HCS Snowmobile Forums - View Single Post - Any 850 Dyno numbers yet ?
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Old 07-16-2018, 05:55 AM   #24 (permalink)
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patrioticinnovations's Avatar
Join Date: Sep 2005
Posts: 15,002
Current Sled(s): 2015 AXYS Pr-S SB Ann 800, 2019 Indy 850.
Previous Sled(s): 2003 XCR 1100, 2000 XCR 800 turbo, 2005 Redline Revolt 800.
Location: SE Lower Michigan
Favorite Riding Area: Cadillac, Gaylord
19-20 Mileage: 715 so far
18-19 Mileage: 849
17-18 Mileage: 1280
16-17 Mileage: 1115
Riding Since: 1982

Originally Posted by rabbi View Post
With all the talk of the magical peak horsepower, that is only part of the equation.
How wide is the torque curve? I remember before everyone was using exhaust valves the horsepower was so peaky sleds were a challenge to clutch. Miss the peak rpm by a few hundred rpm and the sled would fall on its face.
Exactly. Avg torque/hp is the way to evaluate engine power. Peak is not nearly as important. With a typical 2-stroke, dyno results usually aren't the best indicator of in the field performance. Mainly because they only assess WOT and only at a controlled rate of rpm increase.

I've been involved in many in the field vehicle acceleration tests. The low rpm engine response is a key factor in improving acceleration.

A few weeks ago, I loaned a special vaporizing anti-reversion 4 barrel plate to a friend for testing. He gained .2 seconds in the quarter mile.
The car runs in the 9 second range. His previous setup had so much reversion in the carb at WOT that the wide-band O2 sensors were reading around 12:1. When he installed the plate, it went to 16:1. He had to add 4 main jet sizes and it was still 15:1. He ran it anyway. Said it made so much more low end power that he hit the rev limiter before the traps and lost control. This was at Milan Dragway. Had to deploy his chute. Car flipped and was destroyed. He is purchasing the plates for his new car.

I've done the same testing on snowmobiles, dirt bikes, PWCs, etc, with similar results.

The point is that a dyno can't easily assess this effect. DTR Jim and I have discussed this issue numerous times.

Any engine mod that broadens the power band will usually improve in the field performance.

So, don't get hung up on peak power dyno readings.
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