Joined
·
1,136 Posts
Here's the formula to calculate engine RPM:
RPM=(MPH x Rear Ratio x 336 x Trans High Gear ratio) / (Tire Dia inches x Torque Conv Efficiency)
Your case:
Assume 70 MPH Speed
Rear Ratio 4.56:1
Trans OD ratio .70:1
Tire dia 28"
Torque converter efficiency 1 because lock up torque converter. Non lock up is about .9 or .95 efficiency.
Plugging in the numbers, your engine will be spinning 2681 RPM at 70 MPH
Obviously if you're not running a lock up torque converter and you're OD ratio is something other than .70:1 the engine RPM number will change.
Plugging in 55_327 numbers and assuming 28" dia tires, his engine was spinning 3830 RPM at 70 MPH. Big difference. He also probably had tires smaller than 28" which would make it scream even more. Let's assume a 25" tire. That would make his engine spin 4290 RPM at 70 MPH. Not a good highway gear at all.
RPM=(MPH x Rear Ratio x 336 x Trans High Gear ratio) / (Tire Dia inches x Torque Conv Efficiency)
Your case:
Assume 70 MPH Speed
Rear Ratio 4.56:1
Trans OD ratio .70:1
Tire dia 28"
Torque converter efficiency 1 because lock up torque converter. Non lock up is about .9 or .95 efficiency.
Plugging in the numbers, your engine will be spinning 2681 RPM at 70 MPH
Obviously if you're not running a lock up torque converter and you're OD ratio is something other than .70:1 the engine RPM number will change.
Plugging in 55_327 numbers and assuming 28" dia tires, his engine was spinning 3830 RPM at 70 MPH. Big difference. He also probably had tires smaller than 28" which would make it scream even more. Let's assume a 25" tire. That would make his engine spin 4290 RPM at 70 MPH. Not a good highway gear at all.
