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I'm certainly no expert on turbos but I have turbo
charged two automobiles in my time. My personal opinion is that the Mazda
stock turbo is designed to augment power at low engine rpms on the automobile
(at least the single pre 1993 turbo) to give it that 0-60MPH kick in the
pants. Its my opinion (and that is all it is) that the stock Mazda turbo
would need to have a larger turbine housing (increased A/R ratio) OR as I have
seen done by some of the Aussies some of the housing milled out around the edge
of the turbine blades to provide for exhaust gas escape.
This would move the boost range up and lessen the
exhaust back pressure at the lower rpms as well as reduce heat load and actually
provide more top end power. Also, I question whether Mazda expected their
stock turbo to run at a constant boost for long periods of time. They
probably expected it to boost for considerably less than 30 seconds on each
application (foot in the gas tank), so extend boost for extended periods could
cause problems.
Non stock turbos may or may not be suitable
depending on their mass flow rate and turbine A/R housing size. Not trying
to discourage anyone from using the stock Mazda ( I have one sitting in my
shop). An external and larger waste gate can alleviate exhaust gas log
jam that to some degree, I would think. Still its well to consider the
limitations or expected use profile that the engineers may have had in
mind.
Ed
Ed Anderson
RV-6A N494BW Rotary Powered
Matthews, NC
----- Original Message -----
Sent: Tuesday, April 20, 2004 2:27
PM
Subject: [FlyRotary] Re: Wanted - single
stage turbo
John, sorry to hear
about the busted turbo. You caught my attention. Since I am in the
middle of a rebuild I could think about changing my set-up. Do you think
that the turbo was about to go anyway, or is it just not the right turbo for
our application? Were you running a wastegate? What MAP were you
running when the turbo blew? Rusty’s turbo is the same as yours, do you
plan to replace it with an Identical turbo? Todd and I (and Mecanair and
perhaps some others) are also running that turbo.
-----Original
Message-----
From: Rotary
motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of John Slade
Sent: Tuesday, April 20, 2004 10:38
AM
To: Rotary motors in
aircraft
Subject: [FlyRotary]
Wanted - single stage turbo
Does anyone have a
good second gen single stage turbo they want to sell?
Failing that - can
someone recommend a good supplier / rebuilder?
Yes, you guessed it
- I flew for almost an hour this morning, then fried the turbo. I'd
noticed a bit of slack in the bearings, so was expecting to have to rebuild it
anyway - just not quite this soon.
The good news is
that the failure mode was fairly benign. I was trying out the turbo at 5000ft
and just passing through 170 kts making large circles over the field.
The rpm dropped from about the 4500 I was using to 3500 and no amount of
throttle would increase it from there. Below 3500 the engine ran almost
normally, so I had enough power to climb if needed. It was maybe a tad
rough, but not so's you'd notice. An observer says I put out a puff of white
smoke, and was trailing a small amout of white smoke as I headed back in for a
normal landing. In all I ran the engine for about 10 minutes after the turbo
shaft broke. I lost about 1 pint of oil and the same of coolant through the
collapsed bearings, so perhaps another 10 minutes or more would have been ok
if the field had been further. The exhaust wheel was floating around in
the wastegate housing, but too large to get through the hole, so all it did
was block the exhaust a bit.
I guess this is the
"experimental" part of the exercise. :)
Rotary Cozy IV
(currently sans
turbo)
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