Would you do it?? 13.5 to 1

8 replies to this topic
  • Wyatt

Posted July 03, 2004 - 11:29 AM


I have a 13.5 Wiseco Piston that I have been thinking of putting into my bike. My bike doesn't need a rebuild yet, but i got the piston direct from Wiseco on certificate that I won at a local race (50% off).

I thought that it would be something to do while I am rehabing my knee. But, I am wondering if I should ever put it in. I know that some of you are thinking, "man, you can't use all of the power your bike has now". Well, that is probably true, but extra power off of the line is always better.

The thing that makes me wonder the most whether it is a good move or not is that the '05 yamaha actualy lowered the compression on the new bikes. I guess this is an attempt to make them more subtle in their power delivery.

I guess my concern is because I am happy with my bike now. More power would be great, but I don't want to turn my bike into something that I am unhappy with.

I would like to hear from any of you that have changed to 13.5 pistons.

  • FFRacing79

Posted July 03, 2004 - 11:41 AM


The higher comp piston will add about 2hp but where it shines is in the increase in torque! That translates to just making it easier to ride in my opinion. One slight drawback to the Wiseco pistons is they are machined to allow a .003" clearance. I had my cylinder re-coated to tighten it up to .001". Not absolutely required, but it will get the most out of the added compression and the piston will last longer. :thumbsup:

  • Hamish

Posted July 03, 2004 - 12:10 PM


as long as you don't replate your cyl, you can change it back in an afternoon if you don't like it. I'd advise checking piston to valve clearance before installing it.

  • Wyatt

Posted July 03, 2004 - 12:46 PM


Thanks for the info. FFR, thanks for the info on the clearances. When I do decide to install the piston, I plan on having it coated by Polydyn Coatings here in Houston. They can put a teflon based coating on the skirt and a ceramic heat barrier to the the top of the piston.

The coatings should leave a buildup of approx .0002 to .0007. So, if the pistons are a tad on the "loose" side, as you stated, when I check the clearances they should still be good with the coating.

If the added Hp shines in the motor's torque output, that may be just the thing for me. I'm a lugger not a revver.

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  • YZDAD1

Posted July 04, 2004 - 02:33 AM


I've been running the higher compression pistons this year with no issues. I also coat the skirts and tops. Real good performance. :thumbsup:

  • Wyatt

Posted July 04, 2004 - 04:17 AM


Thanks...thats just the type of info I was looking for. :thumbsup:

  • markvan

Posted July 04, 2004 - 07:31 AM


I also coat the skirts and tops.

What are you refering to by 'coating the skirts and tops'?

  • YZDAD1

Posted July 04, 2004 - 09:03 AM


"Anti-Scuff" skirt coating and "Thermal-Barrier" dome coatings to help insulate the tops of the piston.

  • ironhead

Posted July 04, 2004 - 03:21 PM


does the increase make it stall any easier? I have an 01 426 which I think is 12.5 and it seems to stall easy when you lug it down. I put a wr stator/flywheel on which should help but I didnt try it yet. what fuel requirements do you have with that setup? :thumbsup:

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