Gearing and Torque:

So I took it upon my self to write a tech thread in reference to the effect Gearing has on Torque. I was inspired to write this thread after seeing god knows how many post where people ask “How can I get more HP?” or “What shall I do turbo or sc?” or “Cams or Header first?” or “What size turbo should I buy?” Before you fork out cash on various parts, think of this alternate option.

Ok so let’s start by saying that a lot of people neglect the affect of Gearing on the overall performance of your car.

Now, Torque is a measure of how much force acting on an object causes that object to rotate. In relation to Horsepower the equation is HP = [Torque x Rpm] x [1 / 5252]. From this it is seen that the HP is proportional to the Torque. So the HP will always follow the Torque curve in that way.

So you may be thinking, well I know Torque is important but where do gears some in? The answer is the gears multiply the Torque that the engine produces on its own. Think about it a stock GS-R may put down 110 lbs-ft at the wheels. Most people can put 110 lbs-ft Torque on a wrench. But we can’t push our cars and make them go as fast. Why? Because gears multiply the amount of Torque depending on the size of the gear. So let’s take 3rd gear in a GS-R (1.36) this means that the driveshaft will turn once every 1.36 times the engine spins. Also for every 4.4 times the driveshaft turns, the Final Gear (differential) will turn once. This is connected right to the axels that turn the wheels. So you can multiply, 1.36*4.4= 5.984 (this is called Absolute Gear Ratio). This means for every 5.984 turns of the motor, the wheels will turn once. So the amount of Torque the engine creates gets multiplied by that number. So 1.36*4.4*110= 658.24 lbs-ft of Torque, a lot more than we can create with our arms on a wrench.

Ok so now we have that down why not look at the effects that different gearing has a Torque. Take a stock GS-R, assuming it makes 110 lbs-ft of torque in 3rd gear using these different tranny’s we can see the Torque difference.

GS-R tranny, 1.36*4.4*110= 628.24 lbs-ft
ITR tranny, 1.458*4.4*110= 705.672 lbs-ft
JDM ITR tranny, 1.458*4.785*110= 767.418 lbs-ft
LS tranny, 1.269*4.266*110= 595.490 lbs-ft

So from this it is seen that gearing dramatically affects the amount of Torque that gets applied to the wheels. Now yes a lot of people do not want a high final gear like the JDM ITR because they will be driving on the highway at 5k.

So if you were to buy a JDM ITR final gear for your GS-R the effects would yield

Stock GS-R ll GS-R w/ JDM ITR Final Gear ll Gain
1st- 1563.32 lbs-ft ll 1st- 1700.110 lbs-ft ll 136.79 lbs-ft
2nd- 919.6 lbs-ft ll 2nd- 1000.065 lbs-ft ll 81.05 lbs-ft
3rd- 628.024 lbs-ft ll 3rd- 715.836 lbs-ft ll 87.812 lbs-ft
4th- 500.456 lbs-ft ll 4th- 544.245 lbs-ft ll 43.789 lbs-ft
5th- 380.908 lbs-ft ll 5th- 414.237 lbs-ft ll 33.329 lbs-ft

So it is seen that when multiplied out it adds a significant amount of Torque. The average gain was 76.554 lbs-ft of Torque. The price of a JDM ITR final gear is about $400. The same price as some middle priced headers. The JDM ITR final gear will bring the Torque curve of a GS-R very close to the USDM ITR. Here is a useful chart.

http://=http://img.photobucket...t.jpg

From this we can see how close this makes the GS-R with a JDM ITR Final Gear to a stock USDM ITR.

Since we already clarified that the HP curve follows the Torque curve we can draw that both HP and Torque will be affected by this upgrade. Thus you can expect quite a different change in your cars acceleration.

So maybe next time you think that you might want to spend money on a header or an intake and exhaust. First think about the more power you can make with upgrading your gearing.

This is only an intro thread i may make more on the affects of combining different ratios for different gears, and maybe a thread about gearing on boosted motors soon. I hope this helps.
-James

Modified by Bitchin_Teg at 11:17 PM 10/7/2005


Modified by Bitchin_Teg at 8:54 AM 10/8/2005


Modified by Bitchin_Teg at 8:01 PM 10/8/2005

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Bitchin_Teg &raquo;</TD></TR><TR><TD CLASS="quote">Since we already clarified that the HP curve follows the Torque curve we can draw that both HP and Torque will be affected by this upgrade. </TD></TR></TABLE>

Your cause and effect is backwards. The transmission does not effect the engine output, the engine drives the transmission. Torque is a measure of force, and horsepower is a measure of work performed by that force. Some simple math will reveal that horsepower at the wheels is the same in every gear, while torque is not. The engine must spin faster to provide the same wheel speed, so even though you have more torque at the wheels, the engine traveled more distance, rotationally, to achieve it, and thus did the same amount of work.

You are correct, however, in saying that gearing makes a huge difference in the acceleration of the car. And as you noted, there is a tradeoff of a higher rpm for a given vehicle speed. This is the reason choosing the right gear ratios is important.

 

So the higher gear you go the more the engine has to spin to achieve certain amount of torque?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by drdisco69 &raquo;</TD></TR><TR><TD CLASS="quote"> The transmission does not effect the engine output, the engine drives the transmission. </TD></TR></TABLE>

yes you are true, thought i had a clear explanation.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by drdisco69 &raquo;</TD></TR><TR><TD CLASS="quote"> Torque is a measure of force, and horsepower is a measure of work performed by that force. Some simple math will reveal that horsepower at the wheels is the same in every gear, while torque is not. </TD></TR></TABLE>

Sorry i thought i made it clear at the begining that the HP curve would be affected.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Bitchin_Teg &raquo;</TD></TR><TR><TD CLASS="quote">Sorry i thought i made it clear at the begining that the HP curve would be affected. </TD></TR></TABLE>

But it's not.