Jim Torongo

What we are looking for is maximum acceleration and what **** points will deliver it. Step one is to get a dyno graph of our engine's power/ torque spread. To calculate shift points we are concerned with RPMs and torque (not horsepower) as torque accelerates an automobile. Next we need to determine the RPM loss when we shift from one gear to the next. How much RPM will we lose shifting from 1st to 2nd gear? To find out we divide the 1st gear ratio into the second gear ratio that results in a percentage which, when multiplied by the rpm in 1st, will give us the equivalent rpm in 2nd. So we have the following formula:

RPM after shift = Gear Ratio shift into / Gear ratio shift from X RPM before shift

Let's plug some numbers, 1st gear ratio is 2.25, 2nd gear ratio is 1.65 and we shift at 5000 rpm, thus

RPM after shift = 1.65 / 2.25 X 5000= 3666 RPM

Subtracting 3666 from 5000 gives us a RPM drop of 1334 RPM or about 26%. You apply the same formula to shifts from 2nd to 3rd etc.

The next step is to figure the torque at the drive wheels at 200 RPM intervals or whatever intervals our dyno graph makes convenient. Lets say we have 173 FtLbs @ 5800 RPM, to get the wheel torque we multiply the engine torque at the crank shaft by the gear ratio in question. So the drive wheel torque in 1st gear is 173 X 2.20 = 380.6 FtLbs. When we shift to 2nd RPM drops 1334 RPM and lets say the engine crank torque at that speed is 163 FtLbs. Multiply that by the 2nd rear ratio of 1.65 and you get 268.9 FtLbs or drop of 111.7 FtLbs.

Now to find the ideal shift points we need to plot the numbers on a chart based on this hypothetical dyno chart:

RPM LB-FT BHP
6000 340 194
6200 280 331
6400 255 311
6600 240 302
6800 190 246
7000 160 213

Then post to this chart:

SHIFT FROM 1st (2.20 ratio) TO 2nd (1.66 ratio)
RPM 1st TORQUE 1st RPM 2nd TORQUE 2nd LOSS/GAIN

6000 660 4527 548 -112
6200 616 4678 548 -68
6400 561 4829 540 -21
6600 528 4980 523 -5
6800 418 5131 515 +97
7000 352 5282 515 +165

We want to shift a 6600-rpm so we have the least difference in before and after torque. If we shift before 6600 we will have a big drop off in torque in 2nd or if we shift after 6600 we will have a big drop off in torque in first before we shift. In either case our drive will suffer. We then repeat this process of each gear change and then we can go to the strip and know when to shift in each gear for the best possible run (this is done by ALL serious drag racers). JIM

Stuart B

Please use a spell check on your first sentence! Well, it made me laugh ) (nt)

JimT

Spell check has no chance agaisnt me- I'm that bad at spelling. JIM

StuartB

Enough to make your hair and toes curl. The amazing thing being that our customers have not even noticed the mistakes when they have been big enough to trip over!

Stuart B

Like the 'i' in things..... ) I hope Friday comes soon!!!!!!!!!

IAsTTeve

do we have data to compute these now?? stock 180Q, etc (nt)

JimT

I don't have a dyno chart on the stock motor - does anybody have one?

mne

theres one on Garretts site... "www.giacusa.com" of a dyno pull before/after, HP/torque

John S

MOTOR 180PS 225PS
RPM ft•lbs ft•lbs

1000 105.84 122.09
1050 108.94 125.86
1100 111.96 129.55
1150 114.78 133.06
1200 117.32 136.40
1250 119.69 139.76
1300 122.07 143.19
1350 124.61 146.34
1400 127.26 148.91
1450 129.97 151.36
1500 132.69 154.56
1550 135.68 159.08
1600 139.21 163.76
1650 143.43 167.46
1700 148.16 170.59
1750 153.42 173.76
1800 159.48 177.11
1850 165.44 180.58
1900 170.09 183.96
1950 172.63 186.86
2000 173.00 189.23
2050 173.00 191.87
2100 173.00 195.65
2150 173.00 200.75
2200 173.00 206.63
2250 173.00 207.00
2300 173.00 207.00
2350 173.00 207.00
2400 173.00 207.00
2450 173.00 207.00
2500 173.00 207.00
2550 173.00 207.00
2600 173.00 207.00
2650 173.00 207.00
2700 173.00 207.00
2750 173.00 207.00
2800 173.00 207.00
2850 173.00 207.00
2900 173.00 207.00
2950 173.00 207.00
3000 173.00 207.00
3050 173.00 207.00
3100 173.00 207.00
3150 173.00 207.00
3200 173.00 207.00
3250 173.00 207.00
3300 173.00 207.00
3350 173.00 207.00
3400 173.00 207.00
3450 173.00 207.00
3500 173.00 207.00
3550 173.00 207.00
3600 173.00 207.00
3650 173.00 207.00
3700 173.00 207.00
3750 173.00 207.00
3800 173.00 207.00
3850 173.00 207.00
3900 173.00 207.00
3950 173.00 207.00
4000 173.00 207.00
4050 173.00 207.00
4100 173.00 207.00
4150 173.00 207.00
4200 173.00 207.00
4250 173.00 207.00
4300 173.00 207.00
4350 173.00 207.00
4400 173.00 207.00
4450 173.00 207.00
4500 173.00 207.00
4550 173.00 207.00
4600 173.00 207.00
4650 173.00 207.00
4700 173.00 207.00
4750 173.00 207.00
4800 173.00 207.00
4850 172.97 207.00
4900 172.90 207.00
4950 172.79 207.00
5000 172.61 207.00
5050 172.38 207.00
5100 172.16 207.00
5150 172.01 207.00
5200 171.87 207.00
5250 171.69 207.00
5300 171.39 207.00
5350 170.90 207.00
5400 170.14 207.00
5450 169.10 207.00
5500 167.83 206.56
5550 166.42 205.46
5600 164.92 204.21
5650 163.41 203.12
5700 161.92 202.11
5750 160.43 201.07
5800 158.95 199.87
5850 157.46 198.38
5900 155.97 196.54
5950 154.49 194.42
6000 153.00 192.17
6050 151.51 189.89
6100 150.02 187.65
6150 148.53 185.48
6200 147.05 183.43
6250 145.56 181.47
6300 144.07 179.53
6350 142.58 177.52
6400 141.10 175.41
6450 139.61 173.20
6500 138.12 170.92
6550 136.63 168.60
6600 135.14 166.25

Jim T

John where are you getting these #s- Audi? Dyno graph I just got from Garret is not that flat. JIM