Mazda RX8 Horsepower Controversy

Mazda RX8 Horsepower Controversy

Since its launch, the Mazda RX8 has been the subject of close scrutiny by enthusiasts. The high level of attention is not only due to the car’s admirable driving dynamics but, in part to the early reports of below-than-expected performance. To be more specific: wheel horsepower measured on several chassis dynamometer runs resulted in values well below the expected 17%~20% drivetrain parasitic losses. And quarter mile runs of anywhere between 0.5 and 1.5 seconds off of those produced by magazines on allegedly pre-production vehicles.

In connection with the RX8’s horsepower rating: the original marketing material from Mazda North America (MNAO) advertised the 6 speed manual transmission RX8 at 247hp @ 8,500rpm. Assuming parasitic drivetrain loses between 17%-20% -common for modern rear wheel drive vehicles, a stock RX8 should measure between 205~197 horsepower at the rear wheels (rwhp) -depending on elevation, barometric pressure, temperature and correction factors applied. Instead, a stock RX8 chassis dyno run shows results ranging anywhere from mid-high ~160 to ~185rwhp. Such readings would represent parasitic drivetrain loses in excess of 25%. To say that, it is unacceptable to experience such a high level of loss through the drivetrain of a “sports car” with a carbon fiber drive shaft -amongst other things- is an understatement.

To further consolidate doubts about the actual power output of the new Renesis, several owners were unable to reproduce mid-low 14 second quarter mile passes -as seen published by well known U.S. car magazines. Low trap speeds were another hint towards the apparent lack of power output.

Shortly after, several debates on online enthusiast forums and discussion boards turned into heated arguments as to what was causing such poor “straight line performance.” Many former Miata owners remembered a previous “snafu” in Mazda’s history, when the manufacturer admittedly overstated the horsepower figures of their redesigned Mazda Miata.

After a few months, MNAO came forward and explained that they had misrepresented the Renesis’ power output. The revised figure was now 238hp @ 8,500rpm; however, according to MNAO, this revision did not change the previously achieved track performance results.

Speculations about the reasons behind the sudden lack of power output were many. However, there are currently two schools of thought:

  • The first one supports the idea that the RX-8’s engine management unit (ECU), in conjunction with the many “nanny” devices -such as ABS & TCS- do not allow to obtain accurate readings from a chassis dynamometer. To simplify, when the car is run on a chassis dyno, only the driven wheels are turning. The RX-8’s ECU would detect an abnormal driving situation and retard timing and apply other safety measures to preserve either the “driver” or the “engine” -or both- from damage (read: skidding situation, or a car going out of the road.)
  • The second one believes that MNAO was forced to re-engineer the software that runs the engine management even before the first batch of RX-8’s reached U.S. shores, due to upcoming Federal emissions regulations. I have read of one in particular, which requires catalytic converter lifespan of ~100,000 miles. The enemy number one of catalytic converters on any vehicle is heat (and heat is the number one attribute of rotary engine’s exhaust gases.)

MNAO offered two options to those who had pre-ordered an RX-8, or had purchased no late than September 2003:

  • They would buy back the vehicle, no questions asked.
  • They would offer FREE Scheduled Maintenance for the life of the warranty, plus a 500 dollar “gift card” to those who opted to keep the car.

I was among those who opted to keep their RX-8. After all, the driving experience had not changed since test driving the vehicle prior to purchasing it. Since August 2003 I have clocked well over 20,000 miles -as of 1/18/2005- and I have but one ounce of regret about my decision. If you’d like to read more about owners’ opinions, visit this thread @

There have been a number of ECU “updates” released during the past 2 years. To the best of my knowledge, all early samples of ’04 RX-8s, came from port with level “J” of engine management software. Since then, we have escalated all the way through the alphabet to “M” -which was released on a TSB campaign by Mazda North America (MSP04) in order to have ALL vehicles taken in for Service @ Authorized Dealers flashed to “M” calibration.

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