Intake manifold construction, intercoolers

[Bernd Felsche]

Craig Dotson tapped away at the keyboard with:

> > 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

> 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

You're quite mistaken there. 20% dynamic supercharge is achieved in
many small engines with tuned manifolds over a limited rev range.
Some engines claim about 60% dynamic supercharge over certain rev
ranges at valve opening using tuned and variable manifolds on NA
engines. You're looking at nett VE in excess of 100%. The dynamic
supercharge is more useful in a NA engine as the valve opens because
a vacuum hasn't yet been established to move the air.

If there were no tangible benefit, car manufacturers wouldn't put
all those trick manifolds on their cars; to make their V6's feel
like V8's and the V8's feel like steam engines.

Adding the dynamic supercharge to the forced induction can benefit
cylinder filling if tuned appropriately. It can also _reduce_ the
effective boost due to dynamic rarification at certain engine
speeds, in the very same way as in a NA engine. It's only the
baseline pressure (and temperature) that's higher in a
forced-induction engine. The effect is the same; magnitudes are
somewhat different.

-- 
Bernd Felsche - Innovative Reckoning, Perth, Western Australia
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