Small Engines (Lawn Mowers, etc.): More power from small engine., degree pitch, go karting

Question
QUESTION: I put a 10HP engine on my hovercraft, Briggs (205332-0537)The engine weighs about 63pds. I have to keep the weight down but I want more power to turn a 36 inch propeller with 18 degree pitch. Would shaving the head be the easiest way to gain power, if so how much would I have to shave. If not what else could I do. This is a new engine.

ANSWER: If you have a tachometer check the engine RPM.  You can safely run the engine at 3600 RPM.

As for shaving the head, you can increase power but there are no specifications available to indicate how much material can be removed.  Most of the time shaving the head is a trial and error effort.  The main parts to consider when shaving the head is the valve to head clearance.  Removing too much material could allow the valves to hit the top of the head causing severe engine damage.  Many high performace engine builder use clay to measure the clearance while machining the head.  

Do you have accesss to a mill and spare heads?
Let me know.
Eric

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QUESTION: I do not have access to a mill and spare heads? Also what about higher octane fuel, like 100 octane racing fuel? Would that help or hurt?


Answer
100 octance will not hurt the engine is used once in a while.  Go cart racers have temperature gauges that are inserted between the sparkplug and head to monitor the head temperature.

I would check the go karting sites and price a temperature meter to monitor the head temp.  Take a baseline reading using 87-91 oct fuel.  Record the baseline temp.

Change fuel to the 100 oct and observe the temperature.  Compare the recorded 87-91 oct to the 100 oct.

A cheaper method may be to use and infrared non-contact thermometer to measure the temperature.

I wish I had a mill to play with!  I start by shaving .010 off a head, use some clay installed under the head, istall headgasket, torque head bolts then rotate engine several times.  Remove head, measure the clay to determine clearance and try to measure the head gasket squish.  This could get expensive due to the newer head gasket design.  In the old days the head gaskets could be re-used 2-3 times before they had to be replaced.  Did I mention I wish I had access to a mill?

Have you checked the racing go-kart websites for hp tips.  Most of the karting community used to use 5 hp Briggs and they had all kinds of power mods from alcohal, to superchargers to turbos.  Neat stuff but expensive to tinker with.

Eric