Finally drove the car to see how it deals with a straight “16-lb” wastegate spring and no ECU control. The figure’s in quotes because the manufacturer states that the rating assumes that intake and exhaust gas pressure are equal. If they aren’t, the actual pressure may be higher or lower. Mine has always been a bit higher (I think that’s a good thing), with it actually running 230 kpa, or 19 pounds; not a big deal but interesting. What is a big deal is that after many acceleration runs, there hasn’t been one MAP drop. This seems to show that the problem is either wastegate float due to using a weaker spring, or the ECU isn’t controlling boost properly (I suspect the former).
The next step is to reduce spring pressure to 14 psi (the maximum I’m willing to run on 91 octane gasoline), then use the ECU and boost control valve to adjust boost higher for ethanol. So – changing only one thing at a time – the spring will be changed but still have no ECU involvement. If there’s no MAP drop, then the boost control valve will be plumbed back in and we’ll go from there.
Separately, I’ve noticed that under hard acceleration, the air/fuel ratio gets a bit lower/richer than it should. Closed-loop lambda control is enabled, but even though the richest target mixture at the high end is 0.78 lambda, it’s dropping as low as 0.69. Anyhow, a question regarding lambda PID has be posted to the ECU forum. Somewhat related, injector duty cycle is maxing out at 89%, right on the edge for being undersized. Once the mixture is leaned out slightly, that should improve injector margin (and/or I can increase fuel pressure).
My brother has been pestering me about doing a trackday event – it has been a long time. The choices are Autoclub Speedway, about 90 minutes away. Further away are Willow Springs, Streets of Willow, Buttonwillow, and Laguna Seca, in that order. I’d like to get a rematch with Willow Springs, but almost as good is Streets of Willow, located next door, which is very twisty, favoring light cars which handle. There’s also a large skidpad there; I want to take Midlana out and do some traction-limit/drifting turns to get an idea of its threshold balance. It’s simply been too dangerous/foolhardy to do so on the street.
I’ve been to Buttonwillow once before, but for whatever reason don’t really like it – not sure why, maybe it’s just a lack of familiarity. Autoclub Speedway is the closest and the cheapest, but it’s also the highest speed course with scary concrete walls, though going off in the dirt at Willow can end as badly if the car hooks and rolls. Than of course there’s Laguna Seca, sort of the holy grail of tracks. I have to run Midlana there at least once, but it’s the furthest away, typically the most expensive, and has a really low noise limit. We’ll see.