Intake manifold construction, intercoolers

[Axel Rietschin]

----- Original Message -----
From: "Craig Dotson" <crdotson at vt.edu>
To: <diy_efi at diy-efi.org>
Sent: Wednesday, December 05, 2001 9:24 PM
Subject: Re: Intake manifold construction, intercoolers

[...]

> Many engines use multi-valve arrangements to increase flow area.  The same
> benefits go for a turbo'd car as an NA car in this area...more volume into
> the cylinder at a given pressure loss, or the same volume into the
cylinder
> at a lower pressure loss...at the price of less turbulence.

Thank you, that was precisely my point. Turbo-ed responds just as well as NA
to intake tuning.

[...]

> If atmospheric pressure doubled, I don't think it will make an appreciable
> difference in the way an intake manifold worked.

Perfect. What does a turbo then? IMHO it just raises the 'atmosphere'
pressure, as seen at the intake. The engine still swallows the same volume
of air (a function of its displacement and VE). The turbo just makes that
volume 'heavier' but the fluid dynamics at the intake is probably not so
drastically altered.

[...]

> If atmospheric pressure doubled you'd still need to do
> this, as exhaust pressure will double accordingly, but with turbocharging
> the exhaust pressure increase (it's all absolute pressure here of course)
is
> small compared to the intake pressure increase.

>  Tuning the manifold to gain
> a small number of pascals pressure will have an insignificant impact when
> combined with the already large pressure differential between boost
pressure
> and exhaust pressure.

I disagree. On a perfectly matched turbo-engine setup the exhaust back
pressure should be roughly equal to the boost pressure at max power rpm,
there is no "large pressure differential between boost pressure and exhaust
pressure", at some point exhaust pressure actually becomes higher than
boost.

--Axel

> Craig Dotson
> crdotson at vt.edu
> 2002 VT FormulaSAE


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