It Only Takes Two!

Dyno Results
Maximum power with three carburetors functioning
Timing: 36-degrees
Jets: 0.070/0.064/0.070
RPM TQ HP
4,300 493.62 405.28
4,400 491.89 409.34
4,500 490.64 418.14
4,600 489.66 426.64
4,700 488.94 435.50
4,800 487.48 443.07
4,900 484.75 449.82
5,000 480.63 455.54
5,100 473.27 457.08
5,200 467.99 460.81
5,300 462.70 464.87
5,400 453.66 464.28
5,500 443.57 462.56
5,600 435.73 463.03
5,700 431.45 465.85
5,800 426.33 468.43
5,900 421.34 471.42
6,000 416.18 473.30
6,100 407.49 470.91
AVG 460.39 450.83

When first exposed to the thought of testing a Tri-Power equipped Pontiac with the two outboard carburetors disconnected, the knee-jerk reaction is probably, why?

Jim Taylor’s reasoning behind this final test we did that day was to assign a hard number to the kick one feels when matting the throttle and allowing for the improved volumetric efficiency that the other two Rochester carburetors bring to the game. Well, with this engine that number is approximately 123 hp. The 421 made a hair shy of 350 hp when running on the center two barrel alone. Jim finally got his answer to a question he has been asking himself for decades.

As the author, this test not only satisfied Jim’s curiosity but also proved something I believe more valuable—it debunked the age-old myth that a Tri-Power manifold would offer poor fuel distribution during street driving.

For as long as I can remember, it was believed stunning performance and good drivability were not achievable with three carburetors. If that was the case then the engine would not have made 350 hp on the dyno with excellent loading and good fuel distribution. The only caveat being that the carburetors need to be set up properly, and Jim certainly knows how to do that.

The moral of the story is if you have a Tri-Power Pontiac that suffers from poor light-load performance, stop blaming the manifold design. When they are right, they are right, and when they are wrong—well, you know the result!

Dyno Results
Power with only the center two-barrel operational
Timing: 36-degrees
Jets: 0.064
RPM TQ HP
4,200 397.08 315.79
4,300 395.24 321.56
4,400 394.29 328.02
4,500 391.38 341.20
4,600 389.09 346.60
4,700 384.03 349.00
4,800 376.73 349.74
4,900 365.91 346.64
5,000 356.05 343.97
5,100 346.82 341.79
5,200 336.10 337.52
5,300 326.74 334.17
5,400 317.51 331.14
5,500 309.15 328.20
5,600 301.01 325.34
5,700 293.27 322.39
5,800 283.74 317.41
AVG 353.15 334.18

SOURCE
Jim Taylor Engine Service
P.O. Box 462
Revere
PA  18953
610-294-9707
UEM Pistons
800-648-7970
www.uempistons.com