-thru systems, but this is something easily addressed during the preparation of the carb.

Ken saw some of this with his recent dyno testing which is in Car Craft magazine, and the thread running on the "Race" section of this sit.

My first choice for a blow thru q-jet would be a 1971-74 Pontiac unit, followed by a 76-79 350 or 400 Pontiac carb. They all have the large front vent, which is located outside the air cleaner seal.....Cliff

[Z Code 400]

Cliff,

I would think that venting the carb to the outside (atmospheric) would be best, but in a Q-Jet, there are so many places for pressure to enter the carb, like around the secondary needles, etc.

How does the pressure affect the Power Piston????....Robert

[Cliff R]

Robert, the factory turbo carbs routed the vacuum to the power piston from oustide the carb, thru a valve to keep from pressurizing the PP under boost.

You are not going to prevent the fuel bowl from getting pressurized with any carb, so the fuel pressure has to rise when the boost pressure does.

FWIW, I would take the PP out of equation, if building a turbo carb here, it would run straight off the jets and not use any primary metering rods at all.....Cliff

[Z Code 400]

So much easier to supercharge EFI. I have never used a 'pressure plenum' as my only experience with blow-through supercharging was with the 312 CID Fords and that was ducted right into the top of the carbuertor....Robert

[carbking]

Cliff - curious as to what you used for floats? For AFB's, we thought the foam floats would be the cat's meow; but got failure at about 12 pounds boost. Eventually went back to the tried and true brass with custom aluminum inserts, just like Carter did with the blow-through Studebaker Avantis. Ended our float issues.

Jon.

[Cliff R]

Jon, haven't had the opportunity as of yet to set up any q-jets for blow thru set-ups. I've provide some assistance to a few folks who have done so, and no float issues have been mentioned to date......Cliff

[arrowem]

Cliff, have you had any chance to do a blow through QJet yet?

[PONTIAC LARRY]

Originally Posted by Z Code 400

I remember a Turbo V6 Buick once that had a remote-mounted Q-Jet...Robert

Yep, Thats a draw thru like the 301 was. I would not run a blow thru on a Qjet, seems like alot of potential problems and a disaster in the making. A draw thru setup with a larger single turbo is a different story though.

[Kenth]

Originally Posted by Z Code 400

Anybody running one of these on the street????

http://www.originalho.com/TFProjectUpdate1b.html

[PONTIAC LARRY]

Originally Posted by Kenth

http://www.originalho.com/TFProjectUpdate1b.html

I remember reading that article and they had hell keeping enough fuel in the Qjet.. that car has probably not been driven or raced much but would like to hear more feedback about it.

[Craig Hendrickson]

Originally Posted by PONTIAC LARRY

I remember reading that article and they had hell keeping enough fuel in the Qjet.. that car has probably not been driven or raced much but would like to hear more feedback about it.

This 76 Bird with original TurboForce is one of my project cars. It has been driven 630 miles round trip to Pontiac Heaven and displayed 4 times (latest last April).

There are three critical points about blowing through a QJet. One is the fuel delivery system, another is sealing all the external leak points, and the third is pressure hat design.

The fuel delivery system is pretty easy. Just use a system like on a 10 second drag car but with a boost-referenced regulator (Holley makes one) up front. The boost reference should come from near the front bowl vent. Set the pressure at 5.5-6.0 psi over boost and use the large needle & seat. The stock short fulcrum float works fine up to 15psi boost and will not collapse. There is no problem using the stock power piston and spring since under boost it does not know the difference.

Sealing the external leak points is straight forward (see ref'd website for details). On my project car, I changed to a pressure air seal at the accelerator pump hole in the air horn. I did this because any rubber seal I tried would either lock up the accelerator pump shaft under boost or blow out (leak).

The pressure hat is the "trick" to successfully blowing through a QJet. The H-O Turboforce hat had two design features which are critical to successful operation. One is the diffuser section (wedge shaped transition from round pipe to hat). This slows down the air stream and partly kills the swirl. The second feature is a fore-aft vane on the inside. This further kills the swirl and ensures an even pressure distribution inside the QJet air horn. Below are a couple of pictures to illustrate.




Unfortunately, the H-O pressure hat is no longer being manufactured and there are no plans to do so. The Extreme Velocity hat would probably work, but would require modification of the QJet air horn and will NOT fit under the hood of a Gen-2 Firebird.

[Cliff R]

One must keep in mind that there are at least half a dozen different designs of the q-jets airhorn. Some have quite a few places to vent inside the air cleaner assembly.

The best unit to start with, IMHO, would be a 1971 to 74 Pontiac carb. They have the large front vent, and internally vented for the POE wells, with no other venting inside the air cleaner or hat assembly, aside where the metering rods go thru the gasket.

A 1975 to 79 Pontiac carb would be equally as good if the large vent at the back of the choke housing were epoxied over.

I've worked with a few folks on blow thru stuff, but haven't had the opportunity to have a car up here to work with.

As for the power piston assembly, I'd set the carb up to run straight off the jets, for a turbo application right to start with, just takes any potential issues there out of the equation......Cliff

[KEN CROCIE]

The Q-Jets with external venting ports (outside of the air cleaner mounting ring) MUST be vented to the inside of the air hat/bonnet otherwise fuel will blow out of the vent under boost. The H-O bonnet had a provision for the Q-jet vent that was precision machined and was supplied with an O-ring for a leak proof seal. There is no need to disable the power piston function .

[Half-Inch Stud]

""""""As for the power piston assembly, I'd set the carb up to run straight off the jets, for a turbo application...""""""

Cliff, Does that mean certain E-Q-JETs (17085204) are just as good (better?) as the Regular Q-JET(17058230) for a 455+60 ?

[Cliff R]

Ken, good info on the external vent deal. Since blow thru carbs make up less than .0000001 percent of my business, I have about the same percentage of interest in them. If ever given the opportunity, we'll set one up and successfully tune it for a blow-thru application, but I'm really not looking forward to it, since the phone NEVER rings for someone wanting one, or parts for one!

HIS, I really don't understand the question?

Pretty much all later q-jets with the larger castings are equal from a performance standpoint. Some have a few better features right out of the box, but any differences between all of them quickly disappear when you know how to set one up.

As far as running straight off the jets, we have quite a few very successful units doing this, and when you know how to set one up, they work perfect, street and at the track. I don't recomend going this route for most units, but it is an easy way to use an later ECM controlled unit for big HP and stock look, or any racing, turbo application, etc. The "pull-thru" units actually routed vacuum to the power piston externally, so they could switch it off when the engine went under boost. Blocking the vacuum to the PP and running straight off the jets eliminates the need to do this, and we've done enough street, dyno and track testing to tell us that the carb will run flawlessly everyplace when set up correctly......Cliff