[wagglebee]

That’s why we were examining “energy content”. This should be a good indicator of how far you can travel, unless a gas vs natgas engine has a vastly different efficiency factor.

That's the big question for me. I'm more interested in how far I can go per dollar than BTUs.

For instance, yesterday I paid $2.57 to fill up my tank and I know that I'm getting just over 25 MPG, so it will cost me about $0.10 in gas per mile. What's that cost with NG?

[MrB]

And that’s what I’m/we’re saying - if the efficiency of the two engines is the same, you can take the ratios of BTUs per dollar and translate that directly to ratios of miles per dollar.

[thackney]

I know that I'm getting just over 25 MPG

You won't get the same miles per gallon. And for an individual, my opinion, you don't want LNG. So for CNG, you won't even measure it gallons.

It is reasonable to get the energy efficiency in an internal combustion engine. So same energy in should result in the same energy out, distance traveled.

You can apply the ratio of energy per dollar to miles per dollar and have a reasonable comparison.