Jesc..

1st point about rpms dropping faster w/ lwfw ... of course yes

2nd point about "the graphs apply to stock oem clutch/fwl".... dead wrong.. that chart applies to any combo of clutch or flywheel as my post stated gearing doesn't change one bit.

Have a nice day!

 

I agree LWFW is not relevant to this discussion for the reasons eloquently stated above.

 

Thanks

few questions:
1. This calculator shows the speed on the particular gear
2, In the gear ratio gaps am I put the stock ratio i.e. 3,82 (1st) and in the axel ratio 4.0:1.

 

hey, paul 996 and jmeager
thanks for taking time to clarify my post.
both are correct ,and i incorrectly stated that "graphs apply to oem fwl".
i was trying to convey that shifting should be at/near redline as nj-gt posted,
again, always humble and ready to learn.
no intention on highjacking post , so back at reading more knowledgebe guys
cheers

 

Jesc,

No sweat I think we are all on the same page now.

I agree that normally redline is the right place and what I do but taking into consideration what is coming up.

Dell's question is interesting regarding purely determining the optimal shift point based on the HP/TQ chart. I am open to some new info on why redline maybe isn't always best. ??? dunno

I say to Dell to set some baselines and then vary your shift point based on the data in the HP/TQ chart and see if there really is an improvement... heck you probably already have the baseline

 

At the end of the day, if you are looking for max WOT acceleration in a straight line, then the change point is effectively just short of the redline where the GT3 engine makes max HP.

If you are going around a bend, then the best gear is simply the one that puts you in the sweet spot torque wise for max drive out of the bend, but more importantly - the gear that allows you to make the smoothest progress through the bend without unsettling the car. In this instance, there are an infinite number of possibilities based on entry speed, stance, corner radius, etc etc etc.

 

Redline to get the maximum area under the HP curve for each gear.

 

I always go near to redline too. Some of you yanks shift like my granny

 

Hey, I resemble that remark!

 

My granny is a yank

 

N-GT is right. You need only look at the hp curve. looking at that you should redline every gear except possibly 4th to 5th. That should still be taken to probably 8k though.

To get a better idea if you are very torque minded think about the following. In the next higher gear, you're in a another gear... Sounds stupid, duh, but if you actually think about what that means you'll understand. In a higher gear you have less mechanical advantage so for a given rpm where the engine produces a given torque, the force at the wheels will be smaller in a higher gear. So the mathematical formula to tell you when to shift would be:

(next gear ratio/current gear ratio) * next gear torque > current gear torque

If this condition is met you should shift. So even if your torque is much lower than your torque would be in the next gear it has to be lower than your ratio would drop:

(next gear ratio/current gear ratio) > (current gear torque/next gear torque)

(note the flipped order)

Now consider the following.

(next gear ratio/current gear ratio) = (next gear rpm/current gear rpm)

Insert this into our previous relation.

(next gear rpm/current gear rpm) > (current gear torque/next gear torque)

Put everything on one side.

1 > (current gear rpm/next gear rpm)*(current gear torque/next gear torque)

current gear rpm * current gear torque / 5250 = current gear hp (see the dyno chart) Insert this into the above and cancel the 5250 on the top and bottom

So we shift if

1 > (current gear hp)/ (next gear hp)

So by looking at torque and how that relates to actual force on the ground depending on gears we found that the hp curve is actually all we need to look at when considering shift points. And it seems that hp always drops when upshifting in the GT-3 so you should redline for the best acceleration. BTW the torque drop is magnified in your chart since the bottom of the graph is cut off. 380-325 nm is not much of a torque drop at all. That's only a 14% drop. My darn WRX drops from 290 foot pounds to 200 by 6500 rpm. That's a 31% drop.

 

^^^ Too scientific for my little brain.

Optimal shift point=rev limiter minus 1 rpm

 

That's been my stance until I started this thread.

Actually, here is my shift point.....
1,2,3, I hit redline (well about 8K), then in 4 I shift just a tad sooner on the front stretch at BEFORE the car is fully into the kin at the timing tower. If I don't I'll bang on the limiter for a few hundred feet going into the braking zone. I don't think I am gaining or even losing anything but rather it keeps be smooth going into the T1 brake zone.

The long back stretch I hit fifth pretty close to redline in 4th (crest of the top of the hill).

Looks like I'll just keep on with what I have been doing.


Thanks all for the great input (both scientific and anecdotal)

 

From a purely physics pov, it is the torque available at the drive wheels that accelerates the car. Since the transmission multiplies this torque (by the gear ratio), the ideal shift strategy is to shift when the current torque drops below that which is available at the same speed in the next higher gear. Since the GT3 makes such high torque at the top end of the RPM range, you'll see that (again, theoretically) the best shift point is redline (since the available torque there is still higher than that which is available immediately after shifting). The attached chart shows the torque v. rpm for the engine, and after the transmission.

 

All good to know, and were I racing this car or someone else owned it, I would be shifting close to redline. I understand that now.

For those of us who own the car and drive it just in DEs, though, where is the sweet spot where the power is very good but the cost of making that power, in engine wear, is not high? I find myself shifting around 7500 RPM, I think, in gears 2-4, but I sure shift lower (not sure where) in gear 1.