Help with gearbox and rear end please

[Smokin Joe]

Just got dyno back on my new V6 motor

Peak horses (flywheel) 320@ 6500rpm, sustainable rpm 7500, max rpm 8000rpm

Peak torque (flywheel) 279@5000rpm

Tire size is 205/50/15.

Car weight with all fluids 1370 lbs with driver 1530lbs

 

I have a choice of the following rear end ratios

A 3.08

B 3.42

C 3.73

and the following gear boxes.

D 2.95, 1.94, 1.34, 1.00, 0.74 (5 speed)

E 2.97, 2.07, 1.43, 1.00, 0.80, 0.62 (6 speed)

F 2.66, 1.78, 1.30, 1.00, 0.74, 0.50 (6 speed)

 

Here in the good ole USA we travel long mileage so a cruise gear is useful for the motorway/highway (to preserve hearing and motor) any input much appreciated.

 

 

[Peter Carmichael]

Well in the canon of Seven engines, your V6 does not rev very highly. There isn't much point in going more than 500rpm beyond power peak, so gear for 7000rpm.

 

I am tempted to view Gearboxes D and E as the same, but with an extra ratio on top for the six speeder. You might use it for trolling along at 2000 rpm on a cruise but the following table shows that even with gearbox D you have a hyperdrive top gear. Gearbox E is a bit nasty in detail because of the larger 3rd to 4th jump. I would avoid gearbox E.

 

With gearbox D and final drive B, you might get:

 

Gear Mph per 1000 RPM Mph @6500 RPM Mph @7000 RPM

--------------------------------------------------------

1 6.80 44 48

2 10.34 67 72

3 14.98 97 105

4 20.07 130 140

5 27.12 176 190

 

Mph RPM (in Gears)

-------------------------------------------------

1 2 3 4 5

-------------------------------------------------

5 735 483 334 249 184

10 1470 967 668 498 369

15 2205 1450 1002 747 553

20 2940 1933 1335 997 737

25 3675 2417 1669 1246 922

30 4410 2900 2003 1495 1106

35 5145 3383 2337 1744 1291

40 5880 3867 2671 1993 1475

45 6615 4350 3005 2242 1659

50 4834 3339 2492 1844

55 5317 3672 2741 2028

60 5800 4006 2990 2212

65 6284 4340 3239 2397

70 6767 4674 3488 2581

75 5008 3737 2766

80 5342 3986 2950

85 5676 4236 3134

90 6010 4485 3319

95 6343 4734 3503

100 6677 4983 3687

105 5232 3872

110 5481 4056

115 5730 4241

120 5980 4425

125 6229 4609

130 6478 4794

135 6727 4978

140 6976 5162

145 5347

150 5531

155 5716

160 5900

165 6084

170 6269

175 6453

180 6637

185 6822

 

Gear Change RPM drop (change @6500) RPM drop (change @7000)

-------------------------------------------------------------

1 -> 2 -2225 (to 4275) -2397 (to 4603)

2 -> 3 -2010 (to 4490) -2165 (to 4835)

3 -> 4 -1649 (to 4851) -1776 (to 5224)

4 -> 5 -1690 (to 4810) -1820 (to 5180)

 

Gearbox F has a tighter earlier set of ratios (consider it as a five speeder and ignore top and you will see what I mean) and shortening the final drive will compensate for the taller first and give you more ratios in the frame for general use (I am uncertain as to whether you will ever use 6th):

 

Gear Mph per 1000 RPM Mph @6500 RPM Mph @7000 RPM

--------------------------------------------------------

1 6.92 45 48

2 10.34 67 72

3 14.15 92 99

4 18.40 120 129

5 24.87 162 174

6 36.80 239 258

 

Mph RPM (in Gears)

----------------------------------------------------------

1 2 3 4 5 6

----------------------------------------------------------

5 723 484 353 272 201 136

10 1446 967 707 543 402 272

15 2168 1451 1060 815 603 408

20 2891 1935 1413 1087 804 543

25 3614 2418 1766 1359 1005 679

30 4337 2902 2120 1630 1207 815

35 5060 3386 2473 1902 1408 951

40 5783 3870 2826 2174 1609 1087

45 6505 4353 3179 2446 1810 1223

50 4837 3533 2717 2011 1359

55 5321 3886 2989 2212 1495

60 5804 4239 3261 2413 1630

65 6288 4592 3533 2614 1766

70 6772 4946 3804 2815 1902

75 5299 4076 3016 2038

80 5652 4348 3217 2174

85 6005 4619 3418 2310

90 6359 4891 3620 2446

95 6712 5163 3821 2581

100 5435 4022 2717

105 5706 4223 2853

110 5978 4424 2989

115 6250 4625 3125

120 6522 4826 3261

125 6793 5027 3397

130 5228 3533

135 5429 3668

140 5630 3804

145 5831 3940

150 6033 4076

155 6234 4212

160 6435 4348

165 6636 4484

170 6837 4619

175 4755

180 4891

185 5027

190 5163

195 5299

200 5435

205 5571

210 5706

215 5842

220 5978

225 6114

230 6250

235 6386

240 6522

245 6658

250 6793

255 6929

 

Gear Change RPM drop (change @6500) RPM drop (change @7000)

-------------------------------------------------------------

1 -> 2 -2150 (to 4350) -2316 (to 4684)

2 -> 3 -1753 (to 4747) -1888 (to 5112)

3 -> 4 -1500 (to 5000) -1615 (to 5385)

4 -> 5 -1690 (to 4810) -1820 (to 5180)

5 -> 6 -2108 (to 4392) -2270 (to 4730)

[Smokin Joe]

Thanks Peter,

 

B and D were my first choice too, especially as the large amount of torque is fairly flat from 2000rpm on, thereby providing steam without having to wait for the revs to build. gearbox D is actually the Borg Warner T5, extremely cheap and plentiful here, and is fine up to about 400 hp.

 

Any other comments or suggestions most welcome