What is the highest compression ratio that E85 is able to run at without undue harm? What are the chances that the automotive manufacturers will make a car that can only run on E85, and gain power by using a lighter engine of smaller displacement?

The maximum CR for E85 depends on so many factors(ball valve), its probably not worth listing them all.

Regardless, an engine that is designed to run solely on E85 could have a higher CR than a felexfule engine.  We have to remember though the increased octane rating of E85 will never make up for the reduced energy density.

For use in my next posting

Adiabatic compression:
P1V1k=P2V2k

Gas Law:
P1V1÷T1=P2V2÷T2

Divide the first equation by the second:
T1V1(k-1)=T2V2(k-1)

Regroup temperatures and volumes:
T1÷T2=(V2÷V1)(k-1)

Move powers to other side:
(T1÷T2)1÷(k-1)=V2÷V1

I don't really like all this gamma or k stuff - the ratio of the specific heats, so let me simplify it.

Cv is the number of degrees of freedom in the gas, and Cp is two more. So k=(dof+2)/dof and k-1=2/dof. So 1÷(k-1) = dof/2. Before combustion air molecules don't reach the sort of temperatures needed to make them vibrate, so the number of degrees of freedom is say 5 and power is therefore 5/2.

Now if state 1 is autoignition and state 2 is the start of compression with ambient air let's write the equation again.

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