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High compression piston

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Does it give a noticable amount of extra power? I know they dont last as long as the 2 compression ring, but if changed often is it worth it for more power? I do mostly hill climbs and trails. YZF

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The compression of the piston really depends on the application. What is the compression of the piston in the bike now. For a stock YZ250F going much over 13.5:1 compression isnt going to gain much and may cost some power. If you have an 06 or 07 you can put an 08 piston in it and you will notice a little more power since the 06 and 07 have a compression ratio of 12.5:1 compared to the 13.5:1 piston from the 08. Another thing you can do in addition to that is to remove the second compression ring to reduce friction in the cylinder. Give a little more info ie what bike and if its stock or not and it will be easier to determine what works best for your application.

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I just rebuilt my 08 yz250f and put a wiseco 14:1 in it and have ridden it for about an hour so far and I noticed a significant difference in torque. It pulls better in the top and bottom. I would recommend this piston. I got it for $160. Way better than the pro circuit 13:5:1 for like 280$

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It's an 07 YZF. I bought the bike with a high comp. piston and don't want to downgrade my power.

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Install a new cam chain while your at it. They tend to stretch over time, so for $19 it's a wise investment.

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I looked at getting an 08 piston for my 07, the yam dealer by me said you can fit the 08 piston but it is a Tiny tiny bit taller so I didn't want to risk it just incase it hit the valves. Is this true?

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I looked at getting an 08 piston for my 07, the yam dealer by me said you can fit the 08 piston but it is a Tiny tiny bit taller so I didn't want to risk it just incase it hit the valves. Is this true?

It is a tiny bit taller, this is why it is a higher compression. The valve reliefs are the same however, since everything else in the engine is the same between the 07 and 08. The 08 piston works fine in the 07 engine.

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Get wiseco 14:1. It will fit the same and it's only 170$ for the piston with rings, pin, circlips..etc.

Get wiseco 14:1. It will fit the same and it's only 170$ for the piston with rings, pin, circlips..etc.

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Get wiseco 14:1. It will fit the same and it's only 170$ for the piston with rings, pin, circlips..etc.

Get wiseco 14:1. It will fit the same and it's only 170$ for the piston with rings, pin, circlips..etc.

Why bother? The stock 08 piston is also forged and is half the price for all the same parts.

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Why bother? The stock 08 piston is also forged and is half the price for all the same parts.

Exactly. The stock kit is $130 for everything and just as good, if not better than the $190 wiseco kit.

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right, im in the same boat, ive got a 09 yzf250 and want to fresh up the motor, now over here a std yamaha dealer piston is £80+vat, rings £20+vat and pin £18+vat from memory when i priced it up today, vats at 20%.so thats £120+ 20% for a piston kit, now im thinking of a high comp wossner piston at £125 all in. what i need to know is can i run 95 ron pump fuel? will a high comp piston help with hot starting as there will be more compression? how long do they tend to last as a wossner has a coating on the skirts to help reduce friction and wear. then another factor is what about the big end/conrod situation because of the higher stress on them, uprated and what to buy? anyone with expirience on this to give me guidence would be greatfull, im not in search of more power really as i want to learn how to ride the ass of it first to then really benifit from upgrades.

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Stock one didnt last me as long as my wiseco has., rings wore out faster

The stock one must not have been broken in properly i.e. the rings werent seated properly. I have used the Wiseco pistons and the stock pistons and never had any noticable variation in ring wear or piston longevity. As KJ mentioned the stock one is a lot cheaper too.

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My bike was broken in properly. But for a little more money you get higher compression.

And have to run race gas all the time. I just dont think the slight if any gain you will get is worth the overall cost.

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Ok, you do NOT have to run race gas in an 08/09 yz250F, 91 octane works just fine, not sure where you got that info, but every dirt bike out there is designed to run pump gas when you receive it from the dealership. Putting a high comp OEM piston into an 06 or 07 yz250F is not considered a mod, it's just considered updating the motor to current OEM specs.

As for rings wearing out prematurely because of a high compression piston, also not true, the wear on the rings is relative to the number of up/down strokes the motor does, that's how the wear happens, 12.5 to 1 or 13:5 to 1 does not matter to the rings one bit, it doesn not push them into the cylinder wall any harder causing more wear, their own tension is all that pushes them into the cylinder wall.

If you do all the proper maintenance on your bike, rings should last you 50 hours easy, and everyone knows you need to rering a 4 stroke at 50 hours to save your piston from slapping.

I just changed out my rings at 50 hours, cylinder is perfect, piston is perfect and rings had the smalles amount of wear (almost not noticeable stacked onto the new rings), probably had another 30-40 hours left before anything got critical.

And yes - if you're doing a top end or reringing, your timing chain should be replaced as well, standard time frame is the same as rings - 50 hours, any more and you risk it, the chain is a weak point on 4 strokes, my chain had about 1/2 a link stretch when I changed it.

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