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Discussion Starter #1
I'm going to be putting a c-locker and 31-spline axles in my rearend, and if I'm ever going to change gears, now would be the time.

It's a 96 Cobra with 500 Novi 2000-blown rwhp, 7100 rpm redline/max hp. Currently has 4.30 gears, 26" ET Streets, and crosses traps almost near redline in 4th, a good run is [email protected] or so. It's pretty heavy, I shift slow (and suck).

I can't decide if I should go to a lower gear, or go to 28" slicks, or do nothing... here's the data I'm looking at... I'd appreciate any comments/suggestions:

===============

Dyno graph: http://john.slagel.com/jsdyno.jpg

T56 Tranny Ratios
1 2.97
2 2.07
3 1.43
4 1.00
5 0.80
6 0.62

7000 rpms redline ... and peak HP there.

Tires: 26" ET Streets, radius = 12.5"

In the 1/4 mile I go 12.3 @ 118 now

Here's my calculated speed at redlines with various gears, the current 4.30s are on the money...

MPH @ 7000 rpm
Gear 1st 2nd 3rd 4th
2.73 64 93 133 190
3.01 58 83 120 172
3.55 49 70 102 146
3.73 46 67 97 139
4.10 42 61 88 126
4.30 40 58 84 121

I have 4.30's.

Going to 3.01 gears would be pointless, I could get the same effect by starting in 2nd gear with 4.30s.
Same for 2.73s... I could get 4.10's and start from 2nd gear.

This narrows the choice to 3.55 - 4.10 ... all of which require me shifting into 4th.

With my 4.30's though, I need to go to 5th if I want MPH over 121 !!!!!

So switching to 3.73's would actually give me a little more headroom on the
top end in 4th, and a little more distance in 1st before I need to shift,
which would be good.

However, if I keep my 4.30's and go with 28" tires, I get this:

MPH @ 7000 rpm
Gear 1st 2nd 3rd 4th
3.55 53 76 110 158
3.73 50 72 105 150 (same as 3.55's with 26" tire)
4.10 46 66 95 137 (same as 3.73's with 26" tire)
4.30 44 63 91 130 (somewhere btwn 3.73 and 4.10 with 26" tire)
 

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The one thing you forgot to mention is the 60's. I personally would go to the 28" route as a taller tire will give a bigger foot print over the shorter tire with equal width.
 

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Discussion Starter #3
Here's a timeslip of a good 60' for me... I tend to get around 1.8 - 2.0. I have stock axles and 4.30 gears, so I don't launch in the full powerband, probably at 5000 rpm tops. Once I get my 31-splines in, I'll go full force.

 
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