I think I can put an end to the 'different diameter wheels/tyres affect the torque at the wheel' argument. Reason being is that Boxster and S2000 have EXACTLY the same wheel/tyre sizes. Boxster2.7 comes with 225/50/16 tyres at the back - just like the S2000. You can get bigger wheels from Porsche (you can even get 18" with the S) but they still match the 225/50/16" diameter of a 'regular' Boxster and S2000. Therefore, the tyres/wheels are non-issue here.

If you look at Boxster2.7 and S2000 then they weight the same and have the same wheel/tyre size. Therefore all that makes difference here is the power and gearing (and aerodynamics at higer speeds).

If you're looking at BoxsterS and S2000 then again the wheels/tyres are the same diameter and the weight is almost the same ('stock' BoxsterS weights only 3% more than S2000). So again, you really just need the power and gearing and then account for 3% weight difference.

 

.... sigh ....

My intention was not to revive the eternal discussion of whether the S2000 is a better car than the Bosxter. Grown men (& women) have gone past that and acknowledge they are both nice pieces of machinery .

What I was trying to contribute was some insight into the power delivery of the S2000, 2.7 and 3.2 porsche engines. Quoting maximum torque numbers for engines is NOT a way of comparing performance potential. Full stop.

I also agree that measuring F (and M) on the ground is the best way of comparing. However we run into problems very quickly.

Mass is constant and easily factorable.

Force is dependent on engine torque, gearing, tyre size and drive train losses. You may estimate the latter. The others can be known.

The problem is when people start to complain about low end torque. To analyse these claims you need to define "low-end", and measure F when shifting accordingly. It's doable but we need a consensus. That is why I though the power vs rev range curves I plotted above were a bit more appopriate to this discussion. You just suit yourself with whatever low-end definition you are comfortable with.

In the past I have done and posted what you asked for. These were the results I came to: (Y axis: traction measured in kgf (divide by .45 to get lb), X axis: speed measured in km/h (to get mph divide by 1.6)).



It's also easy to perceive the "low-end" torque problems of the S2000 in this chart. I have presented data without commenting, but before anyone jumps to conclusions, I believe the difference is not that important.

As Chris D'Elena stated, it does give you a disadvantage on corners where you are trying to avoid an upshift and select a higher gearing than would be appropriate, but in general the little 1,997cc engine does rather well.

 

Interesting thread. I have measured the performance of many different cars. One thing I'd like to add is that in no-torque cars the subjective throttle response can be soft down low. As in needing to step on the gas pedal further than other cars to obtain X amount of torque. You can see this if you do what I call 3D dyno plots. That's where you run the test at various fixed throttle opening. Often there are HUGE differences. Two cars may have similar torque curves when floored but not at say 20% throttle. The one that has lower torque at lower throttle openings feels much weaker. Some cars have something like 40% less torque at the lower throttle openings than other cars with comparable wide open throttle. Drive by wire can really improve this subjective characteristic. Also, generally speaking, the subjective problem goes away with revs. For example, you could accel with 1/4 throttle and it feels weak but then above some rev it feels much better. Coming up on the cam so to speak. Torquey cars feel like they are always on the cam with 3D dynos that match the WOT dynos except the curves are displaced downward. Hope this makes sense!! It's not just the raw tech info - there are human factors to consider as well.

Stan

 

Luis, thanks VERY much for those last graphs! This is exactly the information I was hoping to get.

My take on your analysis:

1. Driven in a relaxed way (no VTEC), the S2000's thrust is within 15% of a Boxster S driven the same way in all gears but first. Since the Boxster S weighs a few percent more, the S2000's ability to accelerate is that much closer, perhaps 90% of a Boxster S. It's interesting to see that the difference disappears in 6th gear at high speed (or is the Honda VTECing by then?).

2. Driven hard (redline shifts), the S2000 gives away nothing to a redlined Boxster S above first gear.

3. The reason for the first gear exceptions is simply that Honda chose a tall first gear for the S2000. This complicates standing starts but enables a driver to downshift to first in tight corners, which he can then exit at maximum acceleration. Since the S2000 is intended for road racing and not drag racing, this is an excellent compromise.

4. So, assuming equally skilled drivers, a Boxster S is probably a bit quicker than an S2000 in the quarter mile (because of the S2000's tall first gear) but not on a road course.

Thanks again. I always enjoy your posts.

 

-------------------------
2. Driven hard (redline shifts), the S2000 gives away nothing to a redlined Boxster S above first gear.
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I think you ment to say 'ABOVE 2ND GEAR' ... correct? Going by nothing else but the graphs posted in this thread, it's above 100kph (62mph) that the 2 curvers are more or less equal. Untill then the BoxsterS is clearly above. Good 25% higher in the 1st gear and about 10% higher in the 2nd.

Or are you discarding the 10% advantage in the 2nd gear?

ps. I worked out something interesting .... try replotting these graph/s with the S2000 having 10% more torque and see what happens. You get a pretty close match with the BoxsterS curve (even bellow 100kph). That mean that the current engine enlarged to 2.2L (while retaining the current characteristics and redline) is all that's needed.

 

Great info, thanks I know it took a little time to put together.


Hugh

 

[QUOTE]Originally posted by DavidM
[B]I think you ment to say 'ABOVE 2ND GEAR' ... correct? Going by nothing else but the graphs posted in this thread, it's above 100kph (62mph) that the 2 curvers are more or less equal. Untill then the BoxsterS is clearly above. Good 25% higher in the 1st gear and about 10% higher in the 2nd.

 

Hey if you've got a spare hour or two throw in the M Roadster engine, last years. It would be interesting to compare truly different types of engines with similar performance. The boxster engine, especially the S, really lives somewhere between the M the the S2000.

Hugh

 

[QUOTE]Originally posted by Luis
[B].... sigh ....

My intention was not to revive the eternal discussion of whether the S2000 is a better car than the Bosxter. Grown men (& women) have gone past that and acknowledge they are both nice pieces of machinery .

 

Hi

Apologies if this looks awful - first time I have tried this.

I think everybody is really after a graph which plots what is known as tractive effort (corresponds to F) in each gear - i.e. all the relevant factors of gear ratios, final drive ratios and wheel sizes are included and plotted against speed.

By also plotting the product of drag coefficient and frontal area plus frictional losses, where the two curves cross is the point where tractive effort is overcome by resistance i.e. theoretical top speed. Where the curves for the respective gears cross is also the optimum shift point - not always at the redline although for a revvy little unit like the S2K I rather suspect it is close to the redline.

Paul 1/2p

PS
Where are the cheapest S2Ks in Europe before taxes?? Wanna order one and have diplomatic tax free status.