[kyleb]

Thanks Mike, I had forgotten all about this.
I have since added a blower and cam etc so I should test it again, but prior to doing all this I grabbed a sound meter and was getting around 100db at 4000rpm.
I think it's a good result with the limited pipe length that you have to work with..
If I was to do it again I probably wouldn't use stainless for the internals therefore you would possibly get even less heat transfer whilst stationary..