REFLECTOR: Replacing low compression pistons for standard compression
John Dibble
aminetech at bluefrog.com
Thu May 17 13:32:15 CDT 2012
Scott,
My experience is that for low compression engines, CHTs run higher when
high octane fuel is used. High octane fuel is for high compression
engines. The high octane fuel burns slower and avoids detonation that
the high compression causes if low octane fuel is used. Since high
octane fuel burns slower, some of the heat of combustion may not get
converted to HP in a low compression engine (where combustion is already
slower because of the lower compression) and instead contribute to
higher engine temperatures. 8.5:1 is still low and better suited for
lower octane. Still it should be better than 7.5:1 with 100 LL.
John
On 5/17/2012 8:10 AM, Scott Derrick wrote:
> I'm thinking of replacing the 7.5:1 pistons in my IO520 with Std 8.5:1
> pistons.
>
> For the obvious reason of gaining 18 HP.
>
> I think somebody mentioned that they thought that the CHT's would drop
> with that change because we are running 100 octane fuel?
>
> Can whoever mentioned that temperature difference elaborate?
>
> Scott
>
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