Hi Guys,

Been reading this thread and trying to understand all the numbers because I have been thinking about making a gear change as well. I have a 2010 with a 6MT with Stillen Gen 3 CAI, Berk Resonated test pipes, and Ark DT-S exhaust. My diff let got the other night and fortunately for me I already have an appointment to have and OS Geiken 1.5 diff installed. I was thinking of going up to a 3.9 or 4.08 but want to understand if will have the desired effect I am going for, which better acceleration for drag/roll racing performance. It seems like from the info post that the WHP will go down some but the torque will go up. Will this give me that improved acceleration I am looking for or am I misunderstanding?

OS Giken is a good choice. When my car just had bolt on's, I had 4.08's installed. It definitely helped with low end performance. I feel it's a good upgrade for a car with bolt ons. Once I went forced induction, I went back to the stock 3.69 ratio. First gear became absolutely useless and the lower gearing isn't needed with added power. That's just my opinion.

:iagree:

N/A, the 4.08 works good for the strip. Going boost. Most guys want to go to the 3.54, or the 3.30 gears. As 1st gear, and the bottom of 2nd gear is overpowered by engine torque.

Using the OS Giken diff. You have to use the OS Giken lube to keep it quite. Otherwise, it gets noisy. After install, change the lube after 1000 miles. The lube used to be $70.00 a liter. Now I see it's $50.00 a liter. I have one, and it works great. Get the Z1 finned diff cover too. I recorded temps of 265F in my diff. The cover will hold an extra 1/2 liter of lube.

Thanks for the info and advice. Yes I already have the z1 diff cover on the build list. It is getting done July 9th. Unfortunately I am down until then as the planetary gears in the stock diff let go Thursday night. It is totally dead for now.

If you go boosted, you will want 3.33 gears. If you don't know which way to go stay stock gearing for now.

:iagree: