August 16, 2009

Renegade Miata's 5th Event & Thoughts

Long day at Autocross today. It was a great course with a lot of areas you can pick up a lot of speed on. I managed to score a 1'18.9 clean with the top time in the Other Mazdas class being 1'15. Not bad, though I could do some improvement on specific parts I suppose. I did however learn from Brian Lavesque. Big ups to him for teaching me proper tire pressure and that, surprisingly, I was running VERY high tire pressures.

I went over my pressures with him and he co-drove with me in the morning to test out some pressures. From 37 all around, we found out that 29 in the front and 32 - 33 in the rear was a much better setup. The car felt completely different, and bit very well into the turns with just the right rotation I needed for the rear. I'll be taking a different approach for now on for tire pressures and using them on the course.

Sadly, at the end of the event, not only did I have to deal with exhaust buzzing (which we've narrowed down to my header, and the buzzing is resonating throughout the midpipe) but I began to get a very loud, heatshield like rattle. I was getting it at idle a bit, and then at acceleration, the car sounds like the heatshield is under gun fire. It's very loud, terrible sounding, and I noticed out of no where a loss in power. It was the same feeling I've felt before when my catalytic converter had gotten clogged. I also pulled a check engine light for "catalytic converter below accepted performance threshold". Now I know I'm catless, so that CEL would come up at some point, but right when I start getting the rattling and then loss of power? I don't know.

At this point I'm in a bit of a slump. The rattling COULD be this here. Especially since I switched back to stock catback which is a much bigger exhaust, but it could be something totally different. And after finding out that pulling the screens from my intake is a bad idea (the screens apparently smooth the airflow over the maf), I'm not exactly running like I should be.

And this is the slump. What do I do? How should I do it? I've thought about replacing the intake with a Mazdaspeed version as I've read dyno charts that the Mazdaspeed offers better midrange and a bit more torque, where as the modified intake deal offers more horsepower. I could try and find a used intake as well, thats not an issue. I have a feeling I may get better response once I fix my intake. As for the exhaust, it's a completely different ball game.

I spoke with Bill of Small Fortune Racing and he suggested the use of heat wrap around my headers to potentially kill the buzz. The buzz could be due to thin walls of the header, or length of the runners, or both. The wrap may dull that out since it will be wrapped around the runners and added some "weight" to them essentially, sort of like a sound deadening material. If that doesn't work, I need to get a new header before the buzzing drives me nuts. Now as I've explained before, it's not a light buzz or something easily ignorable... It really sounds like a 2 stroke chain saw, and it's terrible. The midpipe is taking the buzz and due to the design (we're guessing, judging by what we saw and how it is made in there) it looks like it's being taken and amplified, while the rest of the noises are being dulled and silenced. As for the rattle, the slight power loss and check engine light? No idea. I suspect I'm going to do some sort of big change though to solve this problem, but in the meantime, I'm open to anyone's thoughts and comments on this.

Results on this event and results so far for the season are here. Looks like I moved from 2nd to 4th for the year. I guess I'll try and aim for 3rd, but no promises.
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