7.5-model 9181 inboard-rotary valve-old version

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7.5-model 9181 inboard-rotary valve-old version

Postby EPOXYHEAD » Tue Mar 02, 2010 7:57 am

The piston of this engine has a crescent cutout on the bottom lip on the wristpin /pad side. What is the purpose of this and according to the schematic it should face the exhaust side,no. But, since the exhaust port is open with no split, the pin would fall out . Does this have something to do with using a tuned pipe? Will having the wristpin opposite the exhaust port affect the performance?
Thanks
Don
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Re: 7.5-model 9181 inboard-rotary valve-old version

Postby K+B.91 » Tue May 25, 2010 6:34 pm

EPOXYHEAD wrote:The piston of this engine has a crescent cutout on the bottom lip on the wristpin /pad side. What is the purpose of this and according to the schematic it should face the exhaust side,no. But, since the exhaust port is open with no split, the pin would fall out . Does this have something to do with using a tuned pipe? Will having the wristpin opposite the exhaust port affect the performance?
Thanks
Don

This is known as 'skirting' the piston, it unshrouds the boost port and if carried far enough to the sides, it also boosts the schnuerle ports. It boosts power by allowing more charge to enter the combustion chamber.
It definitely faces opposite the exhaust, your engine will not run if it faces the exhaust, the incoming charge will be forced out of the exhaust port and no compression will take place.
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