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Mazda Engineering on RX-8 and Dynos
Submitted by SuperUser on Wednesday, September 24, 2003 - 5:51pm

Statement: There is no true way to generate flywheel horsepower from a chassis dynamometer because of frictional losses in the driveline, clutch, transmission, differential and tires. Also, variations in testing procedures will cause highly disparate readings: open/closed hood, high/low humidity, high/low ambient temperature, tire pressure, how tightly the car is tied down, which gear the car is tested in, etc. In addition, we have determined that, in order to prevent damage to the catalytic converter and the entire driveline, when the PCM determines unusual operating parameters such as excessive slip in the drivetrain from the front to the rear wheels, it causes a rich high-RPM mixture and retardation of the timing. All these items combine to cause apparent considerable horsepower loss. BACKGROUND: Horsepower Measurement There is only one true method for measuring engine horsepower: on an engine dynamometer at constant speed and utilizing variable load. The engine should use the same intake and exhaust system as in the car. HP results must be corrected to SAE J1349 standards as listed below:

77 degrees Fahrenheit
Sea level
0% humidity
Correction factors must be applied to reference the measurements to SAE J1349 standards. Any correction factor beyond 7% is considered invalid. Chassis Dynamometers SAE has produced a technical paper (SAE Technical Paper Series 2002-01-0887) that attempts to address the ongoing debate about inertia dyno horsepower versus OEM net horsepower. You can order a copy by visiting their website at www.sae.org -- we have no intentions of getting mired in the middle of this discussion. Bottom line: If used properly, chassis dynos are great tools to assist with tuning and modifying vehicles. It is impossible to measure the actual flywheel horsepower because there are simply too many variables. Other issues that are unique to the RX-8: The RX-8 uses a very advanced engine management system. Besides precisely controlling the operating parameters of the engine, self-preservation (of both the engine and the catalytic converter) is also considered. The engine management system continuously monitors all engine functions and adjusts accordingly. For example: Under heavy load acceleration, the timing is retarded and the fuel mixture richened to reduce the likelihood of pre-ignition or spark knock. If spark knock is encountered, a knock sensor senses the condition and further retards the timing. Gradually timing is advanced and fuel mixture leaned after the load is reduced. A second reason for fuel enrichment is that when timing is retarded, exhaust temperatures increase; a richer mixture lowers the exhaust temperatures and reduces the chances of damaging the catalytic converter. In real world driving, this all goes unnoticed to the driver and appears seamless with no disruptions to the performance of the engine. The car encounters a load under acceleration but the load quickly diminishes as the car accelerates in each gear. Operating on a chassis dynamometer, however, creates a completely different environment. Inertia dynos use a known mass that is accelerated to measure torque at the wheels. This is usually done in one gear under heavy load conditions: Only the rear wheels are turning while the front tires remain stationary. On cars equipped with DSC with traction control, the difference in speed between the front and rear wheels is sensed and the power is reduced immediately to compensate for what the car senses as excess wheel spin. If the DSC is turned off, the traction control is disabled but the brake functions of the DSC are still operational. If the DSC system is completely disabled, this removes the brake functions from the equation, however it does not fully remove the engine management system functions.
  • The ABS hydraulic unit/control module (HU/CM), or the DSC HU/CM for cars with DSC, determines vehicle speed by comparing the speed of all four wheels. If two are turning and two are stationary, it will still compute a speed but senses that the car is experiencing excessive wheel spin. To protect against engine or catalyst damage: The engine management system compares the throttle opening, gear selection (determined by engine speed and road speed) charging efficiency and engine coolant temperature to determine the driving condition.
    • Since the car is under heavy load, in a tall gear (testing is usually performed in third or fourth gear), with a wide throttle position angle (wide open), spark timing is reduced and the fuel mixture is richened to reduce the occurrence of spark knock and to reduce catalytic converter temperatures.

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subject:
Why the buzz?
author:
No Rotor
date:
August 10, 2004 - 2:57am
Hi,

I own a nice red FE RHD in a small little Asian country where cars here cost a bomb because of our tax. What I pay for a Familia here, I can get me an SLK in EU or USA.

My 2 cents, dyno-ing an 8? Let's just leave the output at the wheels and the quarter mile timings. GTech will do just fine thank you. As for shady marketing practices, thumbs-down to Mazda if you're guilty.

But I'll like to remind many owners, lovers or haters of this car here, the FE is like a gymnast, fit, graceful and atheletic. Yet, we are getting lost here trying to measure up its pounds per sq. inch punch as if its a heavy-weight title contender. That just doesn't make any sense. :)
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subject:
No title supplied
author:
No Rotor
date:
December 31, 1969 - 4:00pm
You said:
" the DSC is turned off, the traction control is disabled but the brake functions of the DSC are still operational.

If the DSC system is completely disabled, this removes the brake functions from the equation, however it does not fully remove the engine management system functions."

By testing Ihave determined this is incorrect. When the DSC is fully disabled ( hold button for 5 seconds) ALL power to the sensors is turned off.

Frankly if this whole argument were truthful, then GTechs would show btter results than a dyno.
But they don't Bern is buying into the HYPE
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subject:
No title supplied
author:
No Rotor
date:
December 31, 1969 - 4:00pm
GTechs show the performance... Straight form the forum.

Here
and here







So, please read up a little more on the forum, and stop spreading around the negativity, please!

NB: This comment has been modified by an administrative person on Sep 24, 2003 (11:33 pm)
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subject:
ADMIN-2
author:
No Rotor
date:
December 31, 1969 - 4:00pm
Wish I could take credit, but I had no input on this one, sorry. I do agree with Dan though. GTechs show many things and the performance seems to be there, I can't verify it or back it up, but it just goes to show the inconsistency one finds on forums.

You wrote:
"By testing I have determined this is incorrect"

BTW, do mind sharing your testing procedure on this forum. Just know that others here might be interested.

Cheers,

-Bern
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subject:
I'm confused...
author:
No Rotor
date:
December 31, 1969 - 4:00pm
OK, Mazda are saying we (on a chassis dyno) won't be able to replicate their power/torque figures...but...they still haven't said whether their quoted flywheel figures are accurate...is this right?

In summary, are they saying that no-body but themselves can accurately asses the engine performance?

This makes it even more confusing about their 0-60 times. How did they achieve 6.4secs without the "rich high-RPM mixture and retardation" affecting the run.

I'm afraid this just opens a larger can of worms. It certainly doesn't instill a "that's OK then" feeling.

Hmmmmmm....

Ciaran
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subject:
ADMIN-2
author:
No Rotor
date:
December 31, 1969 - 4:00pm
I'll try to answer with the small amount of knowledge I have on this topic... one at a time.

"OK, Mazda are saying we (on a chassis dyno) won't be able to replicate their power/torque figures...but...they still haven't said whether their quoted flywheel figures are accurate...is this right?"

No, Mazda is sticking to it's quoted 238hp flywheel figure. They say that this # is accurate.


"In summary, are they saying that no-body but themselves can accurately asses the engine performance?"

Mazda is saying, not on a chassis dyno. I'm sure that anyone who is willing to pull an engine, and have it fully analyized on an "engine" dyno, might get close... a lot hard work here though.


"This makes it even more confusing about their 0-60 times. How did they achieve 6.4secs without the "rich high-RPM mixture and retardation" affecting the run."

Because the RX-8 does NOT go into the full proctection mode while on the road, as it does while on a chassis dyno. Other 3rd parties have actually run 0-60 times that match or exceed the Mazda 6.4 runs. Case in point, the GTech runs posted here.

I hope this helps.

-Bern
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subject:
more text?
author:
No Rotor
date:
December 31, 1969 - 4:00pm
It seems as though the article, with a bullet point, ends prematurely in mid-stream. is there more to this than would fit or ? Thanks!
leaning MORE towards 'keeping'...
daniel
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subject:
No title supplied
author:
No Rotor
date:
December 31, 1969 - 4:00pm
Ok. Here it is - few weeks ago.

RX-8 provided for testing by Mazda themselves.
That car then went for cornerweighting on racescales - for finding the real weight of the car + fuel + 2 particular folks in it -> it was total 3344lbs on the race scales.

Then 14 pulls GTech Competition dyno runs were made. Experiments include the car as it is - so everything is supposed to work correct.
Then GTech dyno runs with front wheel rotation sensors disconnected when the ECU was off, front wheel rotation sensors disconnected when the ECU was on and the car running, etc. - to try to upset the ECU thinking the car is not moving or that only the fronts are not moving like on a dyno - so the GTech should measure less power in such situations - as was suggested by Mazda providing the car at that time (and this was not publicly announced to everyone back then).

The results - it was measured about the same horsepower - no matter if all the wheels were moving, or with sensors disconnected so the ECU doesn't register front wheels movement (both with initially the car running or shut off).

Yup the same horsepower. The runs show about 165 hp peak number.

So it didn't work with Mazda's own production car given for testing. Now what will the next Mazda's marketing folks excuse gonna be? That they suddenly "learned" that the car has some optical tracking if the ground under the car is moving? LOL What else? :)

They need something new - because this didn't work as Mazda said:
[quote]
"In addition, we have determined that, in order to prevent damage to the catalytic converter and the entire driveline, when the PCM determines unusual operating parameters such as excessive slip in the drivetrain from the front to the rear wheels, it causes a rich high-RPM mixture and retardation of the timing. All these items combine to cause apparent considerable horsepower loss. "
[/quote]

Alas, as I said the car did the same GTech graphs with and without the ECU detecting the front wheels moving. So either the ECU doesn't detect the front wheels not moving to richen the mixture or either the the ECU is broken and decides always to richen the mixture - even when the car is driven normally

I am sorry, but I can't post the dyno graphs online for public viewing. I hope they will appear in the media soon
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subject:
ESP - ECU Sensory Perception
author:
No Rotor
date:
December 31, 1969 - 4:00pm
...unless the ECU knows it's on a dyno...
...sorry, only kidding, couldn't resist...

Ciaran
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subject:
Electronic horsepower guesstimators
author:
No Rotor
date:
December 31, 1969 - 4:00pm
A GTech declared the Rx-8 produces 165 peak HP? Nothing against the GTech, the manufacturer of the GTech, or any GTech users, but that doesn’t sound right.

In the old days, before the technology to produce affordable electronic horsepower guesstimators existed, we determined horsepower with a pencil, a piece of paper, the weight of the car and the quarter mile trap speed. The trap speed formula was used because it allowed less room for driver error. Now, some may say “this doesn’t take wind resistance, barometric pressure, or temperature into the equation”. That’s true, but neither does a GTech.

A neutral party, Road and Track, says the Rx-8 they tested was doing 96 MPH when it finished the quarter. Someone here previously said an Rx-8 weighed 3344 pounds. If I follow the formula we used in the seventies, ((.00426 times 96 MPH) to the third power) times a weight of 3344, I see 228 horses. If that same Rx-8 produced 165 horsepower, it would have a trap speed of 86 MPH. Interestingly enough, that’s the same trap speed as a Miata. Nothing against the Miata, but does anyone reading this really think the Rx-8 has to work hard to keep up with one?
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subject:
Dear Mazdaguy
author:
No Rotor
date:
December 31, 1969 - 4:00pm
Dear Mazdaguy,

can you please explain me HOW a disconnected sensor can "detect" a spinning wheel?

Normally a spinning wheel are measured by x-pulses/wheel-rotation. A wheel that's not spinning, gives 0 pulses. A disconnected sensor gives 0 pulses also.
If you disconnect the sensor, IMHO, the ECU mesures "wheel not spinning".

I think the only way to simulate a normally running car (read front wheel) to the ECU, must be to connect the wires of the front wheel sensors to the rear wheel sensors (or using the rear wheel sensor signal to trigger the front wheel sensor signal) . In this way the ECU receives the same info from the front and rear wheels. Exacltly the same pulses un both the front and rear wheel means "No slip on the front wheel" to the ECU.

Please excuse my poor english :-)
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subject:
Sorry..
author:
No Rotor
date:
December 31, 1969 - 4:00pm
Sorry, but to quote:

"In real world driving, this all goes unnoticed to the driver and appears seamless with no disruptions to the performance of the engine."

.. is simply garbage. The bottom line is, regardless of what the dyno's plot, rx8 owners are having difficultly breaking 15+ second 1/4 mile times. This goes hand in hand w/ the true underrated HP measures.
The S2000 on the other hand, a car that TRULY puts 240 at the fly as stated, pulls low-mid 14's on avg.
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subject:
Bull S!!(@
author:
No Rotor
date:
December 31, 1969 - 4:00pm
Um.. no, we aren't. There are newbee's to the whole drag rotary thing that don't know what they're doing.

I just got a 14.7 a few Friday's ago. So take your forum fed bull and shove it.
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subject:
No title supplied
author:
No Rotor
date:
December 31, 1969 - 4:00pm
Lets see a timeslip.

If ur pulling #'s from GTECH, dont even bother.
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subject:
Meh
author:
No Rotor
date:
December 31, 1969 - 4:00pm
If people are saying that they can't get a 14 out of the RX8, lets look at WHO was driving it, not WHAT they were driving, shall we?
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subject:
me
author:
No Rotor
date:
December 31, 1969 - 4:00pm
It is partitally tru in the part about high load conditions, which is what we subject the car to when accellerating hard, on full throttle and where we are demanding peak HP.
But the parts about wheel speed and the DSC andABS are mainly a lot of BS.

We unhooked the wheel speed sensors from the front wheels and hooked the sensor output from the rear wheels to the ECU inputs.

The ECU was getting identical readings from front and rear.
This produced no different result than when the front wheels were stationary on the dyno, and when the DSC was turned off.
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subject:
mine
author:
No Rotor
date:
December 31, 1969 - 4:00pm
The cars provided to the press were before the release of production cars in North America, and were running JSpec ECU maps.
In one test session somebody noticed that the power levels did not seem to be up to snuff, and Mazda ended the session, pulled the cars, and said that "there is a problem with a valve sticking in the intake system"

We now can tell that this is also obviously BS.

How honest is Mazda:
Which compnay was assessed the largest penalty for devious and misleading practices in the histroy of the US Federal TRace Commission?
Why that would be Mazda, at 5.25 million dollars for their parcatices in lease ads and agreements! This penaty was assessed in 1999
http://www.ftc.gov/opa/1999/09/mazdafinal.htm
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