NZConvertible

The dyno comment or the acceleration bit? What don't you you understand about it?

True, but you pick your optimum shift points to maximise acceleration, so directly measuring acceleration makes far more sense than guesstimating acceleration from power and torque. There's no aerodynamic drag on a dyno, and that has a hugely different effect in each gear.

That inclinometer I posted a pic of costs considerably less than a single dyno run too (~US$10) and can be used to test handling and braking too.

RETed

Godamnit, go find the freakin' dyno yourself!

http://www.dynojet.com/dyno_centers/...tive/index.php


-Ted

J-Rat

iTrader: (2)

This is the statement that I didnt understand. Its completely incorrect.

So in essence you are saying that wind has a way of SHIFTING your torque peaks?

NZConvertible

Instead of just saying I'm wrong, why don't you explain to me how you think a dyno can accurately determine optimum shift points. How can a dyno tell you exactly how fast the car will be accelerating at any speed in any gear?

There is only one torque peak and it's obviously no shifted but aaerodynamics. But we're talking about shift points, and you don't necessarily shift at peak power and you certainly don't shift at peak torque. Aerodynamics obviously has an effect on acceleration. That shouldn't need to be explained.

J-Rat

iTrader: (2)

I love how you try to turn these discussions around. FACT: Dynos are a PERFECT tool for determining torque curves. FACT: Torque = G force, which equals acceleration. FACT: Torque curves determime optimal shift points.

you DONT shift at the torque peak, you shift at a point that gives you the most time in the fattest area of torque. That means overrunning your torque peak to a point. Its not a hard concept to grasp, even if wind, rain, and the alignment of the stars are NOT in your favor...

SayNoToPistons

youve been posting a lot of inaccurate information lately.

NZConvertible

Turn the discussion around to what? All I'm saying is the best way to determine shifts points is with an accelerometer. Direct measurement under real-world conditions. Do you agree or disagree?

Agreed.

Actually torque (at the wheels, different in each gear) x distance (wheel radius) = force; and force x mass = acceleration. Then there's drag force caused by air resistance which acts against that accelerative force, which rises to the square of speed.

You're completely ignoring gearing and aerodynamics, which both dramatically affect acceleration. You're implying that the shift point is the same in every gear, which is not always the case. The gears are not seperated by the same ratio (i.e. 2nd is 40% taller than 1st, 3rd is 30% than 2nd, etc), so the percentage the engine speed drops at each gear change is different.

Look at the graph I posted above. For maximum acceleration the car in question should be shifted at redline in every gear. But I've also seen the same testing done on other cars that had very different results. One car had to be redlined in 1st and 3rd but had two other different shift points for 2nd and 4th. How are you going to tell that from a dyno curve?

FACT: If you want maximum acceleration through the gears, a $10 inclinometer will give you a much more accurate determination of the ideal shift point in each gear than a $40 (or whatever) dyno run. Pity it's not as "cool" as a dyno sheet...

BTW, you didn't answer my question. Please explain to me exactly how you would use a dyno to accurately determine optimum shift points in each gear. I'm honestly curious to know how you'd go about it.

Trevor

1st off...wind resistance at speed is a constant. When I say that I mean that 90 mph drag is the same regardless if you're in 3rd of 4th. It doesn't matter. The same applies to rolling resistance and mass.

The amount of G's you feel (how hard the car is pulling) is directly related to torque (not HP) and gear multiplication via the trans. You want to maximize the amount of torque applied to the rear diff and therefore how hard the car is pulling. You do this by figuring out which gear will apply maximum torque to the rear diff. You have to know your gear ratios for the two gears you're comparing and the (approximate) flywheel torque...which you can measure indirectly on a chassis dyno or directly on an engine dyno.

Here's a quick example

---------------3rd----4th
---------------1.391-1.000
3500 - 449-625----449
4000 - 478-665----478
4500 - 493-686----493
5000 - 482-670----482
5500 - 466-648----466
6000 - 439-611----439
6500 - 387-538----387
7000 - 343-477----343
7500 - 299-416----299
8000 - 255-355----255

6500 rpm shift from 3>4 would put you at 4680 in 4th. You make 491 crank lb ft there. 538 (see above) vs 491. 3rd gear gets the nod. You should stay in 3rd past 6500.

7000 rpm shift from 3>4 would put you at 5030 in 4th. You make 481 crank lb ft there. 477 vs 481. 4th gear is now superior. You should shift to 4th before 7000.

You can break it down further than 500 rpm increments to get your exact shift points but hopefully you get the picture now. The torque reading off a a dyno chart coupled with knowledge of your gear ratios can allow you to come up with your optimum shift points.

And BTW...that's how the new GTechs with the smart shift lights work. They measure how many current G's you're pulling (torque) and estimate how many G's you'll pull after the shift to decide when to light the shift light.

NZConvertible

We're talking about a car accelerating through it's gears. The drag force acting on the car is definitely not constant, it's increasing to the square of speed like I said.

So they use exactly the same method I keep saying works best. They directly measure acceleration in each gear. Not torque, acceleration.

Trevor

I just spoon fed you the how and why yet you refuse to listen. Come back when you get a clue man.

J-Rat

iTrader: (2)

Torque = acceleration.

Goofy

Torque / Wheel Radius - Drag Force = Acceleration * Vehicle Mass

NZConvertible

Did I criticise your method? Nope, I replied to two specific points.

That's just childish. Come back when you can argue like an adult.

stevenx788

i feel smarter allready sorry bout the hassle.