Mazda RX8 horsepower controversy
Since its launch, the Mazda RX8 has come under close scrutiny from enthusiasts. The high level of attention is due not only to the car’s admirable driving dynamics, but also, in part, to early reports of underperforming. To be more specific: Wheel power measured in several runs of the chassis dyno resulted in values well below the expected powertrain parasitic losses of 17% to 20%. And quarter-mile runs of between 0.5 and 1.5 seconds less than those produced by magazines in supposedly pre-production vehicles.
Regarding the RX8’s power rating: Original Mazda North America (MNAO) marketing material advertised the RX8’s 6-speed manual transmission with 247 hp at 8500 rpm. Assuming the parasitic powertrain loses 17-20%, which is common in modern rear-wheel drive vehicles, a stock RX8 should have 205-197 rear-wheel horsepower (rwhp), depending on lift , barometric pressure, temperature and applied correction factors. Instead, a stock RX8 chassis dyno run shows results ranging from mid-high ~160 to ~185 rwhp. Such readings would represent parasitic powertrain losses of more than 25%. To say that it is unacceptable to experience such a high level of loss through a “sports car” powertrain with a carbon fiber driveshaft – among other things – is an understatement.
To further cement doubts about the true power output of the new Renesis, several owners were unable to reproduce the mid-low 14-second quarter-mile passes, as seen published by well-known US auto magazines. of cheating were another indication of the apparent lack of power output.
Soon after, various 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 recalled an earlier “mess” in Mazda history, when the automaker admitted that it exaggerated horsepower numbers for its redesigned Mazda Miata.
After a few months, MNAO came forward and explained that they had misrepresented the power output of the Renesis. The revised figure was now 238 hp at 8500 rpm; however, according to MNAO, this revision did not change previously obtained track performance results.
Speculations about the reasons behind the sudden lack of power were many. However, there are currently two schools of thought:
- The former supports the idea that the RX-8’s engine management unit (ECU), along with the many “nanny” devices – such as ABS and TCS – do not allow for accurate readings from a chassis dyno. For simplicity, when the car is running on a chassis dyno, only the drive wheels turn. The RX-8’s ECU would detect an abnormal driving situation and retard timing and apply other safety measures to preserve the “driver” or “engine” -or both- from harm (read: skid situation, or a car that gets out of the way.)
- The second believes that MNAO was forced to redesign the software that runs engine management even before the first batch of RX-8s hit US shores, due to upcoming federal emissions regulations. I’ve read of one in particular, that it requires a ~100,000 mile catalytic converter life. The number one enemy of catalytic converters on any vehicle is heat (and heat is the number one attribute of rotary engine exhaust).
MNAO offered two options to those who had pre-ordered an RX-8 or purchased it no later than September 2003:
- They would buy the vehicle again, no questions asked.
- They would offer FREE scheduled maintenance for the life of the warranty, plus a $500 “gift card” for those who chose to keep the car.
I was among those who chose to keep their RX-8. After all, the driving experience hadn’t changed since test driving the vehicle before buying it. Since August 2003 I have driven over 20,000 miles (as of 1/18/2005) and have not more than an ounce of regret for my decision. If you would like to read more about owner feedback, please visit this thread @ RX8Club.com
There have been a number of ECU “updates” released over the past 2 years. As far as I know, all early ’04 RX-8 samples came from the port with the “J” level of engine management software. Since then, we’ve scaled the entire alphabet up to “M”, which was launched in a TSB campaign by Mazda North America (MSP04) to have ALL vehicles brought in for service at authorized dealers to display the “M” calibration. .