500cc max RPM

[nitropimp]

Just curious, what are the rev limits on the big cc single cyl engines?

I am trying to do some calculations for engine RPM using mph/gear ratio/and wheel diameter.
My result is 3,527 rpm as I cross the finish line, 300' drags, in 5th gear. The WR has 5th gear trans ratio of 0.833.
My best mph has been 63. The final drive ratio is 4.66(56/12) and I'm measuring to the top of the paddle for tire diameter, 28".
Looks like I need to get up into the 60+T sprockets, I can get estimated ratios if I new about what rpm the engine stops making power (not kick the rod out the bottom rev).
Eric did a mid-top over rev port job on this engine. But, I think there is more in it if I can ever get the gearing sorted out. Them BIG sprockets are expensive.

 

[dirt bike dave]

I think you are turning much more than 3,527 rpm with your current gearing. It does not appear you are includijng the primary drive reduction ratio in your caclulations. You will need to know what that ratio is to calculate rpm at 63 mph with your current gearing.

http://www.dropbears.com/u/utilities/gearing.htm is a link to a nice spread sheet for calculating rpm & speed.

I don't know what redline is for a modifiec 500cc two stroke WR500, but you might see if you can find some dyno charts online for modded 500cc two strokes and see what rpm they make peak hp at.

 

[nitropimp]

Could be, I am using a formula from tsrsoftware, it's in the tech articles under gearing formulas.
engine rpm = mph x rear axle gear ratio x 336 divided by tire diameter.
How do I include primary reduction, which is 2.625, in the calculation?

I do know that there is more left in high gear. I ran it out a good 100' past the finish line and it was still pulling good.

 

[Rich Rohrich]

This might answer a few of your questions : http://www.ericgorr.com/techarticles/mototech_march_2000.htm

The condensed version is :

Primary reduction (ratio) * Internal reduction (ratio) * Final reduction (ratio) = Total reduction (ratio)

peak rpm / total reduction = rear wheel rpm

rear tire circumference (inches) * rear wheel rpm = inches traveled / min

Convert that to feet traveled per hour and divide by 5280 (feet in a mile) for miles per hour

 

[nitropimp]

Thanks, Rich.
New result is 7715 rpm.

4.97 @ 63 mph in 300' are my best numbers this year.
Nobody else runs a 2 wheeler, or 500 single engines ( I'm surrounded by alky triples & banshee stuff), so I don't have any comparison to other numbers. I think my numbers are ok for a stock displacement, 487cc.
Stinks that we don't have another event until mid January.

 

[gowen]

Hey there, do you know the HP number you are running? I'm working with a guy on getting a dyno reading of my 500 and then will work from there, I have a buddy in sweden that is running 71hp to the REAR wheel! at 6900 rpms.

 

[nitropimp]

I have not had this bike on a chassis dyno. All of the formulas for calculating HP, that I have been able to locate, using weight/ET/mph are for 1/4 mile racing. I have not figured out how to convert the formula to 300' racing.
If anyone can assist me, here are the numbers.
weight of bike, 240 + weight of rider, 200 = 440
300' ET = 4.97
300' mph = 63