[steve25]

First off I would like to thank HPP mag and Jim Taylor of there great work on this build that can be found in the September issue, and formost Jim for giving us a great insite into the workings of those 66 tripower manifolds.
My comments will center on info not put forth in the mag article but can be had just from the facts as presented.
First here` some needed info on 2bbl carbs as used on that motor.
1) 2 bbls are flow rated at 3 Hg, Hg is Mercury, not H2O as used in cylinder air flow testing. As such a test using Mercury will make for quite larger flow numbers then a cylinder head air flow test done at the common 28" of water.
This is why as on page 54 in the article the stated air flow of the center carb was only 190 cfm when that size carb was rated by Rochester at some 350 cfm.
2) The carbs as used had a throttle bore of 1-11/16" and a venturi of 1-3/16". this size carb is second from the bottom of the list of Rochester 2 bbls in terms of airflow, the smallest being 278 cfm and the largest 435 cfm.
3) the total carb airflow as stated on page 58 was 1050 cfm, or 350 cfm per carb.
4) the true jem of this build article was the test that Jim did with just the center 2 bbl feeding the motor.
As can be seen by the HP numbers, the motor made 73% of its total HP on just that carb, and the number of 75% for TQ was had thru that same center 350 cfm carb!
5) Since the motor made 349 HP from that one 350 cfm carb is hard not to see that the motor was making 1 HP per every 1 cfm of carb airflow @3 Hg.
6) The additional power brought in by the two end carbs was 124 HP and 98 ft tq.
This breaks down to 62 HP per carb and 49 ft tq per carb.
Another way to look at this is that each end carb was making for a 13.5% gain in HP and a 12.5% gain in Torque, not too impressive!
Yet another way to look at this would be that each end carb was only using 62 of its total 350 cfm to make for the full HP number seen in the testing of 473.
The real mind blowing kicker here is that opening up the end carbs shifts the HP peak seen up wards by near 1200 rpm!
This confirms to me the fact that the end carbs provide this change in rpm power band by dropping the port velocity.
7) In light of all this it would seem that the best way to get the largest amount of HP gain out of a 1966 trip Manifold is to use a larger center carb.
If the center carb of 350 cfm in this test was swapped out for the 435 cfm version then if the 1 HP per 1 cfm of carb air flow factor holds true, than the additional 85 cfm of airflow should kick the motor well over the 525 HP mark while hitting the majic 500 ft lb level.
8) jetting wise it should be safe to say that since the motor is making 73% of its max HP off of the center carb, than getting the jetting right on said center carb is 73% of the battle.
9) I would also ventrue a guess that stepping up to a larger center carb would drop the whole motors power power band down to a more usealble level, as in my eyes a rpm HP peak as seen in the dyno test of 6000 is a bit high for a motor of 432 cid with a Intake duration of 247 at .050".
10) In getting back to the jettting thing, it would seem that only some 13 % of the total fuel needs of the motor pass thru each of those two end carbs.

Anyway thats just my 2 cents worth, and once again thanks to HPP and Jim Taylor for finally sheading some much needed light on those tri power Manifolds!
Keep it up gang

[Jim Doran]

I'm looking but can't find my copy of the Sept. issue for some reason. I remember that Taylor mounted the 66 base on a 65 center carb body as I recall seeing the 65 style choke on the center carb. Also, did he use a 65 cast iron intake ? Damn, wish I had the article in front of me.

[steve25]

Yes it was a 65 Manifold and they had to make a spacer/adapter to use that 66 base, which then they had to add a spacer of the same height under the other carbs to level out there height for the air cleaner base.

Also the manifolds center carbs throttle bore openings had to get enlarged to match that 66 base plate area.
Spacer height used looked to be 1/2".

[Jim Doran]

So the center carb was a 65 carb with a 66 base plate. The 65 had a larger venturi I think which when matched w/the 66 base with larger throttle blades pressumably is a good way to go.

[jotrout]

This is great information and insight for us who run tripower's! I'd love to have copy of this. Anyway to scan it and post it up?

[steve25]

One would have to get permission from HHP mag I would guess first, but than again it may be found at there web site?

I would also like to note that in my post the comment about the change in the HP and TQ numbers up higher in the power band when the end carbs open up is also due to the shorter runner lenght that they present to the motor.

I would have loved, in fact even paid Jim and the crew to make one last dyno run on just the end Carbs to see what happend to the numbers and the rpm range, this would have really produced alot of insight as to what the flow mass is doing within that Manifold and the change in the A/F ratio seen!!

[tempest1964]

I know this is an older post, but I found these 2 articles online and thought they might be what you guys were talking about. Thought they might be of interest.
http://www.hotrod.com/how-to/engine/...-build-part-1/
http://www.hotrod.com/how-to/engine/...-build-part-2/

[steve25]

It seems to be the same build but the sourse I was posting from was HPP mag.

[Dick Boneske]

Thanks for posting this info on the 432 engine. That engine is nearly identical to the ones in my wife's and my '64 GTO's. The main difference is the cam, which is a Crower 60916, which is quite a bit milder than the one used in the test--specs attached.

It's interesting that peak HP was reached at 6,000 rpm with the Tripower. Ours seems to peak around 5500.

[tempest1964]

It is the same. Pretty sure all HPP articles are now under the HotRod web-site. They did this when HPP met its untimely demise. :-(

[slowbird]

Originally Posted by steve25

First off I would like to thank HPP mag and Jim Taylor of there great work on this build that can be found in the September issue, and formost Jim for giving us a great insite into the workings of those 66 tripower manifolds.
My comments will center on info not put forth in the mag article but can be had just from the facts as presented.
First here` some needed info on 2bbl carbs as used on that motor.
1) 2 bbls are flow rated at 3 Hg, Hg is Mercury, not H2O as used in cylinder air flow testing. As such a test using Mercury will make for quite larger flow numbers then a cylinder head air flow test done at the common 28" of water.
This is why as on page 54 in the article the stated air flow of the center carb was only 190 cfm when that size carb was rated by Rochester at some 350 cfm.
2) The carbs as used had a throttle bore of 1-11/16" and a venturi of 1-3/16". this size carb is second from the bottom of the list of Rochester 2 bbls in terms of airflow, the smallest being 278 cfm and the largest 435 cfm.
3) the total carb airflow as stated on page 58 was 1050 cfm, or 350 cfm per carb.
4) the true jem of this build article was the test that Jim did with just the center 2 bbl feeding the motor.
As can be seen by the HP numbers, the motor made 73% of its total HP on just that carb, and the number of 75% for TQ was had thru that same center 350 cfm carb!
5) Since the motor made 349 HP from that one 350 cfm carb is hard not to see that the motor was making 1 HP per every 1 cfm of carb airflow @3 Hg.
6) The additional power brought in by the two end carbs was 124 HP and 98 ft tq.
This breaks down to 62 HP per carb and 49 ft tq per carb.
Another way to look at this is that each end carb was making for a 13.5% gain in HP and a 12.5% gain in Torque, not too impressive!
Yet another way to look at this would be that each end carb was only using 62 of its total 350 cfm to make for the full HP number seen in the testing of 473.
The real mind blowing kicker here is that opening up the end carbs shifts the HP peak seen up wards by near 1200 rpm!
This confirms to me the fact that the end carbs provide this change in rpm power band by dropping the port velocity.
7) In light of all this it would seem that the best way to get the largest amount of HP gain out of a 1966 trip Manifold is to use a larger center carb.
If the center carb of 350 cfm in this test was swapped out for the 435 cfm version then if the 1 HP per 1 cfm of carb air flow factor holds true, than the additional 85 cfm of airflow should kick the motor well over the 525 HP mark while hitting the majic 500 ft lb level.
8) jetting wise it should be safe to say that since the motor is making 73% of its max HP off of the center carb, than getting the jetting right on said center carb is 73% of the battle.
9) I would also ventrue a guess that stepping up to a larger center carb would drop the whole motors power power band down to a more usealble level, as in my eyes a rpm HP peak as seen in the dyno test of 6000 is a bit high for a motor of 432 cid with a Intake duration of 247 at .050".
10) In getting back to the jettting thing, it would seem that only some 13 % of the total fuel needs of the motor pass thru each of those two end carbs.

Anyway thats just my 2 cents worth, and once again thanks to HPP and Jim Taylor for finally sheading some much needed light on those tri power Manifolds!
Keep it up gang

Center carb does little at full throttle when the end carbs are functional

[tempest1964]

The main difference is the cam, which is a Crower 60916, which is quite a bit milder than the one used in the test--specs attached.
It's interesting that peak HP was reached at 6,000 rpm with the Tripower. Ours seems to peak around 5500.[/QUOTE]
I thought that looked familiar. That's exactly what Jim Hand said in his book : "The rpm at which maximum horsepower and torque are developed increases as a cam's duration is increased". The guy is a friggin' genius when it comes to Pontiacs. What an asset to the hobby.

[tom s]

64 intake pictured and mentioned.Tom

[Tom Vaught]

Originally Posted by slowbird

Center carb does little at full throttle when the end carbs are functional

X2 on that deal. It has to do with pressure drop across the carb(s) (easiest path for the air to take). Your assumption is flawed steve25.

Tom V.

[77 TRASHCAN]

Excellent build, glad Jim was able to share it with us before he passed!

[ponchorob]

what i dont under stand.is.... ok they used a 65 intake and 65 centercarb with 66 carb baseplate and build an adapter for the bigger throttle plates... but if the intake center maifold holes were also enlarged why to they make spacer for the base plates....it should fit like stock....

[mgarblik]

The base plate for the large carb. has a different mounting hole space pattern than the small pattern carburetor. May not have been material available on the manifold to easily mount directly. 421 HO Tri-Power was a great engine package. Had some success with them in NMCA racing back in the 1980's.

[Dick Boneske]

Originally Posted by ponchorob

what i dont under stand.is.... ok they used a 65 intake and 65 centercarb with 66 carb baseplate and build an adapter for the bigger throttle plates... but if the intake center maifold holes were also enlarged why to they make spacer for the base plates....it should fit like stock....

No. The stud pattern on the '65 intake is not the same as a '66 center carb. An adapter/spacer would be needed unless the position of the studs was changed.

The runners, and everything pertaining to the end carbs is nearly identical between the '64, '65, and '66 intakes.

[Tom Vaught]

Reading this thread again.

1) 4-Barrel Carbs have been (before World War II) tested at 20.4 Inches of Water Test Pressure which is 1.5 inches of Mercury Test Pressure.

2) 2-Barrel Carbs have been (before World War II) tested at 40.8 Inches of Water Test Pressure which is 3.0 inches of Mercury Test Pressure.

If you have a Superflow flow bench that cannot generate 40.8 inches of test pressure across the flow passages of the 2-barrel carb (with liquid in the fuel bowls) you are testing the carb improperly to get an accurate flow number.

This is why a Holley 2-Barrel carb rated at 500 cfm air flow will flow a lower air flow number at 20.4 inches of water test pressure/1.5 inches of mercury, and obviously a third WRONG flow number at 28 inches of water test pressure like some cylinder heads are tested at.

If you do not know how to test the carburetors properly then you should not be working on carburetors or testing them on dry flow benches. Carbs are wet flow tested if the testing is done properly.

Changing the flow test pressure from 20.4 inches of water to 28 inches of water was a marketing gimmick by Barry Grant to sell his carbs at a inflated airflow rating to get more sales vs the Holley carb, Carter Carbs, and Rochester Carbs competition.

You can make up any numbers you want if you do not flow liquid thru circuits that have liquid/air flow thru them in normal operation. You are just flowing the bare airflow past the throttle blades.

Tom V.

[ponchorob]

Thanks for clarification..lookin back.. its logic...like the idea 65 large venturi carb with 66 baseplate with big throttle plates... i always likesxthe jim Taylor articles ..there always interesting...remember a
530 hp 455 article with lightly ported iron heads and his special designed cams. . ..he was decades in buisness .and a pontiac specialist..but doesnt have a website even in the past ..