Paul-


Scott from Mazdaspeed Motorsports gave us your name. One of our customers
just competed in his 1st gen RX7 (with a stock 12A engine with a 48IDA Weber
carb) at the NASA Nationals at Miller Motorsports Park in Utah. We were
fighting dyno problems all week as it seemed the dyno was giving wrong
numbers for the rotary engines.

In speaking to Dynojet, manufacturer of the dyno being used, their computers
are based on a four stroke engine with a volumetric efficiency of 85%. Our
question is: does a rotary engine have the same efficiency? (The racetrack
is at 4400 feet altitude).

We have a Dynojet dyno in our shop in Bakersfield at an altitude of 252 feet
and have done hundreds of pulls on this one particular racecar, never making
over 150hp and usually around 143hp. In Utah, at approximately 4400 feet, we
put the car on the same kind of dyno at the racetrack and we now have a
reading of 151hp. My estimate is that we're about 8hp higher than we should
be right now. We de-tuned the car with timing and jetting and got it down to
144hp. After de-tuning the car, we are now being beaten by our competitors.
Our three closest competitors are Mazda Miatas with 1.6 or 1.8L
fuel-injected, piston motors who are showing lower hp than they normally do.
Do you believe that we are racing with an unfair disadvantage per those dyno
results?

On our dyno at 252 feet, we have a modification normally of 1 to 1.5. At
4400 feet at the racetrack, the modification factor was 18%. With your
knowledge of the rotary engine, do you believe it is possible that the
piston motors were running with more horsepower than indicated on the dyno,
while the rotaries were running with more?

Any help you could provide would be appreciated as our customer was
disqualified (at least for now) from a first place finish. Unfortunately,
time is of the essence as we are fighting his disqualification.

Again, thanks for any help you can provide.

Regards,
Tom and Bette Dragoun
7s Only Racing



What are the engine modification rules you are suffering under?
What is teh minimum weight on your car and the Miata's?

The equivalent displacement of the 12A engine is 2.4 Liters.
I would have to see the porting on the engine and the intake manifold.
What is the redline you are using?

Many well done side port Mazda rotaries are about 100% VE.
What max RPM are you using? With minor oil system mods the engine will run to
10,000 RPM or more. Do you have a wide band  mixture monitor on
the engine? Max power mixture should be about 12.5:1.
Do you have a compression recording system?

Lynn Hannover do you have any feed back on this subject?

Paul Lamar