Okay!
Exhaust drone post! (because its the easiest)
So I found a decent spectrometer app for my phone which made it a lot easier to analyse the sound of the exhaust in the cabin on the go.
https://play.google.com/store/apps/details?id=com.nfx.specscope&hl=enBecause it was live I was able to pause the drone at the worst point which was much easier than trying to find it in a 20 minute recording after.
BEFORE
AFTER
As you can see I was able to wipe out the drone point very effectively, as well as the octaves as you go up the frequency.
Things get interesting here, I wrapped my exhaust from the headers to the tip. The reasoning behind this is that the hotter exhaust gases have a lower density and will evacuate much easier than colder gases. In reality you won't perceive this on a dyno - the real change may be ~1% or less - but what I did observe is it
significantly reduced the effects of heat soak while on the dyno. Anyone who has been to a dyno knows that you tend to get 3~4 consistent runs then the heat sets in and performance begins to drop until it hits the 'soaked' equilibrium sets in. This can be as much as a 20% loss on a turbo car with no inter-cooler, so it can be very observable. On my little NA engine its not huge, but after a few runs we did see power drop by ~4~5%. After wrapping the exhaust this didn't happen at all. Every single run was the same value within 1kW of the last run, this was over about 20 minutes with about 10~15 runs. Not a bad result for $30.
There was one unexpected side-effect though...
I didn't know this till after, but hotter gasses are louder gasses. The temperature at the tip went from ~140C to about 260C after being wrapped and the cabin volume climbed from 80dB to about 90~95dB.
Things you learn... When its cold, so within half and hour of turning on the car its nice and quiet, but as it gets hotter it gets worse and worse. Free-way driving is totally intolerable with the exhaust just constantly belting out the same tone and being as hot as possible. I'll be switching out the muffler when I drive it down to Melbourne! Definitely something to keep in mind if you're doing something like this, it may not be acceptable.
Oh, and that volume was after insulation the car further than the factory standard.
