Do you daily drive the car? Or just to/from track?

Or if you are still seeing that pesky det now that you reduced the backpressure?

I love that you have legitimate data for all this stuff :likecat:

Ian is part of the diesel hauler flatbed triler for trackdays master race.

I haven't played with the timing with reduced back pressure. In theory, better VE should move MBT to the left -- that is, it should take less timing to get maximum torque out of the motor. I think reduced back pressure will also, in theory, result in a MORE ping-prone motor, because the leftover exhaust gas that didn't get blown out the valve acts a bit like EGR.

And yes, the car goes to the track on a trailer. While it's not a daily driver, it is still something I like to street drive on a regular basis.

--Ian

Backpressure has both ping increasing and reducing effects.
The extra heat from the residual exhaust with increased backpressure tends to increase ping.

So yesterday TK and I put in the RaceLogic Traction Control system. It works.

No decent photos of the install, but it's pretty straightforward. Tap the non-grounded side of the ABS wires, run it to the RL unit. Cut the injector wires (I did it in the extension harness) and insert the RL unit in the middle. They provide you with connectors so that you can just unplug and bypass the RL if you want, later. Give it power, ground, and an RPM signal and poof.

It looks at wheel speeds and when it sees the driven wheels exceeding the reference wheels by more than a specified amount, it will start cutting fuel to individual cylinders to reduce power. There are a bunch of different modes that adjust the thresholds and cylinder dropout algorithms, and it basically just works.

It can datalog the wheels speeds as well. Here's a 2nd/3rd gear run at 200 kpa and in "dry" mode (which allows about 5% slip). Rear wheels are light and dark green, front wheels are light and dark red. The purple spikes are TC events (height indicates which level of misfire it's inducing -- 1 is the lowest), blue is RPM. The rear wheels are alternating which one loses traction, then in 3rd the rear wheels have a very small slip percentage, which the TC unit is leaving alone.

https://www.miataturbo.net/attachmen...ine=1445189137

Here's a 20% slip run, the rear wheels are spiking higher and then getting shut down harder. I dunno which is faster:

https://www.miataturbo.net/attachmen...ine=1445189137

The MS3 sees the TC event as the engine going lean, due to the oxygen with no fuel getting blown through the motor, so I needed to make sure that it's not trying to run closed loop fuel when that happens. I vaguely recall that the MS3 can accept an input pin to disable the closed loop fuel that can be hooked to the RL's "TC active" output, but I haven't done that yet -- right now this is just ignoring the WBO2 value above a boost threshold.

https://www.miataturbo.net/attachmen...ine=1445189137

Because all it has is wheels speeds and RPM, the RL can't tell the difference between wheelspin and brake lockup. In this case, I did a 2nd gear run, then braked hard to get back down to do another 2nd gear run, and got a few ABS trips on the braking. It seems like the RL could do with a brake-on input to suppress the TC events, but if you're braking hard enough for ABS, it's unlikely that you want any throttle at that point, so I'm not it really matters.

https://www.miataturbo.net/attachmen...ine=1445189137

This was all straight-line acceleration runs, I haven't played with it exiting corners yet. I'm a little reluctant to be that visible on the street, maybe I'll find an autox to go play with it at.

--Ian

Is one side of the abs sensor grounded? I thought it was a differential vr signal?

It's not grounded on the sensor, but it is grounded inside the ABS controller.

--Ian

Hmm. OK. Wonder if that will have an effect in my vr sensor board.

Optimal traction is about 6-9% slip:

https://www.miataturbo.net/attachmen...1&d=1445204525

The programmed slip setting is 2 or 3 %; the knob then adds 0% (wet), 5% (dry), or more. Therefore, in Dry mode, you'll have 7-8% total slip, which is right where you want it.

Erring slightly on the low side is more stable: since if the slip increases you get more traction, which itself limits the wheel spin. If you end up on the right side of the peak it becomes unstable: increasing slip decreases traction, which causes more wheel spin, feeding back on itself. Thus you see big spikes of slip in the 20% mode. That doesn't necessarily mean 20% is slower... the traction doesn't drop a lot on the right side, whereas going to the left cuts down your acceleration really quickly.

Last night's test were all straight-line at WOT, and the 5% or 10% modes are probably best in that case. Using the higher slip modes might work better if you're modulating your right foot to keep the traction right at the limit, only using the RLTC to intervene occasionally as it starts to break free. The 5% mode is probably best when coming out of a corner, since it keeps it out of the unstable right side of the traction graph. The harsh interventions of the 20% mode would trip you up mid corner... Not as bad as uncontrolled wheelspin, but not optimal.

It's similar to braking: putting the pedal down hard and letting ABS modulate for you works pretty well; threshold braking works a little better; but combining them is awesome - you can squeeze out another few percent performance by threshold braking right to the limit and only having the ABS intervene when slight surface changes cause one wheel to lock. Which, incidentally, you nailed it in that last graph. :)

Ian,

I bought 4 wheel speed sensors and rings/hubs to install in my 99 so I could add traction control. My car didn't have this or ABS before. I'm not planning to install ABS, just traction control. Would I just ground one side of the VR sensor and feed the other side into the traction control? Probably put the traction control and VR sensors on the same ground plane to be safe?

That's awesome you got it hooked up, I'd want to do this on my car.

So the ABS controller has 8 wires for the 4 sensors (4 pairs), but the TC unit only looks at 4. I'd guess that the right thing to do in your case would be to take one side of the sensors (I don't think it matters which) and ground them all together at the same place as ground on the TC unit. You'll want to check that with someone who actually has a clue about EE though -- I'm a software guy who never quite wrapped his head around the concept of a volt. :)

Are you going to use the RaceLogic?

--Ian

Yeah, I was trying to compare the data logs from last night to see which setting was faster, but I think some of them were uphill and some downhill, so there's way too much noise. That plus the fact that there's noticeable non-repeatability in the 2nd-brake-2nd runs, where it gets a lot fewer TC events in the second 2nd gear run. Whether that's due to warmer tires having more grip or a more heat-soaked intercooler making less power (or both), I dunno.

--Ian

So I went and ran the car at the same dynojet but with the test pipe installed. Wow.

240 kpa:
https://www.miataturbo.net/attachmen...ine=1445556657

265 kpa:
https://www.miataturbo.net/attachmen...ine=1445556657

Yeah, there's a ton more spool and 30-ish hp across the board. (the closeness of the two graphs at 4500 or so is due to a boost spike in the old runs).

So the existing ceramic-core cat is a big restriction. It will be interesting to see how close a metal core one can get to the test pipe.

This explains why Zandr wasn't pulling away very much at Laguna -- with the test pipe in the car on the track, even at 200 kpa it was making 280+ at the wheels.

--Ian

That sounds about right from my knowledge. (also not an EE, but have studied it to learn some of the basics) Being a VR sensor they do have polarity, so I'd have to make sure I get them all wired the same so one isn't inverted relative to the others.

Probably race logic, unless there's an equal and cheaper option. I've read excellent reviews of the race logic unit though, it seems to be popular.

Good data to see, thanks.

I'd love to see that too, the metal core cat comparison. Pretty sure mine is a metal core cat, and I've always wondered how much HP it's costing me. Mine's a street car so I don't plan to remove it unless it's really terrible. If it is, then yeah probably install something better.

That computer has a floppy drive?

Oh, and holy shit. No wonder you had an 18 mph advantage over me up the hill between 6 and 7.

It's a VM, so it has a virtual floppy drive, yes. :)

--Ian

Since a couple of you asked, here's my spark table after the test pipe dyno tuning. I don't claim this to be well-shaped, my goal was to analyze the effects of the back pressure from the cat vs a straight pipe, so I didn't spend a lot of time trying to optimize the individual cells.

https://www.miataturbo.net/attachmen...ine=1445625020

100 octane gasoline, no E85, and 265 is the highest I ran it on the dyno. Up through 215 it's at MBT, the 240 row is right on the edge, and the 265 rows is octane-limited. I did a bunch of pulls to re-find MBT in the 165 row (it had moved 4 degrees less advanced), and assumed the same delta for 190 and 215. 240 had previously been octane-limited, so after retarding it the same 4 degrees I slowly advanced it again, and got more power putting all 4 of those degrees back in. I tried +5, it pinged and didn't seem to make much more power, so I went back to +4. 265 is the same.

The discontinuity between 140 and 165 is because I didn't retune 140. I don't plan to run the car long-term without the cat, so I didn't want to spend a lot of money on dyno time making it right. 140 kpa is also below the mechanical wastegate pressure, so it's not going to spend much time there.

--Ian

Your boosted cells are pretty similar to mine. Only real difference is after 6,500 I keep adding timing, you keep it flat from 6500 up. Why is that? Dyno said no more power? Or you don't rev that high?