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


THE CLASS WE RUN (AND THE MIATAS) USES A HORSEPOWER TO WEIGHT FORMULA WITH A
MINIMUM ADJUSTED RATIO OF 16.50:1.

NO PORTING HAS BEEN DONE. THE INTAKE MANIFOLD IS AN
AFTERMARKET PIECE FROM MAZDA TO ADAPT TO THE 48IDA WEBER CARB

THE ENGINE IS STOCK.

WE USE EGTS READING 1650.

THE WIDEBAND ON OUR DYNO IN BAKERSFIELD IS SHOWING ABOUT 12.5

No compression recording system.

I THINK WHAT WE'RE TRYING TO FIND OUT IS IF ALTITUDE CAN AFFECT THE STOCK
12A VOLUMETRIC EFFICIENCY MAKING THE DYNO'S BUILT-IN COMPENSATION FACTOR
WRONG. IT SEEMS WE GOT HIGHER HORSEPOWER READINGS FROM THE TRACK DYNO WHILE
THE PISTON GUYS GOT LOWER READINGS.

THANKS FOR YOUR PROMPT RESPONSE. WE APPRECIATE IT.

BETTE
7s Only Racing

It is conceivable that the VE can vary slightly with altitude due
to organ pipe effects in the intake and exhaust system. The overall length
of the manifold runner has a drastic effect on where the torque peak
occurs and how much power the engine makes.


What range of RPM are you running?

Can you send a picture of the intake manifold?
Are you using the stock exhaust system?

The compression recording system is essential for assessing the health
of the rotor sealing system. Small sealing leaks can have a drastic affect
on the HP.

Here is a system you can make if you have a bit of electronic skill.
Otherwise Mazda sells an expensive system the dealers buy.

A coating system called DLC can reduce the friction in the
engine and increase the HP. Mazda is now using it in the RX8
engine corner seals.

Races are won by inches. The winners pay attention to the details.

Paul Lamar