[Singleton]

It's common knowledge that Pontiac used a larger center carb on the 66 tri-power, vs the 59-65 TP's. Obviously the 66 unit flowed slightly more cfm. But what was the reason for the change from 1965 to 1966? The 389 & 421 engines between the two years were basically identical, with the same horsepower rating.
The engineering dept must have had a reason to make the change. Anyone know?

[Old Man Taylor]

My guess is that they didn't want to continue to make two different sizes - commonality of parts. B/T/W, I don't think there is an appreciable difference in the flow of a '65-'66 tri-power as the throttle bore of the '65 is either the same size or larger than the '66.

[jotrout]

Good question. I'll be following the responses. I run the 66 tripower, and have learned here that the 65 center carb venturi is larger than the 66 center carb and flows higher cfm's. And as stated, engineers design for a reason.

Joe

[Singleton]

According to this thread, http://http://forums.maxperformancei...66+cfm+Venturi , even though the 66 Venturi is smaller than the 65, the 66 center carb flows more air due to the larger openings at the inlet and outlet.

I speculate that the reason for the change to the larger center carb in 1966 could have been because the engineers knew that in 1967 larger engines were on the way,(400, 428), with better flowing heads. So maybe they made the intake for that reason, not knowing that GM would pull the plug on multiple-carb engines after 1966. I see no reason to retool a new manifold for 66, when the engines were the same as the previous year, unless there were shortcomings of the 65 manifold that the engineers were aware of.

[steve25]

It's called keepin up with the competition, as in a Olds!

[Tom Vaught]

Originally Posted by Old Man Taylor

My guess is that they didn't want to continue to make two different sizes - commonality of parts. B/T/W, I don't think there is an appreciable difference in the flow of a '65-'66 tri-power as the throttle bore of the '65 is either the same size or larger than the '66.

Agree with Jim but want to adjust his post slightly:

The 65 base uses a smaller throttle blade size vs the 66.

The carburetor venturi (which sets the air flow of the carb) was the same or larger on the 65 carb vs the 66 carb. The air horn on the 66 carb (larger) made a slight difference in flow which probably offset the difference in the carbs too.

Tom Vaught.

[77 TRASHCAN]

I read in a High Perfromance Pontiac article, here recently, that Pontiac toyed with the idea of trying to keep the tripower setup by making a common baseplate for the three 2G carbs to mount to, to stay in compliance with the "No multi carb" edict from the management wheels in charge.....

No, I don't believe everything I read In car magazines...

IF, it's true, I wonder if any of those carbs, where ever tooled up, or if it was just on paper????

What were the differences in CFM between 65 and 66?

[Tom Vaught]

Malcolm McKeller had a 62-63 Pontiac 421 Overhead Camshaft engine in his car (given to him on his retirement by Pontiac) that had a "single base" Tri-Power carb set-up on it.

So they looked at it before 1962. Tri-Power for Pontiacs went away in 1966 (as we know) but GM continued with Tri-Power on the corvette using Holley carbs.

Single base would have made installation (on the line) easier (Linkage, fuel lines, mounting as an assembly to the manifold) according to MaLcolm (when I asked him, MAY HE REST IN PEACE).

Tom Vaught

[1969GiPper]

Originally Posted by Tom Vaught

Malcolm McKeller had a 62-63 Pontiac 421 Overhead Camshaft engine in his car (given to him on his retirement by Pontiac) that had a "single base" Tri-Power carb set-up on it.

So they looked at it before 1962. Tri-Power for Pontiacs went away in 1966 (as we know) but GM continued with Tri-Power on the corvette using Holley carbs.

Single base would have made installation (on the line) easier (Linkage, fuel lines, mounting as an assembly to the manifold) according to MaLcolm (when I asked him, MAY HE REST IN PEACE).

Tom Vaught

The orders from upper GM management was for no more multiple carbs on "passenger" cars. While the Corvette could/did carry a passenger, it was considered by management to be a "sports" car. Therefore the order from management didn't apply.