In my efforts to understand what has been happening with the RX-8 power "loss", I've undertaken an analysis comparing the original Mazda specs, Mazda "published" crank specs, and the real dyno data gathered by other members of the forum.

I began with the original crank torque curve found in some of the original Mazda promotional materials. I took data points from this Nm curve and converted them into HP and ft-lbs. The resulting peak numbers from my sampling this graph (which includes some level of inaccuracy) were 247.1 HP at 8500 RPM and 162.2 ft-lbs at 6000 RPM. Since these numbers are very close to the original published specs for the RX-8 (247 HP @ 8500 RPM & 159 ft-lbs @ 6000 RPM), I decided that this torque curve was indeed correct. The resulting HP from this curve is plotted on the graph below.

Next I plotted the HP results of the best dyno run I've found published on this site so far (also using my graphical data point sampling technique). We clearly see the charateristic sawtooth pattern discontinouties at each of the port opening RPMs that have been seen in every dyno so far. My sampled data has a peak of 189 RWHP.

Now the interesting part comes when I wished to estimate the amount of drivetrain losses. Much debate has gone back and forth on this site about the drivetrain losses being too high (>17%) in comparison to other RWD cars. My understanding of the behaviour of the losses accross different RPMs is limited at best, so someone stop me if I'm completely off base, but I modeled the drivetrain loss as a constant percentage reduction of the HP/Torque at any RPM. Then I ignored the dyno data >6250 RPM and matched the crank data with a constant drivetrain loss to the <6250 RPM dyno results. It turns out that a 14% drivetrain loss matches the two plots almost perfectly <6250 RPM (see graph). Also 14% is a much more typical number when compared to other RWD cars.

So if we take the drivetrain loss of the RX-8 to be 14%, where does that leave us in >6250 RPM range? Well, way down. At 14% loss and from the crank curve, the peak should be about 212 RWHP. Except the dyno curve shows a RWHP peak of only 189. This is down about 11% (equivilent to adding more than 300 lbs to the car). The Mazda stated reduction of the peak HP to 238 represents a 3.6% reduction. A plot of an additional fixed 3.6% reduction accross the RPM shows that this revised number seems resonably accurate for <7250 RPM, but is still an overestamate for the peak HP at 8500 RPM which should be about 205 RWHP. A plot with a constant 11% reduction instead of the Mazda stated 3.6% does indeed match the peak RWHP, but does not accuratly track the rest of the dyno HP plot, and thus stating an 11% loss is also mostly innacurate.

It is clear that the overall shape of the Rensis output curve has been altered from what was in the original crank curve. This should be obvious due to the large discontinouities in the dyno results, and it seems clear to me that the source of these discontinouities is exactly the primary cause in the reduced top end power (as the lower plot seems to agree with the published specs). Mazda has already stated that its reasons for reducing the published peak HP number were due to changes needed to meet emissions in the US. It seems to me that the only way to accomplish this "last minute" would have been to change ecu mappings (different cats etc. would have been infeasable in a short time frame and would have obviously changed the HP spec so they probably would have retested). The ECU change could have been a case of left hand not knowing what the right hand was doing (no visable design change), which would explain the screw up if no one notified the testing department (and if it was last minute).

Also I can't think of any possibly mechanical change that could cause the type of discontinouties we see in the resulting dynos. Other people finger the discontinouties as port opening and closing artifacts, and I think that is only partialy true. If the HP/torque is truely that much lower with the switched over intake track, then the swichover points are WRONG, and should be placed at higher RPMs (where the curves meet without discontinouty). Yet again the points are controled by the ECU.

While normaly an ECU modification would not gain large amounts of HP in a NA engine, that may not be the case here if a de-tuned setup has specificaly been put in place. If this is truely the case, an optimised setup may gain as much as 23 RWHP at the peak, but may not provide any gain <6250 RPM. Looking forward to appling my $500 debit to this kind of mod.

Observations and reactions are most welcome.


Caveat:
If someone else has an understanding of the behaviour of drivetrain loss at different RPMs, please chime in. If there is a good reason that the drivetrain loss is a higher fraction for higher RPMs (significantly non-linear in an increasing manor), then this will have implications for the above analysis. This analysis is based on my very basic understanding of kinetic friction from physics class/textbook. It says that the fictional force between two moving objects does not depend on the relative velocity of those two objects (does depends on coefficient of kinetic friction, normal force, and surface area). Thus a constant fraction applied to the torque at all RPMs should be accurate, also since HP is directly related to torque, the same fraction can be applied directly to the HP.


References:

"Best" Dyno Data -
http://www.rx8forum.com/showthread.php?s=&threadid=9939

 

Thats the best news I've heard on this forum in a long time.

You are probably correct that all Mazda had time to do was a firmware update, and that a more restrictive cat was not installed, and I am with you in the hope that someone can access the ECU map and just 'dial-up' another 20 horses.....

However, I am not holding my breath. That ECU will be a bitch to access, with all sorts of downside if it is not properly executed.

On the upside though, you have helped me decide not to get the extended warranty, ($2000+) because I realise that something serious will have to be done to get up to acceptable power levels, and that warranty would be 'out the window'.

Thanks for all your 'plotting'!
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doc

 

Bravo to the reply. Now, who's willing to invest in the Dealer equipment to reprogram the ECU, and get the code from the J-spec RX-8.. Then start offering mail-order $100 ECU upgrades to J-spec?

Maybe one of the bigger sellers out there would offer this? Or perhaps someone knows how to source a group buy from Japan of replacement ECU modules for 'temporary' J-spec compatability, while maintaining the potential for US EPA conformance?

OverLOAD

 

Thanks OdinGuru - I'd been meaning to do that analysis myself excellent work.

If I understand correctly what you're saying is that the green plot (which is assuming 14% loss from early Mazda published graphs) is an extremely close fit to the real world dyno results (black). However post 6000 and especially post 7250 the engine power just drops completely compare to the prediction.

So 14% loss it is then, which means 220hp crank then?

If it is all down to the ECU and emissions we in Europe could be getting the very same engine since we've been told to expect 228hp!

It's also interesting to note that someone posted 5% tolerance as the legal limit in the States and 228 (uk) *1.05 = 239 is not far off the 238hp claim for the states.

 

The ECU map data is fairly easily available from Japanese sources.
If you email me off list I can send it to you.

As for doing it, I understand that the dealers equipment will be able to.
However they would not do it as the Japan ECU maps would make the car violate emissions regs for the car.

A better possible match is the Euro 3 maps, which make power closer to the 238HP claim. These maps should be legalin most jurisdictions, with California being an obvious exception.

I think a more easily achievable route is to convince your dealer to seek permission from Mazda to install the Euro 3 maps into your ECU.

Of course your dealer would have to be willing to rock the boat on your behalf for this, so I do not hold out much hope.

 

There are normally plenty of ECU upgrades made avaialble to aftermarket cars.. I'm sure that plenty of them start to violate EPA emissions regulations.

I doubt that this will be any more legal than going that route, however I'm hoping to regain the power before the 12 months that these aftermarket 'chippers' start to offer an ECU upgrade..

OverLOAD

 

So from this data, basically any possible fix to the HP issue will void the warranty of the car. Now another question is, does this change to the ECU also affect the gas mpg people have seen?

 

20 whp are missing after 7300 rpms!

With each 10lbft drop at each change over and there is 2 of those drops. If you can tune the ECU you can get back those lost 20 WHP.

BTW, the RX-8 is running rich, more air to the egine with hi octane can get you some whp.

 

Illegal, schmegal.

In the wonderful province of Alberta we don't even have emmissions tests, no requirements, no inspections, no rules about taking bits off or putting bits on.

So why should my '8' be hobbled by the over-rich under-powered fuel map designed for "Kalifornia Kompliance" in the year 2005?

Bring it on! I will be the first customer!
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doc

 

I made the suggestion in another thread that when Mazda North America were *surprised* by the emmissions requirements for LEV-1 in the USA (the regs must have been in a sealed envelope that they get to open only when the first cars arrive at port ) that rather then try to invent new ECU settings they would be better off using cleaner ECU settings they had finalized for another region.

More specifically I think Mazda North America decided to use the Euro Stage 4 ECU map which is MUCH stricter than anything required in the USA. Of course that only puts out 228hp (231PS) but that is within 5% of 238hp so they are safe. This implies some deceit on the part of Mazda North America for stating 238hp when they knew it was less but within the legal 5% variance.

Or (without deceit but some incompetance ) perhaps Mazda North America grabbed the Euro Stage 3 settings (about 238hp/240PS) from Europe without realizing they had recently gone with the 2004 Euro Stage 4 regs. I think Euro Stage 3 (as used in Australia) is still better than LEV-1 (target for USA) so an Australian ECU mapping might give a REAL 238hp and also be legal in all 50 states...

Can anyone confirm that Euro Stage 3 is better than Mazda's emmissions target for the USA?

 

You wouldn't need the dealer's magic jukebox to reflash the EPROM. All you have to do is open up the ECU. The EPROM should be removeable. All you need is a homebuilt interface board (typically use LPT port) and a program (plenty exist) to read from and write to the EPROM. My little sister is sending me such a board (she built it with $60 in parts). I WON'T be jacking around with the 8, though, as I don't actually know how to use the stuff yet. If EPROM is soldered in, it could still be done, but would be some extra work. If it is epoxied in, we're screwed!

 

It's not that easy; the contents of said EPROM are usually encrypted. The aftermarket chip makers will admit to that; they essentially have to reverse engineer the data to find the ECU maps, that's why they're not available to do anything on any car and why they usually don't hit the market until around a year after a given car does. I've even heard before that the encryption is an EPA mandate, though I've never looked through the regs to try and prove/disprove it...

 

Hi Pelucidor,

You should be able view the current US regs at:

http://www.ncseonline.org/NLE/CRSrep...TOKEN=72983641

I previously did a comparison of the different worldwide standards in the below post:

https://www.rx8club.com/showthread.p...774#post103774

As a short recap, the US standards seem to be the toughest in the world (if my numbers are correct). Part of the major problem is that the US tests the cars after 50,000 and 120,000 miles.
Perhaps the previous state of tune could pass the regs new, but a change was needed for long-term emissions performance?

Brian

 

It gets worse. Technically reverse engineering or copying any of it without permission is a violation in US fo the Digital Millennium Copyright Act (DMCA)

Recently Direct TV have sent their lawyers out in a huge troll of people who have purchased PROM card programmers.
Their reasoning is that anyone buying on of those is "obviously" a satallite TV pirate.
See:
http://www.hackhu.com/
http://www.eff.org/directvdefense/20030812_eff_pr.php
http://news.com.com/2008-1082-996787.html
http://www.tndf.net/

In another case, a company that makes remotes for garage door openers was sued under these similar provisions of the DMCA.
See:
http://www.eff.org/news/breaking/arc..._09.php#000460

If you find this kind of behaviour objectionable, I suggest you buy a membership in the Electronic Frontier Foundation:
https://secure.eff.org/

 

Bill, that is for sure. I never meant to imply that re-mapping the system would be easy, only that writing a new "firmware" to EPROM pretty much is. Yeah, it would definitely take someone a whole lot smarter than me to actually decrypt it, find the maps, come up with good ones (depending on your application), and re-encrypt the image file.

 

Good grief! How did I miss this great thread that started 9 months ago. Superb and *detailed* information as always Brian - makes any point I was alluding to totally invalid. I will shut up now, except to ask how Mazda North America could not know the Tier 2 emmissions requirements for the USA before the cars hit port?

 

I'll be very interested to see how other cars (namely the ones everyone likes to compare with the 8) are affected by the new standards as they start to roll out for 2004. Maybe it'll level the field a bit, so to speak. Or maybe not, will be interesting to see.

 

The Euro 4 regulations apply for the first 100,000 km of a car's life so they are not very different from US regulations in that respect.

Just looking at the numbers, the Euro standards seem much less strict than the US standards, contrary to what we have been lead to believe by Mazda which has always spec'ed the Euro horsepower as lower.

However, I believe there is a difference in the low temperature tests. The US test does not monitor HC's at low temperature, the Euro test does. This is why the Euro HC levels appear so high - they have to be met at low temperature which is much tougher.

It may be that when you take all this into account the Euro and US standards are about as tough as each other and Mazda has used the same ECU map for both.

FWIW, Mazda UK have hinted that the Euro horsepower figures (228 hp) have to be accurate because they have to be submitted as part of the EU homologation. Then again, they haven't sold any European cars yet so I guess there is still time for them to change the numbers.

 

In terms of the DMCA (BS laws made by BS politicians), you wouldn't be violating it. You could copy an existing JDM spec RX-8 ECU onto yours. No problems.

The problem is the ECU doesn't look like it's on a nice big PROM chip (those 28-pin DIP chips with the little UV erase circle).. Those are from 15 years ago.. Ever look at the chips on your motherboard? 1MB or 2MB flash roms, 20-pin QFPGA packages. Easy to reprogram, I've got access to any kind of flash programmer I need, but with no source data, there's nothing to put back in there..

If someone has the code for the JDM spec ECU, and knows which part holds the mapping data, I'll look to see if I can get the data off the North America ECU.

From what I understand of the EPA laws as well, it's only how the cars are sold from the manufacturer that is the key point. End-user (i.e. owner) modifications are not necessarily subject to the same EPA rules.