Intake manifold construction, intercoolers

[Axel Rietschin]

Hmm... so why high perf turbo engines have multi-valves heads and high lift
cams just as their NA counterparts? If tomorrow the atmosphere pressure
changes from 101kPa to 202kPa, will this change something to what happens
inside an engine intake manifold?

--Axel

----- Original Message -----
From: "Craig Dotson" <crdotson at vt.edu>
To: <diy_efi at diy-efi.org>
Sent: Wednesday, December 05, 2001 3:56 PM
Subject: Re: Intake manifold construction, intercoolers


>
> > In a N/A your waiting for atmospheric pressure to fill the void as the
> > piston moves down.  In a boosted motor, the plenum pressure is helping
to
> > push the piston down.  In a N/A engine, there are all sorts of wave
> > activities, that can help or HURT cylinder filling, and that is about
mute
> > when in boost.
> >   If you think these issues are minor then look at the rod failure
> > differences between the two types of motors then
> > Bruce
>
> I agree here, and I also agree with Bruce's earlier opinion that you are
> thinking in NA rather than turbo terms.
>
> When you tune an intake manifold for an NA car, you're trying to take
> advantage of the acoustics generated inside the manifold when you have
flow
> into the cylinders.  The most you can get out of such tuning is maybe a
> handful of pascals.....not even kPa...at the right times that help exhaust
> scavenging and cylinder filling at the beginning and end of the intake
valve
> opening.  Bruce is right, typically at frequencies between the resonances
> you actually get a few Pa drop at the beginning and end of the intake
valve
> opening that tend to empty the cylinder more than fill it.  In a turbo
car,
> particularly one with 1.5 bar (150 kPa) boost that will likely never see
> pressures below atmospheric, a handful of Pa basically amounts to jack and
> you're killing yourself for nothing.
>
> The last Formula SAE car my school built with a turbo had approx 30mm
> diameter runners to each cylinder and the "plenum" consisted of about a
50mm
> diameter "log" connecting the runners...and this is on a 600cc 4 cyl
engine.
> I don't know what boost levels were, but I doubt they were as high as 1.5
> bar.  There was absolutely zero thought into "tuning" the intake, it was
the
> absolute minimum necessary to deliver the pressurized air to the
cylinders.
>
> Additionally, why two plenums and two TBs?  I can see it if you're doing
> twin turbo but otherwise I don't see it.  I'd just go for the most direct
> means of delivering the air to the cylinder, trying to line up the port in
> the head with the runner as well as possible.
>
> Craig Dotson
> crdotson at vt.edu
> 2002 VT FormulaSAE
>
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