build diary

August 16, 2005: Thank you Supertrapp!
The sound testing was an interesting process. The way the muffler works is by simply diffusing the sound through a set of discs. The more discs you use, the less muffling goes on and the louder the car is. It seems a little counter-intuitive at first until you realise you're basically opening up more area for the exhaust to escape. Unfortunately as you remove discs to quiet the exhaust, you also increase the backpressure. According to Supertrapp, 24 discs is approximately equivalent to no muffler at all with regards to backpressure and I suspect also with regards to silencing.

The first time out, I set the Supertrapp up with 12 discs. It's the most I had. I wanted the worst-case scenario. After a couple of laps I came in and the track owner looked concerned. Obviously I was too loud.

For the second test, I used 6 discs. This made the car noticeably quieter. I came back in after one lap and the track owner told me he wanted a few more samples. I was to go out and lap the track until he waved me in. Sigh, the hard work I have to do for this car. After about 5 laps, he had all he needed. The 6-disc setup knocked about 7 dB off the peak. Excellent. Since the track owner is also a car nut (why else would you do it?) he wanted me to put some discs back in for maximum performance. Oh well, if I must.

The next test was with 9 discs. I let Bill Cardell take the car out so I could watch it. Well, that was the plan. We were also testing transponders so it was suggested I take out the supercharged Miata so we could check how they worked. The Miata had already come in with overheated brakes and was not set up well for the track at all, so I decided to simply play around. I'm sure the noise peaks from that car came from the tires instead of the engine as I practiced my sideways driving. Hee hee!

While I'd been hooning around in the Miata, the Seven had shown itself to be borderline for sound. So we took out one more disc (to 8) and I went out one last time. I also had three transponders stuck on the back of the car. The sound levels were perfect so I just stayed out to play. The car was right at home - the front end stuck well once I sorted out my entry speeds and the slow track (almost all second gear) allowed me to steer the rear of the car whenever, wherever I wanted. The soft springs meant I could still hammer the berms without upsetting the car but the sway bars kept it flat on corners. There are no high speed corners on the track so I couldn't check out the behaviour at the limit, but for a kart track it's a good little car. The transponders showed that I was lapping fairly consistently, ranging from 1:07.234 to 1:07.888 over four laps. Not too bad considering I'm still learning the track and trying different things. The LED tach worked perfectly, allowing me to judge engine speed easily and also acting as a speedo of sorts.

Do I have a great job or what? This sound testing was done in the middle of the day when I was supposed to be at work. Not only was I allowed to go, but my boss came along to play as well. We'll be going back tonight with the others from the office for more "sound testing". Whee!

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