2-Stroke Exhaust systems

[Guest nunans]

This may well be common sense to everyone but I thought it was worth posting just in case.

 

A 503 powered aircraft I purchased not long ago was fitted with a home made exhaust when I bought it. The reason for the home made exhaust I imagine was an attempt to keep it within the cowl so it looked better and neater. The pipe was nicely made and it looked like alot of time was spent on curving the manifold etc so it didn't stick out too far.

 

When I started flying the plane I noticed the climb was never more than 400'/min and the poor climb didn't seem to be due to the prop being set for a fast cuise, as it pottered along at barely 60 knots doing 6000 revs.

 

I checked the static rpm and only got 5400 max, hmmm if i reduced the pitch to get more static rpm like I should be getting then my cruise would be even slower! I pondered cutting a bit off the length of my blades as that would give better static revs and potentially allow more pitch for cruise but chopping a prop to make good rpm, with the real problem being low engine performance I think is robbing peter to pay paul. So I ended up ordering all the new parts (which were hard to get and ended up being made for the order) I chopped and rotated the new cone so it went in the direction I wanted so I could put the muffler under the fuse and gave it a test run.

 

With the correct muffler the 5400 rpm static now runs at 6300!! with no changes to the prop pitch or length :)

 

I'm yet to test fly but I imagine i'll end up needing to up the pitch so it won't over rev in level flight at full throttle.

 

The only negative is that the new exhaust runs outside the cowl and doesn't look as good but I'd rather the performance and safety margin that brings than the looks and neatness of being inside the cowl.

 

So if you have damaged, leaking or non standard exhaust on a two stroke and you're thinking the perfomance isn't what it should be then begin the search right there at the back end ;)