Fuel Additives

TCP is said to be effective, but it's quite volatile – it is recommended that you not keep it in your aircraft (which is a problem if you are refueling anywhere but your home airfield).  I prefer Decalin "RunUp" for XC flights, which does much the same thing but is not as volatile.  This stuff works to reduce the buildup of lead oxide in your oil, which causes sludge, instead converting the lead to lead phosphate, which mostly goes out in your exhaust.  

But be aware that this lead phosphate has been reported to build up on oxygen sensors in fuel-injected systems, and in exhaust systems generally, being more of a problem with "flexible" exhaust pipes.

By far the best solution, IMO, is to use unleaded fuel whenever possible.

Use Decalin instead of TCP. It isn't as corrosive and technically you aren't supposed to carry TCP in the cabin. Evereyone I know that has a FDCT in the US for the most part uses Decalin and we have been for 18 years.

5000 rpm is the peak torque of the IS engine, by definition the most efficient part of the rpm curve.

Therefore 5000 is ideal.

Personally I prefer 5200 rpm and about 23-25 MAP still in eco mode and I get 15-16 l/hr.

RPM is not really a good determinant of engine speed a better one is "mean piston speed" MPS. The reason for this is at high speed the lubrication between the ring and the bore breaks down and wear occurs, the rotating elements ...bearings etc usually are not the limit on wear.

With a long stroke engine like a Lyc O-235 2800 rpm... mps is 9.2 m/s

With a 912 at 5000 rpm the mps is 10.2 m/s

Therefore the Rotax at 5000 is only 10% faster than the Lyc at 2800....if you see what I mean ?

With the more modern materials of the composite rings and the Nikasil barrels this is still very slow. Racing Chevy V8 350 at 8000 rpm has a mps of 24.5....now thats fast.

So do not be concerned the 5000 rpm does seem fast but it is not really

If you come from using direct drive engines then 5000 sounds scary however this is only 2057 prop speed, dont worry.  

Tyler Hathaway wrote:

TCP is said to be effective, but it's quite volatile – it is recommended that you not keep it in your aircraft (which is a problem if you are refueling anywhere but your home airfield).  I prefer Decalin "RunUp" for XC flights, which does much the same thing but is not as volatile.  This stuff works to reduce the buildup of lead oxide in your oil, which causes sludge, instead converting the lead to lead phosphate, which mostly goes out in your exhaust.  

But be aware that this lead phosphate has been reported to build up on oxygen sensors in fuel-injected systems, and in exhaust systems generally, being more of a problem with "flexible" exhaust pipes.

By far the best solution, IMO, is to use unleaded fuel whenever possible.

Rotax engines don't have oxygen sensors. Oxygen sensors are used in "closed loop feedback" engines that have to run at stoichiometric mixture (λ = 1.0) like car engines which is required by the 3-way catalytic converter to be road legal. Rotax engines don't have catalytic converters so they don't need to run at stoichiometric mixture so they don't have any need for oxygen sensors.