>>>> 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.
>
>
>
> I could live with 5 psi boost at sea level. What sort of horsepower
> would that be?
>
> Thanks,
>
> Steve
>
> I would guess around 250 HP at 7500 RPM. You still have to monitor
> the intake air temp very carefully and never let it go beyond 240 F.
> Best to use a PicAXE controller and also monitor the boost.
> I can help you with that.
>
> You will probably be able to flat rate that to 12,000 feet or more
> depending on the efficiency of the intercooler.
>
> I'll be doing some more dwgs soon on the exhaust manifold and waste
> gates.
>
> Paul Lamar ...No rotor no motor.
Paul,
If I could get the numbers you just mentioned that would be
absolutely fantastic. That will be my goal. I think I'll call it a
Lancair 500!
Thanks,
Steve
The trouble with a high compression ratio is you might have to run
it rich and retard the ignition timing to keep it from detonating
or pre ignition. That will not help the fuel burn. The drag racers
don't care about the fuel burn.
--
Paul Lamar ...No rotor no motor.
Paul,
Whatever happened to the TurboChart Spreadsheet that Gordon was
building? Did he get to a final version that can be used for both 2 and
3 rotor engines? Can the current compressor maps be placed into that
program so we can see how the new turbos fit both 2 and 3 rotor
engines?? I'd love to see what he came up with!! The preliminary
versions that I saw looked great!!
Don
I don't know about Gordon but here is Dave Leonard's version.
Paul Lamar ...No rotor no motor.
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