Re: OT: Real world Diesel Mileage?

Posted by Bob M on August 17, 2005 at 07:24:00 from (151.190.254.107):

In Reply to: Re: OT: Real world Diesel Mileage? posted by Hugh Mackay on August 16, 2005 at 18:39:41:

Indeed Hugh! I was thinking a max legal GCW combination with a 14L engine. Obviously a 466 and a lighter load will do much better.

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You and Rod F have both touched on the major reason the current crop of diesel pickups give the fuel mileage figures they do - Weight to HP ratio. Consider this:

A typical P/U might weigh 5,500# and have 250 HP – that’s about 22 lb per engine HP. On the other hand for an 82,000# tractor trailer with “typical” 450 HP engine it works out around 182 lb/HP. That’s a substantial difference!

NOW if you were to build a pickup with a weight to HP ratio on par with the big rig it would have about 30 HP under the hood (and also a 10 or 13 speed manual transmission). This theortical outfit would probably be capable of 40+ mpg. But it’s unlikely few people would accept the sluggish performance and the constant manual gear changing required.

(Or look at it the other way: The OTR truck would require whopping 3,725 HP engine… ….you’re talking railroad locomotive prime mover here….to equal the weight/HP ratio of the typical diesel pickup. Think THAT outfit would give 15 mpg?!!)

The bottom line is it’s a tradeoff: Performance vs economy. The light truck market has demanded performance over economy, and the car companies have responded.

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Incidentally you are right about the pulling ability of the 250 with a Super M on the flatbed Hugh. It walks it up hills almost as easily 1,500 RPM same it as at 2,500 - only difference is less noise!

Follow Ups:

• Re: OT: Real world Diesel Mileage? Hugh MacKay 13:14:55 08/17/05 (0)

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