Quote:
Originally Posted by M_a_t_t
It's called the unicorn corral. How are you calculating fuel mileage based on rpm and speed?
|
Matt,
I do not know how he is calculating his figures.
In overdrive at 70MPH per my BSFC Chart I should expect 0.405 lb/bhp-hr at WOT. Using that as an approximation for other throttle positions, 5-7 MPG would imply burning 14 to 10 gallons an hour, or about 98 to 70 pounds of fuel. Given the BSFC, that implies it would take 241.9 to 172 bhp to cruise down the road. Anyone familiar with the naturally aspirated 6.5L would know that is more HP than the engine makes total, much less at 2200rpms. I would basically have to install two engines to burn that much fuel in that time frame at that RPM at wide open throttle the entire time. This means that no GM vehicle ever produced with a 6.5L non-turbo engine would have ever driven 70MPH on flat ground, regardless of gearing as the road load would be to high.
Checking my numbers, 70 MPH at 24 MPG (which I never claimed, but for arguments sake) is 2.91 gallons, 20.416 lbs diesel, implying 50.41 bhp assuming constant bsfc, or a bit under 1/3 throttle to maintain speed on level ground. In real life efficiency is slightly less at fueling less than WOT, my 70MPH stretches would be lower MPG than the average, but in general that level of road load seems about right to me.