915iS High Manifold Temperature

I'm interested in this question, too. Does nobody out there have an answer?

To answer #1, Rotax clearly believes inlet temps above 50ºC are not good for the engine, else they would not have set that temperature as the upper limit.  

At least one experimental aircraft kit company has abandoned their attempts to develop a firewall-forward package for the 915iS on their airplane because they've been unable to develop a solution that met Rotax's 50ºC max intake temperature limits.  They do a lot of S-LSA "pre-built" business, and per ASTM standards, you have to meet the engine manufacturer's requirements to obtain S-LSA approval.  They have been long-time Rotax customers, and built hundreds of S-LSA with Rotax 912, 912is, and 914 engines.  So they were initially very excited about the 915iS for their customers who fly in the mountain west and wanted more power at high altitudes, but simply could not find a way to keep the inlet temperatures within Rotax specifications, despite multiple redesign attemps around the intercooler and intake tract.  They kept seeing intake temps above 50ºC, which caused the power output to be significantly reduced by the engine management system - most likely to prevent detonation and other nasty things that would destroy the engine otherwise.   I know the company worked extensively with Rotax to find a solution that would manage those inlet temps, but eventually abandoned the efforts to develop a firewall-forward kit for the 915iS in frustration - after literally months (and hundreds of hours) of effort.

As for question #2, I'm not sure, but I doubt it.  Rotax's engine management software appears to reduce the power output IF / WHEN you go above the specified limits, but I doubt it would increase the power output just because you're further away from the limits...  If they could reliably make more power with it, they would probably claim that increased power as the engine's output rating.

I can imagine that an improved intercooler / heat exhanger may not increase the power, but it could help prevent the ECU from reducing power, so it still may be worth the effort. 

Michael, please let me know if you have any ideas for improving the effectiveness of the heat exchanger that could work in the Sling TSi!

Thanks for your respons James.

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.