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From: "David Leonard" <DaveLeonard@cox.net>
X-Original-To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Subject: RE: [FlyRotary] Re: turbo sizing common sense.....
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-----------------------
I've just spent some time looking for a compressor map for the stock turbo,
and I don't think it's available.  The question comes up on the RX-7 list on
occasion, and no one ever has a map to offer.

I also ran some numbers to compare what folks are doing with 2nd gen cars,
and what I propose to do with the plane.  Some folks are running up to 13
psi of boost with S5 turbos at road altitudes.  Keep in mind that we have
roads that are thousands of feet sea level (not here in FL of course <g>),
and the largest change in pressure occurs in the first few thousand feet, so
cars are not sea level only devices.

For the sake of argument, I compared a 13 psi turbo at sea level, with a
normalized turbo at altitude.  From the way I look at it, 7 psi of boost
would normalize my engine right up to about the 18,000 ft VFR ceiling. Even
at that altitude, the pressure ratio is only a hair above what the 13 psi
car guys will see.  To me, this looks like I'll easily be staying within a
known, and well tested limit of the turbo, as long as I can refrain from
turning up the boost knob :-)

Anyone see any flaw with my logic?

Cheers,
Rusty
Turbo 13B powered RV-3... Be Afraid :-)
1993 RX-7 R1... Stock (for now)
-----------------------------------------

Rusty,

That is some of the same thinking that helped me justify the stock turbo.
One additional point though, why normalize when you can run the same 7psi of
boost at all altitudes.  If the turbo can handle 7psi of boost at altitude
it can make the same 7psi of boost at sea level turning even fewer [turbine]
RPM.  The engine can easily handle the horse power, and you have additional
brgging rights.

Dave Leonard