will 3.91 gears work for 1/8th mile track
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demon_408
Well-Known Member
is it a street car and what engine you runnin
mguner
How many is too many?
better than 2.76 or 2.94.... ;)
The rear axle ratio works in concert with the tire size (diameter) to determine what ratio you need for any application.
For example, my car is EXPECTED to run about 102 mph in 1,000 feet (we don't have any quarter-mile drag strips near to where I live.)
I have a friend who offered me a "deal" on a 4.30 rear gearset.
I did the math and found out that if I installed that rear, I'd be turning about 300-400 rpms more than I wanted to at 102 mph, so I had to say "no." Luckily, I ound a 4.10 that filled the bill, nicely.
If I was only going to run 1/8th mile strips, the 4.30 would have been great!!!
I can't imagine that your car is so fast that it would over-rev at the eighth-mile finish line with a 3.91 gear.
Let's say you have a stock 340 with headers and some 28"-tall tires.
That car will probably run about 82 mph in the eighth. With a 3.91 gear and accounting for 4-percent converter slip, you'd be turning about 4,000 rpm at the finish line in third gear. That's with an automatic. A stick would be a little slower rpm, but not much, since it would likely be going a little faster.
Change to a 26" tire and your finish-line rpms would increase to about 4,300.
That's not a bad setup that you can drive on the street.
Put it this way; it beats a 3.23 or 3.55 probably by a couple of car lengths.
That's my best guess. Somebody else will probably have a lot more accurate information.
Good luck with the gears!!!
Bill
For example, my car is EXPECTED to run about 102 mph in 1,000 feet (we don't have any quarter-mile drag strips near to where I live.)
I have a friend who offered me a "deal" on a 4.30 rear gearset.
I did the math and found out that if I installed that rear, I'd be turning about 300-400 rpms more than I wanted to at 102 mph, so I had to say "no." Luckily, I ound a 4.10 that filled the bill, nicely.
If I was only going to run 1/8th mile strips, the 4.30 would have been great!!!
I can't imagine that your car is so fast that it would over-rev at the eighth-mile finish line with a 3.91 gear.
Let's say you have a stock 340 with headers and some 28"-tall tires.
That car will probably run about 82 mph in the eighth. With a 3.91 gear and accounting for 4-percent converter slip, you'd be turning about 4,000 rpm at the finish line in third gear. That's with an automatic. A stick would be a little slower rpm, but not much, since it would likely be going a little faster.
Change to a 26" tire and your finish-line rpms would increase to about 4,300.
That's not a bad setup that you can drive on the street.
Put it this way; it beats a 3.23 or 3.55 probably by a couple of car lengths.
That's my best guess. Somebody else will probably have a lot more accurate information.
Good luck with the gears!!!
Bill
Petzschler
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5.13
440superduster
Well-Known Member
I run 3.91 and shift at 5500 RPM and only use first two gears at 95 MPH
daredevil
Well-Known Member
right i was gonna say 4.56 0r 88. beats hell out of a 3.23 and you could still run the street
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