Hymee

iTrader: (1)

Hi guys,

I know you are all keen on measurements, so in the endless persuit to keep you satisfied with good information, we ran my "no safe mode" RX-8 on the same chassis dyno as we did the other day, to see if there were any +ve or -ve effects on performance.



The black lines are the results as recorded on Monday, posted previously, with the car in standard trim. The red lines are with the "Hymee Cat-Back".

Both times the car had BP Ultimate 98RON fuel.

The weather correction factor today was 1.014 (27 degrees, 40% humidity, 1013 mb baro). The weather correction factor on Monday was set correctly to the conditions then.

In other words, both sets of figures have had a correction factor applied to them to neutralise the environmental characteristics as much as possible, in line with the SAE standard.

So - the good news is it didn't go backwards. The better news is there was a slight gain of about 2kW. Not a lot, but I have been on public record before that I was not expecting huge gains. Like I have also said before, there is not much in the way of restrictions in the new system, so honestly, do you think there is any more to be gained in just the muffler/mid pipe? I tend to think not. The expert pipe man will be doing his research and development into the exhuast sooner to later, so stay tuned!


Cheers,
Hymee.

rx8 - smooth!

Thanks Hymee,

Good to see some honest and objective measurements being done. I am impressed with your integrity. I personally want to get more power gains for my dollars but I will be keeping tuned to see what evolves with the extra stages of the Hymee exhaust.

Once again well done and I am sure that the Hymee exhaust is going to be successful.

Steve

pricer01

Hey Prof!

As I'm a banker and have no scientific blood in my body, coudl I please ask some specific questions on the chart -

1) Do I assume its done with the early reads in 4th and the dips in the chart representing gear changes
2) Why is it necessary to go fast to measure the power - my simple mind thinks that the engines power is the engines power .. where am I wrong.
3) Whats the air fuel stuff?
4) Whats the go with 'safe mode'

Thanks for your patience!!

AMG

Pricer, I'm only a dentist, but I might have go at this.

the dips in the chart are often attributed to either:
1. differences with the air fuel ratios the cars computer is programmed to make as a result of dirrerence rev criteria, or

2. air flow vanes opening, or

3. engine valves opening, or diferent cam profiles (Vtec engines), or

4. all of the above

Dyno's are generally performed in third gear as this is often a relatively close one to one ratio ie, the wheels speed as a direct response to engine revs (basically ungeared), that way the rpm can directly be measured from tyre rotation. Gears are no used on dyno's

An engine has two types of power

Crudely, there is torque, the ability to turn the wheels, and power, the ability to keep the wheels spinning....fast. HP or KW is the ability to keep the wheels spinning, so the more power you have the more spin you get. Whereas high torque engines do not have a lot of power, ie, they can get the wheels spinning esy but they do not have the ability to spin them fast.

petrol on it's own is not enough for an engine, you need an aerosol of petrol in the engine, ie a mixture of petrol and air. This is highly combustible. various modifications to a car's engine by way of internals breathing or exhaust can change the air fuel ration, this makes it lean or rich etc. It is important to get this ratio right to get maximum combustibility and hence power.

Safe mode, that's mazdas way of stopping excessivley long burnouts!

Hymee

iTrader: (1)

AMG,

You pretty muched sumed it up. I'll add some comments of my own.

Pricer01,

Normally dyno runs are attempted in "top" gear - i.e. 1:1. In the RX-8 that is 5th (on the 6 speed). On the Commodores, we did them in 4th, as 5th was an over drive, and 6th a "double overdrive". The reason we aim for "top" gear is that the gearbox is basically going "straight through".

However, on the RX-8, which has a 9000 RPM redline, 5th gear at 9,000 RPM would be going a tad too fast for the dyno operators liking. So we do it in 4th. You can see that it ramps from around 80km/h to about 200km/h to give a pretty good spread over most of the useable RPM range. The "ramp" is done with the throttle wide open, and the computer controlling the dyno controls the rate of acceleration of the rollers, basically by soaking up the power with a big generator (retarder), and measuring it.

The dips in the chart are where the various parts of the 6-ports are doing there bit. The two dips correlate to the RPM (if you where to calculate them from road speed) where the intake runner length is effectively changed with all the SDAIS stuff.

One goal of tuning would be to try to eliminate the dips, so the changeover was more progressive, without power going down.

The engines power is the power. But it makes different power at every RPM from idle all the way to redline. The dyno is actually measuring a force (tractive effort), which is really torque. The Power is directly related to RPM of the dyno rollers, and the measured torque. Hence, the Power figure is calculated, but the calculations are all standard physics stuff. It is not an estimated figure, it is real.

Air Fuel stuff. This is measured with a device called a wideband O2 sensor, or a Lambda sensor. Lambda is a value that indicates the amount of O2 in the exhaust gas. A lambda value of 1 means that all the O2 has been burnt - the ideal combustion, or "stoichiometric". A lambda value lower than 1 is "rich" and a lambda value greater than 1 is lean. A lambda sensor is accurate for all types of fuels. To Air Fuel ratio is the ratio of the amount of fuel in the mixture, to the amount of air. The ideal, or stoichiometric air/fuel ratio for petrol is 14.64:1. To obtain the air fuel ratio from the Lambda sensor, we multiply the Lambda value by the "stoich" value for the fuel. When we are tuning an engine for maximum power, we go a little bit "richer" than the ideal 14.64:1. Normally somewhere in the low 13:1 range. As you can see from what was measured on my car, it is a little bit richer than what we want for maximum power. So there is perhaps a few kW to be found by leaning my car out a bit.

Safe mode. That is something that my car does not have . Why, I don't know. But it does not throw an ABS/TC light like we have seen on Wildcards car, or all the others who report "safe mode". What is basically happening in this "mode", is the PCM (Powertrain Control Module) is sensing a condition where it thinks something is abnormal, so it starts doing things to reduce power slightly, by adding extra fuel hence protecting the catalyctic converters from over heating. The Commodores have something called "Torque Management" and "Cat Protection" we used to turn off for dynoing purposes. Maybe it is a bit like that. But the graph for my car looks like a pretty normal sort of power curve, and the AFR's show that the mixture is not going wildly rich up top.

Maybe I am just lucky...

I hope you liked todays lesson Some cunny funt is going to post "I lost you after the bit when you said 'Normally'". Hehehe.

Cheers,
Hymee.

Lock & Load

Amg

Hymees reply was short and well explained IMO , I JUST HOPE AND PRAY that he doesnt develop into a ROTARYGOD type of 7 page reply .ha ha ha .

MICHAEL

Wildcard

Nice work Hymee. Your dyno chart looks the same as mine did up to 160km/h when my car entered safe mode. It's truly mysterious why your car does not seem to have this problem.

You mentioned that among other things, safe mode may exist to protect the cat from over-temping. Maybe the reason my car went into safe mode was because the day we did the dyno was friggin' hot (>30deg with ++humidity.) I have noticed that most of your dyno runs recently have been done in quite moderate temperatures.

There's gotta be a reason out there somewhere??

Hymee

iTrader: (1)

Wildcard,

I hear what you say, although I can't for the life of me work out why the ABS and TC lights would come on for "Cat Protection"!

I can't remember if my ABS/TC lights cam on that morning when both our cars were on the dyno in quick succession. I seem to recall it was a problem on your car.

Cheers,
Hymee.

Wildcard

My car didn't have any safe mode snags when we did our dyno's back to back. It was only in the afternoon when we re-dyno'd my car that we started running in to safe mode.

By reducing power to the rear wheels, safe mode is effectively a form of traction control, hence why I think the TC light is appropriate.

AMG

Hymee, we know that Im a dentist, Taka is a doctor, L&L is a man of the night come property developer, Pricer is a banker, and most others here are IT blokes/blokettes. But with all this mechanical technical knowledge can we assume you are an engineer?

Hymee

iTrader: (1)

AMG,

Well I am an engineer of sorts. I'm not a mechanic, but I have stripped and rebuilt a couple of engines, and a gearbox.

I used to work as a civil engineering draftsman (Assoc. Dip. Civil Eng), and that is where the Hymee nickname all started.

Now I work as the Principle Software Engineer for the IT company I have worked for for the last 8 years. For that I hold a Bachelor of Information Technology (Software Engineering) with Distinction. (sorry to pose - just reciting what is on my certificate hanging on the wall in front of me).

So I am techinally minded. I don't pretend for a second to know everything. But I do like to understand, and I try to gain knowledge from those experienced enough that are willing to pass it on.

Cheers,
Hymee.

BTW - One of the engines I rebuilt was a 4.4L V8. It started first go for me! OK - I need to go take some modesty pills.

Hymee

iTrader: (1)

Wildcard,

It is really interesting, hey? It might have something to do with the ambient temperature then. That was a hot day when we did your numero uno. It was also less than 30 the last two times I went on the dyno. But what about the guys in NA. It has been pretty cold lately over there


Cheers,
Hymee.

Lock & Load

Hymme

Maybe your car some how missed out on being given the lobbotamy that the wise authorities gave the other RX8 s before they released them to the market .

And hymee yeah take those anti inflammation tablets because i can feel your head sweeling from here.

cheers
michael

pricer01

Is it possible that the leather pack comes with the addition of the safe mode ------ If I recall correctly, the Professor's is the base model ????

Surely not!

Hymee

iTrader: (1)

That might just be it. We need some more people to try out their leather's and cloth packs for comparison.

Or it might be a VIN related factory change. Really weird!

Wildcard

Yes, I did think about this when I made that post. Certainly Canzoomer seemed to be hitting safe mode even in the middle of the Canadian winter. And this got me thinking....

We now know that the North American ECU is different to the Aus ECU. As discovered by L&L, the N. American ECU serial number is:

N 3 H 6

Whereas L&L's leather pack ECU serial no. is:

N 3 J 6

We have assumed thus far that the Aus leather pack and cloth pack RX-8's are mechanically identical. But are they? Do they have the same ECU?

Hymee - check your ECU!! I'd be interested to see if your pov pack has the same ECU serial number as L&L's leather pack.

Why different ECU's? Well the leather pack has an extra 17kg jammed into it. Would this necessitate for the DSC to be programmed slightly differently to account for the marginally different handling characteristics between the cars? 17kg isn't much, but it's something.

Safe mode is controlled by the ECU, so the answer has got to be in there somewhere. Maybe some ECU's are more prone to entering safe mode than others. Or perhaps different ECU's have different criteria for triggering safe mode.