6.5 TD GM pickup - 30mpg?

[jpgmtech]

Hey check out the Bonneville speed racer that Bill Heath built.

maxxTORQUE | THE Magazine of the GM Diesel Community

Claims he can achieve 30mpg at 70mph. I think it is feasible.

[Big Dave]

I think he can do it. Chevy trucks are light by pickup standards. The 6.5 is highly under-rated (although it really does not compete against the Cummins or Powerstroke). Especially if equipped with 6.2 pre-combustion chambers.

I didn't get a good read of the truck's configuration.70 MPH and 2,200 RPM in third gear indicates the very low axle ratio one would expect of a Bonneville car. Probably a T-56 manual. One would expect a nice, slick belly pan on a Bonneville vehicle.

There are stories out of Detroit where in the 80s, A Suburban was fitted up with a 6.2 NA, a 700R4 transmission, and 2.73 gears and was good for 30 MPG. It would not out-accelerate a Benz 240D.

One could go one of two ways with a truck of this vintage. Either a 6.5 GM or a 4BT3.9 Cummins. They weigh about the same and make about the same nominal power. The Cummins has more potential (it is a 12 valve Cummin with two cylinders missing) but the GM is probably smotther. Both are fairly easy to come by.

[jpgmtech]

He is running a stock 4L80e automatic tranny and a Ford 9" rear end for quicker gear swaps.

Got my gears turning... for what I need a pickup for...

[JQmile]

30mpg easy I'd say.....I can get 23mpg with my 89 Dodge at 65mph, and it has a 1:1 high gear! Should be getting an overdrive soon and hope to break 30 myself

[Big Dave]

I wonder, is this guy simply getting 30 MPG as a "snapshot" from a scangauge or is this hand-calculated over a genera duty circuit where he limits his top speed to 70 MPH?

[my first gmc]

I wish GM didn't scrap there 4.5l d-max. Could be getting those kind of mpgs of of half tons.

[jpgmtech]

Originally Posted by Big Dave

I wonder, is this guy simply getting 30 MPG as a "snapshot" from a scangauge or is this hand-calculated over a genera duty circuit where he limits his top speed to 70 MPH?

He's a techie kind of guy if you read his engine build. Being involved in tuning, and installing higher flow-rate injectors, I think he is pretty aware that he can't trust a generic display like scangauge without calibration.

My gut feeling: the number was hand calculated from some freeway driving meant to run-in the engine. And he probably varies his speed and is giving a rough average of 70mph.

I write for the same magazine - and I wrote an article on the "upcoming" 4.5 Dmax in the last issue. Sad to see it axed temporarily - some good engineering in it and I think 30mpg would be easy.