Heat engine efficiency calculation

[smokingwheels]

Homework Statement

I have an spark ignited engine and after modifying it I have improved the efficiency.

What is its efficiency at idle?
Fuel consumption at 650 rpm = 9.8 cc/min measured
Fuel consumption at 750 rpm for normal engine = 25-30 cc/min estimated for about 5 HP
Normal engine efficiency = 30% unsure at idle
Corrected my engine to 750 rpm = 11.385 cc/min used turbocalc program
Friction and compression losses = 0.5 HP just going on what a starter motor strength

Homework Equations

30 cc = 30% 11.385cc = ?
I was not much good at school

The Attempt at a Solution

30cc/min / 11.385cc/min= 2.635
2.635 * 30% = 79% efficiency at idle

25cc/min / 11.385cc/min= 2.195
2.195 * 30% = 65% efficiency at idle

So as good or better than a diesel but Maybe could possibly double check the carnot law.

I can say when you raise the compression of my engine it reduces combustion losses.
causing less wasted heat in the combustion chamber, I can probably push the compression ratio further until the limit of self ignition my current engine is a mild version of what I had.

I had a high compression engine before and spark plugs would carbon up in 3-4 days, I then lowered the compression and the plugs lasted for 2 months.
I have the plugs on youtube if you would like to see.

I have video of my fuel consumption test online you do not think its possible

 

[AvroArrow]

So my engine is at least as good or better than a standard diesel engine,the efficiency at idle is about 79-65%.