mdvaldosta

There are so many questions asked about gears, I though I would write an article to help educate those not as familiar with what they do and how they effect the performance of your mustang. There are literally hundreds of articles about this subject all over the net, but I want to ensure that anyone reading this will have a clear understanding of what gears will do for you in your car, something we should all know.</P>


To start with, everyone should understand that gears simply multiply engine torque at the sacrafice of increased engine revolutions. The higher the gear ratio, the moretorque being put to the groundand the faster the will rev. As a general (very general) rule, going with a numerically higher rear-end gear (example: 3.73's instead of 2.73's), will result in improved acceleration at the cost of top speed in each gear. </P>


Don't forget that the gears in your transmission influence the torque you put to the ground just as much as rear gears, although they aren't quite as easy to change! The following is a good example of gears at work:</P>


A stock 99+ Mustang GT produces an advertised 302 ft lbs of torque at the engine. With a 3.38 1st gear ratio and 3.27 rear end gears we can determine the following... 302 x 3.38 x 3.27 = 3,337 *.85 (to account for 15% loss of power through the drivetrain)we have <U>2,837</U> ft lbs of torque hitting the pavement in 1st gear. Easy enough! Now, lets swap out those gears for a set of 4.10's... do the math and we come to <U>3,557</U>! Thats an increase of 21% more torque hitting the ground! Wow! It sounds to good to be true? Is it? Well, yes and no.</P>


As mentioned earlier, going numerically higher in gear ratio will generally increase performance (obviously) at the cost of top speed in each gear (most of the time). You see, in a Mustang for example, top speed is drag limited, meaning the motor cannot produce enough power to overcome drag and reach redline in 5th gear, not even close really. In fact, its so far away that your Mustang will top out way before peak horsepower is even reached. So in this case, going to a numerically higher gear will actually improve top speed in 5th gear because with the right gear choice, you would be able to ensure that after you shift from 4th gear, you would remain in the engines power band and be able to continue to accelerate past your old top speed. This of course, also means that you will top out in lower gears faster, so you will be shifting more and will not be able to go 40 mph in 1st gear anymore </P>


Its also important to note that increased gear will not increase horsepower, as horsepower is simply a measure of work being done over a period of time.I won't get into all that right now, other than to say that the increased torqe allows you to get your car moving faster and more quickly get into the rpm band where you make horsepower (do more work) faster. Also it is important to understand that more gear will certainly always equal faster acceleration in each gear, and as long as you are at the proper rpm through each gear while racing, you will speed up faster (traction limited) as well.</P>


Chose your rear gears carefully, remember that not only does the actual ratio of the rear gears make a difference in the end result, but the transmission gear ratio as well as the tire size will make a difference in your choice. What will give you certain acceleration and engine rpm on one car may may give different results on a different car. In addition, driving styles will be a factor in your decision. </P>


As for gear choice on certain cars, well that is all a matter of preference when comparing the pros (increased acceleration) to the cons (less speed per gear). You car can only rev so high, and in general the higher the rpm's your running, the lower your fuel economy. Some people, like myself, am willing to sacrafice running on the interstate at 3,000 rpms to getfaster acceleration over someone else in the same typeof car with numerically lower gears. Others are not.</P>


As a general rule, for the average person, below is what has become the standard in rear gear choice for us Mustang fans:</P>


5.0 Mustangs ... 3.55's to 3.73's</P>


4.6 Mustangs ...3.73's to 4.10's</P>


The main difference in the gear selection between the two is that the 4.6 Mustangs have numerically lower 5th gear ratio's that helps interstate driving, larger wheels and tires reducing the effective final drive ratio, and engine that breath better on the top end with higher redlines. Also, in general, automatic transmission owners may want to chose a numerically higher rear gear ratio because the AT sucks more power than a MT, 4th gear is lower than 5th in a MT, and you don't have to manually shift. Also, the DOHC motors love to rev, and many a Cobra owner have went with 4.30's. </P>


The moral of the story is DON'T FEAR THE GEAR! There is also a myth about gas mileage going down with higher gears, and that is in most cases the opposite of the truth. With the addional torque available to get the car moving, it will require less gas to accelerate at the same rate as before. To keep the rev's down you will likely be in 4th gear where you used to be in 3rd. Gas mileage will only get worse on the interstate.</P>


I hope this answered any unaswered questions you may have had. Any thoughts, suggestions, or question you have should go in this thread.</P><edited><editID>mdvaldosta</editID><editDate>37900.994849537</editDate></edited>

Mysterious

Pretty good as it applies to Mustangs and small engines. Simple and easy to understand, but like you said, its not all of it. It is what works though.</P>


The torque Converter also multiplies torque, but for a short period of time. You can increase the torque at stall speed by as much as 3x with some stators. A clutch is not always faster, in an underpowered or smaller engine, the clutch will go faster, but with enough power to break lose a 11 inch wide drag slick, the auto will beat the clutch. Good choices on gears for the Stangs, 3.55's worked really well in the Fox body cars I built.</P>

nostang

My car actually went slower when I put in a lower gear ratio 1st and 2nd in myC-6 because I was only in 1st for less than 2 seconds and I think I was just spending those two seconds spinning up the motor.With the orginal gears in the trans Iam in 1st for about 3 seconds and it pulls harder for a longer period of time.Also there is less of a jump between 2nd and 3rd.So I agree with everything you said mdvaldosta,but there is a point dependingon your horepower and wieght and a whole bunch of other things where too much gear will make you go slower.Your gear choice for the averageMustang is right on,andgoing lower than what you said won't always be faster and will usually not be very nice to drive on the highway.Just my .02 cents.<IMG src=smileys/smiley1.gif border="0">

Mysterious

</P>


That is kinda what i mean by it works for smaller motors. Biggere engines make mountains of torque, so if you dont use it, and you just move the engine past that rpm range faster, you go slower. That is called overgearing, but for the most part small blocks dont have alot of worry about it. </P>


The 455 Bird has 4.11's but i am switching to 3.42 for exactly that reason, it will pull harder for a greater amount of time in each gear, therefore using the power whereit makes it.</P>

mdvaldosta

Well when you don't have traction with excess torque, then there is no need for lower gears. You may be better off staying in gear longer so you don't lose time from shifting, or get no benefit at all from lower gears because you already can't hold traction with the gear you have. When you multiply torque you will ALWAYS pull harder so long as you have traction, you get slower from wheel spin, not staying in your rpm band, or excessive shifting.