915iS High Manifold Temperature

Michael, are you flying with your prop in Cruise mode? Many TSi owners are recommending flying with the prop in Climb mode, even while cruising. Not only do you get better speeds, but your manifold pressure will be lower, which may in turn lower your manifold temperature. You might try that (if you haven't already) and see if that lowers the manifold temp a bit. Good luck!

Micheal Fletcher wrote:

Hi Mike,

I have had a new core manufactured that I plan to test in the new year.   There is a company in Australia that produces high performance radiators and turbo intercoolers for the race car industry.   They supply to NASCAR and Formula1.  They are confident that I should see better results.   I will post the results once tested.

Awesome. Can't wait to see the results! 

Mike stated:
"... I can imagine that an improved intercooler / heat exhanger may not increase the power ... "

The density of the air can be increased by compressing it (Turbo) or Cooling it, or Both!
The more air molecules you can get into the cylinder the more fuel you can burn. More power!

Reducing the Temp from 50 to 40°C yields a theoretical ~3% increase.  
A 0°C Airbox Temp would produce ~15% more power.

Thanks Bill. That portion of my comment was in deference to James' prior comment that he didn't think it would improve performance. 

Bill Hertzel wrote:

Mike stated:
"... I can imagine that an improved intercooler / heat exhanger may not increase the power ... "

The density of the air can be increased by compressing it (Turbo) or Cooling it, or Both!
The more air molecules you can get into the cylinder the more fuel you can burn. More power!

Reducing the Temp from 50 to 40°C yields a theoretical ~3% increase.  
A 0°C Airbox Temp would produce ~15% more power.

Bill, are you saying that the power ratings Rotax states for the 915iS are only valid for situations where the intake temperature is at exactly 50ºC, and that at intake temps below that upper limit, the engine will produce greater than rated power?  (And if so, why doesn't Rotax publish those higher performance numbers?)

I would have thought Rotax's engine computer / map would actually manage the fuel / air to produce as much of the "rated" power as possible, while providing a margin below the "detonation" range.  I further suspect that if the intake temperatures were already within the specified Rotax limits (specifically ~47ºC as in Mike's case) lowering the intake temps further would be more likely to widen the detonation margin, rather than causing the software to push the engine to develop "more power" right up to that detonation limit across a wide range of intake temperatures...  Doing that would require some form of detonation sensor, right?  Am I missing something here?

Of were you simply discussing the "abstract" case, versus answering Mike's specific question about obtaining a noticeable increase in power from an engine that's already operating typically at 47ºC intake temps?

I'm not trying to be a smart-alec here, but truly wanting to learn!  Thanks!