TRX250R on the Dyno - 2 Stroke Engines

Here are a couple of dynamometer test results using the Dynojet Dyno 150. The base engine is an 1986 TRX 250R (66.25 x 72 mm). This one is fairly highly modified. It is running 192 degrees of exhaust duration and 132 degrees of transfer. The carb is a 39 mm Keihin PWK and the pipe - FMF H49. It was running 113 octane leaded ERC gas during the tests.

There are 3 runs on this sheet. The lower one is the motor with 165 PSI static compression and the squish band set to .055". The two other runs are the same motor with the Pro-Design Cool Head installed and 215 PSI static compression with the squish band set to .035".

The difference is as much as 7 HP at the rear wheel at 7000 RPM and is never less that 3.5 HP across the power range.

Here's a closer look of the peak values. Though the peak is still at 8300, power is up by 3.6 HP at the rear wheel. The power before and after the peak is much greater too. The dip in power in the 7000 RPM range on the upper two runs is being caused by jetting that's too fat (too rich). The darker of the 2 upper runs reflects a main jet change of 1 size - from a 192 to a 190. A few more jet changes were needed. I ended up running a 185 in it as the baseline main jet.

This motor was ready for the higher compression - it already had the porting for it.

Peak SAE corrected HP as measured at the rear wheel is 53.3 with the high compression head and 49.7 with the lower compression head.

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