home |
build diary << | show individual entries | >>March 11, 2007: Am I bragging? Sure, why not. Thanks to David at Grassroots Motorsports for the picture. Okay, enough of that. Thanks again to David at GRM for the picture. In the meantime, it's time to get some serious work done on the Targa Miata.
They had good things to say! Joe - the machinist - figured there was a good chance he could get it out. I left the head and went on to work. A couple of hours later, I got a phone call saying the lifter was out and that nothing was damaged other than the lifter and the valve. No worries there, they're littering the place. While installing my new springs, he also found that all my other lifters were showing really odd wear patterns from constant valve float. So he replaced all of them with the set I had pulled aside for the Targa Miata head. As I might have mentioned, I had the redline set a little high so I could stretch out one of the short chutes at the local track. Down in Texas, I think Burt had been leaning a little harder on the limiter to stretch a longer straight and the abused valvetrain just gave up. Well, I had told him it was safe to work the car hard. At lunch I stopped by to pick up my repaired head - one new (used) valve, 16 new (used) lifters and a new (new) set of valve springs. The used parts came out of the piles of spares that are sitting around at Flyin' Miata and in my garage. That was faster and easier than I'd expected! Back in December 2004, I had the head off the car to fix a problem with the pistons and I considered installing new valve springs to handle higher RPM. If you look carefully at the exhaust valve cutouts, you can see where the valves were hitting the pistons. I didn't see this the last time the head was off, so the float was obviously extreme recently despite the same redline. I cleaned up the pistons with a dremel to take the sharp edges off and some fine Scotchbrite soaked in carb cleaner removed the carbon. Cleaning the headgasket was done with a plastic scraper and a Shop-Vac powerful enough to lift carb cleaner right off the head. No metal shavings in here! At least, I did my best to avoid it.
If you're interested in a free copy, just stop by the GRM website and ask. The Seven is also featured on the front page of B.S. Levy's website along with the Atom. It's really interesting to see the cars together for the first time. We didn't spend a lot of time standing around looking at them, but you can see the differences in scuttle height and placement in this picture. I didn't have the ECU in the Seven set up for high altitude after the trip to Texas, so I was down on power a fair bit - this made the cars fairly evenly matched in a straight line until the Seven could clear its throat at around 5000 rpm. The biggest difference was in the suspension. The Westfield is much softer than my car and rides incredibly well, but I could see it running out of travel once in a while. I'd brace for the bump and the Seven would just drive right over it without any trouble. Bill turned up the damping a bit to compensate (he was running with two people, as was I) but I haven't heard what sort of difference that made. Naturally, Bill and I had a bit of fun on this road. It's about 40 miles of twists and turns and I know it pretty well. We had traffic on the way in to Moab, but we got a pretty clear run on the way back. For some reason, the Miata that was also running with us took a bit longer to get to the end of the road. entry 1364 Brandon rode with me on our trip to and from Moab. It's a pity you can't see what the wind was doing to his hair in motion - it was total chaos. And he was loving every minute of it. entry 1365 May 3, 2007: A lot of people don't seem to believe me when I say that I pulled the engine for the Seven out from under a bench at Flyin' Miata. Well, looking around for a certain picture, I came across this photo on the FM server. That's the Seven's engine on the end with the red cam gears (now found on the Targa Miata). Sure, it's been apart a couple of times since then, but you can see that it was indeed under a bench and covered in dust! The date on this picture is April 8, 2002. entry 1366 May 6, 2007: I received an email today containing a comment I've seen a few times before, and it has to do with the troubles I have with my engine management when I change altitude. The Link system I use doesn't usually have a problem with altitude changes, but I have two things about my car that makes it more sensitive than normal. First, my cams. I don't get a whole lot of vacuum at idle because of their overlap. Second, the throttle bodies. They make the car run in a very narrow range of vacuum. The end result is that when I change altitude - and that's not driving to the top of a hill, but 4000' of change - the range of vacuum my car operates in changes quite a bit. It's a problem that's particularly apparent with a Colorado car that has a tendency to travel around a lot. All of the Sevens on the cross-USA tour a couple of years ago were suffering badly from the change in air pressures - none of them had any way of compensating because they tended to run purely off throttle position. A different ECU might be able to compensate better with a blend of throttle position and pressure sensing. Perhaps a bit more adjustability in the breakpoints in the fuel map would help as well. But it's always going to be hard to be my particular setup to behave with massive altitude changes. At least it's easy to change out the program in the ECU (providing I remember!) and it's a whole lot easier than messing with carbs. I should also point out - in case it's not clear for those reading along - that the problems I was experiencing in Texas for the Car and Driver test had nothing to do with tuning. It was due to the broken PCV valve, something I didn't diagnose until I got back to Colorado.
It's kind of fun to be doing some development on the car again, not that I'm hurting for projects right now. |