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revving high?
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Author:  Dustenn89 [ Tue Mar 28, 2006 2:16 pm ]
Post subject:  revving high?
since i rebuilt my engine and dropped it in my '74 dart swinger it seems to rev higher than it did

going about 70 i am revving about 3500 and if i accelerate into 75 its about 4000 and shakes a whole lot

no rearend gears have been changed and trans was rebuilt before the engine so i know thats not it

also i have no kickdown on it right now

would that have anything to do with it

help please

dustin
Author:  SlantSixDan [ Tue Mar 28, 2006 2:29 pm ]
Post subject:  Re: revving high?
Quote:
going about 70 i am revving about 3500 and if i accelerate into 75 its about 4000 and shakes a whole lot
Let's do some maths. Your '74 with automatic trans would've come with 2.76 final-drive gears, and—just a guess—195/75R14 tires.

A 195/75R14 tire has a nominal diameter of 25.52 inches.

Therefore, its circumference is 80.17 inches.

There are 63,360 inches in a mile.

Therefore, tires of that size make 790 revolutions per mile.

Multiply by 2.76 rear axle ratio to get 2181 driveshaft revolutions per mile, therefore engine revolutions per mile in third gear. 60mph = 1 mile per minute, therefore 2181 RPM is your engine speed in 3rd gear at 60mph.

At 70mph in 3rd gear, your engine speed should be 2545 rpm.

At 75, it should be 2726 rpm.

The gear ratio of 2nd gear in your transmission is 1.45:1

In 2nd gear, therefore, assuming I'm guessing right about your tire size and rear axle ratio, your engine speeds would be as follows:

60mph: 3162 rpm
70mph: 3690 rpm
75mph: 3953 rpm

Looks like I guessed right about your tires. Also looks like I guessed right about your trans not shifting out of 2nd gear.

Driving without a kickdown is not okay unless you like buying multiple transmission rebuilds. Fix it all the way fixed.
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