akrx8

ive got to go with mr.yaw's theroy.any engine running that rich after 5000 rpm would be way off on power not to mention poor fuel mileage.if its not going to switch over automaticly(hope it does)mazda will most likley be able to reflash to get it where its suppose to be.i seriously doubt after the r&d thats in this new rotary that there is anything wrong with this engine. im suprised the dyno operators didnt point this PIG rich condition out.if this was a old school v8 with a carb that could be tuned with jets even a novice carb tuner would see good jump in the numbers with a decrease in jetting to get the air/fuel ratio closer to optimum.im actually happy after looking at the sheet more closely to see how incredbly rich it is,once its where it should be were going to see quite a bit better fuel mileage not to mention our 21hp.

neit_jnf

We've seen that it starts on the lean side and then goes extra rich with increasing rpms. My question is, what A/F ratio is optimal on a general basis? 14.7:1 or what?

kostas*

You can also move your RX8 (if put in neutral) without needing 247HP! The friction increases with the increase of the rotation speed.

Doctorr

Just a couple of further data points......

I have read the thread up to this point, and I am struck by the fact that no-one has mentioned the throttle position?

Is the ECU even opening the 'drive by wire' plate all the way?

I am sure someone in the business could measure this while the car is at max output on the dyno......either from the TPS or directly somehow?

Also, I was under the car for a while, and noticed that the two (secondary & tertiary) alloy parts of the intake runners have little vacuum take off tubes, with rubber caps, that could be used for a vacuum reading. From which we could also deduce if there was some restriction in the intake?
.
.
.
doc

Racer X-8

Am I thinking wrong? I'm wondering about the combination of running rich and not taking it over 4-4.5k rpm for the first 600 miles. Isn't that practically begging for a problem with the notorious carbon buildup?

Wouldn't an excessive carbon buildup have a negative effect, especially with trying to break-in the seals?

I know carbon has a lubricating effect to an extent, but it is also abrasive to an extent. I would think that carbon-free running surfaces with the right amount of oil lube is much more desirable.

Perhaps an occasional decarbing excursion into the 8k range would be beneficial during that first 600 mile "break-in"?

TurboSE

Well, carbon build up usually takes several thousand miles before it is a problem. All turbo rotaries run that rich most of the time and it is not a problem till after 80k miles. For the record, you can expect full compression from a rotary after 2500 miles. Sometimes it takes a little longer but not much more. So Mr. Yaw, I direct this question to you. Do you think a change in afr from 12:1 to say 13:1 at higher rpms is going to result in the missing 25-30 HP?

1stRX8

It doesn't matter. We have been discussing the ECU retarting power for break-in purposes vs. a fundamental problem with the engine or the way it was rated in the first place.

If the ECU is killing power it has many ways to do that. Rich mixture, spark timing, throttle position. If the TPS reports the throat isn't fully opening then we know the ECU or some mechanical adjustment is incorrect. What I am MOST interested in is the power going to be normal at X number of miles. Is the ECU going to switch? Is the break-in period that no-one can agree upon going to make a difference?

Is someone else going to a dyno. If a number of cars in different parts of the country show a similar trend - we go from there. If a number of cars show erratic results - we may have a problem. The point is that there are 80+ posts about a single dyno test of a single car. Is anyone planning on a dyno test before 20k miles?
If not, the majority if this discussion is a moot point. Speculation can only go so far.

ggreen29

My limited understanding is that some carbon buildup along the sides of the rotor and the side of the housing, just outside the chamber boundary, are beneficial as they help the side seals seal the chamber from non-chamber.

TurboSE

you don't want carbon build-up because it makes the springs that sit below the seal stick causing apex and side seals to stick causing lower compression.

pelucidor

There have been 3 dyno tests so far all with the same results, the last on a car with over 2100 miles and DSC defintely off. You have seen this thread I presume.

yawpower

That's a good question, and I don't know the answer. There is no TPS. Since the computer controls the butterfly, it knows exactly where it is.

It does seem that this may be part of a break in mode control though. The timing may be an issue as well.

I haven't worried about it since I saw the A/F ratio. It's pretty clear that they have intentionally slowed it down, so I haven't concerned myself with how they did it.

Carbon buildup is more related to oil in the combustion chamber. A rich condition can certainly add to the problem, but it is the addtitives in crankcase oil that really muck things up.

Mid 13's would make the motor really happy. If this motor has better combustion characteristics than the previous 13B's it may want an even leaner mixture up high.

I understand everyones concern, but I'm not worried. The most recent dyno post showing the A/F ratio answers any questions I would have, and I have as much reason as anyone to be concerned. Afterall, the future of my business is dependant on the success of this car.

PY

pelucidor

Mr. Yaw

For the illiterate amongst us (i.e. me) perhaps you could explain more about why the A/F ratio removes your concerns about low power from the engine.

Thanks

revhappy

It must be running rich based on the Air- Fuel Ratio, thus supporting the switchover theory.

wakeech

when you move away from the stoich A/F point, you start to get very dirty and slow burns, meaning that you're losing power (the speed aspect). what this also does is lower your Exhaust Gas Tempurature, which is why having your A/F ratio lean out is so dangerous; when your seals melt to your combustion chamber, you can kiss the whole motor good-bye (happens when karters try to run their motors right on stoich and miss...).

neit_jnf

And the stoichometric A/F ratio would be what?

wakeech

...IIRC, 14.something?? 14.7lbs air: 1 lb fuel??

86rx7

14.7:1 is stoich, but you wouldnt want to run a motor at stoich for full power, because excess unburnt fuel keeps things nice and cool, and injectors arnt perfect and dont make an even 14.7:1 everywhere in the chamber, thus going a little higher then that will hopefully richen up the to lean areas enough to burn. 13.xx:1 is usually what most motors like, and a Yawpower said rotarys like it a lil on the lean side.

Trust Yawpower, he has been a rotary icon for some time, if he says the map is definatly a break in map, it IS a break in map.

wakeech

see?? no worries.

MrWigggles

Alright,

If the mixture is too rich then more air would yield a linear increase in HP, correct?

So if the upper RPM's where 13.7:1 instead of 12.3:1 then:

184 HP * 13.6/12.2 = 205 HP at the wheels.

And 205 RWHP would be 247HP engine with 17% driveline losses. Not too shabby.

Make sense?

-Mr. Wigggles

yawpower

Because it is so incorrect. Mazda's engineers, or even a reasonably competent tuner would tune for best power, the result being a very different air fuel ratio.

It was obviously done for a reason.

Unfortunately, no. I say unfortunately because I wish it were all that simple. It would make my life a lot easier.

Changing the air fuel ratio results in a change in many other areas. Burn rate, heat (Energy) loss to the oil and water, and who knows what else.

What I'm saying is that it is not a simple linear relationship.

Based on experience though, I can see 20 horsepower there.

Just so everyone knows, what I am saying is not coming from Mazda. The car was engineered in Japan, and I don't speak the language, so I am not in any way speaking for Mazda.

I have been posting my own opinion just to let people know that there is nothing to worry about.

No auto manufacturer is going to quote horsepower numbers that are off by 20 or 30.

If the car was off by 30hp, the magazines would not have gotten the performance numbers that they did.

Enjoy your new car!

PY

Racer X-8

Ok, right you are. So, could you please direct us to the correct bottle of oil?
PS: I'm SO glad you've come here tonight! Peace...

(BOOSTD7? Hey guy, please take that "Junior Member" thingy out from under his name & put "Guru Member" or something like that? Can ya do that please?...)

RodsterinFL

uh, this news of such a possibility is REALLY disappointing. This happened with our 2001 Miata - horsepower advertised not what was there and there were Mazda goodies given. $$$ or free service.

I hope that it is just some newbie fluke and that a chip will change it all soon. Interestingly enough, right before I joined this site I was reading an article link dealing with torque and on that site they gave a formula for horsepower:

horsepower = torque * RPM / 5250 (I think this was it)

If I understand this correctly then the horsepower would be 166.57. I blew this off as someone not really knowing what they were talking about but ...

159 * 5500 / 5252 = 166.50hp

BTW mine is really missing in the morning and the exhaust body panels are covered in soot - HEY REMINDS ME OF THE OLD 300 D Turbodiesel!

Racer X-8

Max HP is NOT at the same RPM as Max. Torque. It's at 8,500 rpm @ 154 lb-ft torque...that's at the point where your torque value starts to drop FASTER than the rpm's are rising. (From 5500 to 8500 rpm, the torque is dropping, but not as much as rpms are rising.) Your formula is good, exept use 5252 to be more precise.

RodsterinFL

so the rpm you place in the upper part of the formula is not the max torque RPM? 5252 thanks. FIXED IT

MrWigggles

You have 20; I have 21; for whatever reason, we are in agreement.

On a very simple level, if 12.2:1 doesn't burn all the fuel and 13.6:1 would come closer then the extra air would mean extra power, etc...

That was my reasoning. Thanks for your help.

-Mr. Wigggles