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The book on Tri-Y headers is that they pump up the midrange torque over a set of four-into-one headers, which is exactly what we saw with this test. In the midrange between 3,600 and 5,200 rpm, the torque jumped as much as 27 lb-ft, but this comes at a price. Note that the average torque gain throughout the entire curve is only a scant 2.6 lb-ft. This is because at the lower engine speeds like 3,000 rpm, the Tri-Ys lost 32 lb-ft compared to the four-into-one header. Would these Tri-Ys be quicker in a mild street car? When we plugged the two power curves into the Racing Systems Analysis Quarter Pro simulation, the two curves produced very similar results. The four-tube-header version ran a scant 0.08-second and 1.1-mph quicker through the quarter than the Tri-Ys. Much of the difference was due to the slower 60-foot time exhibited by the Tri-Ys because of the torque loss below 3,400 rpm. The simulation used a 2,600-stall converter. It's possible that with a little carburetor work, that torque loss could be overcome. The Tri-Ys might have over-scavenged the engine at low rpm, requiring more fuel, and that could make these two headers more even in the car. But there appears to be no significant gain in performance with the Tri-Ys. It's mostly about where you want the torque gain to occur within the engine's power curve.
[/ QUOTE ] Was the TRI-Y's they tested made by Thorley ??? Wasn't that test on a car not a truck ?? It looks to me that they say a little tuning at the carb overcomes the torque loss. I'd still go with Thorley TRI-Y's.
