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Date: Sat, 08 May 2004 17:27:13 +0100
From: Johannes H Andersen <johsnospamfitter_nos_pam.com>
Subject: Re: Compression ratio w/turbo blowing ?


-Bob- wrote: > > On Sat, 8 May 2004 17:21:29 +0200, "MH" <nomailnospamere.no> wrote: > > >The compression ratio does not depend on the boost pressure, it is the ratio > >of the smallest and largest volume in one cylinder (piston at TDC and at > >BDC). > >see http://en.wikipedia.org/wiki/Compression_ratio > > > >Max boost pressure in a FPT 900 is 0,7 bar (over atmospheric pressure = 1 > >bar), at that pressure the waste gate will (or should) open. > > But wouldn't the "effective" compression ratio be higher since the > charge is denser than a normal charge ? Or does the turbo simply make > the pump run faster ? But such an "effective" compression ratio wouldn't be constant, since the cylinders don't fill so readily at higher rpm. But the geometric compression ratio is lowered to compensate for the higher degree of filling of the cylinders due to the turbo pressure, effectively increasing the volume of the engine compared to an NA engine. (Positive displacement engine). Hence the compressed space must also be larger.

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