1969 Tri-Power Carb CFM Ratings?

[Clem Z.]

Re: 1969 Tri-Power Carb CFM Ratings?

[quote=Duke Williams (22045);553462]Most V-8 manifold designs are compromised to one degree or another. The ideal set up would be identical inlet runner geometry on each cylinder (although Can-Am engines used two different length inlet trumpets, which helped smooth out the torque curve, but other than trumpet length, the runners were pretty much identical.)
i under stand the different lengths were done because 2 ports on each head turn into the center of the chamber and 2 ports turn into the chamber wall which hurt the flow in those 2 cylinders. that may have smoothed out the torque curve.

[Duke W.]

Re: 1969 Tri-Power Carb CFM Ratings?

It's a matter of packaging. If you want a low/compact manifold, the center four cylinder runners are shorter than the outer four.

In fact, the high response pressure transducers that I used in my research on a Chevy 283 at the U. of Wisconsin Engine Research Center circa late sixties, clearly showed different wave patterns between the short and long runners.

There's a lot of complicated physics going on inside a carburetor-manifold system. It's a damned wonder that they work as well as they do - at least in terms of power, but there was no way to control the A/F variation under all speed and load conditions to meet proposed future emission standards, which is why their days were numbered. GM and Honda hung onto carburetors way too long IMO - to the point where the carburetor systems and all the related hardware to meet emissions were probably as expensive as a multiport EFI system.

GM tried to make TBI work, but TBI still had fuel distribution issues.

As far as the Pontiac tri-power engines are concerned, I believe all had different cams and possibly other differences from the single four barrel engines of the same displacement, so it was never an apples to apples comparison.

Also, different gearing will have a significant effect on quarter mile times, so they cannot be used directly to compare engine output.

Duke

[Clem Z.]

Re: 1969 Tri-Power Carb CFM Ratings?

those computer controled carbs were expensive and even more expensive today if you need a replacement. i often wondered why GM did the computer controlled carbs and then the throttle bodies before going to true fuel injection. they must not have had the software under patent till later.

[Clem Z.]

Re: 1969 Tri-Power Carb CFM Ratings?

Seen more than one 425 vs 435 side by side race, never saw a 435 win. There is a definite "seat of the pants" difference between the two, the 425 feels stonger. Just my 1/2 cent worth

back in the day SCCA wanted big block corvettes and small block corvettes to run the same class with the big block running a certain size restrictor plate under the carb. since SCCA did not say how many barrels you could use i built a 3 X 2 set up using the restrictor plates. the advantage was 6 restricted throttle bores where the guys with a 4 barrel had only 4 throttle bores the same size.