You have a 5 spd. I was quoting 5 spd transmission ratios. You do not have a 6th gear.
Let me make this simple.
You have an 81 2+2, then your rear end is a 3.9 stock, which is the best you could have for acceleration, but hurts your top end.
The T-5 only came in the turbos, the non-turbo were not T-5.
If you have the stock transmission, your gears are:
1 3.062
2 1.858
3 1.308
4 1.000
5 0.745
If you changed the transmission to a T-5 out of the turbo, your gears would be:
1 3.500
2 2.144
3 1.375
4 1.000
5 0.780
Either way, you have the same ratio for 4th, and 5th is a minute difference. Your top speed is governed by your gear ratio. You can calculate what your car can and cannot do with this data, and at a given rpm. Your valves float above 6500rpm, correct? So we can calulate the maximum speed that you can do in each gear as well.
You are not doing 130 mph at 5K rpm even in 5th gear - physical max is 119.3 - and I'm giving you every benefit of the doubt. You physically do not have the gears to do it below 5500rpm. The only way to do it would to be put on taller tires, so that you change your gear ratio. For this, you would need to make more power also, as OD is a very weak gear and will not pull well. 1/2 mile is a long way to have to go to creep up 10 mph.






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