Looks like the GT40 has been vastly improved over the
old stand by TO4. 5% more efficient which is a lot when it
comes to turbine and compressors. Probably due to CFD.
Also Garrett uses a bypass trick to shift the surge line to the left.
All and all it looks like a much easier turbo to tune.
New Garrett charts do not label the RPM lines unfortunately
but as you can see from the old TO4 chart we are operating
down in the lower RPM ranges which is good for turbine life
when running a super hot exhaust rotary engine.
--
Paul Lamar ...No rotor no motor.
Paul,
You have vastly exceeded my knowledge of turbos but all sounds good
to me. Practically speaking, how would I go about figuring the
horsepower this thing puts out and more importantly, establishing
good solid operating limitations.
Thanks,
Steve
A rough way of doing it is start with the NA HP of around 200 HP
with a good side port manifold. That is at sea level which is
15 psi absolute pressure. Assume the power is roughly proportional
to the manifold pressure so 15 psi boost is 30 psi absolute.
That is twice sea level pressure so HP would be twice 200 or 400.
Then you look at the turbo charger compressor chart over on the
left vertical axis and guess that the turbine can provide the
required power to the compressor so it will double the manifold
pressure or 15 psi boost. there is lots of empirical evidence
that this is true.
There is at least 250 HP waste energy in the 200 HP rotary engine
exhaust (same percentage more or less in all IC engines) so it is
probably no problem what so ever for the exhaust turbine to drive that
compressor to 15 psi boost. In addition a car turbo charger turbine
must be designed to extract enough HP from the exhaust to
accelerate the turbo charger from 50,000 RPM at idle or so to
100,000 RPM
in a fraction of a second. That probably requires at least twice as
much
HP out of the exhaust and the turbine. For aircraft use our main
problem is to keep the turbine RPM down so the turbine does
not over rev and blow up at high altitude where the back
pressure on the turbine is much lower. So we choose a high A/R number.
"* Turbine A/R - Turbine performance [HP] is greatly affected by
changing the A/R of the housing. Using a smaller A/R will
increase the exhaust gas velocity into the turbine wheel,
causing the wheel to spin faster at lower engine RPMs giving
a quicker boost rise. This will also tend to increase exhaust
back pressure and reduce the max power at high RPM. Conversely,
using a larger A/R will lower exhaust gas velocity, and delay
boost rise, but the lower back pressure will give better high RPM
power."
Somebody on the Internet :)
Paul Lamar ...No rotor no motor.
Thanks Paul,
How does the already high compression of the renesis play into this?
Detonation is the enemy we want to avoid at all cost right? What
exactly is detonation? Why do you have a bigger chance of detonation
w/ a high compression engine than a low one? What's the dif between
low compression boosted a bunch and high compression boosted not so
much?,
Steve
Oh I had no idea you were going to turbo an RX8 engine. That could be a serious
problem. The compression ratio is too high and there is no way to lower
it. Well you can tolerate some mild boost say 5 to 7 PSI.
The engine compression
further increase the temperature of the mixture causing it to prematurely
explode. Do you have the engine already? Perhaps you could trade it for a
good 3rd gen :)
Paul Lamar ...No rotor no motor.
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