Jan wrote,
>Greg,
> Maybe Jarrid would comment, but I think a lot of pre-detonation is
>caused by the combustion chamber's squish band not properly designed for
>the engine use. High octane can be a remedy and/or a requirement (due to
>the higher compression pressures). But I know from my 2-stroke engine
>work that the squish band is very important.
>Jan
The squish on the alpine engine is kinda funny.
With the bathtub shaped combustion chambers and the rather large distance
between
the piston at TDC and the flat of the head (which makes the squish zone), it
appears that the alpine is not only a weak squish engine, but that the
turbulance
that the compression imparts is not very directional.
Squish is important for improving thermal efficiency, but but then again so
is
materials selection (alloy) and surface finish (smooth), and cumbustion
chamber
shape (hemi VS wedge ect).
Today, stock auto engines run 10/1 compression on 92 octane fuel.
Pre-detonation can be caused from a whole slew of evils, where octane is the
typical band-aid.
For those building hypo alpine engines, you should probably consider that
the alpine engine is not a well engineered machine in these respects and
that
you will likely have to through octane at the beast to prevent detonation.
One thing I'd like to see some day, would be some alpine pop-up pistons
that would allow a nice holbay-like combustion chamber, with a reasonably
high compression ratio. Such a piston might produce a superior swirl
in the combustion chamber, and perhaps allow for lower octane requirements.
Jarrid
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