'Kick-down' acceleration

[Physician]

OK ....... Kieran - you were bored. Any good at mathematics? I'm useless, but would like to know the following if someone can work it out for me. It doesn't need to be precise, + or - 10% would be adequate.

You are travelling at 30 mph (in a std VR4). You use the kick down accelerator. How many seconds (or parts of a second) will it take to reach 40 mph, 45 mph, 50 mph and finally 60 mph?

Is there a member named Einstein out there? :-D

Thanks guys and gals,

Richard

[pjjohnson]

five

[Physician]

five

Haha! I take it you're another maths failure pjj

There must be a formula around somewhere to calculate this.

[SGHOM]

steady @ 30 mph, you'll probably be in 4th gear. hit the loud pedal & wait................... the car will take a deep breath, select 1st gear, & you'll be doing 50 mph before you can look at your stop watch !!
It's the delay factor, in the gear change thats the problem ! And also, regardless of what speed you're doing, It always selects a lower gear than you actually need.

[enigma]

Tried it tonight with my Apexi RSM set to measure from 50kph to 100kph.......near as dammit 30mph to 60mph. Anyway as Derek assumed it was in 4th at a sedate 49kph.........ket it up for 3-4 seconds then booted it. It dropped in to 2nd and not 1st as estimated and took a total time of 4.29 seconds.

[Physician]

Tried it tonight with my Apexi RSM set to measure from 50kph to 100kph.......near as dammit 30mph to 60mph. Anyway as Derek assumed it was in 4th at a sedate 49kph.........ket it up for 3-4 seconds then booted it. It dropped in to 2nd and not 1st as estimated and took a total time of 4.29 seconds.

Wow! thanks for doing that Dave. I must say I'm very surprised at that figure. I would have thought somewhere in the region of 2.5 to 3.0 secs from 30 to 60 mph. And somewhere around 1.5 to 2.0 secs 30 to 40 mph.

I base this thinking on the fact that you were running 4.69 from 0 - 60 mph with a bit of Nitrous and of course you've got the initial resistance it getting the whole heap moving from zero.

I lost some figures I downloaded which you once quoted about terminal speeds in each gear and can't find it again here on the forum, but I guess it will be much faster using the 'manual' side and booting it from 30 mph to 60 mph in, preferably 2nd gear, if it will go to 60 mph in 2nd (otherwise 3rd).

Thanks,

Richard

[enigma]

You have to remember that when doing a steady 29mph you are not accelerating. When doing a 0-60mph when you reach 29mph you have quite a rate of acceleration!

If we go back to physics......

End velocity = start velocity + (acceleration X time)

60mph = 26.66 m/s
30mph = 13.33 m/s
0mph = 0m/s (!)

So assuming constant acceleration:

0-60 in 4.69s

26.66 = 0 + (a X 4.69)

so

a = 5.68 m/s^2

now for 30mph-60mph

26.66=13.33 + (a X 4.21)

so

a = 3.17 m/s^2

If we use these acceleration figures in each others equations and solve for time we get:

0-60 with acceleration of 3.17m/s^2

26.66 = 0 + (3.17 X t)

so

t = 8.4 seconds

and for 30mph - 60mph

26.66 = 13.33 + (5.68 X t)

so

t = 2.34

which is somewhere near your estimate. It all revolves around getting a body moving from 'rest' where 'rest' can be stationary or a condition of no acceleration.

Now I am nbot sure what all the above was about, but essentially what I am trying to say is that if you reduce the problem to its simplist form you wont get the results you expect.

I will do a 'rolling' 30-60 tonight on the way home and see what we get! (it will also tell me how many metres I travel in doing so!)

[pjjohnson]

Its still five

[Nigelator]

why dont u guys try this in tip/manual mode I am expecting that the Auto reduces all the power down while it changes gear, (and unfornently it anit a porshe unit just their down grade),

I am gona catch a friend to give this a couple of run, if our weather clears up
(waiting for the thunder lol )

[calum]

Based on the above, I would have to disagree with pjjohnson.

I think it's 4.

[enigma]

Tried a rolling 30-60mph last night as promised. Not the best of runs and I think the box decided to change from 1st to 2nd at bang on 30mh causing a slowish time but..........clocked a 3.56 seconds. :rolleyes5 This was with my car runnning 0.7Bar boost (only very slightly more than standard).

Will try in tip mode and see if I can squeeze it down a bit!

I will also (if I remember) try and clock it at Japshow in October with more boost, race fuel and a little bit of pixie gas! I would expect low to mid 2 seconds under these conditions.

[Physician]

Thanks Dave ........ all very interesting having taken most of yesterday trying to understand the maths!

Although I have no means of measurement (electronic tech equipment like yours) I have been doing some runs myself and it is certainly much faster in tip (manual) by selecting and holding in 2nd at 30 mph and then flooring it. (In fact it felt like V2 ...... time to 'rotate' :-D )

Thanks for the help.

Richard

[pjjohnson]

Depends on which way the winds blowing, and the velocity of your foot when you press the on the gas. And on the temperature and viscosity of the oil in the gearbox. And also on when you start the timing, from the thought, or the press on the gas, or from the start of acceleration. And other things as well.
Its still five, plus or minus a bit of course.

[enigma]

And also on when you start the timing, from the thought, or the press on the gas, or from the start of acceleration.

Timing starts at 50kph (~30mph) and stops at 100kph (~60mph)......period!

Anyway 2 mre tests:

First steady 29mph in 2nd (tip) and boot it.......result 3.91 seconds

Second accelerate from a standstill in tip and change to 2nd at 25mph to avoid including the time to change gear........result 3.35 seconds

[pjjohnson]

Still five.