[pgfpro]

Great question and I've tested this on my Talon.

Ethanol takes about 40-50% more fuel for the same power. So, you will use more of it then petrol at the same A/F ratio equivalent.

Even increasing the engines compression will give you a very limited increase in efficiency.

The only way to increase FE at 7psi is to run a lean-burn engine.

On my setup I can run 7psi at 20:1 A/F ratio on petrol.

At 7psi with a 20:1 A/F at a BSFC of .45 lb/hr vs 7psi with a 12.5 A/F ratio at a BSFC of .55 the gain in torque is around 12 ft/lbs. The amount of fuel saved is 18 lbs/hr. around 3 gallons with a gain in torque of 12 ft/lbs. This is a petrol-to-petrol comparison at 3500rpm loaded on a 2.0L. engine with a total 100 ft/lbs of torque at the BSFC of .45 lbs/hr.

So, with the above example you could lower the boost to say 6psi and still have the same total amount of torque and increase the FE.

With a lean burn engine at this low rpm you have to increase tumble and swirl due to the low velocity of the air and a bunch of other modifications to make this work.

Forgot to add this as you can see its 100 ft/lbs of torque total so this would be used only to climb a hill or getting up to speed on a on ramp etc.