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Kasjok

OEM vs JE 13.5 piston

11 posts in this topic

I read and read old posts and I just can`t decide which to choose. I could get OEM for 110 + shipping and a 13.5:1 JE piston for 140 + shipping.

I just can`t decide. 2007 yz450f has, for me, a bit too mellow low-end. So I think HC piston should make all the difference.

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OR I just install new rings and call it good. My bike has 34 hours on it right now.

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I don't see a reason not to do the 13.5 cr piston when you do decide to do the piston. I did a search and found a culculator that computes HP change with compression ratio change. For round numbers I went with it starting with 50 hp and the 12.3 cr yamaha states. It ends up being a 2% change and giving 51 hp.

http://www.bgsoflex.com/crchange.html

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Reliability is also a factor for me. As I am not able to take all our from my bike, I would better like to have a good reliability, then some minor hp increase(which is not a bad thing).

Some aftermarket pistons have a coating of some kind on the skirt which I belive is ment to get a better brake- in.

Some say that JEs have some problems performance, some say that wiseco has some problems with piston pins braking , some say that OEM is the best, some say that CP is for ultimate quality( costing a lot $$$). I just don`t know.

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I've been running the Je 13.5:1 for a year and a half in my 03 and haven't had any trouble....

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I wish I had only 34 hours on my 06. Im going on 2 years on original piston and rings. Check Valves about every 4 ride. Bike is still running strong. Always starts easy, hot or cold. I wont push it too much longer. But will put in a genuine Yamaha piston and rings.

One of the most reliable bikes I ever owned. I almost hate to by a new next year, because i dont want to start all over setting it up with all the add ons and getting it set up the way I like it. Im sure I could be pushed in the right direction though!

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lets hear everyone's opinions on this. I'm in the same boat as KAsjok....except my bike has double his hours. I'm getting it port and polished and am thinking about a H.C. Piston. Maybe Pro Circuit or CP?

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What about those A, B, C and D category pistons. When I have bought pistons from local shop I have been given them to choose from ( for example Athena Pistons). I was thinking that maybe an aftermarket piston from B or C category would give me tighter fit then the OEM one that comes (I think) with the original diameter.

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What about those A, B, C and D category pistons.
These are pistons made in small, incrementally larger sizes, often .001" or less difference between them. To determine which to use, you need to measure your cylinder precisely and figure out which of the different sizes will give you the clearance the piston manufacturer specifies.

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you dont really have to go full 13.5 to 1 on the je. you can opt for the 12.8 to 1 which is stil .5 to 1 over the 12.3 to 1 stocker.

an improvement and no need for possible heavier valve springs, cam changes and or higher octane fuel requirements.

if you wanted a bit more you could use a custom thinner base gasket, or split the oem head gasket (3 piece unit), and take out the center, only using the top and bottom sections. (poor mans high compression piston).

you have options. ski

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an improvement and no need for possible heavier valve springs, cam changes and or higher octane fuel requirements.

Why would a change to the compression ratio ever require valve springs or cams to be changed?

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