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I multiplied Torque (Nm) by the gear and final ratio then divided by 1.356 (NM/lbft) then divided by the effective radius of the tire (in feet - different for GT4 and GTS) to get lbs of thrust at the wheel contact surface with the ground. Now, I do not have drive train losses included. So, as a comparison - it is *reasonable* - but don't expect it to be a correct absolute number. I calculated the speed and thrust (lbs) for each gear then took the max of all gears at each speed. Make sense?
I multiplied Torque (Nm) by the gear and final ratio then divided by 1.356 (NM/lbft) then divided by the effective radius of the tire (in feet - different for GT4 and GTS) to get lbs of thrust at the wheel contact surface with the ground. Now, I do not have drive train losses included. So, as a comparison - it is *reasonable* - but don't expect it to be a correct absolute number. I calculated the speed and thrust (lbs) for each gear then took the max of all gears at each speed. Make sense?
I'm the one that made those graphs in the other conversation and you are correct to a point. However, gearing really plays a large part in it as well (potentially even more than the base torque curve). When accelerating/racing, you will shift to be in the best torque position you can be in with the combined torque curve and available gearing. A high rev'ing N/A motor will not spend time in the low RPMs except during first gear. Having the higher RPM to stay in a lower gear longer gets that better multiplier for the lower gear for a longer time.
Here is a chart comparing max torque at the wheels at all speeds for manual gearbox 2.5 GTS, 4.0 GTS, and GT4. The only location that a 2.5 GTS will have an advantage is under 30 mph. On a race track that would be mostly above 30mph, the GTS 4.0 will be quicker. On city streets, from stop light to stop light, the GTS 2.5 will in theory have the advantage. However, I suspect that is only true if you are launching and have pre-loaded the turbo. There is a lag on a 2.5 GTS to get it to spin up the turbo and get full torque. I have been pleasantly surprised with the 4.0 motor in how much torque it has down low and how quickly it responds to inputs.
*Edit* - PS: There is an effect with wheel spin that I'm not sure I understand as well. If both cars have enough torque to break the wheels loose at low speeds there may be a limit on "useful" torque at low speeds........
Thanks for helping out with this? I'm curious though, are you taking them all to red line before your calculation shifts to the next gear?
I have some of this in a spreadsheet also but haven't convinced myself of my calculations yet.
Thanks for helping out with this? I'm curious though, are you taking them all to red line before your calculation shifts to the next gear?
I have some of this in a spreadsheet also but haven't convinced myself of my calculations yet.
Schmaybe ...
This might help to explain what I did. Here is a comparison of the GTS 4.0 PDK versus the GTS 4.0 Manual. I plotted thrust at the wheels at 1500 through 7800 rpm at every 500 rpm except for 7800 which is the max that the GTS is allowed.
So at first gear it is obvious that going to redline is better than switching to the next higher gear prior. At 7800 rpm in first gear at around 42 mph in the (PDK) there is still ~3300 lbs of thrust but if I was in second gear I would only be at 4500 rpm and ~2200 lbs of thrust. As you get in the higher gears the lines start to collapse and it may be that you want to switch down a gear before 7800 rpm but it is close. The difference is so small that unless you really want to memorize a bunch of tables that taking it to red line is the fastest for acceleration.
So the same plot with GTS 4.0 PDK and manual where I just plot the max thrust in the best gear available is below.
There really should be a vertical line connecting the "gears" but I only plotted every 500 rpm for data points so the shifts actually have a little slope. I thought about recalculating the rpm at the shift point for the next higher gear but it looked like a lot of work when this was so easy and was close enough.
The lines really collapse above 100 mph to no difference between PDK and manual (unless drive train losses or weight become a factor). 7th gear in the PDK does nothing for the track or acceleration - it is just for better gas mileage. I have no idea why they made a big deal about it being lower. My only guess is that the cylinder deactivation needed a little more torque with only 3 cylinders active.
Folks, Janko Lind is entitled to his own opinion. I rather like him.
Even if I disagree with him on the GTS 4.0. I didn't drive it, but I drove the GTS 2.5. It's a very powerful engine but it sounds terrible from idle (maybe not if you're into tractors). I preferred the 20 mm lowered PASM over the 10 mm lowered PASM of my previous 981. But I like the 30 mm GT chassis of my Spyder even more...
I like him too, I’m sure many here do, he provides some nice Porsche content.
In this review however he says some bizarre things, His comment about the GTS 4.0 weight being an issue but it’s not on the Spyder The GTS being ‘incomparable’ to the Spyder etc
To me, and I don’t know him that well, it came across very much a ‘purchase justification’ sort of review.
Originally Posted by Yellow Submarine
Folks, Janko Lind is entitled to his own opinion. I rather like him.
Even if I disagree with him on the GTS 4.0. I didn't drive it, but I drove the GTS 2.5. It's a very powerful engine but it sounds terrible from idle (maybe not if you're into tractors). I preferred the 20 mm lowered PASM over the 10 mm lowered PASM of my previous 981. But I like the 30 mm GT chassis of my Spyder even more...
This might help to explain what I did. Here is a comparison of the GTS 4.0 PDK versus the GTS 4.0 Manual. I plotted thrust at the wheels at 1500 through 7800 rpm at every 500 rpm except for 7800 which is the max that the GTS is allowed.
So at first gear it is obvious that going to redline is better than switching to the next higher gear prior. At 7800 rpm in first gear at around 42 mph in the (PDK) there is still ~3300 lbs of thrust but if I was in second gear I would only be at 4500 rpm and ~2200 lbs of thrust. As you get in the higher gears the lines start to collapse and it may be that you want to switch down a gear before 7800 rpm but it is close. The difference is so small that unless you really want to memorize a bunch of tables that taking it to red line is the fastest for acceleration.
So the same plot with GTS 4.0 PDK and manual where I just plot the max thrust in the best gear available is below.
There really should be a vertical line connecting the "gears" but I only plotted every 500 rpm for data points so the shifts actually have a little slope. I thought about recalculating the rpm at the shift point for the next higher gear but it looked like a lot of work when this was so easy and was close enough.
The lines really collapse above 100 mph to no difference between PDK and manual (unless drive train losses or weight become a factor). 7th gear in the PDK does nothing for the track or acceleration - it is just for better gas mileage. I have no idea why they made a big deal about it being lower. My only guess is that the cylinder deactivation needed a little more torque with only 3 cylinders active.
Greg_STL:
Thanks for all this information. I needed to convince myself but I understand now.
Thank you!
12-30-2020, 04:57 PM
The GTS being ‘incomparable’ to the Spyder etc
