Date registered: Aug 2006
Vehicle: 85 300D
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Thanks for the technical info Jon, I to am an engineer, although a side branch of mechanical (I'm a marine engineer).
The otto cycle (the gasoline's constant volume cycle) is actually MORE efficient than a diesel sycle (constant pressure) WITH THE SAME COMPRESSION RATIO. However, as Jon said, diesel's run far higher ratios. The 617 in my 85 300D and my 93 7.3L International Harvestor have a 21.5:1 compression ratio. You'll rarley see above an 11:1 compression ratio on a gasser, and that car either runs racing fuel or high test so it won't ping.
An yes, comparing a 300hp gasser and a 97hp diesel is silly. However, my 93 F-250 extra cab got 20mpg before my injection pump started wearing out (got some bad injectors too). My buddy with the same year gasser (I think a 302, but maybe a 351) and a 5 speed tranny with the same rear end got 8-10 mpg, and my truck is an extra cab. That 351 can't be more than 230hp, and my truck had 185hp. That's a fairly close apples to apples comparisson of diesel efficiency. And you should have seen that thing try to tow. I thought it was going to die towing a 13,000lb bob cat and trailer where my naturally aspired engine would pull the hill at the same speed and less stress.
Also, one of my professors told me once that diesel is driven up over economics. Not only is it driven up since people have been buying more diesel's (supply and demand), but also, we crack our crude oils in a difficult way. We crack it to get more gasoline, and that results in below par diesel (compared to Europe), and since there is less supply, the price goes up. Least that's what we were told in class.
'85 300D. 225,000 miles and counting again! AMG Pentas, Euros/clear corners, VDO Boost/EGT guages in center vents, A/W IC in progress, Liberty VNT turbo soon.
'93 Ford F-250 7.3L IDI N/A 217,000 and still counting, it's gonna rot around that nice engine
'64 Ford Falcon Futura hardtop 2 door with a '68 302... not grannies old 'Coon