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I currently have the stock 5 speed with the stock 4.1 rear ratio. My car has about 160 something rwkw and will probably go up bit with the future plans to maybe 200ish. I am considering putting in a 3.6 rear end ratio so that I will be able to use 2nd gear at qr for what I am currently using 3rd for turns 3 pretty much on and i will be able to use 3rd for turns 1 and 2. However will the higher geared rear end put too much stress on the box? I am thinking that the 5 speed will give up at some point at which time it will be a quaife semi helical gear set or a 6 speed. so if I go 6 speed i will need the 3.6 or the gearing will be useless but thats another store all together as I will need to get different headers. If the box will give up quicker then I wont do it but if it should be fine then I may. what do you guys think?

You should have the grunt to pull a taller final gear ratio no worries.
I found with my turbo setup, at similar power levels with a torsen diff (4.1:1 ratio), that first gear was useless at anything over 1/2 throttle even with R spec tyres.
I am planning a similar ratio (I would prefer 3.7:1) for my new setup but I am running a RX7 rear end.
Jake