[Tech @ BG]

We're working on our 3x2 6-Shooter systems for Pontiac engines. Curious if anyone has run an original 3x2 setup vs. a new single 4bl intake like a Performer or Performer RPM and knows the difference in Tq & HP. Also, is there anything specific you guys would want to see in a new 3x2 Pontiac setup?

Thanks,

[Tom Vaught]

I have a few things.

Do a better job on the linkage for the pontiac vs the "Hot Rod" linkage for the Chebby stuff. I can tell you what the linkage needs to look like if you want to do it right.

Because the carbs will all be mechanical secondary, there is enough room on the 1966 pontiac intake manifold to run Demon Race Bowls with the gas fitting on the passenger side of the engine. This would make it more like a true PONTIAC system vs the Chebby stuff you currently offer and would be simply a fuel line design change. This will draw in the Pontiac enthusiasts.

Make the filters individual (like the original system) again more like the traditional Pontiac system was.

Make all three carbs large cfm carbs as the vast majority of the engines are 400/421/428/455 OR BIGGER.

To drive the system down the road, the PONTIAC Engineers realized that they needed the LARGE center carb to run only on that carb at 70+ mph. Otherwise you are into the outer carbs a lot. Maybe in 64 and 65 when gas was cheap you could get away with that but not today.

Calibrate the end carbs idle circuit for 1/2 the typical idle circuit flow. This will basically allow the same idle calibration as a typical 4 corner idle carb, but you will have some control over the distribution on the end carbs for fine tuning.

Leave the power valves in the rear carbs metering blocks. The fuel bowls all face to the front so no chance of ever uncovering the outboard power valves like on a double pumper. This will allow a better transition when you do touch the outer carbs without going "pig rich" If the owner wants to take out the power valves and jet up for racing so be it.

Make sure you either use thick blades on the outboard carbs or have a throttle blade screw that keeps the blades from contacting the bores. Repop Chebby "knock offs" of factory end carbs do not have that provision.
It is already there on the 4412 type carbs.

Any more questions feel free to e-mail me.

Tom V.

[slowbird]

That about sums it up. I would like to stress what Tom said about engine size. The most people are running 455 so carb size needs to be size for our larger engines.

[Tech @ BG]

Tom,

Thanks for the input. A few more questions for you:

Are you referring to the linkage I'm using on my SBC system, or the factory style linkage? We've got a progressive system that allows you to drive off of the center carburetor, and then brings in the outer carbs later like a mechanical secondary carburetor. It makes for a really nice driving system.

Putting center hung bowls on the carburetors actually makes the fuel rail much more cumbersome, and puts it in the way of tuning vs. the single high side rail like we’re doing on our other systems.

The idle circuitry on the outer carburetors will be reduced, and set up like a vacuum secondary carburetor volume wise. We already use really thick butterflies in the outer carbs to make sure they seal properly.

Do you have any baseline power numbers from an original or modified Pontiac Tri-Power to a decent single 4bl on a street engine? I’ve got some numbers from a few engine builders, but would like to hear what other people are seeing.

Thanks again for the feedback.

[Robert Williams]

Are you going to make your own intake manifold or use the aluminum intake that is available now? The aluminum manifold that is available now will flow approximately 260 cfm, a little bit more than a stock 66 cast iron Tri-Power intake will flow. If your going to make your own manifold then how about one that will flow 300 plus cfm for the big engines. The venturi sizes on the original 66 Tri-Power Rochester carbs are 1-3/8" for the front and rear, the center carb on the 66 had a 1-3/16" venturi, all 3 had 1-11/16" throttle bores. I have had very good luck using the 68-69 400" 2-bbl Rochester for the center carb on the big engines because this 68-69 400" carb has a 1-1/4" venturi 1/16" larger than the original center venturi and works very well, 1-3/8" venturi would be better yet. The 68-69 350" Rochester 2-bbl carbs have the same size venturi as the original 66 center at 1-3/16". Good luck with this project, i can't wait to see one but make it to flow some big air for the big engines.

[Bad Karma]

I sincerely agree with everyones ideas and statements so far.
First off Barry, I would like to commend your downright unheard of approach of actual hobby members!

Just for that I will be doing some business with your company when I can/needed.


I don't know all these venturi sizes I have to be honest. What I would like to add if possible is a few small points of interest.


There should be a few options on the air cleaner:
It would be nice to see a Low pro 6 pack that the hood spaced challenged could utilize. I'm sure you would get some sales if those guys in the pontiac hobby were included. Included in this is the T/A Firebirds with the shaker hood. Maybe find a way for a "shaker" model or offer it with a modified "dude scoop" or someone elses so It can be used with stock hoods?

Second, I Honestly and sincerely believe in my gut that It would be of great interest to offer this Six Pack with the ability ( Maybe just the bare minimun needed) to bolt in to factory ram air systems ( I dont know if this can really happen BUT...) you would have the ability to market your product to people who don't want to change thier expensive Ram Air Hood/System out just to use your 6 pack.

3rd the linkage. It needs to be FOOL Proof! Alot of people are scared of Tri power set ups because of the "carb timing" and the issues it can cause. The complete manifold IMHO should come ready to run (more or less) and not need any adjustment to the carbs as far as making sure they run on center carb only until outside carbs are needed.I can try to explain farther but I think you will get my point there.

The most important Is the CFM issue. We need atleast 300 cfm intake option preferably more if possible. We dont want the intake to be the choke point.
Maybe make it an optional point of purchase upgrade?



Not sure how feasible all that was but I just wanted to help in anyway I can. I was very happy to read this may be an Induction feature in the future for my future 512 tiger headed roller cam engine!

I hope this will in some way help you and the end users of what I can only imagine to be another great BG product. Best of luck and happy holidays!

[Tom Vaught]

Quote:

"Are you referring to the linkage I'm using on my SBC system, or the factory style linkage? We've got a progressive system that allows you to drive off of the center carburetor, and then brings in the outer carbs later like a mechanical secondary carburetor. It makes for a really nice driving system."

Have you actually driven a true 1965/66 tri-power car with Pontiac Linkage? I think you would find your present system still needs some help even though it is simple. Your system is more like the old "tube and plunger" early 60s SD type system which really was not that great. You are using a modified (almost Dual Quad) type linkage vs a true "Tri-power Slotted rod" set-up.

Quote:

"Putting center hung bowls on the carburetors actually makes the fuel rail much more cumbersome, and puts it in the way of tuning vs. the single high side rail like we’re doing on our other systems."

Yep, difference between doing it right vs easy.

Your system is much like the old single inlet side hung 4 bbl carbs that used the transfer tube. You don't see very many performance carbs using that system in drag racing applications except on Dual Quad deals for the old Pure Stock classes (FE Fords with the dual quads). Any racing or larger cid engine will have a 3/8" dual feed line kit going to race bowls. Again your original deal was sized for a SB Chebby.

Quote:

"The idle circuitry on the outer carburetors will be reduced, and set up like a vacuum secondary carburetor volume wise. We already use really thick butterflies in the outer carbs to make sure they seal properly."

Excellent!

Quote:

"Do you have any baseline power numbers from an original or modified Pontiac Tri-Power to a decent single 4bl on a street engine? I’ve got some numbers from a few engine builders, but would like to hear what other people are seeing."

I have run the old "Edelbrock calibration" MECHANICAL secondary Holley six pack carbs on a nash style tunnel ram vs an 850 carb and the "tri-power was much better in the quarter (like 3 tenths).

I have run the Vacuum Mopar style six pack carbs on a cast iron 66 intake vs a 4 barrel torquer 1 intake and a 850 dp and the tri-power was a better all round driving package.

Tom V.

No I do not have dyno numbers.

[DiamondJim]

Tripowers can be made to run. IMHO,what we have available now(tripowers) takes more work and most people take the easy way out by using a 4 barrell. I just broke into the 11's with my street driven, pump gas, iron head, 66 Tripower Ram-Air set-up(11.94/117) and I am in the process of making a few changes that should improve on that this Winter. If you do design a new intake, make it flow 300 plus cfm, that should be possible using the factory RA4 port size(Felpro 1233), with all the new heads coming out that would be nice. Also like others have said, a larger center carb(500cfm?) would be sweet for our 455's. By all means a simple/adjustable progressive mechanical linkage. Thanks -Jim

[carbking]

It may sound like heresy to many Pontiac enthusiasts, but in my opinion Ford did a better job with the progressive linkage than GM.

Take a look at the factory linkage on the old Ford FE tripowers. The center carb is the control, with slotted rods from the center to each of the ends.

This differs from the Pontiac linkage where again the center is the control, but only one slotted rod to the rear, and then a fixed front-to-rear rod.

The Ford engineers found that by staggering the opening of the front and rear carbs (by 5 degrees if memory is working), there was less of a shock to the system, and less problems with hesitation when the secondary carbs were opened.

Making each slotted rod adjustable would be useful.

Jon.

[DiamondJim]

Hey Jon, now you come up with this, just when I was getting good at bending the rod for the end carb!...... J/K. I agree with you wholeheartily on the solid/positive Ford end carb linkage. -Jim

[Kenth]

Ford Tripower Tech Link (from Tom V i believe):

http://www.gerlecreek.com/documents/tptechnical.htm

[DiamondJim]

Threaded adjustments (similiar to a turnbuckle), with a solid threaded rod would work best(less flex when you hammer it-LOL) -Jim

[Dick Boneske]

Some of the posters above have not driven a STOCK Pontiac Tripower car with factory mechanical linkage. There is NO bog or hesitation when the end carbs open. The Ford linkage that opens the end carbs at different rates is totally unnecessary. Ditto for the idle circuit on the end carbs--idle with a stock Tripower is perfect with the center carb only--the engine does not know the end carbs are there at idle if the throttle plates are adjusted for a good seal. Pontiac sold many 455's with a single two barrel in the early '70's. There is also no reason for a power valve on the end carbs. The power valve in the center carb takes care of driveability at part throttle, which is what the power valve does in any engine. Four barrel carbs rely on the power valve in the primary barrels only.

The biggest advantage of Tripower over many four barrels is the shot of fuel from the two end carb accelerator pumps when they are opened.

Larger venturis in any or all of the carbs is a good idea, but the other mods mentioned will likely make the system less driveable and likely not quicker under any conditions.

As I stated above, apparently many of you have not driven a correctly set up stock Tripower with mechanical linkage.

[Tom Vaught]

Dick,

I would disagree on two of your comments:

I believe you are basing your statement purely on Pontiac tri-powers without ever driving a properly set-up Holley "Tri-power" with power valves and a idle circuit on the end carbs.

All of the later corvette and Mopar carbs had a "fixed" idle circuit
built into the carbs. All vacuum holley 4 barrel carbs have a fixed idle circuit. The circuit is there to get rid of stale gas that would be in the rear bowls IF the car was not driven hard for a while. While I agree that most people that would buy the BG system will probably be into the tri-power more than they are out of it, the system is still a good thing. A second part is the Adjustable idle system allows most guys with Larger CAMS to be able to add fuel at idle without messing with idle feed restrictions etc.

Same deal for the power valve side of it. A big motor will want more
enrichment fuel vs what the typical power valve channel restrictions will offer without drilling. Having the other power valve channnel restriction tuning capability will offset that weakness.

JMO

By the way I know a little bit about Holley Tri-power carbs.

Tom V.

Quote:

Ford Tripower Tech Link (from Tom V i believe):"

Did you read the info in the link, by the way?

[Junkyard Dog]

What about BG's three valve cylinder head for Pontiac engines?

[slowbird]

I agree with Tom again. Once you start going with bigger cam and more power. Having more control of the idle would be nice along with power valves. We have ran 10.14 at 129mph with our tri-power but the carbs have been extensively modified to do it. Our intake flows right 300cfm, biggest improvement I can think of to do to the intake is put more material in the roof for porting. If BG is really going to do it they better be able to out perform out stock setups. With completely stock 65 tri-power (it was just port matched to our HO heads) ran 7.0s in the 1/8th at 95-96mph.

[Junkyard Dog]

Will it fit an HEI distributor?

[Kenth]

Tom V, guess i missed the :wink:

You bet i read it.........

[Tom Vaught]

I looked the other day and I think I still have at least two complete sets of the Mopar Mechanical six pack carbs (in like new condition) on the shelves. They were really good carbs but needed more CID than the 366 engine had to offer.

Tom V.

[DiamondJim]

Dick, I run a basically stock 66 Tripower the 11's. My end carbs seal well, it responds when I hammer it. I have played with and adjusted Tripowers since the mid-sixties. I do think there is room for improvement with an aftermarket set-up. IMHO, solid rods with slots to make it progressive would be an improvement over the smaller(bendable for adjustment rod) for the front carb. A larger, easy to tune center carb for the 455+ motors would be an improvement also. Don't forget we are talking about Holley carbs. It is my thought that if Rochesters are not being used, originality is no longer an issue, so make all improvements possible. For me I will probably continue to use the set-up I am running now(with minor improvements). -Jim