Mazda RX8 horsepower controversy
Since its launch, the Mazda RX8 has come under close scrutiny from enthusiasts. The high level of attention is not only due to the car’s admirable driving dynamics, but, in part, to early reports of subpar performance. To be more specific: Wheel horsepower measured across multiple chassis dynamometer runs resulted in values well below the expected 17% to 20% parasitic losses in the powertrain. And quarter-mile races between 0.5 and 1.5 seconds of those produced by magazines in supposedly pre-production vehicles.
In relation to the RX8’s power rating: Mazda North America (MNAO) original marketing material advertised the RX8 6-speed manual transmission at 247 hp at 8,500 rpm. Assuming the parasitic powertrain loses between 17% and 20%, which is common for modern rear-wheel drive vehicles, a standard RX8 should measure between 205 ~ 197 rear wheel horsepower (rwhp), depending on lift , barometric pressure, temperature and applied correction factors. Instead, a standard RX8 chassis dynamometer run shows results ranging from medium-high ~ 160 to ~ 185rwhp. Such readings would represent drivetrain parasitic losses greater than 25%. To say that, it is unacceptable to experience such a high level of loss through the transmission of a “sports car” with a carbon fiber driveshaft – among other things – is an understatement.
To further consolidate doubts about the actual power output of the new Renesis, several owners were unable to reproduce 14-second quarter-mile passes from medium to low, as seen published by renowned US auto magazines. Low trap speeds were another indication of the apparent lack of power output.
Soon after, various discussions on online enthusiast forums and discussion boards turned into heated discussions about what was causing such poor “straight-line performance.” Many former Miata owners recalled an earlier “mistake” in Mazda history, when the manufacturer acknowledged that it exaggerated the horsepower figures of its redesigned Mazda Miata.
After a few months, MNAO came forward and explained that they had misrepresented Renesis’s power output. The revised figure was now 238 hp at 8,500 rpm; however, according to the MNAO, this review did not change previously obtained track performance results.
There was a lot of speculation about the reasons behind the sudden lack of power production. 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 accurate readings from a chassis dynamometer. 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 delay time and apply other safety measures to preserve the “driver” or the “engine” – or both – from damage (read: skidding situation, or a car heading from the road.)
- The second believes that MNAO was forced to redesign the software that runs engine management even before the first batch of RX-8s made it to the US shores, due to upcoming federal emissions regulations. I’ve read about one in particular, which requires a catalytic converter life of ~ 100,000 miles. The number one enemy of catalytic converters in any vehicle is heat (and heat is the number one attribute of rotary engine exhaust).
MNAO offered two options to those who had reserved an RX-8 or who had 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” to those who choose to keep the car.
I was among those who chose to keep their RX-8. After all, the driving experience hadn’t changed since testing the vehicle before buying it. Since August 2003 I have traveled more than 20,000 miles – as of 1/18/2005 – and I regret one iota of my decision. If you want to read more about the owners opinions, visit this thread @ RX8Club.com
There have been a number of ECU “updates” released over the last 2 years. To the best of my knowledge, all early 2004 RX-8 samples came from the port with the “J” level engine management software. Since then, we have scaled all the way through the alphabet to “M”, which was launched in a TSB campaign by Mazda North America (MSP04) for ALL vehicles accepted for Service @ Authorized Dealers to flash at the “M” calibration. . .