This is a list of the pistons I have weighed. I weighed each piston as a complete package with its own rings clips and pin. These gram weights are exactly what the rod swings as the motor is running. Going from heavy to light here they are:

Factory stock 100mm...555.23g
RW old style 11.5:1- 100mm...540.54g
HPR 730 nitrous big bore 13:1- 105.5mm...527.79g
Pami stock bore 11:1?(very small dome) 100mm...515.17g
RW-THE BOM- 14:1 lightweight 100mm...515.09g
HPR 730 big bore lightweight 13:1- 105.5mm...509.31g
HPR 2003-14:1 lightweight 100mm...489.33g
HPR 2006-14:1 lightweight 100mm...482.33g

 

Any idea how much faster the engain would rev in these cases? Additional RPMs you could get out of just those weight differecnes?

 

mr. hp, will the difference in piston weight from stock cause more engine vibration??

 

awesome info, thankyou!!

its very surprising that none of these forgings are actually heavier than the cast stocker, considering their dome! I mean in appearance my old pami piston looks like it would have to weigh more than the stocker, but its quite a bit lighter.


some people, including a couple magazines, have complained about the rotax motor vibing too much from factory. this could be caused from either too much counterweight or not enough. I know from experience that my engine vibe did not feel any different to me after going to the pami piston. if the weight change was significant enough it can cause a change in vibe amplitude, but whether or not the amplitude goes up or down depends on how well it was balanced in the first place. I wish I would have thought of all this before, because I perform vibration analysis on industrial equipment and would have taken vibe signatures before and after the swap on the crank bearings with our equipment hear at work, but too late now.

If I had to guess though, I'd say the counterweight if anything is undersized?? If this is the case, and is merely a guess mind you, then any reduction in piston weight would bring you closer to better balance. Then again, I know nothing of how combustion effects vibes and balance, so I may be totally screwed up, just thinking outloud.

 

who cares? you can take one to a machine shop and lighten it.

 

MrHp..... I know my hands are sensitive, but I didn't think I could feel three grams by holding two pistons in my hands! I guess I can feel 33grams though. Wonder if a rod can?

Hightower.... I agree- I've never felt any more vibration in a DS with a lighter piston- if anything I think it might be smoother. But, I've never thought the DS has any more vibration than other quads- maybe all those years in the Z28 with the stereo too loud numbed me to vibrations?

Shee.... really?? good luck... I wonder why MrHp didn't think of that, considering he has owned and made his living in a machine shop for about 20 years now?

DragonDJ11... I don't know any mathematical formulas for your question- all I know is that you can really feel the difference. A long time ago, I replaced the stock piston with one of those pistons listed above in my tt bike and it slowed down (lost 2hp on an independent dyo). Real close to stock weight, but the ring package was killing power.

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So if I changed from a RW old style 100mm to a 2006 hpr 100mm I would lose a little over 2 ounces... Sounds like a decent savings, Does anyone know how many ponies I would gain? Or how much faster it would rev?



Mr hp, Are you sure you dont have an eight ball stuffed in the dome of them old pistons?lol

 

hey three 2s, then why dont he?????????? lets see how light we realy can get?????hmmmmmmm..




maybe we dont want anyone comming back saying its a junk piston....


ran good for a while....

 

wrong answer, try again...

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so why not make it lighter? its better right? thats what this post is about. MRPH is the lightest and the strongest.