> Posted for "Al Gietzen" <alventures@email.msn.com>:
>
>
> Tracy wrote:
> ran well below best power mixture in the
> Sun 100 race (16.5 GPH) and stayed ahead of half the 180 HP RVs.
>
> BTW; Tracy, what EGTs were you showing at that point.  What
> do you get at best power?
>
> Al
>
> EGT during race was around 1650 (LOP).  Best
> power is around 1750.
>
> Tracy
>
> Hum-m-m; based on my results, these EGTs seem a bit on the high side.  I
> found best power EGTs (WOT) about as follows: 5000 rpm - 1560, 6000 rpm -
> 1630.  What does it mean?

>Al

Good question Al, here's my best guess(es).
Ignition advance affects EGT more than expected so that could be a factor.
Note that EGT continues to fall when advancing the ignition timing past the
point of best power but this probably is not the case here.   EGT probe
placement could also account for some difference.   My CR is slightly higher
but this causes lower EGT, not higher.  Maybe its my tuned intake manifold
giving higher effective manifold pressures.  EGT does go up at higher
manifold pressure, all else being equal.  My readings were at WOT near SL.

Another factor may be my stinginess with the mixture control.  I think you
are correct that *absolute best* power is ~ 150 deg F rich of peak.  I don't
usually push it that far because the power increase past about 50 deg is
very small and unless it is a war emergency situation, the increase in power
is not worth the additional fuel burn.  The figures I gave reflect this.
Looking back over my notes I see that 1750 is only about 20 - 25 degrees
below peak.

Thanks for passing along the other dyno data.  It is amazingly close to the
figures I calculated.  My economy cruise BSFC  number was .46 - .47.

Tracy