brian, you take my words and twist them around to make it sound as if i said the opposite of what i actually said. is this your intention?

and while i am admittedly a generalist, in college i had to do structural calculations, using lots of algebra, etc. we learned to round to three significant figures on all calculations. this type of process is engineering. i did very well with it, thank you.

as for estimating, what does it matter to this discussion if a 21% gear ratio change resulted in 17% better economy or 18% better economy. i said that the benefit is very close to the gear change. not exactly the same.

i know exactly how to measure fuel economy. i keep track of each fill and i keep it to the nearest tenth of a gallon. i use full tanks and i fill usually in the same station at the same pump. i always let the pump shut itself off. i don't estimate it. i calculate the mileage with the calculator on my cell phone.

the 240 with the 20% larger 300 engine and the 307 axle ratio consistantly got 30 mpg running at my usual 75 mph.

the 240 with the 240 engine and the 369 gears (20% lower gearing) is lucky to hit 30 under similar conditions ( i actually run only 72 in a stock 240).

the bottom line is that the higher gear equalized the increased displacement and made the fuel economy equal. in other words both cars pump about the same amount of air through the engine per mile traveled.

now this wouldnt work if both cars began with their gearing optomized to their engines for maximum fuel economy. they are heavily compromised from the factory to give excellent all around service. in my example the gear change worked as it worked. in another situation it may not work. on newer cars which are much more optomized for economy i am sure these results would not be possible.

i checked the odometers and speedos on both cars against the highway markers. i know how to do this.

if you didnt get as good a results with your rear end swap, i have no explanation for that.

and while you may have kept strict scientific records at chrysler, i bet you didnt have those controlled conditions when you checked you own 247 gear swap, did you.

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.