What rpm does 3:91 gears give at the end of the 1/4 mile

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PG Duster

PG Duster

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I have a 360 magnum in a 1974 Duster, With 28.2” tall tires and a tight 3500 stall converter, 727 trans with 3:91 gears. What trap RPM will I see at the end of the quarter mile?
 
  • How tall are the rear tires ???
  • Automatic or manual transmission ???
  • If automatic, how much slippage in the converter ???
 
318willrun said:
  • How tall are the rear tires ???
  • Automatic or manual transmission ???
  • If automatic, how much slippage in the converter ???
Click to expand...
275/60 Mickey Thompson drag radials 28.2” tall, trans will be a 727 auto trans. I don’t know the percent of converter slippage, I bought a street fighter TCI-142200 3000-3500 stall speed converter.
 
PG Duster said:
I have a 360 magnum in a 1974 Duster, With 28.2” tall tires and a tight 3500 stall converter, 727 trans with 3:91 gears. What trap RPM will I see at the end of the quarter mile?
Click to expand...


It depends on how much power you have. For example if you have 380 hp, a 3550 pound car with you in it, that gear and tire will get you about 5500 rpm. If you have 450 hp then you would be at 6100-6200. Unless you have well over 400 hp you don’t have near enough gear or too tall a tire. That will make the converter very inefficient. A 1 inch change in tire diameter can make a converter much more efficient.
 
PG Duster said:
275/60 Mickey Thompson drag radials 28.2” tall, trans will be a 727 auto trans. I don’t know the percent of converter slippage, I bought a street fighter TCI-142200 3000-3500 stall speed converter.
Click to expand...
I see you edited your original post. Well, do you plan on your car doing 95 mph or 110 mph when you cross the line ??? If your car is a slug, your RPM's will obviously be lower. So.... lets say it this way.....
100 mph will be about 4700 RPM's with ZERO slippage of your converter. I promise you that TCI converter will be slipping plenty, how much I don't know. But at 100 mph you'll be over 5k rpms for sure.
 
Google Wallace racing calculator and others
Assume 10 percent converter slippage if you have a 3500 {ball Park}
My 70 Dart 3.91 gears, 24.5 tires, 1 to 1 trans ratio, 500 hp, 3500 converter with10 slippage should cross the line
6200-6300 which is as far as im willing to turn my 360 mag with stock heads, crank, block, rods , pistons
 
my old yellow dart with 3.91 gear, 904 trans, dynamic 9.5" converter and 26" tires used to go through the traps at about 5900 rpm at 108 mph
 
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Rat Bastid said:
It depends on how much power you have. For example if you have 380 hp, a 3550 pound car with you in it, that gear and tire will get you about 5500 rpm. If you have 450 hp then you would be at 6100-6200. Unless you have well over 400 hp you don’t have near enough gear or too tall a tire. That will make the converter very inefficient. A 1 inch change in tire diameter can make a converter much more efficient.
Click to expand...
With me in the car about you hit the weight right on the money and about 350 to 380 I’m guessing on the conservative side of HP. Are you saying I may need about a 27” tire.
 
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What is your anticipated MPH at end of 1/4

115 around 5900/6000 RPMMPH with your figures
 
Rat Bastid said:
It depends on how much power you have. For example if you have 380 hp, a 3550 pound car with you in it, that gear and tire will get you about 5500 rpm. If you have 450 hp then you would be at 6100-6200. Unless you have well over 400 hp you don’t have near enough gear or too tall a tire. That will make the converter very inefficient. A 1 inch change in tire diameter can make a converter much more efficient.
Click to expand...
Dangit ratamous, you got another one right. What are we gonna do with you?
 
Also on a stock bottom end 360 Magnum, what is the max safe rpm on that engine.
 
PG Duster said:
Also on a stock bottom end 360 Magnum, what is the max safe rpm on that engine.
Click to expand...
Puke a rod out the side, build it back and back her down about 250 RPM.

Seriously, probably like 5800 for an absolute max. I'm a little conservative.
 
My combo is geared for 93=6160 in Second-over with 3.55s; for the Eighth mile, which is mathematically same as 106@7000
Oh you said 3.91s;
Well then, the gearing will take it to;
93=6340 in Third with 3.91s, which would be 106@5160 in Fourth or 5636 in Third-over.
But If I had enough power to go 115; 3.91s would do it at 5600 in Fourth or 6120 in Third over.

The point is, you said;
PG Duster said:
I have a 360 magnum in a 1974 Duster, With 28.2” tall tires and a tight 3500 stall converter, 727 trans with 3:91 gears. What trap RPM will I see at the end of the quarter mile?
Click to expand...
which by itself has no answer.
 
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