First Post! Try not to flame me too much, I'm fairly new to the tuner community. I read a bunch of content on this from bense. Alot of his writeups have been taken off the site though which sucks for me. Anyways I'm having a really hard time understanding what the different numbers on gear ratios really mean, and what makes a gear longer or shorter.

I'm trying to decide which transmission to go with for my high horsepower turbo setup on my B18C1 motor. I can't decide between a GSR or ITR transmission. So far I know that the ITR has shorter gears which is better for acceleration(please someone correct me if i'm wrong).

So when comparing ITR gear ratios with the GSR what makes it a shorter gear? Is it the difference between the gears, or is it the number presented below? All of the ITR gear ratios are greater numbers then the GSR. What does the final drive do? I see people going nuts for the 4.7 final drive. If anyone can clear this up for me it would be much appreciated. I tryed to read bense's write-ups and have searched on this topic. However i'm confused on this topic. The type R tranny is only 300$ more then the GSR LSD tranny, and I want to make the right choice.


GSR

1st: 3.23
2nd: 1.9
3rd: 1.36
4th: 1.034
5th: 0.787
FD: 4.4


ITR 95-97

1st: 3.23
2nd: 2.105
3rd: 1.458
4th: 1.107
5th: 0.848
FD: 4.4


ITR 98-01

1st: 3.23
2nd: 2.105
3rd: 1.458
4th: 1.034
5th: 0.787
FD: 4.785

Mad respect to anyone that cares to help rather then flame the uninformed. Thanks again.

 

How much power are you making?

How high are you going to rev the car?

What size tire?

Then pick the shortest geared tranny setup that will work with what goals you have.

 

I am going to assume you mean 300+ whp for high power?

Anyways the answer to your question is tough without a bit more detail, but I will try my best to explain it.

The 'shorter' a gear is, then the higher the number for the ratio. The ratio is compared to output shaft speed, so a good way to think about it is for every 1 output shaft revolution the gear in question spins it's ratio of revolutions. This is how the term 'overdrive' came about, because an overdrive gear always spins the output shaft faster than the input. (has a ratio less than 1) Whereas the other gears work in opposite, with ratios greater than 1. Fourth gear is special on many RWD cars, as it traditionally just locks the input and output shaft. Check the gear ratios of many RWD cars, you will mostly find 4th being a 1 ratio.

Now the output shaft is meshed to the differential ring gear, or 'final drive' (FD). Again the ratio equation is the same, but you are dealing with two different sets of gears. For this one, the number is how many revolutions the output shaft (or perhaps it is the spider gears, I forget exactly) make per revolution of the ring gear.

Although it is called the final drive, your tire/wheel assemblies are actually gears too, but they are not meshed, to the ground, and rely on friction. Which is why drastically changing wheel tire combos can throw your speedometer off.

And again, not sure on your power output, but my friend's YS1 was really too short of a transmission for his ~340 whp Integra, even with a 9000 RPM redline. But the important part to think about is how fast you plan on driving. For lots of highway cruising, you would want really tall gears to cut down on noise. If you are planning on doing drag races under ~200 km/H, and not much 'cruising' then yeah, you will want the shorter gears.
Another thing to keep in mind is how poor FWDs are at keeping traction in high power applications, and gear ratios mean jack if you cannot get the power through the tires to the ground.
So if it came down to what to spend your money on, I personally believe the $300 would be better invested in tires, especially if you are planning on getting into 250-300+ whp territory.