At the dragstrip
 
    I commuted to work this entire week with the Omni. It did really well. On Thursday I finally got the new oil pan. (Did I mention my weld job in the old one weeped oil?) So I swapped that out. That required me to remove the front motor mount. A bit more work than I expected, but I got it done. I noticed when I went to jack the car up that the core support doesn’t like to be used as a lifting point for the car anymore. I’ll have to drive the car up on blocks of wood, so I can get the jack to the core support from now on.
    I found the “auto-tune” feature in Megatune this week. Megatune is the software I run on the laptop to interface with the Megasquirt. It helped take some of the burden off the O2 sensor while cruising, as it was doing a whole lot of adjusting most of the time.
    The patch I made in the exhaust system between the downpipe, and the rest of the exhaust didn’t hold up for long. I ended up taking the car to a muffler shop Friday before the race to have that fixed. Once it was fixed, my O2 sensor started reading a whole lot differently. Suddenly fuel curves that I thought were just right were seriously too rich. Apparently that patch I made had been sucking in quite a bit of fresh air under load and contaminating the exhaust gasses so the O2 sensor couldn’t read correctly. More on this in my drag race report below..
    I also got the car in for an alignment Friday morning before the race. The alignment machine indicated that my k-member, right control arm, or possibly even the part of the car that the k-member bolts to is tweaked a bit. Lovely. I’ll start with replacing the k-member sometime in the future and see what that does for me. But he was able to fix all my other alignment issues. The car is sooo much smoother going down the road now.
I noticed in some of my datalogs that the air temperature was really climbing when the car would sit and idle for awhile. I figured this was mostly due to the air temp sensor just hanging freely in the air. So I decided to put it into my POS air filter. I drilled and tapped a hole in the cap on the end of it. Then installed the sensor.
At the dragstrip
Sunday, April 8, 2007
    I’m definitely measuring the temp of the air going into the engine now. I wasn’t too concerned about destroying the air filter when I did this, since it’s such a POS air filter. But now, I’m thinking I really need to start looking into getting the filter out of the engine bay, the air temp went as high as 151f at the dragstrip. It’s normally around 80f on the freeway. Granted, it was a WARM day, but only about 75f.
The Dragstrip Report
I didn’t do as well as I had hoped, but nothing broke! And it’s always a good day at the strip if you don’t break something. First run, I spun the tires really bad until the car caught up with them in 1st. I got a 2.624 60’. That’s pretty bad. I ran a 16.208 at 85.99mph. My second run was actually my best.
    But first let me go off on a tangent and whine. This was the first event of the season, and all the little rice kids were there with their Honduh’s. The first race of the season is always seriously over crowded and this stinkin track won’t run past dusk at all. Second you might need headlights, you’re out of there. So I got there as soon as they opened at 3pm, waited about an hour and a half in line to get through the gates, and then got a wopping 4 runs in. Over an hour between all but the first-second run, which was about 45 minutes apart.
    My second complaint would be my laptop. I normally datalog on the laptop, and email the datalogs to myself when I get home, so I can view the datalogs on my Mac in the comfort of my living room. Well I needed to be able to view the datalogs at the strip, so I installed the datalog viewer just before I left. I get to the track and try to run it, and the stinkin thing needs the Java Runtime Environment.. Which I happen to know won’t install on that laptop due to the lack of ram (32megs).  So when I got done with a run, I had to load the datalogs into Wordpad to view them. And I was viewing them in a pretty primitive way at best. I could look for points where the throttle position was 100%, and see the RPM’s climbing, and then I had the O2 sensor voltage. Kind hard to convert the wideband 9.35-21:1 0-5v reading to a usable AF number. So I had to try my best to convert the numbers in my head. At best I had a rough idea. I knew 2.45v was 14.7:1, aka, too lean for WOT. It seemed to me that 1.5v was as rich as I wanted to let it get (lower voltage is richer).
    After my first run I decided to remove 3% fuel across the top of my curve. This did help alot, but unfortunately, after making those changes, I thought I was about to run again, so I turned on datalogging and forgot about it. It turned into a 45 minute wait before my next run, and I even left the ignition on that whole time. So when I finally got done with that run, the datalog was HUGE, and I was unable to even view it in wordpad. So that completely killed my ability to do ANY tuning after that run.
    I got a wopping four runs the whole day, due to the place being so crowded. So I removed more fuel after the 3rd run. The 4th run, I was just flat pissed and didn’t even run the car very hard because I knew I didn’t have it right yet.
    If you’ve never used MegaLogViewer before, the above graph probably makes absolutely no sense to you. Sorry if that’s the case. This is what my datalogs look like. I have it zoomed in to show just my run down the track, this is my 4th run.
    Ok, time for me to go off on a short tangent again. My factory tach is off by about 500rpm when it’s over 3grand. I was shifting just after the tach would go past the end of the gauge at 7grand.. So about 7100rpm on my dash. As you can see from the log, that was 6600rpm in second gear.. 3rd I shifted early, and I didn’t get to the top of 4th before the end of the track. Let me tell you, it is SOOO WEIRD going past 6grand at all in that car. Having driven it as a turbo 2.2 for so long with the 8v head, I had gotten so used to shifting at 5500rpm.
    Ok, back to the above graph.. My air fuel ratios were 11:1 at best, and the low spot I have the marker at on that graph shows 9.8:1. Megasquirt’s manual has an awesome equation for fixing your VE tables by using the wideband AF ratio in the log. It goes like this:
  Current VE% * (current AF / desired AF) = New VE%
Really freakin easy if you ask me. So I looked for places in the above log that lined up directly with tables in my VE.. So if I had a 6300rpm table, I’d find 6300rpm in the datalog and see what the AF was there. I very quickly had some new numbers. I think I dropped it almost 20% in some places. Once I had those good solid numbers in, I brought the surrounding numbers down to match. It worked great, I took it for a spin on a good long back road near my house the next day, while datalogging. Dead on except around 5900rpm. At 5900rpm my throttlebody became a bit of a bottleneck (using the smaller 48mm TB), the MAP dropped down to 89kpa because of it. Well I had MS set to be open loop at anything over 92kpa. Now that my fuel was right, it was close enough that the MS was able to instantly pull it back to stoich the second it got down to 89kpa. I just about laughed out loud when I saw that in the datalog and it occured to me why it did it. I changed the open loop setting to 85kpa and the problem is gone. I’ll look into a bigger TB before I go to the track again.
Ok, with all of my excuses above (datalogged and graphed for proof.. haha), my best run was 15.762 at 88.01mph. It was the only run I didn’t spin the tires through 1st gear. I babied it through 1st instead. I got a 2.478 60’. I got a 2.2 with this car when it was automatic with the turbo engine. I imagine I could do it with this new setup if I get more practice in. Maybe some new tires would help too, since as I mentioned last week, these tires are pretty bald and very old. So if you go by the rule of thumb that every 10th of a second off the 60’ is 2/10ths off the 1/4 ET, that would put this car at 15.2, which is very close to the 14.913 it ran when it was turbo. Get all that extra fuel out, and open up the throttle body so it can breathe better on the top end, and I think the car is every bit as fast as it was before (before being, the first time I took it to the strip, running 14lbs of boost without an intercooler, running about a 98octane mix of premium gas and toluene paint thinner.).
    After fixing the VE tables, my duty cycle on my injectors went from flat out pegged down to 81%. Turns out I don’t need bigger injectors like I had thought I did. That exhaust leak was really messing with my numbers.
    One last thing I want to do before going to the track again is get the car on a dyno. Not even so much for tuning, as for viewing my powerband so I can intelligently decide where to shift. The Megasquirt has the ability to run a shift light, so I’m going to set it up to do that, rather than try to rely on my innacurate factory tach.
    That’s it for this week. I don’t have new gas mileage numbers because my odometer stopped working when it went to roll over from 124999 to 125000. I hit a good bump in the road on the way to the track, and it started working again. So I’ll be able to start comparing gas mileage again soon. Not to mention, if I was getting 28mpg with that exhaust leak causing the wideband to be so far off at WOT, I’ve got to imagine it was just as far off during cruise. Then there’s the alignment, the tires aren’t scrubbing their tread off on the freeway anymore, so that’ll help gas mileage too.