Corky's engine choice

On 24 Jul 2003 18:56:58 -0700, (Jay) wrote:

Hey Corky,

What was your beef with the 13B? I have to replace a car coming off
lease in the next few months and I'm seriously looking at older RX-7s
just to get a flavor for the power plant.

I like the idea of a no-seize failure mode and the idea of it being 2
co-axial engines in one. The higher fuel burn I can deal with,
especially since its mogas.

I initially liked the engine for all the reasons you and many others
liked it. But as I tore it apart and rebuilt it, I started to have
doubts. I didn't have doubts about the engine durability, the doubts
I had were about living with it when it was done.

I had the engine some 10 years ago and at that time, the only real
choice for a PSRU was Ross Aero. Lou Ross was a raconteur and loved
to go on about how people over engineer things and that keeping stuff
simple was the best way. During this time, there was another company
trying to use the Mazda engine and they were running into huge
problems with torsional vibration. They spent years engineering and
machining until they finally got something that would last longer than
a few minutes without braking the prop right off.

This was unnerving, although Lou said nothing of the sort was
happening with his gearbox.

So I sat down and wrote down all the pluses I could think of and all
the minuses. There were a lot more minuses than pluses.

On the debit side were the following:

1. I have to fabricate a new intake manifold.
2. The exhaust system runs some 400 to 500 degrees hotter than a four
stroke cycle engine.
3. Fuel milage appeared to be somewhat worse than a four stroke cycle
engine of similar power.
4. The recommendation was to remove the oil injector pump (this is the
pump that drips oil into the intake manifold to lubricate the rotor
tip seals) This meant that you had to carry oil you would be adding
to the fuel tanks. This also meant that you had to calculate how much
oil you had to add to the tanks every time you refueled.
5. The engine is unbelievably loud sounding like a cross between a two
stroke motorcycle dragster and chainsaw held next to your head. There
would definately be a need for a muffler.

On the plus side, it was an engine that was close to being
indestructable. Even if it blew a seal it would have run till you
landed. Would not have started again, but it would get you down.

I pictured myself having to refuel more frequently and having to add
oil to the tanks and decided that I really didn't want to do that.

In the end, I felt it was better to deal with the devil you knew than
the devil you didn't know.

Corky Scott