Wildstar

I was having an argument with one of my friends over this, and thought I'd tap into the Rennlist brain pool. What is the optimal shifting RPM for acceleration? 3K/4K/Tach pointing straight up/Red line?? Inquiring minds want to know.

PS - A lunch bet is on the line, so don't let me down!!!!

SidViscous

Which car?

Best shifting point is at peak TQ. Varries from car to car.

turbo944

We've kind of discusses this before I think on the 951 board, but in general you have better acceleration by accelerating to nearly the redline as acceleration in 1st gear from 5k-6k is faster accelerating than it is to shift to second and accelerate from 3k-4k or whatever the revs happen to be after shift. Somebody had posted acceleration in gears from one speed to another and as long as you could accelerate in one gear it was better. That said, you also in accelerating through the gears want to not wait too long to hit the rev limiter either or that will slow you down.

I've seen it long said that you should shift at the torque peak, but if you still are getting better acceleration in the lower gear, stay in it even if the torque falls off a bit as there is a multiplication of that through the gears.

Now, in a car where ALL of the power and torque are down way low, you may end up having to shift below those higher numbers for the best acceleration. If you shift at peak torque in even a Mustang though, you'd go from 3000rpm back down and you'd never pass that rpm in acceleration, which is definitely not fast acceleration. Normally torque peaks much lower than HP does and some cars have very flat torque curves and you wouldn't want to shift because you'd hit the high point at 3500 and it is only 20lb-ft less another 2000rpm up. You'd wait for the horsepower curve to peak. But either way, it's still not as sound as using the rpms that you have in the lower gear first. Especially in lower gears in a fast car where you are lucky to not hit the rev limiter as you accelerate hard, let alone pick a number to shift at.

adrial

You dont want to shift at peak engine torque, you want to shift when Force delivered to the wheels would be greater if you shift than it is in the gear you're in.

Generally...
For 1st, 2nd and maybe 3rd this means shifting at redline or maybe a tiny bit below. For the higher gears, you can shift earlier because the spacing between the gears is smaller.

Wildstar

OK, so what about my S2. My friend says I wind it out way too much. I say I shift like I'm suppose to ~4K-5K.

Waterguy

Exactly what Adrial said. Shift point depends on the shape of the torque curve (particularly how it falls off after peak rpm) and the gear spacing. For example, a stock 951 falls off pretty quick after its power peak at 5,800 rpm. For a stock 951 with maximum torque about 3,600-4,500 rpm, optimum shift points are as follows:

1-2: red line (6,450). rpm after shift 3,800
2-3: 6,300. rpm after shift 4,150
3-4: 6,100. rpm after shift 4,500
4-5: 5,900. rpm after shift 4,700

Modifications that allow better power at high rpm with less drop-off generally increase shift points. For example, a stock 951S holds more boost at high rpm, so its optimum shift points are:

1-2: 6,400. rpm after shift 3,750
2-3: 6,300. rpm after shift 4,150
3-4: 6,200. rpm after shift 4,600
4-5: 6,100. rpm after shift 4,900

These shift points are calculated from actual dyno torque curves, and will vary from car to car and even run to run. So there is no single right answer.

Waterguy

The four-valve S2 breathes better at high rpms and benefits from higher shift points. Based on Tom Pultz's dyno chart (which does have an aftermarket Welt chip, but dynos of stock 944S2s all the way to the red line are hard to find), optimum shift points are:

1-2: red line (6,450)
2-3: red line (6,450)
3-4: 6,400
4-5: 6,400

I think what you are really talking about though is normal driving and not full throttle acceleration runs. Generally you should shift at whatever rpm will prevent lugging in the next gear. Porsches love to run up higher in the rpm band, though, so I am with you (higher shift points after the engine is fully warm.)

Wildstar

Thx to all in the community for the input!

Fishey

For my s2 I have found that a near redline is faster because it alows me to be going up higher in the next gear. Hold it as long as possible and jump for the next gear. If I shifted at max TQ 4100rpm's I would be going so slow that my car wouldnt go anywere. I think the max TQ of my car is higher then that anyways because at 4100rmp's is were the engine just starts to come to life.

RSflared72e

When shifting for max acceleration in a straight line, my theory has always been:

The shift point should always be in between the HP and TQ peaks, just ever closer to the HP peak.

In lower gears, shift closer to the torque peak without inducing wheelspin(unless you want to for S&Gs) or lugging.

As you move up through the gears, move your shift point closer and closer to the horsepower peak. In many cars there is not a huge difference between these 2 points - in others quite a bit...

Many variables between cars, and within the same car in different situations - just my dos centavos...Al

Magnus

If you want maximum acceleration shift like Waterguy suggests, that will let you use the motors maximum power in the best way. It's HP that makes things move. If someone with more TQ but less HP is passing you, you are in the wrong gear.

//Magnus