Subject: Re: Calculating the optimum gear ratio for my car by BeachBum on 2011/8/21 4:34:09
Quote:
djxib wrote: (1992 C4)
Assuming that all goes well with my new motor, it should be good for about 7000 RPM. It is a forged 383 and I will be upgrading the supercharger from an old S trim to a newer T (or later) model running about 14 pounds of boost. Target HP around 650.
The car has stock gears (it is an MN6).
My last time out to the strip I saw 12.3 at 117 with a 2.3 60'. The tach was showing around 5700 RPM across the line in 4th gear.
I definitely want to see low 11's, and I'm thinking that with the new motor, a better launch, and decent tune, I should see 11.2 at 120 or better.
So.. given that the motor 'could' go to 7000RPM (although I'd probably stay less than that), I'm thinking that I could also go with a lower gear ratio. I see a lot of guys run 4.10 gears but I cant find a calculator that would definitely tell me what RPM that would be at 120 MPH. Does anyone here have a calculator or real experience of 4.10 gears at the track with a MN6?
Cheers!
Just as a note, you probably want to run your present gear and see how much power you have and what you actually trap and then make the decision on gear.
If you actually hit your target HP of 650 HP.... your trap speed won't be 120 mph (Which is achievable with right around 475 HP).... you'll be up around 130 minimum and probably in the 135 mph area. If you gear for 120 mph.... you'll be way off. In addition, you'll have a better idea of where your HP peak and shift point are.
