Another old message 12 Jun 2000

Paul wrote:

Took the turbo off and found some cracks. C, DE, E, and F. I took it down
and showed it to John at Mazdatrix. He gave me the history on the Turbo II
turbo
problems. According to John the cracks will get worse and worse and
the manifold will crack eventually as well. It took Mazda three years
to solve the problems so if you have a 1990 through 1992 Turbo II engine
it might work better. This one is an 87. John also said the built in waste
gate was too small and the unit might over speed with an open exhaust at
high altitudes. The built in waste gate is indeed very small.

Here is how it works. At low to medium power, passage B is blocked
by a door located in the exhaust manifold. All exhaust goes through
passage A spinning the turbine up faster. At higher speed the door opens
and both passages get full exhaust. Unfortunately the divider then also
sees the full exhaust and reaches a higher temp then the rest of the housing
causing heat stress cracks. John says it is good for about 100K in a car
and then you need a new one ($1800 from Mazda) along with all new hoses and
connectors. In an airplane we will call on it a lot with both passages open.
In fact I had planned on fixing the door open at all times.

In 1990 Mazda redesigned it making it better but still probably not
good enough for use in an airplane.

He suggested a custom manifold and an Inconel TO4 for durability. A TO3 is
about the same size as this turbo but it too would be subject to
the higher heat stress.

Too bad. Real nice packaging on the part of Mazda.

BTW the turbo alone weighs 23 pounds. I don't have the exhaust manifold
off yet but I would guess it is around ten or twelve pounds.

Paul Lamar

Another update. The waste gate on the 89-92 is larger. I changed my
mind about the 89-92 not being good enough after I saw one. It was
vastly improved over the 87-88 shown here. BTW my 87 exhaust manifold
was indeed cracked.

Paul Lamar

Long time ago I understood that adding a turbo on AC engine is a complicated
affair beyond my mechanical abilities. So I went with all the changes to get
the most of my Cosmo 13-B without the turbo (BTW I'm watching a show on TNN
about turbo's in automotive engines as I'm writing this). Later if I find
that NA engine is too weak (I doubt it) I may install NO2 boost short time
boost?
Bulent

My ideal is to have plenty of HP up high where drag is low and I can cruise
well over 200 MPH.

Paul Lamar

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