Rusty Exhaust = Fast Exhaust?

[KartRacingDriver0822]

Hey guys! I am a kart racing driver racing in a 125 two stroke series. Our engines are all sealed and standardized, so no tuning allowed! Now of course, like many racing series that claim to be equal, it's a load of bs. There's definitely a performance advantage in some engines and other components. Something that I noticed is that a lot of performance can be found in the exhaust. Specifically, a lot of the big teams have exhausts that just sound "off". They sound a lot more hollow, metallic and sometimes they sound like they're leaking. Often these exhausts are the most beat up things imaginable, rusty and crusty beyond all hell. A story goes that the big teams intentionally let their exhausts rust and oxidize by just letting them sit outside in the rain for a few months. Another theory is that they somehow sand blast their exhausts from the inside. That's all just theories, no hard evidence. I'm just a driver, not really big on how to gain performance in two stroke in ways like this. So what do you two stroke experts think? I'm curious to hear your opinion!

[sav0r (CL MotoTech)]

Are the engines randomized or do you rent or purchase one from a builder?

[m in sc]

this is a reach... but it may have something to do with a created boundary layer due to the surface being rough. can NOT say as ive ever heard of this applied to an exhaust though. but, i could see it being possibly feasible? interesting for sure.

[teazer]

Sounds more like they rust them to hide the fact that they are modified and are illegal.  What?  That rusty thing over there.  nah. Of course it's legal....

[ajb]

Perhaps its due to frequent de-coking with chemicals?

The Aprilia RSA 125 chaps used to decoke between each test session on the bench, if you read Jan Thiel / Frits Overmars threads on pit-lane.biz.