Until this year, when the SCCA started making us use racing fuel, I used

93

octane
pump gas with no alcohol, and added cheap 30 weight motor oil. 7 oz. to

5

gallons of fuel, to kill off as much octane as I could. Daryl Drummond

says

we lose 8HP at the top just by using the high octane fuel.

Lynn E Hanover
lehanover@aol.com

That is very interesting.

Paul Lamar

Paul Yaw wrote:

Hey Paul,

Drummond speaks the truth.  He is referring to a 9,500 rpm GT motor I'm
sure, but it is true.  Octane and burn rate are not the same thing, but
GENERALLY speaking a higher octane fuel will burn slower.  Good racing gas
will normally have a good burn rate for its octane, but the octane is always
much more than we need, and the burn rate still ends up being slower than 87
octane pump gas.  VP has a good handle on this, and the fuel they recommend
for high rpm two strokes makes very good power.  Trick isn't too bad either,
but Unocal 76 is REALLY slow.  You can put a ton of advance in it and it
still loses power and lights up  the headers.  Plain old Chevron 87 makes
the best power naturally aspirated.

The power loss Drummond is referring to increases with rpm.  It's hard to
get everything burned in time.  Keeping the fire in the motor instead of
wasting it in the pipes really pays off.

I don't buy the crap about premix making better power because of the reduced
octane.  Less friction, yes.  That and how well the seals fit the chamber.
If you don't premix, the seals get REALLY hot.  If you are running one piece
carbon seals, they jam between the side housings and bow in the middle.  If
you are running two or three piece cast iron seals the corner piece moves
out of the way to allow for the expansion, creating a big leakage path.  In
either instance, you make less power because the motor doesn't seal as well.
You can turn the octane to nothing, but if the fuel does not burn faster you
will not make any more power. Burn rate is the key, not octane.

The other Paul

 
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