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That's pretty interesting. My diesel is pre cat era, but it also has a computer, first era of the power stroke. Of my understanding, the computer just takes the TPS signal and temp signal, and injects the amount of fuel it thinks is right. There's no O2 sensor or any kind of feed back system that I'm aware of. The newer trucks 99+ had a exhaust pressure sensor before the turbo if I remember right, or maybe it was a boost sensor. They also have a bigger turbo with waste gate, mine has no waste gate, all of the air gets forced into the engine. I don't recall if there's a cat on those 99+ trucks or not. I suspect there isn't an O2 sensor on them if there's no cat since diesel doesn't really care too much about AFR, as long as there's enough O2 in the air and enough pressure (heat technically), it will combust. Maybe big rigs are designed differently than consumer trucks though.
I haven't gotten too close to too many semi trucks, but I suspect most are still purely diesel powered, I never see a semi getting filled up for CNG or propane, I don't think the truck stock gas stations even have those fuels.
Anyway, if under the same throttle the engine used to make 550 ft/lbs of torque, and with propane it jumped up to 630 ft/lbs (floored max power dyno run I'm assuming from the vid, my stock engine is rated 450 ft/lbs), then that's + 80 ft/lbs, or a 12.7% increase in power. I suspect he's running 20% propane so I guess I need to check out the energy content of each fuel and see how much of a gain it really is based on his numbers.
Probably not the best figures to use, but I'll base it on BTU of energy per fuel.
Diesel 1 gal = 137,381 btu
Propane 1 gal = 91,502 btu
So propane has 33% less energy content than diesel. Diesel alone in this math works out to being 250 btu per ft-lb. So if it was possible to run a diesel 100% on propane, it should make roughly 366 fb-lbs, of course it will burn differently and more completely so not a perfect measurement. Interestingly enough.... 20% of 366 is 73.2 fb-lbs, almost a perfect match to the power difference of pure diesel vs diesel + propane. Maybe I just debunked this concept with this shotty math lol. Either case, propane is cheaper than diesel, so using 20% of a fuel that costs less should in theory save money, but the extra time for fill up and the cost to add the second fuel system doesn't seem worth it.
I wonder if those mpg claims originated from IDI engines.
Either case, I know my math isn't a perfect way of doing that, but should be ball park figure close enough (I don't know how to do it in a better way off the top of my head).
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