Variable Compression, Variable Displacement you deside

[Espen Hilde]

it depends on turbo charger sizing.You can put on a small turbo and have a 
low rpm.torque boost.At high rpm,s this charger will develop high back
pressure
on engine.VE will drop, but you will read high boost pressure.Problem with
turbos is they have a smaller "user aria" than the engine.New types of
turbos
with variable vanes,will help.I think speed density systems used with
turbos
should have exsaust pressure as a part of fuel calculation.When the turbo
speeds up the backpressure is higher.Means lessVE ,Higher backpressure
gives higher combustion tempratures,and the engine needs less timing.A
sudden opening of waste gate will lover back pressure,but not boost before
turbo has slowed down.(maybe a cople of cylinders will get VERY good VE.)
At high boost pressures this get worse,I think this is the main cause of
turbo engine failure. Please give a comment if you are of another wiew.

Espen Hilde

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> From: bruce plecan <nacelp at bright.net>
> To: diy_efi at efi332.eng.ohio-state.edu
> Subject: Re: Variable Compression, Variable Displacement you deside
> Date: 17. februar 1998 20:31
> 
> I'd like to hear from a ME type, and know which/why is most
> accurate to describe a super/turbocharge engine.  While
> compression ratio is a mechanical calculation, and the
> engine size doesn't increase due to "boost" the VE does,
> so what term most accurately describes what happens to the
> engine?.  A rather well known engine builder keeps calling them
> variale compression motors, is this accurate?.
>   Also what is the limit for VE?.  Seems like a turbo street engine
> ala Buick GN gets to 120% rather easily?.
>   Would this VE be as easy as using a bar conversion and saing
> at 1.5 bar boost it would be 150% VE (turbo apllication),  Yes we
> are ignoring intake air heating, but just as a place to start thinking 
> about what's going on.
>   Something else I'm curious about is once you exceed peak
> torque at WOT and are approaching max HP does the pulse
> lenght for the injector really need to be much longer?.  Or
> since there are more of them per amount of time, things just
> kinda work out?. 
> Bruce   The guy with the cone shaped hat, and chin strap
>             way too tight.