The Thread Spread - Revisited
_______________________________________
-Measuring Thunder-
Power Losses; No Wonder
The Question - I know your busy but 1 quick question reading the article at http://www.macdizzy.com/trx_dyno.htm. You say the TRX250 was getting 53.3 HP at the rear wheel with the high compression head and 49.7 HP with the lower compression head. Any idea what those HP numbers would be at the crankshaft ?
I like the stuff you posted on the software you are evaluating.
Thanks and keep up the good work.
hoser
The Response - Power losses associated with the driveline (transmission, primary gears, clutch, oils sprockets and chains) is normally considered to be 14% to 17% for a modern 250 cc motocross bike. Therefore 53.3 HP @8300 RPM at the rear wheel translates into 62.3 HP at the crankshaft if using the 17% factor and 60.7 if using the 14% number. Using this information it is
easy to calculate the BMEP (brake mean effective pressure) of this engine.
53.3 * 17% = 62.3 at the crankshaft.
62.3 / 8300 * 5252 = 39.45 Torque.
39.45 * 1236 / 250 cc = 195.08 psi BMEP.
Aren't you glad you don't have a snowmobile that loses as much as 50% of its power between the crank and the track?!?
Rick
Ok , Thanks
I do have a 540cc Yamaha snowmobile... about 50% ouch that's a lot... 62.3 HP is a respectable number coming from 250cc. I would be happy to get 62.3 hp and 39.45 Torque out of my 400cc Pilot motor ( stock its rated at 37hp).
Thanks again
hoser :)
The TRX250R was rated at 36 HP from the factory. Figuring in the normal 50% over design factor necessary to satisfy most engineers and a few more percent than that because this is real life - there is plenty of room to work within most engines. The only thing that's a little questionable with that engine is the long stroke which prevents it from stratospheric rev levels.
Considering you have a 400 cc modern high output engine, I would think that if it were blueprinted and optimized to run race fuel, horsepower numbers like you want are not impossible. However if you want to have your cake and eat it too you will have troubles. Engines designed for ultimate power eat and drink expensive, high quality parts and fluids and require frequent maintenance. Tuning into this sweet-zone is a one way street - once you experience the thrill you'll never enjoy riding the Pilot the old way again. Letting kids, wives, friends and just about anyone else drive it becomes something that will just never happen again.
Rick
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