2.73 Rear Gear Experience?

[ColoStang12]

Looking for anyone who has tried a 2.73 rear gear. I have 3.08 now and considering 2.73 for Texas Mile to increase potential top speed. I'd be interested in hearing thoughts from anyone who has tried 2.73's since it seems like a somewhat drastic drop from 3.08 to 2.73.

Mine will be turned by an MT82 built by Ben so 1.0:1 5th gear.

 

[noldevin]

What gear/rpm and speed are you currently finishing the mile with?

 

[Paul.]

Also consider how much power you're making. At a certain point, without enough power you're going to run out of power/aero before you run out of gear.

 

[Fabbed5.0]

I have a slightly used set. 4 passes down the 1/4 and 100 street miles ill let go for cheap.

 

[wakebum2507]

what power level is necessary for the 2.73's to be a good idea?

I've been curious about the 3.08 vs 2.73 idea.

 

[mastwolf]

I have a slightly used set. 4 passes down the 1/4 and 100 street miles ill let go for cheap.

how much? lol

 

[Paul.]

what power level is necessary for the 2.73's to be a good idea?

I've been curious about the 3.08 vs 2.73 idea.

I couldn't spitball that. It's a lot of math and physics.

My stock GT won't accelerate much/at all in 5th gear using a 28.7" tire at the 1/2 mile races around 140 mph.

 

[ColoStang12]

What gear/rpm and speed are you currently finishing the mile with?

Last year I went through the traps at about 7,200 rpm in 5th gear with a speed of 192. I had a little less than 800 uncorrected whp. This year I will have about 980-1,000 uncorrected whp.

 

[Paul.]

I think I'd try a taller tire before swapping gears. With more power, you're now likely going to be hitting the limiter in 5th so you have to do SOMETHING, but I'd be a little concerned about the drop in mechanical advantage from 3.08 to 2.73. What tire are you running today?

 

[wakebum2507]

set up is a large Borg T6, built auto, MPR sleeved motor, and 28" tire.

so with 1000+....is 2.73 fine? i'm trying to keep the car from shifting into 5th on half mile stuff.

 

[Paul.]

So doing some math with a simple online calculator, here's what I came up with. This is really for illustrative purposes only.

3.08 gear
192 mph
28" tire
1.00 5th gear = 7096 rpms

2.73 gear
192 mph
28" tire
1.32 4th gear = 8303 rpms

It appears that staying in fourth gear probably isn't going to be a reality at those kind of speeds without other changes.

Using the 2.73 gear and 5th gear, you have:
2.73 gear
192 mph
28" tire
1.00 5th gear = 6290 rpm.

That may give you the extra "room" you need to get north of 200 mph, assuming you're in the sweet spot in terms of torque production vs the aero drag.

Paul.

 

[ColoStang12]

Good analysis. My tires are 315/30/20 Toyo r888's. They have to be DOT approved for (Y) speed rating so no drag radials at the mile events unfortunately. They're about 27.25 inches tall. There is only one taller tire that would make sense. The Hoosier R7 (about an inch taller than mine), but a pair of those tires on 19x11 wheels would cost just under $2,000 for the pair. That's just to much money for what will likely be 6 passes down the mile. Thus my interest in swapping gears instead.

Thanks for the info!

 

[Paul.]

That's stupid that they don't allow drag radials. There are guys running 200+ in the half mile here in Phoenix on drag radials. Just doesn't seem to be a reasonable limitation. I can see excluding bias-ply tires, but radials would be safe.

Good luck! Let us know how it goes.

Paul.

 

[5lho]

That's stupid that they don't allow drag radials. There are guys running 200+ in the half mile here in Phoenix on drag radials. Just doesn't seem to be a reasonable limitation. I can see excluding bias-ply tires, but radials would be safe.

Good luck! Let us know how it goes.

Paul.

Drag radials are not designed for sustained high speeds. They'd be definitely dangerous over mile distances, in my view.

German mags test tires at sustained high speeds properly. I'd look for recommendations there.

 

[Fabbed5.0]

how much? lol

100 shipped

 

[TJ Whelan]

100 shipped

Great seller. Horrible person. Decent lover.

 

[MRSUPRA]

Interested in this too. Especially with 4th gear being so short.

 

[MRSUPRA]

Here's the max speed by gear with the 2.73 and 27.2 inch tire:

500 4 6 9 11 15 23
600 5 7 11 13 18 27
700 6 9 12 16 21 32
800 6 10 14 18 24 36
900 7 11 16 20 27 41
1000 8 12 18 22 30 46
1100 9 13 19 25 33 50
1200 10 15 21 27 36 55
1300 11 16 23 29 39 59
1400 11 17 25 31 42 64
1500 12 18 26 34 44 68
1600 13 20 28 36 47 73
1700 14 21 30 38 50 78
1800 15 22 32 40 53 82
1900 15 23 33 43 56 87
2000 16 24 35 45 59 91
2100 17 26 37 47 62 96
2200 18 27 39 49 65 100
2300 19 28 40 52 68 105
2400 19 29 42 54 71 109
2500 20 31 44 56 74 114
2600 21 32 46 58 77 119
2700 22 33 47 61 80 123
2800 23 34 49 63 83 128
2900 23 35 51 65 86 132
3000 24 37 53 67 89 137
3100 25 38 54 70 92 141
3200 26 39 56 72 95 146
3300 27 40 58 74 98 151
3400 28 41 60 76 101 155
3500 28 43 61 79 104 160
3600 29 44 63 81 107 164
3700 30 45 65 83 110 169
3800 31 46 67 85 113 173
3900 32 48 68 88 116 178
4000 32 49 70 90 119 182
4100 33 50 72 92 122 187
4200 34 51 74 94 125 192
4300 35 52 75 97 127 196
4400 36 54 77 99 130 201
4500 36 55 79 101 133 205
4600 37 56 81 103 136 210
4700 38 57 82 106 139 214
4800 39 59 84 108 142 219
4900 40 60 86 110 145 223
5000 41 61 88 112 148 228
5100 41 62 89 115 151 233
5200 42 63 91 117 154 237
5300 43 65 93 119 157 242
5400 44 66 95 121 160 246
5500 45 67 96 124 163 251
5600 45 68 98 126 166 255
5700 46 70 100 128 169 260
5800 47 71 102 130 172 265
5900 48 72 103 133 175 269
6000 49 73 105 135 178 274
6100 49 74 107 137 181 278
6200 50 76 109 139 184 283
6300 51 77 111 141 187 287
6400 52 78 112 144 190 292
6500 53 79 114 146 193 296
6600 53 81 116 148 196 301
6700 54 82 118 150 199 306
6800 55 83 119 153 202 310
6900 56 84 121 155 205 315
7000 57 85 123 157 208 319
7100 58 87 125 159 210 324
7200 58 88 126 162 213 328
7300 59 89 128 164 216 333
7400 60 90 130 166 219 338
7500 61 92 132 168 222 342

 

[Fabbed5.0]

Great seller. Horrible person. Decent lover.

LMAO:beer: