[catc]

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

[shaker455]

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

[Tom Vaught]

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.

[jm455ho]

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).

[shaker455]

Originally Posted by Tom Vaught

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.

Thanks for posting Tom, you knowledge is always appreciated!

[shaker455]

Originally Posted by jm455ho

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).

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.

[shaker455]

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.

[jm455ho]

Originally Posted by shaker455

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

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.

[shaker455]

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

[frankyboy455]

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

[jm455ho]

Originally Posted by frankyboy455

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

And yet, according to my AFR gauge, I am still running lean. That's why I am going to try a similarly built Qjet, but withouth removing the primary booster rings.

[shaker455]

I see a few things you could do to richen it up

[77 TRASHCAN]

Originally Posted by frankyboy455

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

I was thinking same. Not remembering for sure...
I seemed like, when Cliff was running without pri rods, his jets were in the 60's number wise, seemed like 65? Cliff? Of course, I pretty sure his carb still had both rings. This may be beneficial for going without pri rods....

[shaker455]

I believe I have 78 jets with 36 or 38 rods so I think Jim is close, to where he should be.
And yes no rods for race but I have guys who run both ways.
I'm not sure what Jim's combo is these days?

[jm455ho]

4.15 x 4.00 = 433 cid. Stock iron heads (1968 #16) with good valve job. Around 11.2:1 compression. SFT cam, 250-256. A little mismatched on parts, but I used what I had on hand to build this engine. Was supposed to be a temporary install in the car while completing full on race engine. Well, the race engine is sold, so I'm stuck with this one for the foreseeable future. It's a good engine, and the car is running well, so I'm happy as is. Swapped out the RPM intake and Holley for cast iron intake and Qjet. Best time with Qjet so far is 11.02. I think I can get into the 10's. Future plans include swapping the heads for some ported early d-ports similar to the 16's. Hopefully get into the 10.70's. That's fast enough for me, I just want to go rounds and win a race or two.

[shaker455]

That's Awesome!
Are you thinking SD's CNC ported cast iron heads?

[jm455ho]

Originally Posted by shaker455

That's Awesome!
Are you thinking SD's CNC ported cast iron heads?

I had a pair of SD ported heads years ago, wish I still had them.

My local machinist is doing up a set for me. Old school meticulous machinist who seems to know his stuff. Everything he's done for me so far has been spot on. I'm curious to see what he can do with my heads.

[shaker455]

A few mock up booster extension pics:
Venturi is still rough machined, not cleaned up yet.

['ol Pinion head]

sweet, looking forward to further shaping & testing!

[shaker455]

Going to last mock up, a more modified booster.