Top end rebuild

I have a 2009 yz450f. I'm probably going to do a piston n rings this winter. Don't feel the compression it used to have while kicking. My question is what brand piston n rings has the most durability and maybe any info on valves n cams. I'd like to add a little horse power if possible. I don't race but do ride the track from time to time. Any help/suggestions would be helpful.

Genuine Yamaha standard pistons are as reliable as anything on the market, if not more so.  If you have an otherwise stock '09, get rid of the complete exhaust system to begin with.  While stock YZF exhausts have almost all been at least OK, virtually any replacement for the '08-'09 "shorty" pipe will add 5 or more horsepower at around 5000 RPM, which makes a major difference in the mid range.  Next cheap fix would be the CDI box from an '06 or an '04.  This is more effective for an '08 because the '08 CDI was worse than yours, but the '09 unit was also dialed back some by comparison.  The third thing you can do is use the exhaust cam from an '06 also.  This will also beef up the low end while retaining most of the top end.

 

These "hop ups" will give good results without impairing reliability significantly at all. 

And if you need an '04 YZ450F CDI, PM me, I've got one that I don't plan on using that I'll sell cheap.

pro x 13.5;1 piston, its higher compression than stock but still runs on pump fuel, its made in the same factory as oem yamaha pistons and it costs less. I use pro x pistons in many many bikes.

You have to be careful with ProX stuff.  For example, they do sell the same $25 Borg-Warner timing chain as does Yamaha , but last I saw, they wanted $60 for it.

Thank you for the input. Got a couple months before I start this project.

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