June 13, 2011 - Track test again!
This time, I was at Grand Junction Motor Speedway. It's a very familiar track and I've got a good library of lap times there, so it's a good test on if the car's any faster or not.
I went back and forth with the computer programmer, sending in a number of logs for various drive cycles. The 5000' elevation doesn't actually make a difference, of course, as the computer is running off a MAP sensor with the MAF unplugged. It's just tuned wrong. Since I didn't have the ability to make any changes, there really wasn't anything I could do. The computer is going back to him to be unlocked (again) and hopefully a new tune. I almost nixed the test session on the track because, even with the MAF disconnected and the car running in closed loop, it wasn't completely happy. On the morning of the track day, however, I decided to run it anyhow.
The track is tight, with slow corners connected by short straights. Definitely not a place to sort out high-speed handling although there is one section that's 70 mph in a big sweeper. The biggest problem is that there are very few high-speed corner entries. But it's a well-known venue.
The car was particularly unhappy under braking. Last year, before the engine swap, I'd found the rear brakes simply weren't contributing enough. And they're still not. On my first session, I managed to hit 75 mph in the fastest section and then had to get fairly creative while trying to gather the car up for an off-camber braking zone. Usually, we can't run more than about 70 mph through there! I held it together, but also locked the front wheels in the process. The tires were already slightly flatspotted but after that episode they felt completely square. So they had a tendency to lock very easily. The car was also understeering on the tightest corners, likely due to the clutch-type differential. It was similar to what I'd seen with the OS Giken diff with the four-cylinder.
Still, even with some handling quirks and a driver that really wasn't doing a great job behind the wheel, I managed to hustle the car around faster than ever. Not a lot faster due to the braking problems, but it counts. My fastest time was a 1:03.725 before I flat-spotted the tires, and it got worse from there. My previous best was a 1:03.796. Like I said, not a lot faster! It's interesting to note that in 2007, the first time this car took to the track, I turned a 1:03.733 in the Seven.
As always, the GM diff hooked up extremely well. I could light up the rear coming off a corner, but it took more effort than you'd expect. That might partially be due to the rich air/fuel mixture cutting power, but it's in line with the sort of traction this diff provides.
There's more time in it with round tires and a driver who's settled down a bit. By the end of the day, I knew the tires were toast so I just started playing around with leaving black stripes around the track like the child I am. You have to, right?
I did have one exciting moment. In my third session, I was just coming off the last corner on to the straight when the engine died. A half-second later, I got a big whiff of fuel. I immediately cut the ignition (the fuel pump control in the engine computer was disabled by the tuner, so it's run off the ignition) because I had a feeling I knew what had happened. And I was right. The push-on fitting for the fuel feed had come apart popped off. It happened a couple of times during the build and I suspect it was damaged or defective. It had been good for a while, though. When that happens, the fuel feed sprays 60 psi fuel all over the engine. I was still moving fairly well and right by the pit entrance, so I brought it into the pits and bailed out to open the hood right away. Luckily, no fire. Whew. A couple of hours later, I had a replacement and everything seems to be working as intended. We've used these fittings on a lot of cars and never had a problem.
So, not a bad day. I'm going to change out the spring rates to the expected Targa setup and set up the ride height for the rally. Then I'll start to really fine-tune the handling. I'm also going to pull out the engine computer and send it back to be reflashed. That will let us tune it properly for this engine.
tags: fuel pressure |
THE DIARY