Quote:
Originally Posted by Lucky21
Hi everyone. I'm thinking of swapping my final drive to acheive a higher top speed in my 86. I am boosted 300whp in my auto 86 but 5th gear is still useless. My question is will going for a higher final drive (4.556) be more beneficial than a 3.9 fd if the only goal is to make 5th gear usable.
|
Good website to give you an idea of max speed changes per gear. Google the ratios and tire diameter, etc. Diff ratio will be what you adjust based on your FD choice.
https://www.blocklayer.com/rpm-gear
On a stock car, here's following top speeds on 5th gear based on your FD.
4.6 FD: 118
4.3 FD: 126
4.1 FD: 132
3.9 FD: 139
3.7 FD: 146
Technically, your 5th gear should be the least of your worry. How often are you in the 100-146 mph range that your 5th gear will mean that much to you? Usually people complain more about the lower gears, as with more power, you are going through the gears quicker, making 1st and 2nd gears more "useless" as you say. So lowering your FD to something like 3.7 will give you more time in each gear and help reduce tire spin as well.