Does octane affect EGT?

by Mike Hoare in General Tech Discussion 10 years ago

Gurus: wondering if EGTs, CHT and eventually oil temp are related to choice of fuel octane. I used to run 98 in my 912ULS, but this summer I started using 95, marginally cheaper and I couldn't see any performance difference. Could be wrong, but also seemed as if my oil temp is lower with 95 than with 98. Anyone got some views on octane influence on performance and EGTs on our Rotax's?

Re: Does octane affect EGT?

by Rob Seaton » 10 years ago

Rob Seaton

3 1.32k 240

I am no fuel guru but higher octane does not do anything for performance; it just does a better job of preventing detonation. Higher octane should give you a better margin of error as some octane is lost by fuel handling and storage time.

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Re: Does octane affect EGT?

by Roger Lee » 10 years ago

Roger Lee

126 5.13k 4.56k

I'm with Rob. It shouldn't change anything other than help with detonation prevention.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

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Re: Does octane affect EGT?

by Mike Hoare » 10 years ago

Mike Hoare

10 16 0

Interesting, learn something every day. That being said however, would you always recomend using the highest octane available? Are some setups more prone to detonation than others? I have a fixed pitch prop but might variable pitch be more likely to cause detonation at high manifold pressure and low rpm?

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Re: Does octane affect EGT?

by Roger Lee » 10 years ago

Roger Lee

126 5.13k 4.56k

Hi Mike,

91 oct. or higher is good. In the US it is usually 91-93 oct. Failing to do some maint. and or trying to out guess the Rotax MFG and change the engine settings (i.e. carb jets) and even a weather change (from hot to cold) can put you in a scenario where detonation is more likely to occur.

The prop type won't necessarily cause detonation, but setting it up wrong can be a factor, especially if you changed other thing on the engine. The main thing with props as a general statement is don't overload your engine. It was designed to run at or above certain rpm. These guys that think they are doing good by having a prop that only turns at 5200 or less aren't doing themselves any favors.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

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Does octane affect EGT?

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