Took a quick video on the way to work this morning. The first segment is a leisurely acceleration through 1st and 2nd up to around 7k RPM. The flyby is accelerating from 5-7k RPM:
<iframe src="http://player.vimeo.com/video/24317079?title=0&byline=0&portrait=0" width="400" height="300" frameborder="0"></iframe><p><a href="http://vimeo.com/24317079">Untitled</a> from <a href="http://vimeo.com/user1744194">Dave</a> on <a href="http://vimeo.com">Vimeo</a>.</p>
This is still the loud mode with exhaust going direct from the headers through 2.25” and 3” piping to basically straight out the back. There’s a little muffler and some flow/resonance tuning, but it is about as free-flowing and power-producing as you’ll get. Needless to say, I love it! With an aluminum tuned resonator to cancel the drone frequency, it’s actually not that bad for daily-driving if you can get over the stench from not having my cats piped in (which they will be this weekend when I get my new quiet muffler welded in).
I’ve also learned a lot about exhaust piping material resonances. Most of the “rasp” in exhausts comes from exhaust piping material resonances. Given the same dimensions (pipe diameter, wall thickness, and length), different materials greatly influence the resonance sound and give some exhausts their characteristic “ring,” ala Kreisiegg, Capristo, Aprakovic, etc. Because I use cheap, light 18ga carbon steel, I tend to get rasp. Interestingly, the rasp only forms above 4k RPM, and I notice that if I accelerate moderately up to around 4k RPM and then exceed it, I avoid the rasp. i.e., once the 4k RPM excitation frequency passes from the engine, if the exhaust material isn’t already ringing, rasp doesn’t form above this RPM. But, if I go WOT through the rev band, the rasp forms at 4k RPM and just keeps ringing until redline. Even if I do let the rasp form, I would say that it’s no worse than the pretzel exhausts out there, but I still don’t really care for it.
I’m getting a Flowmaster 60-series 2” muffler in the mail today. Hopefully it will be quiet enough in conjunction with my cat to make it daily-driver friendly. The only problem is that it weighs ~13-14 pounds. Oh well. Total with cats/valve will be around 35 pounds, which is still about the best you can get with this performance potential, sound, and then having it very quiet when needed.
Not quite LFA, Ferrari, or F1, but it’s definitely as close as you’ll get to those from our engine, and it has it’s own unique sound. I can finally say it’s time to now focus on my aero mods and then do my engine rebuild….
Dave
