Fuel Consumption Graph

[joetiii]

I'm curious about the fuel consumption graph in my 69 owners manual. It appears as a dome shaped curve which to me shows that fuel consumption is similar at 2000 rpm as it is at 5000 rpm.

Am I reading this correct?

What is the significance?

[0687]

hi,

when looking at the fuel consumption graph, note that the units are in lbs/hp-hr or g/kw-hr and are taken at WOT, which means that, with WOT, you are consuming roughly the same fuel weight per hp produced at 2000 as at 5000. The key is per hp produced - obviously a lot more at 5 than 2. Hope this helps.

[joetiii]

OK, that makes sense. But what is the significance?

[0687]

not sure if there is any real significance other than it's relation to the T and S curves, where you can see differences in the amounts in the flat part of the curves as well as the slope of the curves toward the higher rev range. There it's obvious the S retains it's volumetric efficiency much better than the E and T, but at the expense of lower VE (and higher consumption) at the lower speed ranges. It's probably just the extremely thorough job the Porsche factory did in documenting all performance aspects of their vehicles during that time frame. I don't think there have been many if any OEM's that published the brake specific fuel consumption numbers of their engines since - anyone know of any done now?

Chip