[DML] On Wankels and forced induction [longish]

[William T Wilson <fluffy@xxxx>]

Anybody that wishes to discuss the pros and cons of a Wankel conversion
please email me privately. In short, the problems are:
1) Cooling
2) Intercooling the (more or less essential) turbo setup
3) Cost (especially for the Japan spec engines)
4) The Wankels are very compact but they are heavier than they look.
Weight will probably not be saved (probably won't increase either).

Fuel economy is not that bad compared to other engines with comparable
performance. My '84 RX-7 gets 20-23 MPG and makes as much power as the
PRV.

As for turbos and superchargers:
Obviously both of them have their applications or they wouldn't both be
produced in such volume.

I think it is a matter of personal preference which one is better.
Superchargers have greater drivability, but turbochargers are more
efficient due to their lower (not zero! But less than a supercharger)
drag on the engine, and they tend to be able to produce higher levels of
boost. Turbochargers also produce less wear on the engine, as they don't
make boost all the time. But they are harder to tune and install. Both
sides have many pros and cons.

Someone asked about the maximum safe boost. With existing turbo kits,
maximum recommended boost is 6 psi, unless you are at high altitude, then
you can probably get away with 7-8. The problem is the lack of
intercooling and fuel. Above 7-8 psi, it is almost impossible to prevent
knock on pump gas unless you have an intercooler. With an intercooler,
however, much higher boost levels are possible. The DeLorean has a very
low compression ratio which makes it extremely well suited to high boost
applications. Proper fuel system modifications and intercooling should
allow it to run 12 psi of boost or more, which would be good for 230-250
HP on stock engine internals. None of the existing turbo kits include
these components, but there is no fundamental reason why they couldn't be
used.

One thing I noticed looking at the dyno charts is that the turbocharged
engines produce buckets of torque at midrange RPM, but fall off
dramatically at high RPM. I would be curious to know if any of the people
whose turbo cars were dynoed also have a boost gauge. Optimally, the
torque curve should mimic the stock torque curve, if anything moving to
higher RPM, not lower. Was the boost falling off too (in which case it is
a turbo problem) or was the engine just not making power (in which case it
is an ignition or fuel problem).