Optimun Gear Shifts

[TBO240]

After getting a bit of topic in another thread I decided to start my own thread .I believe that there is a definite benefit by using the edit to lift the rev limit as it helps to improve the optimum gear shift point over the ¼ mile. There are others that believe that because the xr6t maximum torque starts to fall away after 4500-5000 rpm there is no need to rev past this point. Using your dyno sheet and this site http://www.bgsoflex.com/shifter.html it illustrates that there is a benefit to be had by reving past the 5800 rev limit.using my own dyno sheet I imputed these values (don’t use decimal point it wont work) and also tried to predict hw much the power curve would fall away to at 6500rpm .

Rpm rwhp

2500 191

3000 216

3500 241

4000 287

4500 310

5000 332

5500 344

6000 341

6500 291

here were the results

Optimum Shift Calculator by Bowling and Grippo

Input Parameters Are the Following:

Transmission Ratio One = 2.50 to 1

Transmission Ratio Two = 1.49 to 1

Transmission Ratio Three = 1.00 to 1

Transmission Ratio Four = 0.68 to 1

Horsepower = 191 at 2500 RPM

Horsepower = 216 at 3000 RPM

Horsepower = 241 at 3500 RPM

Horsepower = 287 at 4000 RPM

Horsepower = 310 at 4500 RPM

Horsepower = 332 at 5000 RPM

Horsepower = 344 at 5500 RPM

Horsepower = 341 at 6000 RPM

Horsepower = 291 at 6500 RPM

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Computation Results

Using the Criterion for Maintaining the Same Horsepower Before and After Shift:

Finding Best Shift Placement Points For Ratio 2.50 to 1.49: Error: Search outside range - need more RPM range in HP table! Finding Best Shift Placement Points For Ratio 1.49 to 1.00:

Found optimum shift RPM at 6426, which achieves 303 horsepower and lowers the RPM To 4312 after shift

Finding Best Shift Placement Points For Ratio 1.00 to 0.68:

Found optimum shift RPM at 6415, which achieves 305 horsepower and lowers the RPM To 4362 after shift

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Maximizing the Area Under the Horsepower Curve:

Finding Best Shift Placement Points For Ratio 2.50 to 1.49:

Found optimum shift RPM at 6493, which achieves maximum area under horsepower curve, and lowers the RPM to 3870 after shift

Finding Best Shift Placement Points For Ratio 1.49 to 1.00:

Found optimum shift RPM at 6496, which achieves maximum area under horsepower curve, and lowers the RPM to 4360 after shift

Finding Best Shift Placement Points For Ratio 1.00 to 0.68:

Found optimum shift RPM at 6500, which achieves maximum area under horsepower curve, and lowers the RPM to 4420 after shift

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Bruce A. Bowling

Al C. Grippo

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that's my 2 cents worth .

[TBO240]

Can someone with a edit that has a dyno graph that shows the rpm on the bottom of there graph please post it here so that I can repeat the exercise without having to try and predict as to where the power falls away to.

[ZAP]

TBO,

I see what you are saying, but as the Barra motor is under square, you will be running a huge risk of ventalating the block with a rod if you are reving at 6500rpm. If the motor is built to handle the high revs, then it is a great option, but a stock motor is asking for trouble.

[blueboost]

I take it that that is with after market valve springs,

I know I would like the soft limit the most, I stuff up a lot of good runs because of the hard cut, I dont think I would like taking my standed internal motor to 6500 though.

David

[TBO240]

I could be wrong but I think most of the cars that have had custom edit have 6500 rpm rev limits

[sixfan]

  TBO240 said:

I could be wrong but I think most of the cars that have had custom edit have 6500 rpm rev limits

Dunno about custom...my edit limiter came on at 6200 a nice smooth cut it was too... You may have a point Mathematically but I think ZAP's right and I would not like to do that to my primary mode of transport....

[TBO240]

  sixfan said:

  TBO240 said:

I could be wrong but I think most of the cars that have had custom edit have 6500 rpm rev limits

<{POST_SNAPBACK}>

Dunno about custom...my edit limiter came on at 6200 a nice smooth cut it was too... You may have a point Mathematically but I think ZAP's right and I would not like to do that to my primary mode of transport....

<{POST_SNAPBACK}>

even a 6200 rev limit would be a improvement.

[sixfan]

  TBO240 said:

  sixfan said:

  TBO240 said:

I could be wrong but I think most of the cars that have had custom edit have 6500 rpm rev limits

Dunno about custom...my edit limiter came on at 6200 a nice smooth cut it was too... You may have a point Mathematically but I think ZAP's right and I would not like to do that to my primary mode of transport....

even a 6200 rev limit would be a improvement.

certainly drives a lot nicer when giving it a bit of stick!

[bjc]

This is what the owner of Nizpro wrote in a reply on a thread in there forum-

"Std limiter is set at 6000 rpm we normally move it to 6500 rpm. It not a good idea to use the rpm limit. It dose no favors to the engine starting and stopping it"

_________________

Proprietor

Nizpro Turbocharging

I assume he is saying that set it to 6500rpm but dont use the whole range to the new rev limit? So as to give some margin of error on shifting gears while drag racing and change around 6000-6200rpm to stop the rev limit putting you through the windscreen if you accidentally hit it.

Brett.

[Lawsy]

Its funny you guys mention this, was doing a bit of theory on this the other day, but the maths is quite simple...

We all torque () in power for a reason. That reason is this, if you have a car geared relatively well, then you want to shift so you have maximum area under the power curve from the shift points. Power, in a sense, gives you an idea of the tractive effort through each gear in comparison to the next, if you will.... In theory, this is completely wrong, but in a practical sense, the average tractive effort through each gear mates perfectly with optimising the area under the power curve.

Its actually quite amusing at how well all of the various power, torque and tractive effort comparison(s)/graph(s) all come together perfectly to give you the best indication of where to shift. Physics, its a wonderful thing!

The maths is simple, but involves torque and tractive effort more than power to get the point accross.

Your torque values are in NM

6500  318.8
6000  404.7
5500  445.4
5000  472.8
4500  490.5
4000  510.9 * max torque
3500  490.3

This is what the tractive effort table looks like, all I've done is multiplied the overall gearing by torque(Nm), all over the rolling radius (mm), eg (318*(2.5*3.45)*1000)/300 = 9179.5

Here goes.

  2.5      1.49       1       0.68
  1st      2nd      3rd      4th
9179.5*   5471.0*  3671.8*  2496.8
11653.2   6945.3*  4661.3*  3169.7
12824.4   7643.3   5129.8   3488.2
13614.7   8114.4   5445.9   3703.2
14125.0   8418.5   5650.0   3842.0
14711.7   8768.2+  5884.7+  4001.6+
14118.5   8414.6+  5647.4   3840.2

As you can see, no where in 2nd gear do you have more tractive effort than you do at redline in 1st gear. This anoys me because it seems that every gearbox manufacture spreads 2nd gear to far away from 1st.... Most gearboxes accomodate a 6000rpm TORQUE band. No car makes 80+% torque through 6000rpm, or none that I know of.... 2nd gear is always too long it seems... Anyway..

So, infact, you could increase the rev limit, as long as your engine is capable, another 200rpm (to 6700rpm) and still be going faster than otherwise following the current trend of your information.

Its all about the gear spacing.

With the new 6 speed however, its similar, but you can see clearly that, once out of 2nd gear, the gearing definately helps to get a higher average tractive effort, or power figure, to the tarmac than the current 4 speed (this is with the correct diff ratio also).

4.17       2.34     1.52     1.14     0.87     0.69
1st       2nd       3rd      4th      5th      6th
12116.0*  6798.9*   4416.4*  3312.3*  2527.8*  2004.8
15381.0   8631.0*   5606.5*  4204.9*  3209.0*  2545.1
16926.8   9498.5    6170.0   4627.5   3531.5   2800.8
17970.0   10083.9   6550.2   4912.7   3749.1   2973.5
18643.6   10461.9   6795.7+  5096.8+  3889.7+  3084.9+
19417.9   10896.4+  7078.0   5308.5   4051.2   3213.0
18635.0   10457.0   6792.6   5094.5   3887.9   3083.5

The asterix denote at roughly what point you should shift, and the plus signs denote where you hope the revs don't drop below.

As you can see, with the 6 speed you can shift slightly earlier with this power curve, but still accelerate faster than if you have the 4 speed. This is because the average applied tractive effort until Vmax will be greater...

This means that you would shift at redline in 1st (or 6900 if you could), 6300rpm in 2nd, at 6200 for 3rd and 4th, then at 6000 in 5th...

So just from looking at those figures and doing a rough average, you can clearly see that there's alot more tractive effort, on average, applied to the tarmac with the ZF6 speed than what is possible in the current 4 speed. You would also only need about 6000rpm to do the same thing with the ZF.

Hope that helps.