Converting Standard 2 Barrells to Tri-Power
 

I would like experienced opinions on converting standard 2 barrel carbs to tri-power using modified standard bases, or aftermarket tri-power bases and air horns that are available. Over the years I have collected three 7029060 69 carbs for my 69 Lemans (with GTO hood) with the intent of creating a "what if" tri-power ram air setup complete with modified aftermarket hood pans, etc. I've heard conflicting opinions about how well the standard carbs work when converted so I thought I'd get professional opinions. Thank you.

Speedway Motors, I think, makes a kit to do this. It's more aimed at the Chevy crowd though. Never done it so I have no experience with it. Looks to be fairly expensive.

If you use aftermarket bases & airhorns, the conversion is quite simple. If you use an aftermarket Tripower airhorn ($90), the only mod needed to your float bowl would be to disable the power valve passage to block fuel from entering that hole. That can be done by leaving the original power valve in place in the float bowl. If you use your original airhorns, insert a short 5/16-24 screw or bolt in place of the power valve to block fuel. No further mods are needed to the float bowl or airhorn other than removing the choke pieces.

If you decide to use your original throttle bases, the idle passages need to be blocked. The easiest way to do this is from the top surface just behind the idle adj. screws. Drill & tap the holes to insert threaded rods to block flow or use JB weld to block the holes. You can do the same for the two holes where the idle adj. screws were located.

The center carb can be used unmodified, as it is nearly identical to the OEM '66 Tripower center carb. I'd use main jets of .062" for startup. If the 7029060 carbs have similar venturi sizes to the OEM Tripower end carbs, main metering jets would be around .070".

To summarize--using an aftermarket Triopwer end carb base makes the project simple. Using your OEM airhorns would require making custom fuel lines vs. aftermarket Tripower airhorns which would use stock '66 Tripower fuel lines. Either way would be cheaper and just as functional as the Speedway kit.

Very Nice work Dick, on the mods and as you posted, if you can get good aftermarket bases and decent tops that will take stock type fuel line kits, the rest of the mods are pretty straight forward. Deal is though a reworked set by you will probably fire right up and run very well immediately after installed.

Tom V.

clones
 

Looking back on some of your posts it appears that you have (had?) a 65 tri-power setup on a (presumably 1969) 350 engine and you have plans on upgrading to a 428-size engine. If so, I can't see why you would go to the effort to "build" a set of carbs to go with a 66 manifold.

I would mention the fact that, although the 65 center carb’s top plate is small (2 ½“ airhorn), its venturi bore ( 1 1/4") is larger than the large (3” airhorn) 1966 center carb‘s venturi (1 3/16") and larger than your 7029060 1969 carbs ( 1 3/16"). In essence, your 7029060 “cloned” center carb would have some 10.8% less cross-sectional venturi area than a stock 65 center carb. Of course, you could have the 7029060 bores enlarged at some effort and expense.

Likewise, the 65-66 end carb venturi bores are 1 5/16" and your 7029060 venturi bores are only 1 3/16". Without having your 7029060 bores enlarged, your cloned end carbs would have some 22.16% less cross-sectional venturi area than either a stock 65 or 66 end carb.

All in all, I suggest that your 65 tri-power setup would likely perform just as well as a cloned 66 setup that used 7029060 1969 carbs that don’t have their venturi bores enlarged.

In any case, I suggest you check out Mike Wasson’s “how to” videos at these websites:

https://www.youtube.com/watch?v=EQ17SZ_520Q 1:17
https://www.youtube.com/watch?v=WN0ISOzMjWg 4:06

Note that at time 1:17 in the first video Mike seems to suggest that end carb venturi bores are 1 3/8” and he also does at time 4:06 in the second video. I recently quoted that venturi info and I was corrected by Dick and others that the end carb venturi are 1 5/16”. I subsequently measured a rear carb tagged 7013065 and a rear carb with a bowl circled number of 7029863, both measured 1 5/16”.

Note that there is a series of Wasson’s other 2009-vintage YouTube articles regarding tri-powers which are quite informative. Note that the prices mentioned on those videos are different than current pricings in his catalog.

Apparently, you have already "solved" the issues of 1969 timing cover and 1969 valley pan fitment problems with 65-66 tri-power manifolds, not to mention fitment problems with an HEI distributor.

Good luck!

Venturi area is not everything on Three 2-BBL set-ups.

A good example was Bill Klausing's 63 station wagon with a 455 engine and a 66 Tri-Power set-up with adaptors (perfect match on modded manifold) using THREE of the 6425 Holley 625 cfm (2 bbl rated) carburetors. Pictures attached

His 63 wagon drag car at 4400 lbs could run 12.06 in the quarter. Do the math on the HP of the engine. That being said when he had all three cars adjusted for max blade opening of the three carbs and max venturi area, the car ran slower vs if he set the end carbs to run at 3/4 open. A swap to 3 Holley 4412 (500 cfm each) Holleys would work better for his application.

So now we are talking a street car that wants the Tri-Power look and feel.
That 1/16 of an inch venturi difference is not going to make any real difference in the scheme of things. What Dick B is doing is just fine for 99% of the people that do not have access to pure Tri-Power parts. It has to do with Carb Signal and fuel atomization.

Tom V.

Sorry for my non-response. Even with my recent retirement, life still gets in the way of the fun stuff.
Thanks so much for the replies and great advice and information. I really appreciate it and will take all into consideration. Just to clarify, I failed to include that my plan would include an aftermarket aluminum intake manifold. The intake on my car actually belongs to a friend that has no car to run it on. I also like the idea of a Holley conversion, as well as other combinations.
I don't know if I will move on with this, or go a different direction. So many options these days, but it's so much better than the "old days" when the options were mostly limited to factory parts. Fun times for Pontiac stuff.
Thanks again!

I have 6 carbs sitting in a box, one guy didn't care what air horns or bases he used and another at least tried and got the air horns correct. Then i found a 65 gto set so i put the 6 back in the box lol. perhaps one day i will build another set. perhaps. Good info in this section. me likey