@Roda Thank you for linking that site and the comparison with the other K-swapped car. That's a huge difference in number of shifts.
Do you happen to know if he revs to the same RPM as you? I've been comparing both of the ratios on the site and it doesn't seem too bad for our local track, but certainly different RPMs throughout. I can see how it would be busier at larger tracks (or tracks with larger straights?).

@BenR Thanks for sharing that info. Comparing the data from the site to my videos, it seems I'll have to short-shift T14, upshift to 4th in T2 and keep 3rd in T3-4, then upshift to 4th in the back-straight. Scooter's top-speed on the front straight is usually 88-90mph, which would be right at the limiter of the 6 speed in 4th gear according to the calculator, and in the backstraight 77-79mph which would be 4th gear. Overall it seems I gain 1 or 2 extra shift on the course depending on how much speed I carry on T5 where I can either hold the limiter or grab 4th for a moment.



HA! Launching in 2nd?! I guess we'll see. I'm not good at launching so I tend to roll first a little. I don't really use launch control either because it hurts my soul a bit. I will keep your 2nd gear advice in mind. Autocross is going to be rough anyways. Looking at the videos, the 6sp would put me between 2nd and 3rd in many places.

 

I don't recall what the other car was running for diff gearing, but IIRC was either 4.1 or 4.3. He was on 245s, which are a bit shorter than the 225s I was running. His was also a stock K24, and IIRC he had his limiter set similar to mine (7600).

FWIW, when there are two gears to choose for a corner, I've almost always gotten the faster lap time in the higher gear. As long as it's not lugging out of the corner.

 

That tracks. It makes the braking zone a bit more spicy, but I think you should probably already be flat throttle through T2, shifting into 4th right before the start of the rumble strip in T2 and be in 3rd in T3-4 with your setup currently. Only 6 and 9 should be 2nd gear corners. Assuming the repaving hasn't degraded the grip to a significant degree.



It's that mechanical empathy trade off.

 

Noted. Thank you, sir.

I find that shifting to 4th in T2 loses me 1 or 2mph total, so I hold 3rd and downshift to 2nd in T3-4. I didn't consider holding 3rd through T3-4 before as I thought it would be too low RPM. I should try it in April.

 

Took the car for a quick blast today and got it up to temperature. Grabbed some logs and it was the perfect time to look at the slightly high idle issue. I think I've found the culprit.

When I finished the drive I turned off the engine and let it sit for 15-20 minutes to heatsoak it some. Started it and it was idling lower than target (750RPM) then caught up. In this screenshot you can see it happy on target with a reasonable IAC duty.


Warm start. RPM is right on target, idle valve needs more duty than base, TPS Voltage is 0.38

After letting the fan cycle on/off for extra data, I gave it a blip and noticed it was lean and idling higher. In this screenshot you can see why. The TPS voltage is 0.40 and the IAC is at the minimum clamp of 15%.


Here is the issue. Idle is 70 RPM above target and the idle valve is at the minimum duty. TPS Voltage is 0.40

So the throttles are not closing correctly after a blip which is likely too much tension on the cable when everything is up to temperature. Will adjust that tomorrow.

And because this is Alpha-N, I get to retune a good portion of the lower throttle areas after I recalibrate the TPS.

 

What's your idle ignition min/max? In the first screen shot your on target at 9 degrees, 2nd screen shot is 60rpm over target but ignition is 7. I'd expect ~14 when on target, 7-8 degrees when 60rpm off.

I wouldn't think .02 volts on your TPS is a smoking gun. It's a 0-5v sensor, usually operating in the .5-4.5v range. so .02v is roughly 0.5%. Also looks like your fan settings aren't adding quite enough duty, it adds a little then has to add more after a few seconds, both times.

 

The min/max are 0/25 for idle ignition, target of 10 and using 0.5 P currently.

you’re correct that 0.02v is only about 0.5%. I find it’s even less, around 0.3%, which I’ve found is enough to change fueling needs and cause higher idle. Notice how it’s also running leaner in the second screenshot. But I could be wrong, and you do have more experience on this stuff than me.

And regarding the fan, yes totally. I think I’ve had the throttle too tight (or some other issue maybe) since the VVT swap and I tuned around it (ie less duty than needed), so I need to retouch all of that now if my hunch is correct.

 

Try 1.0p and 0.5d, my ignition numbers are 6/16/26, I think 10 is too low of a target, BPs seem much happier around 12-16 base.

 

Thanks Curly. I’ll try your suggestions. I was using numbers closer to what you’re suggesting on the BP4W before these high idle issues. I lowered the target to 10 to get a bit more duty cycle from the idle valve, but I don’t think it made a large difference.

regarding the PD, I find with 1/0.5 the ignition angle jumps around a lot and seems unstable. Is that ok? It could also be placebo, but I “feel” it idles smoother with less D, I can hear a difference in how it idles, but the RPMs are stable. Just wondering what’s normal or OK, vs too far in your experience. Adam in the link forum said to increase P until Dwell becomes unstable, but that felt wrong to me 😆

 

I spent a little while messing with this.

I loosened the throttle adjuster all the way and recalibrated the TPS. I played around with it with the engine off and did see it was too tight before.

I set the ignition control PD as you suggested and it seemed happy. I then tried 12 to 15 as target, and landed at 13 to give the idle valve some more duty. With 15 target it was going as low as 18% DC, while at 13 it hangs around 22-23% DC. It does sound happier idling around 13 than 10 without doubt. Thank you @curly

As for the throttles, something is sticking in that last 0.1% TPS. It improved after loosening the tension but the issue is still present. What I’m seeing is that the car is idling on target and if I feather the throttle some, it won’t return to 0.38V, and instead stays around 0.39V with a slightly high idle. If I do a large blip, it goes back to 0.38V and idle is back to normal. The cable is as loose as I can make it now, but I might have trimmed it too short. Could be that something needs lubing, or maybe the cable is getting caught somewhere. Will have to investigate that further but will likely leave it be for now.

 

Any way to add tension to the ITB return springs? I know my Skunk2 TB had that issue before I added more tension to the spring. I mean it still does have that issue, to be honest, just a lot less. Ha.

 

I don’t know an easy way other than to add heavier springs. It is so heavy already that I hope I don’t need to do that.

 

It’s been a wild couple of weeks on my end of the world, but seems I’ll get to race this weekend. The plan is to regain confidence with the car and play with the suspension setup some.

The car is loaded and the wife will be tagging along. Should be a fun day.



First mess up came early. Too close for comfort.

 

Nice! Good luck brother. Hope the wife enjoys it as well!

 

Thank you, Zak!

The day went pretty well. It was another two day event, but I only had time for one day (Saturday). Got the car prepped in time and went out for a shakedown session, wife as passenger. She was giggling and laughing which was a great sign haha. Right away the car felt good, but the left tires had less grip than before, so any right turn took a lot of patience, otherwise, push central. Started with 10 clicks on front and rear shocks, much softer than I ran before. At the end of the day I ran 11/11 from full soft and liked the feel overall, with much better grip on the exit of the hair pin. Might try a click or two stiffer next time to see where it starts to have wheel spin again. Dropped tire pressures to 23psi lukewarm and it felt good that way. Tire scrub is right at the line before hitting the sidewall, so I think those are the right pressure for these with the current alignment.

Things got exciting on the second session. After the first lap I noticed the car had some snap oversteer and I started wondering if I had a corded tire or leaked some fluid onto the tires. I started leaving some margin in case I had to catch it at some point and it was then I noticed the massive oil slick in Turn 6. I was already at what I thought was the edge of grip for the conditions and as soon as I breathed on the throttle it snapped hard and had to catch it with the quickness! I'm surprised I caught it at all. As always, the video doesn't do it justice. Not knowing what that slick was from I backed off thinking it was me, but turned out to be a VW Beetle and Scooter was groovy. The track was sketchy the subsequent sessions with oil in some corners that we had to avoid by turning in much sooner than I would like. Fastest time was a 1:34.68 which I'm happy with and should put me in first place again, or at least podium (results haven't been announced, and awards were done on Sunday). These Acceleras are also very dead now, so it's time for another set of tires. I know I said I would do Falkens, but after talking with a couple more peeps about delamination, I'm going to spring for the Nankangs.

All in all, it was a great day. Wife had fun, hung out with friends, talked ****, got to see some Sprinters race in the dirt oval, and the car, truck and trailer made it home with no issues or accidents.

Video of the fastest lap of the day and a exciting moment at the end:

 

Ordered a set of 225/45/15 Nankang CRS V2s to put on the 6ULs I got from @Fireindc . I may not use them for a while, but rather have the car all ready for FM Summer Camp asap. I’m helping two other Miata friends get their cars done before summer camp so time is tight.

here is a milestone Tim and I achieved yesterday in his soon to be K swap. This one has Drag Cartel 2.2 cams :







Another friend is swapping from a voodoo box to a Link G4X on his turbo NB2. It’ll be a busy April/May

 

Video's broken in your last post FYI,

Jealous that you're making it out to Summer Camp. We were just talking about trying to organize a crew of our local people to make it out some year.

Get some heat into those Nankangs and they should be pretty great. FWIW the new 660+ is supposed to have fixed the delamination issues and have a bit more lateral grip than the previous 660's. One of the spec classes for autocross (SSC) just had their pax increased to account for the better performance from the newer tires. I'm still tempted to grab some of the old closeout 660's from tire rack. I never had issues with the 2 sets I went through.

 

Ah. Thanks for letting me know. I keep messing up attachments, but they should be fixed now.

Would be awesome if you make it out there sometime!

I had read and heard the same about the 660+, and then saw the Rugged Badget Racing video where they delaminated the majority of their sets and decided to wait a bit longer to see what happens with the new compound. Interesting about the extra grip and PAX increase. Had not heard about that.

 

Glad you spotted that oil early!

I hadn't heard anything about the 660+ delaminating, but I've mostly been looking at Nankangs and Vitour's lately, so that's probably why. My friend who races in SSC is forced to run those tires, so I'll see if he's heard anything about it.

 

FWIW, Rugged Badger were running some pretty funky alignment numbers, as well as really low hot pressures and I think that contributed to the problems with their first set of 660+. Falken sent out a rep for their following race, and with some more typical Miata alignment numbers and higher pressures, they didn't suffer the same delamination and wear issues with a follow up batch. With as much as we've been autoXing our NC, I think I'm probably going to buy a set of 660+ for it.

You won't be disappointed with the CR-S, though...