30th September 2006 Rolling Road Day

[markc]

Noel,

I see what you mean, I think I took your data and plotted torque between 3K and 8K revs in each gear graph. Torque is on the y axis and speed is on the x axis. See pic...

Now I've confused myself.

Reading off the speeds at where torque in the lower gear is exceeded by torque in the higher gear does this, contrary to my earlier statement, prove that you don't have to change gear at the limiter for max acceleration? If not what the hell have I done?

The crossovers occur at the following speeds and revs 43mph (7,489rpm), 66mph (7,135rpm), 89mph (6,980rpm), 122mph (7,507rpm), 139mph (6,950rpm)

Confused but intriegued

Mark

[Kevin]

That's what the graph says. So assuming you've calculated right, and graphed accurately it's what you say. You've proved yourself wrong!

It's probably worse in other that don't have the good torque curve of a Honda VTEC.

[markc]

Hah, yes done in by myself

I'll wait for Noel to comment as I used his data, spreadsheet and graph. I just input his torque (at the wheels) results into the graph and changed the x axis scale and titles.

I'll be amazed if this, that you can change up this early and still have more torque hitting the road, is true. It must be very unusual!

Please someone prove me wrong, I don't want to have to start changing up early and miss out on upto 1,300rpm's worth of VTEC nirvana so that I can go faster

Mark

[simonprelude]

If I am reading that right you need to change up to 6th at 140mph on a vmax run ??

[markc]

Yes Simon, that's what my graph says... I NEED someone to look at the data and prove it wrong!

Mark

[simonprelude]

I'll see if I have some time

Yes Simon, that's what my graph says... I NEED someone to look at the data and prove it wrong!

Mark

[Kevin]

Hopefully we can test it out, by doing a run for one car at TDi, once in 2nd gear and one in 3rd.

Hah, yes done in by myself

I'll wait for Noel to comment as I used his data, spreadsheet and graph. I just input his torque (at the wheels) results into the graph and changed the x axis scale and titles.

I'll be amazed if this, that you can change up this early and still have more torque hitting the road, is true. It must be very unusual!

Please someone prove me wrong, I don't want to have to start changing up early and miss out on upto 1,300rpm's worth of VTEC nirvana so that I can go faster

Mark

[NoelWatson]

Noel,

I see what you mean, I think I took your data and plotted torque between 3K and 8K revs in each gear graph. Torque is on the y axis and speed is on the x axis. See pic...

Now I've confused myself.

Reading off the speeds at where torque in the lower gear is exceeded by torque in the higher gear does this, contrary to my earlier statement, prove that you don't have to change gear at the limiter for max acceleration? If not what the hell have I done?

The crossovers occur at the following speeds and revs 43mph (7,489rpm), 66mph (7,135rpm), 89mph (6,980rpm), 122mph (7,507rpm), 139mph (6,950rpm)

Confused but intriegued

Mark

Mark,

Maybe using the term "torque at the wheels" is a bit misleading, because this will be a function of gearing. This site explains it better than I can - the lower the gear, the greater the torque multiplication.

http://www.mustangsandmore.com/ubb/D...orqueVsHP.html

I did all this in my Engineering degree donkies ago, forgotten most of it, but am pretty certain that a graph of torque at the wheels without taking into account gearing is misleading.

We still need to what out what the rev limit is!!

[Kevin]

Just to bring back this old thread....again

I've been doing a little reading.

Fact 1. The BHP figure and ft/lb figure are numerically the same at 5253rpm. This is due to the way BHP is calculated from torque. So on a graph, BHP and TQ always cross over at 5253. If they don't suspect something.

Fact 2. HP = TQ * RPM / 5253.5

I've been playing with a calculator, and seems some of the figures below don't add up.

So at 6500RPM, the HP should be 277, given the TQ number. However at
7000rpm the HP is 290.

With the competitive nature of some people here, those 1 or 2 hp here and there make all the difference.

I realise the figures came from the graph so errors will creep in, next time, we need hard figures not graphic printouts.

Every little helps.

My figures for S2 from the graph are;

RPM BHP lb/ft
1500 42 140
2000 76 176
2500 93 192
3000 118 201
3500 140 210
4000 165 212
4500 184 214
5000 204 212
5500 232 222
6000 254 222
6500 283 224
7000 286 218
7500 na na

[markc]

I've been obsessing about this and with the help of Noel and Kevin now understand why the torque vs speed graph I plotted is utter bo!!ocks Essentially it makes no allowance for gearing ie torque multplication.

So, I made a statement (that you ALWAYS have to shift at the limiter for max acceleration), then apparently proved myself wrong (with said graph), then disagreed with myself, and finally I've proved myself to have been right in the first place! Schizophrenic or wot

Anyway... Kevin built a spreadsheet which properly allowed calculations and graphs of torque vs speed to be plotted. I have added a number of variations of NSX model years and gearing options, including tyres to illustrate the effect. I used the power and torque outputs from Kevin's car in all instances. (attached zip file)

Graphs of the two extremes, a bone stock 1991 car on rear 225/50/16's and a Short geared, 4.44:1 diff car on 245/45x17's are pictured below.

Please feel free to comment on correct any faults you find in the spreadsheet.

One exercise I want to do with this info and these graphs is to calculate the area under each curve (total torque) and the aggregate of this for each sample car/gearing/tyre combination.

I do know I need to get out more....

Cheers

Mark