[MetroMPG]

Note: Phil Knox has given me permission to repost items that he originally posted at MaxMPG. Here's another. - Darin

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Hellow all. As I continue data reduction on T-100 roadtest results, Ive run into something I want to throw out now rather than later.

As I combed my library form aero-related literature to help substantiate my findings, I was caught by surprise by a paper submitted to the Society of Automotive Engineers SAE. Heres the crux of it. When you streamline, you reduce the engine load which in itself is not a bad thing, infact its the whole idea.

The catch is that as you continue to lower drag,you continue to lower the load, the throttle body begins to close down, volumetric efficiency begins to suffer and the engines brake specific fuel consumption ( the amount of fuel the engine uses to produce each horsepower in an hour ) actually goes up.

By lowering the numerical ratio of the final drive you can increases the load on the engine and move its brake specific fuel consumption back up its engine "map" into more efficient territory.

Here's the big rub! If you don't do the gear-matching, you can loose up to 40% of the streamlining benefit.

This may explain why the T-100 was still getting 32-mpg at 75-mph. It takes over 20% more horsepower to go 75 than it does to go 70. From the increase from 25 to 32mpg I calculated that the drag coefficient would have to be on the order of Cd 0.25, a 28% reduction from Cd 0.44. It's quite possible that the blister and boattail have reduced the drag although is not showing as might be expected because of this conundrum.Drat!!!

I don't know any powertrain guys. All my phone numbers at GM are no good now.I once could just call up Glen Scharf at the aero lab and bounce numbers off him. If anybody knows any real aerodynamicists we could noodle with I'd like to know. I pulled another 32-mpg this last weekend and I hope the T-100 is not stuck there.

Since Toyota does not offer a range of differential gears as the BIG-THREE, I'd be forced to try and put some enormous tires on the back of the truck and then "lower" it to get the standard body rake back.I'll keep scratching my head on this one.

Since some of you are actively modifying your vehicles,I'd like every one of you see the highest possible returns on your investments. I feel personally responsible for some of your efforts,don't want to screw the pooch and have you going down a deadend road. More soon, Phil.