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Actually it doesn't if you have four cylinders. The two that go up displace the same as the two that come down, so it is not a problem, other than the 1 to 3 hp that you lose pumping it about at 10,000rpm ... But the reason that the crankcase is vented to airbox / atmosphere is to keep oil in the motor (oil seals and gaskets), and prevent it getting past valves and rings into the combustion area and getting burned - which in the case of a turbo bike is dangerous since oil drastically lowers the cylinders detonation limit as it is very low octane. When your engine runs gas gets past pistons and into the case, if this was not allowed to escape it would build pressure until it equalled that in the top of the motor! And something would give. Why would anyone want to pressure a casing on purpose? What would be the purpose? ----- Original Message ----- From: Bryan <bgoodwin@iquest.net> To: RAW ANT <rawant@webtv.net>; Christer Johansson <christer.johansson@mbox383.swipnet.se> Cc: <turbobike@natvideo.com> Sent: Saturday, November 06, 1999 5:00 PM Subject: Re: [turbobike] turbo question > Do not do it! Your crankcase needs to be able to vent any pressure for the > reciprocating assembly to move freely. > > > At 06:45 PM 11/5/99 -0800, RAW ANT wrote: > >I have compensated for boost pressure in the float bowls and the diaphram. > >Someone metioned that it was a bad idea to pressurize my crank case . What > >do you guys think about that? RAW M.... F..... ANT > bgoodwin@iquest.net > FZR1000 turbo EFI > (aka The Money Pit) >