Exhaust Silencing

[yelwoci]

I thouight I'd share a snippet with y'all regarding the wonders of my RX7 exhaust.

The RX7 12A engines runs very hot and the only real silencing is provided by a tail box approximately oval 8x6in and 30in long.
The center perforrated pipe is 2.5" dia and the packing is a thermal blanket material using in the nuclear industry and foundries (Kaowool and the like).

The backbox takes a bit of a thermal and mechanical hammering, what with over 700C gases, unburnt fuel exploding as it hits cold air and me reversing at speed into gravel traps!

So we decided to rebuild it.
The noise tests this weekend (Silerstone) had me @115dbA off the pit wall at full power. The workshop tests showed 113 @6000rpm.

We have just discovered that the original centre pipe had some 5400 perforations, whereas the new one had only 3500. A simple replacment reduced the workshop test to 102dbA!


IanC

[Steve Hart]

Thanks Ian, very interesting.
Did you notice any difference in power....do you think you see any change on the dyno?

Steve

[Graham De Looze]

I used to make some exhausts in stainless. They were in 304 grade except for the perforated bit which was 409 standard in the exhaust industry. I found that perforated was cheaper than solid and the reason given was that it weighed less. bizarre. What about the extra work in punching it.
graham