I failed at dynoing my RX-8...
 

I didn't do enough of my own research. I dyno'ed the car yesterday to verify power:weight compliance with NASA TTD class limits, and it looks like I got garbage data.

* We couldn't find a good tach signal. I have a T-Rex ignition coil kit (not sure if this affects things), but putting the pick-up on the ignition wire or the coil wire resulted in an RPM signal that was about 2x too high (i.e. at idle, the dyno said 1,600 rpm and the car tach said 800 rpm).

* The ABS light came on, and the car made super clean power up to 6,000 rpms and then power went extremely erratic and the car appeared to go to limp mode. I will upload the crappy dyno chart later, but I was basically making very strong power before things pretty much flat lined and went erratic.

QUESTIONS:

1. Which wire should I use for the RPM signal? This dyno uses a clamp on pick-up.

2. I've heard to need to remove the ABS fuse. Is this all that's needed to avoid the car going into limp mode?

Thanks in advance for the help.

EDIT/UPDATE: DYNO ATTACHED.

No need to remove any fuses. The dyno operator should know this stuff...... But typically the RPM signal should be taken at the coil and some dynos read it VIA OBD, it totally depends on the dyno and how it is set up. As for TREX, maybe you could call those shady noobs and then maybe they could Google it, and then give you some of their "expert" advice.

Hi Matt,

If the RPM signal is 2x too fast you will need to adjust the "firing" setting on the dyno to resolve that issue. It's based on degrees of rotation 360,180 etc. You can switch the dyno setting in real time with the engine running to achive the correct signal.

For the tach signal best results can usually be obtained by connecting the tach pickup to the green wire in the factory harness on the Leading 1 connector closest to the front of the car. Some dyno's have an alligator clip for a vehicle chassis ground, try using that and not using it. Some dyno's are finicky about this.

Start the car and hold the DSC button for about 7-10 seconds until the ABS light comes on, no need to remove any fuses. I would suggest you not remove your room fuse before the test, you may skew the results against your favor.:sad:

If you need any help while it's on the dyno, give me a ring, if I am available I'll be happy to help, Scott

I've seen dozens of rx8s dyno without any issues whatsoever . All that the dyno operator has to do is press the DSC button once to disable DSC . If the operator did that and you still had an issue , it is more likely a problem with your car. I've seen the engine buck on the dyno many times due to forgetting to push dsc , but it's always straight away - never at 6000 rpm.

With the rpm pickup - none of the 4 dynos I've used even hooked one up . They all synced the dyno with the revcounter . You need to tell them that the rev counter is 500rpm out at 9000 though.

Don't the leading (or is it trailing?) spark plugs fire twice per ignition?

I don't think it matters as Brett stated, Steve Kan uses a Mustang dyno and he didn't hook up anything on any of our cars for RPM, just AFR and boost. That is the issue with Dyno results, there is so much to the setup and how it is operated that affects the results. We did a mobile dyno once at a local road course and my car dynoed at 170WHP and then a basically stock NA RX-8 dynoed at 220WHP all the other were all over the place and either reading way over or way under. Then a boosted Caddy got on and made 100+WHP less than he usually makes. The guys operating the dyno had no clue what they were doing.

Sounds more like the dyno operator failed at your dyno 😎

If you don't need torque #'s you don't even need an RPM signal to get HP

The dyno is a Dynojet by the way- should have mentioned.


My car is a base model, no TCS and no DSC. Pretty rare I think? Since there is no DSC button, I think i'll resort to pulling the fuse.


I will contact the dyno operator and ask him if he can set to "two stroke mode", or to adjust for the factor of two RPM error. Should I try hooking the RPM pick-up to a leading or trailing ignition wire?

Excerpts from Mazda RX8 Horsepower Dyno Test- Sport Compact Car Magazine


"Mazda agrees. Multiple sources at Mazda tell us the RX-8 is so computer laden, it's nearly self-aware. When it sees the rear wheels spinning and the fronts sitting still, it realizes there won't be much air flowing across the catalytic converter. It also realizes that 50,000-mile emissions system durability is a federal mandate, and that if it overheats its cat with screaming-hot rotary exhaust, it might get in trouble with the feds. So the RX-8, according to Mazda, goes into don't-overheat-the-cat mode and tries lowering the exhaust temperature by running extra rich. This lowers power output under chassis dyno conditions."


"In hopes of circumventing the startup check, we plugged the sensors back in, started the car, drove it long enough to convince the computer that all was well, then unplugged them while the car was still running. The ABS light came on again, but miraculously, power dropped about 20 hp for the next two runs. The blue line on the chart is the second of these runs. Is this the elusive don't-overheat-the-cat mode?


Maybe.



The next two runs, with the same setup, were back to normal, almost identical to the first six runs. Then we tried our plug-drive-unplug ruse again, but were unable to duplicate the low-output runs. They could be a fluke, an error in zeroing the G-Tech's accelerometer, or the RX-8's salvation. The Dynojet results, and the exhaust temperature logic both suggest that a cat-saving mode would only appear at high rpm..."

Thanks for sharing this, as when I got mine on the dyno, I saw all the same lights you saw, and only 170whp, which now makes sense to me.

where are you doing dyno pulls?

Inline Pro in NOVA. shop owner was understanding and welcomed me back once I have the procedures sorted out. i'm going to contact him and ask about the two stroke mode. he's also capable of just doing road speed.

UPDATE: Attached the dyno to my original post, with some commentary (modifications, HP measurements at SSV and APV, what gear, etc). As you can see, power looked very strong and then was awful. Car has a new fuel pump, new plugs/wires/coil kit. Extremely well maintained, freshly built, pulls VERY hard on the street above 7,000 rpms. I think this is the elusive limp mode.

Start by ditching the "Hypertech tune".

To me it looks like ignition breakup....

Do you have any logs of the timing? Or the AFR's? I would disconnect the knock sensor from the block and insulate it with a rag if it is doing weird timing pulls

+1.

At a guess I would say only reason it is ok on the street is that it doesn't see the same loads that a dyno puts on it . IE you never get to rev that high in 5th gear .

Suggest you invest in an HEI coil tester and test each coil . Follow instructions from this thread :
https://www.rx8club.com/series-i-do-...ight=coil+test

This is in the works! :ylsuper:

Sooo.... at the track I am always seeing 4th, if not 5th gear, and the car is always pulling strongly (like, E36M3 strongly).




I've also had ignition coils and wires go bad before, and the CEL would flash before I could even feel a misfire. I would think, with the look of that dyno, I should have had a flashing CEL?


In addition, would the ignition system be 100% awesome until about 5,000 rpms (based on those horsepower numbers at the bumps) and then rather abruptly go to crap?


I agree with the logging recommendation; it would be nice to have more data. I have datalogging capability and will go do a few road tests (in a low gear, at a safe speed...) to see if I'm getting strange ignition timing or AFR. Any recommendations on what else to log? RPM, MAS?


Then when I get back on the dyno I can also log and compare AFR and ignition timing. The articles I cited would have you believe Mazda programmed the limp mode to cause AFR to go very rich and to pull ignition timing to preserve the cat.

perhaps mis-information. edited.

yes

Goes to show you the internet is full of "crap" information ;)