This is for the vaunted Lycoming O-360-A4M
or O-360-A4A 180 HP running at peak EGT.
No longer allowed by Lycoming BTW.

Compression ratio is 8.5 which sounds a bit
marginal for auto fuel and such big cylinders.
The bore is 5.125 inches in dia. for $%#@^ sakes!
The book says use 100LL.

Piper did not publish BSFC directly in this
book so we have to derive it from this chart.

The endurance with 48 usable gallons at 2000 feet
is  7.4 hours at 55% power. That is 6.49 gallons per hour.
6.49 gallons times 6.1 pounds per gallon is 39.59 pounds
of fuel per hour. 55% of 180 HP is 99 HP.
39.59/99 = .40 BSFC. Excellent.

This is a carb engine with a bit of continuos carb heat by
virtue of the fact the intake manifold runs through the oil 
pan. Must have good mixture distribution. The runners are 
also equal length unlike the runners on my O-470.

At 65% max HP or 117 HP the engine burns 7.9 gallons per
hour or 48 pounds per hour. The BSFC is then .41.
At 75% power (max power level allowed for leaning of old Lyc engines)
The burn is 9.1 gallons per hour or 55 pounds per hour.
HP is 135 and BSFC is again .41. 

Outstanding engine for low fuel consumption. Probably due to 
low friction as the engine has few cylinders for large displacement. 
Fours always do well when it comes to fuel economy.

Paul Lamar
 
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