rule of thumb for calculating rear ratio/ TC stall from power band
12-08-2002, 09:29 AM
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Car: 1991 Corvette Coupe
Engine: L98
Transmission: 700R4/4L60 same trans different name
rule of thumb for calculating rear ratio/ TC stall from power band
???
ok, i wanna learn here, teach me
lets say an engine makes its peak torque at 3500 RPM
figure about 400 lb ft
we'll have a 25" diameter tire
4.10 rear
this rear end ratio would actually bring the powerband down to about 2200/2300 rpm am i correct?
so for this setup we would want about a 2100/2200 stall converter
these are my guesses, but i would like somebody to explain this to me better please so i can understand how to calculate appropriate rear end ration and TC stall speeds
thanx
ok, i wanna learn here, teach me
lets say an engine makes its peak torque at 3500 RPM
figure about 400 lb ft
we'll have a 25" diameter tire
4.10 rear
this rear end ratio would actually bring the powerband down to about 2200/2300 rpm am i correct?
so for this setup we would want about a 2100/2200 stall converter
these are my guesses, but i would like somebody to explain this to me better please so i can understand how to calculate appropriate rear end ration and TC stall speeds
thanx
12-08-2002, 10:44 AM
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Car: 99 Formula
Engine: LS1
Transmission: T56
Axle/Gears: 342
Maybe I'm confused, but the powerband of a motor can't be changed by a rear gear ratio.
The powerband is determined by the engine setup, cam/intake stuff like that.
The powerband is determined by the engine setup, cam/intake stuff like that.
12-08-2002, 10:51 AM
#3
Supreme Member
Sorry, non of that makes any sense.
The operation range of a motor can be guesstimated
by the .050* durtation spec of the camshaft.
More duration= higher powerband.
There are other things that affect this number range but cam duration is the biggie.
Next you have to approximate the horsepower of the motor and weight of the car. This will determine the MPH at the end of a quarter mile. Leave the et for just a minute.
you want to gear the car so that it reaches its MPH #
while reaching the rpm the peak horsepower occurs.
This can be approximated very closely based on head flow # size of the motor, cam duration.
Now that you've determined the rear gear needed
you can get the right stall converter. Again based on camshaft duration and cubic in . You want the converter to stall about 500/800 rpm below peak torque. so if the peak torque is at 4000 rpm then a 3300 3500 stall is right.
This is for setting up a car for quarter mile acceleration.
On the street you may fine that the gearing is too high
or the stall is too high and the tires can't handle this torque.
In that case you'll have to factor that into your final choice.
One thing to avoid is useing a high stall converter with a low # gear like 2.73. this is a mismatch for all but the lightest cars.
The motor will all ways be "on the converter" Not very responsive to drive.
Crane cams used to have a good chart for matching up rear gear, compression, stall etc with their cams based on .050" duration and cruiseing rpm @60mph . this chart is relevent to any other cam company too.
Wolverine Blue racer has a computer program that guides you through selecting the right cam based on other engine chassis inputs. It's called "CamSelect"
get it here http://www.jason.fletcher.net/tech/d.../downloads.htm
The operation range of a motor can be guesstimated
by the .050* durtation spec of the camshaft.
More duration= higher powerband.
There are other things that affect this number range but cam duration is the biggie.
Next you have to approximate the horsepower of the motor and weight of the car. This will determine the MPH at the end of a quarter mile. Leave the et for just a minute.
you want to gear the car so that it reaches its MPH #
while reaching the rpm the peak horsepower occurs.
This can be approximated very closely based on head flow # size of the motor, cam duration.
Now that you've determined the rear gear needed
you can get the right stall converter. Again based on camshaft duration and cubic in . You want the converter to stall about 500/800 rpm below peak torque. so if the peak torque is at 4000 rpm then a 3300 3500 stall is right.
This is for setting up a car for quarter mile acceleration.
On the street you may fine that the gearing is too high
or the stall is too high and the tires can't handle this torque.
In that case you'll have to factor that into your final choice.
One thing to avoid is useing a high stall converter with a low # gear like 2.73. this is a mismatch for all but the lightest cars.
The motor will all ways be "on the converter" Not very responsive to drive.
Crane cams used to have a good chart for matching up rear gear, compression, stall etc with their cams based on .050" duration and cruiseing rpm @60mph . this chart is relevent to any other cam company too.
Wolverine Blue racer has a computer program that guides you through selecting the right cam based on other engine chassis inputs. It's called "CamSelect"
get it here http://www.jason.fletcher.net/tech/d.../downloads.htm
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