Building a one off Qjet
 

I'm working on a neat project and though I would share some of the build.

I've had a lot of success in the past with my single ring 71' 455HO Qjet that I modified years ago to go along with the current combo in my 71' Trans Am.

I had another forum member approach me with a box of parts asking to build something from them which I like to do for his combo.

I like the SD-455 Qjet and I'm modeling it after that...like to call it a "Super SD"...

Combo is very close to mine, another 455HO with 10.25:1 & nice VooDoo roller.

I usually do not mix parts but I think this one off deal will be cool.

I'm going to use a 74' Pontiac airhorn & Base with a Buick 800 main body.

Also removing outer booster rings and then extend the main booster like my HO to help enhance the reduction in signal strength.

The pieces will be recolored and plated and choke will be converted to elec.

I'll post some pics..

Good stuff, thanks for posting

Mr Shaker, doesn't removing the bigger booster affects the instant throttle response in a negative way?

Not if it's calibrated correctly Mr 76MM.

The regular Qjets do not have extended booster like the factory single ring.

very nice, idea on price when done?

No prices & winter project.

Can you elaborate on "extend the main booster" ? I know a 71 HO has no booster outer ring, but what about "extend the main booster" ???

I am guessing a sleeve.

no sleeve,
I'm going to machine an extension that will attach to the booster and come to the same length as the HO,

Oh I did not know the HO had a longer booster. I always thought the only difference was the missing outer ring.

I've had quite a few of those HO carbs over the years and never noticed that. Learn something new every day !

Is that "extension" so to speak supposed to increase the signal ? Can and will you post pics ? That sure will be interesting.

Love to see Quadrajet tweaks !

Yes I will post more pics and as I go.
If you look at the HO the inner booster extends about as far as the outer ring on regular units.
The extension does not have to be a straight diameter, it can have a taper to it to enhance sheer or venturi effect.

The outer ring works like a shear step on the bottom of a Holley HP downleg booster:
Standard downleg w/taper on left, middle HP downleg, Annular on right

An Ebay unit someone cut outer ring from

Jeff have you ever tried welding on these castings?

I'm just curious how it would work, never had time to try it.

Possibly silver brazing would be better?
Or maybe tig brazing with silbronze?

The castings are zinc so welding may do damage.

Very cool project!

Yes I'm liking it!

i'm anxious to see how this turns out and photos along the way!! !i enjoy seeing the Q-Jet Mods and am very grateful for members showing us and sharing some of their secrets...Thanks Jeff

Since Curtis and I both run Q-jets I will be tracking your progress, Jeff. Always something new to learn everyday.

Hey Mike & Gates!
This is a cool project and I've been wanting to do this for about 8 years.
I may run a similar assortment on my 67' GP but that's all stock so outer booster rings will do.

I'm currently machining open & rebuilding the plenum on an old squarebore P4B plenum that I have to also accept QJ.. along with removing exhaust crossover and separate water crossover.... another test mule!

I'll machine out the rings first then come up with a booster design that will fit and secure well.

Damage to the person welding.....

Not welding...

Hey Shaker,

have you worked on that project lately ? Frank.

Frank,
I've been gathering parts and working on extension design to machine.
I'll post pics when outer rings are removed with some extension mock ups.

Lol, you've got a lot of projects to keep us all updated on...besides everything else you do!!'

Yes Jeff I keep very busy:juggle::bolt:
Jeff

Hey Jeff hope all is well, I’m also on the watch list on this endeavour. Very neat project....

Hey Andy,
I can't wait to test it on my car!
You got PM

Going to machine out rings this weekend.

In 2000 (I believe) Jim Hand was running wagon at the yearly (fall)event at Ark City, Kansas.
The track is an old WWII aircraft training tacility it it 2 long stretches of concrete. One stretch runs North-South, the other runs East-West. The pits are all concrete, a rare opportunity for every car at the event to park on pavement. Track is west of town, right on highway surrounded by corn fields, the bigger, better stretchs Eastward (pit side).
I was likely at that event...

Jim Hand had his awesome wagon running 11.30's. The air was superb that day.
Someone wrote something about that event, stating that it was only possible to do so, running the aftermarket parts he had on engine that day...suggesting that was only was the feat could be accomplished....i am pretty sure he had a Performer RPM and a large Holley carb.
This put Jim in action to get his wagon as well as possible with O.E. Parts. I was thrilled at what parts he used. I had/have 6X-4 heads, iron intakes, a few Quadrajets....I sure relished the idea of the quadrajet on his engine, especially!!!

I'd like to think that Ernie and Andy could further the cause, of at least the carb end of it, by squeezing a little more out a quadrajet on their engines. It's a part of the Pontiac mystery of making Pontiacs run SO well. Buying a $20.00 carb at a swap meet, and making simple, at home modifications....a vision that makes my day!!!

It would be nice to get a bit more flow out of the primary side.

. This project with Shakers carb is exactly the type of stuff that lots of us like . It takes vision and some careful engineering to make something work in real conditions. Keep at it Jeff , know this isnt a quick project.
Since this is the street section everyone strives to have something that starts without issue and have driveability . There are 4 guys around here that run well with pontiacs and quads , and lots of street miles layed down.
Since my quad had its magic done to it i have had very few incidents.
Yes Trashcan i do know there is more to be had. It really is about CFM flow and of course the requirements of a particular combo. Like to take it to the next level ...So Jeff will be chatting with you later on about that.

I may no longer use a Quadrajet but I respect those who do and the results do speak for themselves. I still have in my small track tool box Quadrajet metering rods and an allen wrench for the secondary air flap. Usually a couple times a year the parts or tool gets loaned out.
I agree with Andy it takes time and patience to modify or dial in parts to work in "real" conditions not "copy and paste" theory or internet rhetoric. By real conditions I agree its the street manners first while holding the same et's at the track.
Sometime if I'm bored I play around again with a Quadrajet, I do have a bin full of parts and carbs and a few intakes.

To date my best recorded et/mpg combination is 10.81/126.70 and 15.75mpg on the same day. Not bad for a basically stock Holley.

Sounds good Ernie but some time you should borrow Andy's Carb and give it a shot.
Either way.. your times are great and I admire both you guy's efforts!
I would enjoy a day with you two @ the track!

It would be a good test.

As promised into the milling machine we go!

Rough out removal or outer ring to make way for the fit of new booster extension.

That alone opened up to quite a bit of airflow.

My Race only guys that I offered this mod should reconsider, as this unit is going on a HP street/ strip combo.

One more pic..hope you guy's enjoy!
The Super Shaker SD is taking shape...:Ithink::thumbup::Peace::rant:

WOW!!!Looking good ,Jeff,,ok ,...as of now ..would this be the same as the 71 455 HO carb primary venturi?

Hey Mike,
No, the 800 venturi is larger than the 71' 455HO as the HO is a 750 casting with no outer ring.

1st pic is 71' 455HO compared to the outer ring removed on this 800

Also, if you look close the HO carb has the airhorn in place and you can see how much the choke housing obstructs the opening on the right hand side so that are will be addressed.

quite a difference...i don't know anything about the 71 455 HO carb,so was it rated at 800?..if so..this 800 is gonna flow some air!!Thanks for the photos ,Jeff...

I just took a measurement on the smallest venturi diameter around the booster with inside deep reach veriners.

1 st pic: 71' HO approx: 1.080"
2nd: 800 approx: 1.225"

Quite a difference!

WOW!!!!.never thought it would be that much....

That's makes the 800 approx .145" larger than 750

Holley did some Extended Booster castings at one time, bit they were to help with distribution problems on a intake manifold that Chevrolet used for a Truck Application.

Basically the longer booster did two things:

1) The intake pulse from the cylinder was a bit sharper with the longer downleg style booster

2) The fuel from the booster had a little bit better "fuel cone" before the fuel went past the throttle blade and into the runner.

HP wise, I do not remember anyone saying that the dyno numbers went up at all.

Maybe on a track application (Drag Racing) there might be something there at the end of the day and the carb sorted out well.

If you assume 3 boosters on the top row, 2 boosters in the middle row, and three boosters on the bottom row:

The THIRD BOOSTER on the top row with the extended lower section, was actually a Dominator Booster designed to RESTRICT flow and increase signal on a Dominator Carburetor. That booster was used on 850 cfm Dominators (normal cfm = 1050 cfm).
So messing with the booster can do some things for you. Good luck on your Q-Jet Project Jeff.

Tom V.

JMTs Tom V.

Very interesting project. I built myself a race Qjet, in which I removed the outer primary rings. I pulled the Performer RPM and Holley HP750 off my race car, and replaced with cast iron intake (plenum ported) and the Qjet I built. 60 ft and MPH are the same. So far, best et with Qjet/iron intake is 0.07 slower than RPM intake/Holley combo. I built another Qjet over the winter, this one without removing the outer rings. I will try the two carbs back to back at the track this year. I am sure I can match and best my RPM/Holley times using Qjet and iron intake. Both carbs are the same number, late 70's Pontiac carbs (800 cfm).

Thanks for posting Tom, you knowledge is always appreciated!

Jim,
I've always saw better numbers when testing my factory single ring which is the smaller 750 casting against standard units with the outer ring in place.

So I'm wondering how yours is calibrated?...maybe you can post or PM me?

I've done a few back to back tests on Lenny Caverly's dyno in the past and he just started a 74' SD-455 build for a customer so maybe I can do some testing on that.

Even though my factory single ring casting has full length boosters I still had to go with more jet and less rod to achieve the performance level desired.

Meaning it still looses signal as compared to a outer ring unit.

I would assume the condition would be worse on the street with half the booster length and increased distance from the throttle blade.

So maybe my extended booster mod will help reduce this effect and make for a more spirited driving on the primary side.

This project will see if extending the booster like the factory HO will yield improved signal over simply cutting outer rings out.

Next project beyond this will be booster replacement to a modern design in single ring configuration that will enhance signal strength while yielding more primary CFM.

That will entail using a flow bench to measure the gains.

Idle tubes - 0.039
Idle down channel - 0.063
lower idle bleed - 0.070
upper air bleed - 0.070
accel pump discharge - 0.033
main air bleed body - 0.070
main air bleed airhorn - 0.070
sec POE well - 0.040
sec POE restriction - 0.063
sec tube restriction - 0.036
idle bypass air - 0.110
mixture screw holes - 0.106
float level - 0.250
fuel inlet - 0.147
main jets - 72 or 74 (don't remember what I ended with)
primary rods - deleted
power piston hole - plugged
secondary rods - custom machined (don't remember exactly what I ended with, pretty thin)

Although I pm'ed you, I posted here as well for others.

Thanks Jim!
Great info and not far from my own.

wow, 72 or 74 main jets combined with .070" main air bleeds and NO primary metering rod seems VERY rich ??