Who can tell me what is the best rev range to change gears for the fastest launch in an unmodded vrs, and why (in laymans terms please). i.e. is redline every gear, or changing at 5000ish faster? Just wondering which and why?

Cheers,

Damo

I would have thought you'd want to change up just before you hit the rev limiter for maximum power/acceleration?

Theoretically change up where your power and torque curves cross, which will usually be below the redline.

On the plus side, if you change up before the redline you haven't lost too much torque. The power delivery slows down after the peak torque. You should hit the next gear in a nice meaty part of the torque curve and get a renewed thrust from the turbo.

On the minus side, gearchanges cost time, so for short sprints, keeping in the lower gear may lead to better times.

I'd've thought you'd change up just after the peak in your torque curve, so that when you've slipped up into the next gear the revs will be sitting roughly at the peak again...

Rob.

At peak power or slightly below, would need to see the graph for a definitive answer. Mine is at 6k.

Speaking of which, does anyone know a good place to find torque curves? Looked for a generic one for the 1.6 8v unit but no joy... :(

Rob.

no graph as no jabba :(

Damo

Damo - below is the torque curve for the 150bhp engine in a Superb...not sure how it would compare to the 180bhp in a vRS, but it might give you an idea of whereabouts to try changing gear...

Rob.

Looks a little stylised to me ....

Well, yes...but it's better'n nothing... :p

Rob.

Want to try my tactic - Take 1st gear up to 4000RPM, dip clutch, put into 2nd, release clutch too early - GRAUUUNCHHH! [5HIT!] dip clutch and try again

Doesn't happen all too often, but it did occur this morning unfortunately. I guess my foot sometimes doesn't realise how long it takes the hand to move the stick! :(

That graph is complete boolox! Power and torque (in a petrol engine) will always cross at 5252 rpm

Oh, right...why's that then?

And spare no details in your explanation...

Rob.

Because of physics.

http://www.howstuffworks.com/question622.htm

That's not physics, that's maths! :p

Rob.

What happens is physics - how you describe it is maths.

So, with regard to the graph - would it make a difference where the performance was measured at? As in, if it's the car's overall performance rather than the engine's alone?

Rob.

That graph is complete boolox! Power and torque (in a petrol engine) will always cross at 5252 rpm

That would be on a Bhp - lb-ft plot where you need the 1 HP = 550 lbft/sec convertion to be devided by the number of 2pi/60 (one rev per minute in rads) which gives

550*60/2*3.1416 = 5252

So the point on the BHP - lbft plot where the torque and HP is equal, hence their ratio is 1 and thus RPM equals to the constant.

However, on a KW - Nm plot, you have

1KW = 1000Joules/sec = 1000NM/sec (Torque and Energy have same dimention only former is a vector ).

In which case to obtain the point of crossing between the two curves you have:

P = T/time -> P = T*(rad/sec) = T*(60/2pi)*RPM

Multiply both sides with 1000 to go to KW, and you have

P (in KW) = T * 1000 * 9.549 * RPM

Set P = T to get the crossing point and obviously the RPM at which this occurs is 9549RPM (out of the shown plot.

Correct me if I'm wrong.

Edit: As for the shown crossing point, bear in mind that the plot shown is out of scale (left and right axes). For the above values to appear as crossings the same vertical numerical scaling should be used.

Edit 2: And it is actually maths not physics as the crossing point has absolutely no physical meaning. It's just a convenient way to convert from Torque to Power and vv on a plot that has only one of the two shown.

You missed a ':' somewhere :p

You can find a spare one on the end of Q's smiley tags!

to Otheos! Very good explanation.

Originally posted by Dutch4x4 in this post

What happens is physics - how you describe it is maths.

Very eloquent.

Sorry, so this still hasn't answered what the optimum point to change gear in an unmodded vrs would be. So could someone (who understands) put all that maths too good use and work it out for me? If you need the unmodded power map I wonder if any kind sole has their pre jabbed map to hand??

Damo

Originally posted by dab in this post

Sorry, so this still hasn't answered what the optimum point to change gear in an unmodded vrs would be.

Sure we did...it'll be at about 5k RPM...

Rob.

I take it that you deduced that from the 5252rpm bit earlier? If so, having read on I thought that this wasn't necessarily true for all cars, as TaviaRS' is round 6000rpm. :confused:

Damo