We've recently completed some back to back testing of exhausts and found one really, really bad exhaust that costs several tenths on track (quite a surprise how significant). All exhausts had an intact cone (inner tube) and fresh wadding. All sealed with silicone at the join. The poorly performing one had a dent in the tube immediately below where it joins to the engine and this is the only obvious difference between the tested units.
I checked with our engine builder who said some exhausts just didn't want to perform and it was usually either a collapsed internal cone/pipe or more likely due to inferior internal welds. Unfortuantely other than on-track, the only way to find out is to cut the pipe open which is terminal for the component.
Anyone else had any similar experience?

Interesting observation. I haven't tested different exhausts myself but I can see how that could be an explanation for some "mystery" problems. Not many would think of switching out the entire exhaust when troubleshooting engine performance.

I think this issue may be a more significant performance issue than it appears. I would really like to hear of anyone else finding any significant performance variation on-track with different exhausts. Also what age of wadding seems optimum.
In the top level Rotax series in UK (Super 1) I have never, ever seen any top team go to track with a new wadding (you can clearly hear a newly wadded exaust) so I think the general rule seems to be that new is not best. There was a fashion for assembling exhausts with double wadding but this is now outlawed.
My engine builder believes there is an interaction between exhaust and power valve which is important for bottom end performance.
Is there a commercially available power valve sensor for the Rotax engine?

I might just take a few exhausts to the track and start testing .


Sensors are available for PI, Unipro, and Alfano. I use a Unipro and the sensor. Been meaning to write up a bit on it for ages now but just haven't done enough with it yet to write anything worthwhile.

anything will do for me..

I ve been out for the same trouble
It give me a big headake until i switched pipe with a friend and .........WOW
After the test i went straight home and put my pipe under the saw
But when i cut the 180 pipe of i didnt found anything that looks wrong ??
When you read the regulations i see it is alot of +- 5 mm on every section on the pipe
So in the total it could be 15 mm longer or taller ????

I am looking forward to see if anyone got a answere to this

Thanks

I just bought a brand new exhaust, tried it back to back with the one (and only) good exhaust we retained, and found it was USELESS!!! I have spoken to my engine tuner who says the only way to find out what is going on is to cut the pipe and inspect, there is great variation in manufactured quality. But that then renders the exhaust useless - so pointless. The only way is to track test and keep the good ones.
At the last Super One UK Rotax round, officials removed the exhaust from one of the leading contenders on the dummy grid and substitited their own selected exhaust. So someone knows there is a difference.

Biggest item of contention in UK at present is slipping clutch, which lets the engine rev higher before engaging and so gains pull out of slow corners.

Hmm slipping the clutch what do you mean ?
And now when you find a pipe that works and one who doesnt
Please try to see if you can find any diffrent meussre everything you can

Or is it someone who know the secret ???

Tho its a problem with the KF class only??

We had a similar problem with a new exhaust on round 5 (junior class). Had to revert to an old exhaust with new fiber and walla !