I'm doing the calculations for header runner length and realized that sound travels at different speeds relative to temperature in air, and our rotary exhausts are very hot.

1. What kind of EGT's do you guys see before the turbos? This will be for a belt driven boosted NA car basically so before turbo temps at about 10psi boost is in the ballpark for my setup.

2. Some calculator on the internet says the speed of sound at 1600f is about twice what it is at 90f, is that really true? I haven't gotten far enough into thermo engineering classes yet to have a textbook on this.

Thanks in advance for any help!



*edit* nevermind, amazing how productive one can be if they search a bit.

But yeah, if anyone's curious, at 900C, sound travels at roughly 870 m/s and in one revolution of a rotary turning 7500 rpm, the wave would travel roughly 7 meters, necessitating a long primary runner length of 3.5 meters for the wave to complete one cycle (down and back) per revolution.

Anyhow, with that out of the way, it's time to ponder the header designs of other NA rotary builders. I'm mostly trying to understand the acoustic tuning effect of traditional long primary setups.

Cheers!

*edit again* Damn, I was wrong, the runner length would be 1.75 meters, four trips of the sound wave per rev. and man that's a good thing, that makes it 68" which is barely feasable for an FC street car!

 

Sounds like your learning just how difficult it is to design a good header from scratch! Don't forget to take into account that the exhaust cools 100's of degrees as it goes through the pipe! Damn, another curve ball, huh? I've been messing with the same project for my EP car.

 

Huh, that's right. I forgot about that.... Actually that is good because it will lower the average temp and speed of sound in the pipe, so I can use something shorter than 68". Thanks for the tip.