2010 YZ 450 piston


9 replies to this topic
  • Pat E

Posted September 27, 2011 - 03:38 PM

#1

I have a 2010 YZ 450 that I bought new, and race pretty much MX. I have around 35 hours on it and am going to do a new piston, rings, etc.. this off season. I checked valves at 30 hrs. and they were almost perfect. I run straight VP U4.4 w/ a full Yosh system and was wondering if there is any benefit to using a GYTR hi-comp piston, or the Cosworth hi-comp pistons are also very nice. Not sure if there is any performance benefit or should I just replace w/ stock? Not looking to do the GYTR cams, head, etc.. just curious if there is any benefit to doing the piston only? Thanks.

  • grayracer513

Posted September 27, 2011 - 03:51 PM

#2

Raising the compression will give you a reasonably significant gain from the low mid range to the upper middle, with less overall gain as you go higher in RPM. It may also require the use of a higher octane fuel, or a better high octane fuel, than is available at the pump in your area. The power increase should be between 2-4%.

IMO, it's not really worth the potential problems. I'd be willing to bet you don't need a piston at all, but you can have a look at it.

  • Pat E

Posted September 27, 2011 - 04:47 PM

#3

Regarding fuel, I only run straight VP U4.4. It may not techinally need a piston, but it's more peace of mind for the 2012 season. If I'm buying a piston anyway, and doing the work, it seems like it's worth a bit of low end performance for a more expensive piston. So... do I go with the GYTR or the Cosworth? BTW... I've heard Cosworth makes a very nice, high quality piston.

  • CaptainKnobby

Posted September 27, 2011 - 06:21 PM

#4

Just some info you might use......I race MX only and have 59.6 hrs on mine and have raced it in 2 classes for two years and haven't changed the piston yet.

I have run 34 races on my 2010 since new and thats not counting days I went to a track to just practice/ride. I race in the 35+and 40+A classes so you can kinda figure the speed there.

Mine still runs strong and has plenty of power and valves still in spec when i checked them at 52.5 hrs. I just run 93 pump octane in it and have had no issues.

  • grayracer513

Posted September 27, 2011 - 06:47 PM

#5

Cosworth and GYT-R are both reputable, and the latter has Yamaha's approval. My preference is CP, if available, and one with two compression rings.

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  • Pat E

Posted September 28, 2011 - 02:54 PM

#6

Thanks for the feedback, but what are some of the "potential problems" mentioned regarding the hi-comp. piston?

  • grayracer513

Posted September 28, 2011 - 03:11 PM

#7

There are some aftermarket pistons that just don't fit as well as the OEM or high grade AM pistons, and this results in noise and accelerated wear.

Some HC pistons are fond of using a single compression ring, which again results in accelerated wear, although mostly to the rings, as a single ring will blow by more and sooner than a pair will.

Since you are running U4.4, you almost certainly will bypass the possibility of any detonation problems, so you can scratch that one off in your case.

And, some don't pay enough attention to weight and put the engine out of balance.

Then too, one manufacturer went through a whole batch of pistons about two years ago that were breaking wrist pins (ugly thing, that was).

Otherwise, if you use a good quality, 3 ring piston, it's one of the safer mods you can do.

  • D5000

Posted October 01, 2011 - 12:52 PM

#8

Just some info you might use......I race MX only and have 59.6 hrs on mine and have raced it in 2 classes for two years and haven't changed the piston yet.

I have run 34 races on my 2010 since new and thats not counting days I went to a track to just practice/ride. I race in the 35+and 40+A classes so you can kinda figure the speed there.

Mine still runs strong and has plenty of power and valves still in spec when i checked them at 52.5 hrs. I just run 93 pump octane in it and have had no issues.


What piston has those hours? The GYTR or the Cosworth?

  • D5000

Posted October 01, 2011 - 12:55 PM

#9

Has anyone run the GYTR head? How is it?

  • rickallen124

Posted October 01, 2011 - 08:04 PM

#10

geshields has discussed the gytr head in his twin air airbox thread.





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