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Yamaha_Chuck

Lower Compression Piston

7 posts in this topic

Some may think that this is a crazy idea but I was wondering if anyone makes a lower compression (like11:1) for the WR. The reason I would like to have one is because sometimes hi octane gas is not always avaliable in remote locations. The lower compression would also extend the life of the engine too, and it would probably only sacrafice a couple of ponies. I have checked with Wiseco and JE but they only offer 12.5:1 and higher.

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You won't find an aftermarket LC piston I have done low comp engines both with a modified std piston and also by just putting in an extra base gasket. The engines run good either way. if you go with the gasket you want to use steel base gaskets ( std on new models, aftermarket on oil in frame bikes)

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you can also fly cut the top of the piston to slightly remove a bit of materal to reduce the compression ration.....But then again, an extra base gasket will be cheaper and an easier solution.

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The reason I would like to have one is because sometimes hi octane gas is not always avaliable in remote locations.

The WR has NO problems running lower octane once in a while. I have run some pretty nasty Mexico/Baja gas and never had an issue. If it was me, I wouldn't worry about it but I also wouldn't make it a regular thing.

The lower compression would also extend the life of the engine too

The motor was designed to hold up to the stock compression ratios. Why try to help an already strong motor...these are not Hondas we are talking about here...

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In lowering the CR by adding base gaskets, you are not doing the engine efficiency any favors what with the fairly dramatic increase in the squish band clearance. Is the stock piston flat top or is there a small compression dome present? If there is a compression dome - make a flat top piston out of it. If the piston is already flat, grind about a 0.5-1 mm smooth depression area at and around the center of the piston top.

As others have pointed out it probably isn't even necessary to modify the engine, or you could always add some octane booster as needed.

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