Tri Power Questions....

Yeah, I know, it been asked a thousand times. But I'd rather hear it fresh, maybe get some things I missed using search.

I'm trying to decide what to use for induction on my 34 pickup project. I have three choices, 4 bbl with Caddy air cleaner, two four setup from an early Vette, or tri power.....I'm kinda leaning toward the tri power at this stage because I think it'll "look" right. But......

OK, here's the infamous question, what carbs to use? It's not really a matter of what I can find the best deal on, because we have a shelf full of 94s and 97s, and lo and behold I was digging around on said shelf and rooted out three Rochester 2Jets. before you ask, no the 2Jets are not currently set up as tri power carbs, but this is a non issue.

So here's what I currently understand from reading various fragments here and there. And this is where I need more info, comments and corrections. I don't think 97s will ever run right on my motor (10.0:1 CR, fairly large cam SBC) my understanding is that they struggle to provide fuel in high load situations. 94s I guess are better in most respects than 97s when it comes to a setup like this??? Again, that's just what I think I understand after reading a bunch of stuff. And once set up with big end ****erflies, plugged idle circuits, etc., the Rochesters will be my best bet.

So are the Rochesters the thing to use?

Not really performance related but also important.....I think the Rochesters will look more at home on this project since they're kinda "chunky"... 97s are kinda little looking, and everything else on the truck is intentionally built to be just a hair bigger than it should be, it's got a "muscular" look, you know, like trucks should Please understand I ultimately want what WORKS the best, but I do consider every detail from an appearence point of view (to a point)

 

Rochesters, looks and performance more in tune with the "feel" of a SBC.


Frank

 

I'm a multi Carb Freek. I also like them to behave. If you have a built sb I'd only consider Rochesters. Find your self a Pontiac set up and rob the carbs off it. They are more plentiful than you think and feed more fule than the 348's or changed over 2g with a kit.
The Wizzard

 

Is that simply because they're jetted differently, or are they diffent carbs? Sorry if that's a dumb*** question, I have virtually no experience with Rochesters. If it's just a jet issue, they're gonna get tuned on a dyno anyhow, so with that in mind are the Pontic ones worth finding?

 

57-8 J-2's, 57-8 Pontiac, and the 348 W motors all used the small base 2GC's. Those are what you will normally find installed on small block Chev aftermarket manifolds.
59-65 Pontiac's all used the larger base 2GC's for the end carbs. 66 Pontiac's (full size and "A" body) (and the 442's I think) used the large base carbs for all three. 65-66 Pontiac with sticks (and maybe the 442) are the only ones to come with manual progressive linkage. This linkage was far superior to anything aftermarket IMHO and I tried bunch over the years. All the rest used a vacuum switch and diaphrams to actuate the end carbs. The factory end carbs used base plates with no idle screws or circuits. They used the main metering and power valve circuits only. They also held enough fuel to get my 65 421 2+2 to a gas station on more than one occasion (4spd car and only if you kept winging the throttle to keep the RPM's up until the clutch was out and the car was excellerating) after I had run out of gas.
If you take the idle screws out of ordinary 2GC's and epoxy the idle p***ages shut, you essentially haveend carbs. EELCO and many others made manual progressive linkage to adapt normal 2GC throttle levers to 3 2bbl configuration.
In additon to the 2 different base sizes, Rochester made the carbs with a number of different size venturis with some of the 2 bbl equipped Pontiacs and Buicks having the largest ones.
Although you'd think the individual chrome top air cleaners that are comonly ***ociated with the highest HP Pontiac's would be the best HP makers, the single large twin snorkel ones actually are better at making power(and they tend to hide the carbs, too, just exactly what you don't want when the main reason you're using them is to show them off).
I've used and built and rebuilt many TriPower Pontiacs over many years and consider 3 X 2's set up like the factory did to be as reliable and untempermental to use as a single 2 bbl if you use good throttle linkage and use good fuel and air filters on them.

 

Hillbilly hell- I have a 10:1 383 with 3 rochesters. It runs very well. I turned a 13.8 in a 3500lb car with it. Let me say this, I had a 292H cam and a 750 double pumper and It dynoed at 285 HP 300 tq at the rear wheels. I put the 3-2's on there and could not get it to idle due to the lack of vacuum from the cam. I was told I would be able too by enlarging the idle tube holes - that didn't work for me, so then I switched cams to a xe286 and it idled and pulled at lower rpms. I dynoed it again and have like 230 rwhp and 245 tq. SO it ain't as strong but runs pretty damn good. It'll roast tires and go.

I like the basic set up like it came from GM, the outer carbs don't have the idel circut and have the special bases that allow the ****erflies to seal shut when closed. This is important so you don't lose vacuum when driving and idling on the center carb. Run them progressive, you'll find a point where you like to kick them in.

Its a sweet set up, you gotta figure if GM sold them on cars that old ladies drove, they gotta work pretty good.

 

I forgot to mention all carbs in factory TriPower (3 X 2) setups used accelerator pumps, (all the GM 3x2 setups for that matter).

My 4165 lb 421 2+2 convertible with a 3.42 rear gear would consistantly get 16 to 18 miles per gallon (17.3 on one I-95 trip I remember in particular) at 70+ miles an hour with the small center carb 65 TriPower (I think I was using #57 main jets in the center carb (down from 61's) and went up 2 jet sizes from stock on the ends to compensate, with the manual progressive linkage set up to start cracking open the end carbs at about 73 miles an hour) depending how smoothly I drove it. Get happy with the loud pedal (the pedal on the right), crack into the end carbs alot, and you could forget about fuel economy.

 

One thing I haven't seen mentioned yet is that the end carbs have no power valves either. If converting be sure to block off the opening in the bowl.


jerry

 

Tudor, It's funny you should mention that 292 number in regards to the cam. The Crane cam I pulled out of my 421 when I pulled it apart was stamped with the number 292 on it's end.

 

If you don't use power valves in the end carbs, you'll have to encrease the main metering jets 6 to 8 sizes to compensate.

 

Stock GM end carbs had no provision for power valves. The originals have the boss there but the p***ages are not drilled out. I've run a 3 deuce setup and used to have about 8 of the original ends and none were tapped or drilled for the valve.

Never did increase the jet size in the main carb and had no trouble with it. It's not like blocking off the power valve in a holley. The ends are there to act as dumps, just putting in fuel and air.


jerry

 

Sorry, sometimes I don't make myself clear. GM 3X2 setups are just like a single 2bbl until you open end carbs (secondaries) and the center carbs can be adjusted and tuned just like the end carbs aren't there.

If you take primary (single) 2bbl's and move them to the end positions on a 3X2 manifold, remove the power valve enrichment and don't increase the main jet size, you'll likely end up with low and mid range stumble once the accellerator pump shot is used up as these carbs are jetted for high vacuum steadystate cruise to maintain some degree of economy and not low vacuum high RPM power.

 

This is pretty insightful so far. It loks fairly simple to use three single carbs to do this, jetting and the carb mods I can handle with no problem.

Now one more probably stupid question. Why the bigger ****erflies and/or the "kit" from Speedway? Is the primary goal to make 100% sure there are no vacuum leaks? I don't see paying $400 for the Speedway kit when I can get throttle shafts and what is likely a better linkage from Eelco.

What am I missing here?

 

Just looked at the Speedway catalog. No reason why regular carb bases can't be modified with epoxy and made to work just fine, we did it that way for years if the 3X2 end carbs couldn't be found.
The Speedway catalog states their linkage is for FACTORY manifolds only, I don't know that I've ever seen a production 3X2 GM manifold for the small block Chev.
Some one made a post about making sure the carb bases are air tight, I always installed a working center carb and the end carb BASES onto a running engine, to get throttle linkage built and adjusted, and make sure everything was tight with no vacuum leaks
I'll state once again, I've used all kinds of linkages, aftermarket and factory, with ball bearing rod ends and without. The simple 65-66 Pontiac manual progressive with the bent end jesus clip tie rod has always worked better for me than anything. If you use this type to connect your end carbs, you can file the hole in the front carb bellcrank slightly for a little front to rear clearance on the conecting rod. This will allow you to make sure both carbs can stay tightly shut with the linkage installed. The factory carbs were done this way.

 

The only problem with this is tha the ****erflies won't seal shut and prevent you from losing vacuum.

When you're running on the center carb only, you need them end two carbs sealed off, the special bases allow the ****erflies to seat and seal.

Otherwise - it would be a better idea to leave the idle circuit in on the end carbs to mix some gas with that air that is getting in.

 

So it's impossible to get stock bases/****erflies to seal?

 

Nope! we used to make these exact mods all the time. we used 2 part epoxy and patience.
I run tri power on my 389 (the progressive linkage is simple as salt if you need pics) and have run a number of 4 barrels on the same set up and the 4's always made more power. (but the 6 pack looks so much tougher!)

the fuel economy of the three also kicks the **** outta the 4's.

 

If ya feel like posting pics, go for it

My feeling is that in my particular case, buying stuff, other than say, long throttle shafts and rebuild stuff, is pointless. If I DO have trouble getting good seal on the ****erflies, I'll simply order bigger ones and put em in, boring concentric holes is not a problem.

I think with the motor I'm running, power levels with three twos will not be a letdown. If I'm anywhere near close on my CFM estimate, the tri power setup will support ~375 crank HP with no problem, and in a 2000 lb car with 5" wide rear tires, I think that'll do.

 

I read somewhere the large base TriPowers could flow in the neighborhood of 950 to 1300 CFM depending on which throttle bodies were used. Using the large Buick or Pontiac singles will inable the largest air flows without modifing the throttle bodies. Of course, if you open up and/or smooth the venturis you would promote the highest possible airflows of whatever you start with.
While adapting a small carb base mouse motor manifold to the large carbs is possible by several means (which depends your skill level), I think I would be tempted to adapt a tunnel ram. By slicing the plenum down to reduce the volumn and tigging a flat plate on top bored to accept the TriPower carbs, you could probably approach the power output of two fours and have it be a ton more livable on the street.
Sometime after the first of the year I might take time to pull apart the 65 and 66 Pontiac units we have around here and post pictures if anyone is that interested (not right now, it being Xmas and all). Maybe take some scans of the factory manual too.

 

I always had far better luck modifing the stock throttle levers to accept my home built linkage mimicking the the stock Pontiac linkage. The long aftermarket throttle shaft puts the bellcrank (throttle arm) too far from the carb base to work anywhere near as smoothly as a stock type setup, and would bend or deflect a little, trying to bind (I think that's why the ball bearing rod ends were used in some kits).

 

Not a chance in hell. Realistic flow numbers are more like ~800 CFM.

Opening up venturis, while promoting airflow, does wonders towards ruining any vacuum signal and promoting general lack of drivability, so I'll just stick with what I have there.

 

Yes, I know this thread is old but i need help with my planned combo:

I want to run a tri pwr setup on a nice running street small block. I would like to make 450-500 hp with my planned 383 chevy. Are these numbers feasible for a street friendly tri pwr setup? If not, what is the hp these carbs can support?

Thanks in advance.

Greg

 

All the later Pontiac tri-power setups used 2GC carbs. The end carbs had no idle air adjustment screws, and naturally longer throttle shafts to accomodate the linkage. Also they were vacuum operated end carbs i nstead of a positive manual linkage

 

Bump

 

The latest Hot Rod magazine has a good article about this. Makes it all pretty simple to understand.

 

Yes I read that one. Great info! Have to make sure I save it so when on do my Tri Power on my 55' I know what to do!

 

The 1965-66 GTOs Olds etc etc.. did away with the vacuume pots for the front and rear. This was also what every hotrodder did back in the day. I have sliced and diced my Tri powers for years and to get the front and rear to seal 100% ,you need a product which the factory also used called Dag213. This will make 100% positive seals on the front and rear . The castings are actually pretty rough on the base plates. One of my Convertibe 400 Firebirds with Tri Power ran 13.7s with a 2:78 Non posi and stock cast manifolds with 2" exhaust and a very mild cam. It now has 2 1/2" exhaust and a 3:42 posi. I have re jetted the front and rear carbs and the center has the idle air bleeds opened up including the idle air slots. This tri power runs frickin quick now. I also run a 12.5 second coupe with a 400 Pontiac 4 bbl thats a basically stock rebuild. The Tri-power seems to feel about the same power after unchoking the engine and gearing, and richening up the carbs.
I would run the 2gcs, run the long throttle shafts and run the front and rear carbs with the linkage on the p***enger side like the stock pontiac linkage. You can now buy just the base plates form Vintage speed with the long shafts which I would recommend to make it easy to use the stock Pontiac linkage. Dag213 will solve all vacuume leaks.
You can buy this stuff and get whatever your needs are from Tri-Power Mike. Call him up!!! http://www.pontiactripower.com/section/Services/

 

Thanks guys for all the info provided, I appreciate it!! I read the HOTROD article and checked out Mike's sight. I will email him some questions but would still like to see if anyone here is running a tri power setup on the street with 450 horsepower or more???? Let me know!

Thanks,

Greg

 

Anybody know what $$$range should i pay for used buildable cores?

 

"twofosho said:
I read somewhere the large base TriPowers could flow in the neighborhood of 950 to 1300 CFM depending on which throttle bodies were used. Using the large Buick or Pontiac singles will inable the largest air flows without modifing the throttle bodies. Of course, if you open up and/or smooth the venturis you would promote the highest possible airflows of whatever you start with.
hillbillyhell said:
Not a chance in hell. Realistic flow numbers are more like ~800 CFM.

Opening up venturis, while promoting airflow, does wonders towards ruining any vacuum signal and promoting general lack of drivability, so I'll just stick with what I have there."



I am bumping this old thread to find out if 800 CFM is an accurate number. I have searched here and found conflicting CFM ratings for tri-power setups. I have read that Small Base Rochester 2Gs without any modifications (aside from a speedway kit) do not flow at the sum of all three but at a lower number. Does anyone have any info on this?