Thanks Mike I was just trying to nail down a possible operational reason
for turbo cracking. A couple more questions if you don't mind.
How many miles on the car when you bought it?

145,000-ish. Car was down on bost a little when I got it, but not too bad
(~8 PSI).

I assume OE means Original Equipment correct?
What did the OE manifold cost?

Yes, and it was about $260 from Mazda Competition Parts

What are the claims for Jethot 2000? Is it claimed to reduce
cracking?

No, it is a ceramic coating designed to keep the heat inside the manifold
instead of radiating. Supposed to increase efficiency, but the heat
reduction underhood is the bigger benefit IMHO. It is applied both inside
and outside. Had this done on my downpipe (see last question) and the
resulting heat reduction was incredible. Also inhibits rust. The 2000
moniker is just for the temp rating - can't use the girly stuff on a rotary
(no offense meant, Chrissy). BTW, after close to 15K miles on the downpipe
with jethot 2K it looks just like new inside and out.

Do you have any data that might explain turbo and manifold cracking
as a function of back pressure or possibly a plugged precat?
Is the replaced precat gutted. Send me private email if you want
on this last question :-)>

Investigative data only. Precat was thoroughly plugged, and was keeping
boost down around 4 PSI or so. I replaced it with a Racing Beat 2.5"
downpipe and modified the stock cat to fit (basically had 3" of pipe welded
on the front side of the cat). Boost went back to 10 PSI. This is from a
known accurate guage BTW, not the stock on-off boostometer.

I should have recognized that I had an exhaust leak too, but I didn't add it
up until the motor was out: exhaust markings on the rear housing, burnt
paint on hood underside (thought this was due to precat heat), extreme wire
embrittlement.

When the water Oring went, but wasn't bad enough to mean I couldn't drive it
yet, I replaced the main cat with a 2.5" 'test pipe' just to have some fun.
Got max of 12 PSI in 4th at speed, with no detonation. Did get a little bit
in 2nd and sometimes 3rd, usually at light load in traffic. When motor was
disassembled, there was no major wear except for the broken Oring land,
stationary bearings were out of spec, and the front and rear housings had
too much stepped wear. Intermediate housing and rotor housings were fine and
are being reused. Rotors and apex seals were fine too, although the apex
seals were worn past the point where I would be comfortable reusing them.
But for a backup racecar motor they will work just fine. :)

Mike Harrington

Thanks Mike for adding a lot to our knowledge of turbo durability issues.

Paul Lamar
 
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