Red Liners!!!

[warteaufmich]

Is it just me or does hitting the AP's rev limiter at 7krpm throw you guys through the windshield too? Not that I'm complaining...

[rfd425]

This car is no fun on the redline compared to my last car. My GSR redlined past 8200 RPM. This one is way short and has taken some time to get used to. I think the short redline is what makes me wish we had a 6th gear sometimes.

Are you saying you routinely redline it in fifth gear?

[spec.B-Jay]

Yes, if you look at the graph :

 

You should keep the revs under the highest part of the line, called the power band.

 

Hold on a second... because I don't believe it's that simple. Taking it to 6500 unquestionably takes you past the torque and horsepower peaks, but that doesn't mean you need to shift up for better performance. As long as the gear that you are in is providing more mechanical advantage than the next highest one - by all means stay in it. Remeber that as you shift up, you are trading torque for speed... the instantaneous torque tells you how hard the car is accelerating - while there may be more torque at the flywheel available if you shift up, due to the taller gear, the torque reaching the drivewheels may decrease. As long as the gear you are in is applying more torque to the wheels than the next one, stay in it.

 

Let's establish a baseline of 3rd gear as a 1:1 scenario. (I know it's not, but for the sake of argument, it will make this easier to understand.) If your 3rd gear is 5/7 shorter than 4th, then at any given RPM, 4th gear applies 5/7 as much torque to the pavement at that same RPM. At 6500 the stock graph looks to be at about 150 ft-lbs of torque. If 4th is 7/5 taller than 3rd, then when you shift from redline in third up to fourth, you drop in engine RPMs by this formula: 6500 * (5/7) = 4600 RPM. At 4600 on the graph, the torque is about 200 ft-lbs. More at the flywheel, yes... but because the gear is 7/5 taller, you correct the amount reaching the wheels to be: 200 * (5/7) = 142 ft-lbs.

 

Now we're comparing apples to apples. In this given situation, despite the falling torque curve, you should be driving right to redline before shifting. More mechanical advantage exists that way.

 

Of course, turbo lag will play a part - if you come off boost at any time, these numbers are out the window.

[spec.B-Jay]

I just found this in another thread... assuming it's true, let's calculate the optimum shift points...

 

"Both GT and XT have the following:

1st: 3.166

2nd: 1.882

3rd: 1.296

4th: .972

5th: .738"

 

So you're driving hard in first gear, and you want to know when to shift up. 2nd gear is .57 taller (1.882/3.166) than 1st. So, if you were to shift up from 6500, you would end up at 3740 RPM in 2nd. The engine is making about 150 ft-lbs TQ at 6500 in 1st, and about 215 ft-lbs at 3740 once you shift. Now, we use the correction factor of the higher gear to see the power reaching the wheels... 215 ft-lbs * .57 = 122.5 ft-lbs. Since 150 ft-lbs > 122.5 ft-lbs, so stay in 1st straight up to redline.

 

Let's repeat for every gear...

 

The 2-3 shift:

(1.296/1.882) = .69 taller.

6500 RPM * .69 = 4485 RPM once you shift to 3rd.

4485 = 205 ft-lbs of torque.

205 * .69 = 141.5 ft-lbs.

Again, 150 ft-lbs exists at 6500... 150 > 141.5, stay in 2nd up to redline

 

The 3-4 shift:

(.972/1.296) = .75 taller

6500 RPM * .75 = 4875 RPM

4875 = 195 ft-lbs of torque.

195 * .75 = 146.3 ft-lbs.

150 > 146.3 -- stay in 3rd until redline.

 

The 4-5 shift:

(.738/.972) = .76 taller

6500 * .76 = 4935 RPM

4935 = 195 ft-lbs

195 * .76 = 148.2 ft-lbs

Again... stay in 4th until redline - but just barely.

 

So basically, from a pure performance standpoint, redline all gears in this car before shifting.

 

If you doubt these numbers, remember that torque is what creates the sensation of acceleration... if you take a look at the numbers, they suggest the biggest drop-off in acceleration is created on the 1-2 shift, and that's a pretty accurate description, wouldn't you say?

 

(Disclaimer: Although I believe I have a pretty good understanding of these types of things, I am not an engineer. If anyone here is, and notices an error I made, I'd love to hear it.)

[spec.B-Jay]

LOL, I just realized there is a flaw in all the work I just did. I'll explain later, I'm at work right now... for the most part, what I wrote above is correct, but not completely.