the stock converter and rear gear ratio are designed to maximize the use of the 1200rpm-4500rpm stock power curve , and give good mileage and low emissions with very little thought of maximizing the peak power.
this limits you to selecting cams in a range of about 195-218 degrees at .050 lift and below to match your gearing and stall speed
changing the cars cam is done to increase the engines effective, volumetric efficiency and resulting power band, upwards at the cost of low rpm torque in exchange for more effective breathing and power in the 2000-6400rpm power band
a 2800rpm-3000rpm stall converter and 3.54:1-3.73:1 rear gear allows you to select, and effectively use a cam, in that higher rpm band, as it allows you to use the higher rpms and bye-pass the area of the power band where you've effectively lost efficient torque production with the longer duration cams designed to maximize the upper power bands breathing, potential. and jump into the raised power curves lower effective range.
horsepower is the way the RATE that the engines rotational torque can be used, is expressed,
the formula is torque x rpm/5252=hp
most engines will make about 1.1 ft lbs per cubic inch of torque in their effective power band
if you make about 385 ft lbs at 4000rpm, thats 293hp, boost the rpm to 6000rpm, the same torque at that rpm results in 439hp
remember the concept of gearing and converter stall selection is to allow you to use the most effective part of the engines power curve over most of your driving
it may help if you think of it this way
if your engine puts out 400ft lbs of torque
a 2.57:1 rear gear ratio puts about 1000 ft lbs of twisting power to the axles
a 4.11 rear gear ratio puts about 1600 ft lbs of twisting power to the axles
if your car weights 3500lbs
youve got 29 percent of the cars weight applied in rotational force with the 2.57 ratio
youve got 46 percent of the cars weight applied in rotational force with the 4.11 ratio
its about mechanical leverage, or efficiency
assuming a 26" tire height and zero mechanical losses, the tires need to turn about 200 revolutions to cross a 1/4 mile
a 2.57 rear gear lets the engine spin thru about 2060 power strokes
a 4.11 rear gear lets the engine spin thru about 3290 power strokes
http://www.jegs.com/i/Richmond-Gear/836 ... tId=750830
http://forum.grumpysperformance.com/viewtopic.php?f=71&t=555
http://forum.grumpysperformance.com/viewtopic.php?f=71&t=1715
http://forum.grumpysperformance.com/viewtopic.php?f=71&t=2400
viewtopic.php?f=52&t=324
viewtopic.php?f=52&t=2782
http://www.drivetrainspecialists.com/ca ... ndp-1.html
http://ratech.stores.yahoo.net/coax84d36sed.html
http://www.differentials.com/install.html
http://www.justdifferentials.com/index. ... ts_id=1773
there are darn few mods you can do to a C4 corvette that will produce the immediate gains in performance , that swapping to a 3.45:1-3.73:1 rear gear ratio and a 2800rpm-3000rpm stall converter will produce, even with a stock engine, simply because they allow the engine to spend a far higher percentage of its time in a higher average torque band, now if the engines got the improved flow levels of a better aftermarket, intake manifold, high flow heads and cam with more duration, to boost that engines power even higher than stock levels, the gains become far more noticeable from already obviously improved levels
Originally Posted by Evilpat
I went with a 3:54 ratio to replace my 2:59. Kept the Dana case, and bought a rebuild kit and US strange "Thick" gear set, which is what you need for the Dana 36 case, thick gears that is. The rebuild kit came with everything needed to replace everything inside the case. I then had a corvette mechanic do the rebuild to make sure it was correctly done. After 500 miles for the break in period, I had to go back and have the rear diff fluid changed to remove the flakes of metal that occur when the gears are setting their pattern (not sure of tech name for it). The gears and rebuild kit were around a total of $400. Try JawsGears.com. The customer service there is awesome as well if you have questions. The install labor was $1100, and then $120 to replace the diff fluid. Over all going from a 2:59 to 3:54 makes the car totally different to drive. Best bang for the buck in mods.
this limits you to selecting cams in a range of about 195-218 degrees at .050 lift and below to match your gearing and stall speed
changing the cars cam is done to increase the engines effective, volumetric efficiency and resulting power band, upwards at the cost of low rpm torque in exchange for more effective breathing and power in the 2000-6400rpm power band
a 2800rpm-3000rpm stall converter and 3.54:1-3.73:1 rear gear allows you to select, and effectively use a cam, in that higher rpm band, as it allows you to use the higher rpms and bye-pass the area of the power band where you've effectively lost efficient torque production with the longer duration cams designed to maximize the upper power bands breathing, potential. and jump into the raised power curves lower effective range.
horsepower is the way the RATE that the engines rotational torque can be used, is expressed,
the formula is torque x rpm/5252=hp
most engines will make about 1.1 ft lbs per cubic inch of torque in their effective power band
if you make about 385 ft lbs at 4000rpm, thats 293hp, boost the rpm to 6000rpm, the same torque at that rpm results in 439hp
remember the concept of gearing and converter stall selection is to allow you to use the most effective part of the engines power curve over most of your driving
it may help if you think of it this way
if your engine puts out 400ft lbs of torque
a 2.57:1 rear gear ratio puts about 1000 ft lbs of twisting power to the axles
a 4.11 rear gear ratio puts about 1600 ft lbs of twisting power to the axles
if your car weights 3500lbs
youve got 29 percent of the cars weight applied in rotational force with the 2.57 ratio
youve got 46 percent of the cars weight applied in rotational force with the 4.11 ratio
its about mechanical leverage, or efficiency
assuming a 26" tire height and zero mechanical losses, the tires need to turn about 200 revolutions to cross a 1/4 mile
a 2.57 rear gear lets the engine spin thru about 2060 power strokes
a 4.11 rear gear lets the engine spin thru about 3290 power strokes
http://www.jegs.com/i/Richmond-Gear/836 ... tId=750830
http://forum.grumpysperformance.com/viewtopic.php?f=71&t=555
http://forum.grumpysperformance.com/viewtopic.php?f=71&t=1715
http://forum.grumpysperformance.com/viewtopic.php?f=71&t=2400
viewtopic.php?f=52&t=324
viewtopic.php?f=52&t=2782
http://www.drivetrainspecialists.com/ca ... ndp-1.html
http://ratech.stores.yahoo.net/coax84d36sed.html
http://www.differentials.com/install.html
http://www.justdifferentials.com/index. ... ts_id=1773
there are darn few mods you can do to a C4 corvette that will produce the immediate gains in performance , that swapping to a 3.45:1-3.73:1 rear gear ratio and a 2800rpm-3000rpm stall converter will produce, even with a stock engine, simply because they allow the engine to spend a far higher percentage of its time in a higher average torque band, now if the engines got the improved flow levels of a better aftermarket, intake manifold, high flow heads and cam with more duration, to boost that engines power even higher than stock levels, the gains become far more noticeable from already obviously improved levels
Originally Posted by Evilpat
I went with a 3:54 ratio to replace my 2:59. Kept the Dana case, and bought a rebuild kit and US strange "Thick" gear set, which is what you need for the Dana 36 case, thick gears that is. The rebuild kit came with everything needed to replace everything inside the case. I then had a corvette mechanic do the rebuild to make sure it was correctly done. After 500 miles for the break in period, I had to go back and have the rear diff fluid changed to remove the flakes of metal that occur when the gears are setting their pattern (not sure of tech name for it). The gears and rebuild kit were around a total of $400. Try JawsGears.com. The customer service there is awesome as well if you have questions. The install labor was $1100, and then $120 to replace the diff fluid. Over all going from a 2:59 to 3:54 makes the car totally different to drive. Best bang for the buck in mods.
