History The General Motors "Tri -Power" story

While the title says GM this is mostly the Pontiac Tri-Power story with just a bit on other GM brands.

Offered on select models from 1957 through 1966, Pontiac’s Tri-Power induction system added a new dimension of performance to the General Motors brand and a colorful new term to the hot rodder’s vocabulary. Tri-Power has an interesting background.

The Pontiac Tri-Power story formally begins in December of 1956 with a General Motors press release announcing the setup’s availability on the 1957 Pontiac line (factory photo below). But we could say the ball actually started rolling back in 1955 when the Rochester 2G series two-barrel carburetor was introduced, which made the Tri-Power concept possible.


1957 Pontiac



In American hot rodding, two and three-carburetor setups were the norm, so Pontiac engineers took the obvious step. A basic design with few components, the Rochester two-barrel had a dirt-cheap unit cost, perhaps $5 to $10 each. This allowed Pontiac to offer the three-carb Tri-Power system for only $90 to $100 per car. This was a fraction of the cost of the fuel-injection system, or alternately, a pair of fussy and expensive four-barrel carburetors from Carter or Holley, and still allowed for a healthy markup.

While the three-carburetor setup looked impressive and complicated, in fact it was fairly simple. Only the center carburetor worked on starting and at low speeds, providing reasonable drivability and fuel economy. But at larger throttle openings, the front and rear carburetors—which had no chokes or idle circuits, only main and accelerator pump circuits—opened progressively via a vacuum servo.

With the Tri-Power induction setup, Pontiac was able to offer performance similar to the fuel-injection system but at a far more reasonable cost. In fact, Motor Trend magazine reported at the time that Tri-Power induction was slightly but measurably faster. And of course, nothing says high performance like a row of three carburetors under the hood. The Tri-Power legend was born.




The other GM divisions were quick to offer their own 3X2 Rochester induction systems, as Oldsmobile, Chevrolet, and Cadillac all offered their own variations on the theme. In January of 1957, Oldsmobile introduced the J-2 package (above) for the 371 CID V8, offering the option for two years. And in 1966, Olds returned with a similar 3X2 system for the 442.

While the Tri-Power name was a Pontiac exclusive, the term quickly gained what is known as the Kleenex effect, becoming a generic trademark. Car enthusiasts began to call all three-carburetor setups “Tri-Power,” regardless of origin. A new term entered the gearhead’s vocabulary, much like the Chevrolet trade name Positraction, which you will hear applied to a limited-slip differential from any manufacturer. You can’t buy that kind of word-of-mouth publicity.



Cadillac offered Rochester 3X2 induction from 1958 through 1960, replacing the expensive 2X4 Carter system used to that point. Chevrolet (shown here) used the three-carb setup to good effect on high-performance versions of its 348 CID V8 from 1958 to 1961. Note the choke thermostat on the center carburetor only, the bowl-type fuel filter, and the mechanical linkage connecting the front and rear carbs.





Pontiac offered Tri-Power on select models and engines (347, 370, 389, and 421 CID) from 1957 through 1966, when it was finally superseded in 1967 by the Rochester Quadrajet four-barrel, a more modern air valve-type carburetor. On the Pontiac GTO (shown) equipped with manual transmission, the vacuum-operated throttle was replaced with a mechanical progressive linkage.





In 1965, Pontiac began to offer an fresh-air induction system, initially as an over-the-counter dealer package that sold for $30 and included a carburetor pan, a foam seal, and instructions for making the external hood scoop functional. While in truth, the scoop was too small and shallow to provide any significant increase in air pressure, Pontiac named the package “Ram Air,” and another familiar hot rodding term was born.



from here:https://macsmotorcitygarage.com/the-pontiac-tri-power-story/#more

 

Good read. Thanks.

 

Great read. Made me misty-eyed when I remembered getting a ride in a '66 2+2 ...

 

Never had one on any of my own stuff but sure have worked on many.

 

Don't forget Nash and Buick stated the compound carburator ball rolling waay back when.

 

I had a 57 Safari wagon with a 389 tripower and a 4 speed in 1970. Wish I still had it.

 

There's nothing that sounds as good as a high stepping Pontiac opening up the tri-power.

Super simple, too.
The key that unlocks the mystery is having the end carb's throttle blades sealed and not dripping fuel. Couple that with progressive mechanical linkage and you're sitting directly in the center of "could not be simpler"

 

wasn't this the first one?

 

Thanks! A very good read. But now a question. So, why is it that whenever someone asks about doing a "Tri Power" set up on their hot rod, the immediate response is, "Too much trouble. Stick with a 4 bbl." Do a search here, on multi-carb advice and that comment will come up. And more than once.

So, what's the mystery? Is it more complicated than it looks? Is there something GM was doing, that gets lost in the hot rod community translation?

 

had one on my 65 gto conv, with a 4spd and a posi, great car

 

A lot of guys can't make one carb work...why would they want to mess with three, at the same time?

The other thing is that when you try to get three 50 year old carbs working, it can be a bit of a challenge even for the guys who are good with them.

 

I don't know about most people who have run such a setup and I am no mechanic so this may be just blowing smoke, but I think that most of the problems with the 3x2 setups is the end carbs developing a vacuum leak.

 

{ Loudbang } THANKS, for all your great post. You add so much too the H.A.M.B. I enjoy all your post. I love Pontiac s. I still have my dads 67 Bonneville conv. That he got new. And have a 389 Tri- power in my 29 coupe for way over 20 years. Ron...

 

Great history lesson! Thank you for the great post and read!

 

The mystery is that some guys use center type carbs on the ends, and can't figure out why they have trouble getting the car to start and idle smoothly. Beyond that, with mechanical linkage, if the 2 end carbs engage at too low of RPM, say the driver mashes the pedal to the floor, the engine will bog. It takes a trained foot to get the best performance, easing into the throttle and allowing the RPM's to come up before kicking in the end carbs. Timing down shifts to occur before the end carbs open. People don't like having to learn something new, they just want everything to work easy for them. Vacuum operated end carbs were used to avoid that bog, but there is more complication with that set up, and then there were complaints of throttles sticking open on those systems too. 4 barrel carbs avoid all of that (but don't look nearly as good).

 

I always enjoy reading about multiple carbs. Here is a link that adds more, although not so detailed on Pontiac.

http://www.thecarburetorshop.com/Multiplecarburetion.htm

And here is a link that will help one identify O.E. multi-carb intakes:

http://www.thecarburetorshop.com/Multiplecarbmanifolds.htm

Jon.

 

One issue that "bites" many enthusiasts is aftermarket progressive linkage. If one is going to use progressive linkage, one should look at the methodology used by the factory engineers. NOTHING was connected solid. All of the linkages had either slots in the linkage or the linkage fit into a slotted arm. This feature has two functions:
(1) the slots allow the two end carburetors to be slightly "staged" as to engagement.
(2) the slots allow for the coefficient of linear expansion, thus allowing BOTH end carbs to be completely closed when they are supposed to be closed.

Bog when engaging the secondaries often is a direct result of ignoring the above.

Jon

 

Another problem was mild mannered Olds or Caddy owners who had never punched it out since delivery, then for some reason floored it, causing the end carbs which were nearly seized from disuse to stick wide open.
I've seen factory issued Olds kits to remove the end carbs, using blockoff plates. Did any of the other 3 divisions list them ?

 

What Ron said X2!

 

One of the guys that I knew (and later became good friends with) bought a 57 Pontiac with tri power with his older brother. It seemed like he NEVER got to drive it (not even sure if I ever got to ride in the salmon/charcoal four door hardtop body the engine was in) but I heard it would smoke the tires. That was about 1960 or so, still wished I could have ridden in the car at full tilt

 

Where are the slots in post one, pictures 4 and 5?

 

I got huge a laugh out of this comment, it's me in spades.... For some reason lately I can't tune my way out of a paper bag. Years ago I could take 3 nasty old carbs and make 'em run great. I had a 427 BBC powered '32 5w with the Corvette 3x2 set-up, that was a fast car and kicking in the secondary carbs was a real kick in the seat of the pants. Right now I have three cars with terminal carburetion issues - one each; 2 - 1 barrels, 3 - 2 barrels, and one stupid 4 bbl I can't conquer. WTF ??? I'm ready to seek professional help......
I do recommend taking a 3x2 equipped car with progressive linkage out for a vigorous joy ride about once a week to cycle the gas in the end carbs though, especially here in California where the gas is funky.
Like someone said, there ain't nothin' like poppin' the hood and seeing a row or two of carburetors.

 

3-2's or dual quads need to be opened up. I do mine at least once a month. Keeps them from getting fuel bowls from over filling. Good for the brain too.

 

OOOh, that's ^^ just beautiful.............

 

The arm on the passenger side front has a small horizontal slot, which is not visible when the clip on the front to rear rod is installed.

http://www.thecarburetorshop.com/Tripowertuning.htm

Jon.

 

Here's my tri-power on the Caddy.

 

In the mid 60's my uncle had a '60 Pontiac Bonneville, 389 Tri-Power, automatic and it was forever sticking open. I remember more than once him trying to brake that thing to a stop, throw it in neutral and turn the ignition off, ALL AT ONCE!!!

Then he'd throw the hood open and wiggle the throttle linkage and off we'd go. Ah, the memories of a 10 yr. old impressionable kid...

 

It is said that the only dumb question is the one you don't ask, so taking a risk that saying may be wrong, here goes.

"the coefficient of linear expansion" You've used this term in a previous post, and in the article you linked to here. Can you explain what it means? I'm trying to read it in context of where it's used, and I still don't know what you mean.

 

< My avatar is a factory tripower car.

 

Blues4U - the coefficient of linear expansion is a measure of how much a specific object will expand or contract with heating or cooling. Different materials expand/contract at different rates. The rate for steel (the front to rear rod) is different from cast iron (the intake manifold). Thus, if one uses linkage bolted directly to the carburetor arms when cold, then either the front or rear would be slightly cracked ajar when hot. Not sufficiently to upset an enthusiast with lots of tolerance for a high idle (and either a manual trans or an automatic with a performance converter); but the unit will never low idle perfectly. The factory engineers knew this, and designed the factory linkage with slots to overcome this issue.

And you are absolutely correct about the question. If you want answers, ask it!.

Jon.