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Originally Posted by t walgamuth
an excellent 240 with a stock 369 rear end will be lucky to break 30 mpg running 75.
my 240 with a fresh 300 engine and the 307 rear end got 30 at 75 mph consistantly.
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Just for the record, you've got two different engines with two different axle ratios.......with "similar" fuel economy. But, we really don't know the exact fuel economy because you are just estimating the economy.............as usual.
The axle ratio certainly didn't give you a 20% increase in fuel economy for that swap........did it?
By your own calculations, if the 3.69 was "lucky to break 30 mpg", then the 3.07 should be giving you over 35 mpg.......but it never even came close to that figure.
Naturally, you will probably blame the fact that you didn't get the 20% fuel economy benefit due to the larger engine. But, it's highly unlikely that the 300 gives up 20% fuel economy to the 240 in the same chassis.