post them...

But you are comparing apples to oranages.

 

Krazik-s2k, I just sent them. and '...apples to oranges' - how's that? They're all roarsters, they all seat only 2. They are all rear wheel drive and they all weight about the same. Also the BoxterS and S2000 have both got 6 speed gearboxes. I would have though that you couldn't compare 2 cars more similar (MMW Z roadster could have gone in but the weight and power difference makes it tougher to compare just with a graph).

I think that the graph is about right. S2000 'can' keep close to BoxterS if it's driven above 7k revs while bellow 4.5k the 2.7 Boxter will perform better. Isn't that roughly where the S2000 fits?

 

David, That is not the best way to do it.

You should multiply the S2K torque curve by the BoxterS/S2K gearing ratio and then plot. To be precise you should include wheel radius into the equation.

Beware that gearing ratio varies with gear which is a problem. You could plot 6 graphs, one per gear, but you'd still miss out the fact that the upshift point is not the same for all cars.

So the real best way of comparing is to take torque at the wheels (better still, divide torque at the wheel by tyre radius, to give you linear force) and plot as a function of vehicle speed assuming optimal upshift points. Repeat with an upshift at 50% of the rev range to give you an idea on how the cars drive at a leisure pace.

If you have real dyno runs of all those 3 cars, send them to me and I'll try to see if I can do what I described.

 

Tyre/wheel size for the Boxter (standard) is the same for both Boxter and S2000. So the diameter is the same. That should not play part here.

Weight is the same too (though BoxterS weights 30-40kg more).

S2000 gearing is about 25% shorter for all gears (compared to BoxterS in particular. Comparing it to Boxter2.7 is hard here 'cos it has 'only' 5 gears). I tryed to take this into account in the 2nd graph which (I think) has the cars well compared. Though, it's not as perfect as I'd like ... hard to say how the 25% decrease in the gear rations really reflects on the S2000 power curve ... u can't jsut add 25% torque everywhere ... or can you? - I could do that and work out the 'new' kW/PS.

 

Not only can, but should. Power can be derived from torque times rpm. There is a constant factor that is dependent on units.

BTW, if the S2000 gearing ratio is equal to 75% of the Boxster S, then you should multiply the S2000 torque by 33.3% not 25%.

You still miss the shift points, reason why the approach I described gives you a better real world feel of how the cars pull.

Do send me the curves and I'll give it a go...

 

I though about this a bit more. S2000, Boxter2.7 as well as BoxterS all have exaclty the same diameter tyres. They also have almost exact weight 1259, 1260, 1295kg for the 3 cars respectively (S2000, Boxter2.7, BoxterS). BoxterS weights 36kg more which translates to 2.8% of S2000 weight (not much diff at all).

Anyway, I decided to plot power in each gear (through the whole rev range) over speed (though so far for only S2000 and BoxterS). This shows the 2 cars accelerating from idle to the maximum 'potential' speed and what power they have available at any given speed. It assumes gear-changes at red-line and no wheel spin. Result is very interesting:
- BoxterS seems to have a fair bit more power up to 58km/h
- Then S2000 has more pull up to 70km/h
- Then BoxterS pulls better to 88km/h
- Then S2000 to 86km/h
- Then BoxterS to 109km/h
- Then S2000 to 134km/h
- Then BoxterS to 154km/h
- Then S2000 to 160km/h
- Then BoxterS to 188km/h
- Then S2000 to 204km/h
- Then BoxterS to 223 km/h
- Then S2000 to 243km/h
- Then finally BoxterS pulls better after that.

It looks like at certain speeds the S2000 'might' actually be quicker. Though, when it is quicker (according to the graph) it is quicker only by a little. On the other hand, when the BoxterS is quicker - it's a fair bit more quicker then when things are reversed.

As I said, those extra 36Kg might handicap the BoxterS a tad more but not much as 36kg can easily be the difference between the loads of the 2 cars (driver, passanger, fuel and load).

Very interesting ... if anyone wants 'this' graph, let me know and I'll send it to you.

 

David and I did some graphing comparing the S2000 with the Boxster S.

In these graphs we plotted forward thrust (that is torque at the wheel divided by tyre radius) in kgf against speed (km/h) for 2 scenarios:

1) shifting at the redline
2) shifting at 60% of the rev range

Draw your own conclusions.