used 05 crf450 needs a good once over

IndyMX

Crash Test Dummy
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Jul 18, 2006
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2strokerfun said:
There was a pretty good video couple years ago with some really good MX rider on an XR650 smoking someone on a 450(I think it was a 450) MX bike. Loved the brake light coming on before every corner!! Can't see vids on work computer anymore (being held down by The Man here), so I can't find it to post the link.


That was Ivan Tedesco.. http://www.youtube.com/watch?v=70jokjTaGT4
 

motometal

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Sep 3, 2001
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dirt bike dave said:
The extra displacement will let you run a much more radical cam in a 1000cc 4 than you could in a 250cc single. So the big bike can put out superior hp/liter numbers.

I never thought much about that. We've all heard a lumpy cam in a big V8, long duration and/or lots of overlap and you lose effective compression, which kills the low end usually. Engine does not want to run there. This would be more pronounced on a single cylinder because you wouldn't have the other cylinders helping push it along. Sure, you could use a heavy flywheel but that's no good on a race engine.
 

Rich Rohrich

Moderator / BioHazard
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Jul 27, 1999
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motometal (or anyone else that wants to play along at home) - Think about these things and the whole thing might be a bit clearer.

- What determines PEAK horsepower?
- What determines PEAK torque?
- What determines the area under the torque peak?
- What does the area under the torque peak on a 4 cyl 600cc Honda look like compared to a Honda CRF450?
- How did they attain that difference in the area under the curve?
- How would that area under the curve difference potentially translate into a difference in service intervals?
 

jsantapau

Member
Nov 10, 2008
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0
just curious as to how much being able to balance the crank and pistons of a multi cylinder engine compared to shooting for the least amount of vibration of a single cylinder affects power
 

motometal

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Sep 3, 2001
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Rich Rohrich said:
motometal (or anyone else that wants to play along at home) - Think about these things and the whole thing might be a bit clearer.

- What determines PEAK horsepower?
- What determines PEAK torque?
- What determines the area under the torque peak?
- What does the area under the torque peak on a 4 cyl 600cc Honda look like compared to a Honda CRF450?
- How did they attain that difference in the area under the curve?
- How would that area under the curve difference potentially translate into a difference in service intervals?

I'll study dyno charts when I get a chance and see what conclusions I can draw. Max rpm and how high the torque peak is in the range, will have a big effect on HP because HP =torque x a constant. A chart with a higher torque peak should have more area under the curve as well. These aren't always the most user friendly motors to run though, if you aren't racing (because you may be way under the peak torque rpm under normal conditions) so it's a balance of brochure bragging rights/selling units vs. making the vehicle practical to ride/drive etc.

It would be interesting to see a piston, a valve, a rod etc. from one cylinder of a 1000 cc sport bike next to a 250F equivalent part.
 
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