Anatomy of a Manual RL SKY: 0 to 60

[Bogie]

Please be kind to the engineer.

Ok folks, this is PURELY ANALYTICAL. Well, to be fair, I did linearize an actual SKY RL dyno chart in order to come up with my virtual dyno values. And I reverse engineered the loaded tire/wheel diameter from GMs published RPM/cruise data. But everything else is pure unadulterated equation crunching. I've never done this before, so I could have possibly screwed something up, or failed to account for something that might have an appreciable effect on the outcome.

On the other hand, given the end result, if I did fail to account for important stuff, it seems whatever I left out has canceled out rather nicely.

These value were produced without any attempt at establishing a preconceived result. I just took the available numbers and chugged the equations.

Seconds are cumulative:

0 to 34 mph (shifting to second): 1.91 sec (max g of .88)
34 to 56.5 mph (shifting to third): 4.51 sec (max g of .52)
56.5 to 60 mph (still in third): 5.51 sec (max g of .34)

Wow, considering the "advertised" zero to sixty number is 5.5, the analytical outcome of 5.51 is pretty darn cool. I guess now I need to do an automatic run. But what do I use for auto shift time? 300 msec?

Assumptions:

1359 kg SKY with a 90 kg driver
Coefficient of Rolling resistance = 0.03 (nominal value for asphalt)
Torque as function of RPM (i.e., a linearized virtual dyno)
1500 - 3000: 200 lb-ft (270N)
3000 - 5300: 225 lb-ft (305N)
5300 - 6200: 200 lb-ft (270N)
(Note: Dyno runs are based on "measured" torque, and therefore account for friction and drivetrain loses.)

Zero wheel spin
Loaded tire/wheelDiameter of 25.81 inches
1500 RPM Launch (can you do this and not spin wheels....don't know, but it's my assumption and I'm sticking to it)
Shift at redline 6200
500 msec shift time (per shift)
No turbo lag reductions.

Edit: Automatic Numbers (300 msec shift):
0 to 37.3 mph (shifting to second): 2.31sec (max g of .80g)
37.3 to 57.8 mph (shifting to third): 4.61 sec (max g of .51g)
57.8 to 60 mph (still in third): 5.2 sec (max g of .36)

Repeat Manual for comparison
0 to 34 mph (shifting to second): 1.91 sec (max g of .88)
34 to 56.5 mph (shifting to third): 4.51 sec (max g of .52)
56.5 to 60 mph (still in third): 5.51 sec (max g of .34)

Observation: The manual is faster in both 1st and 2nd gear. When accelerating, it pulls more Gs than the Automatic at all points except the final 4 mph; the Auto has a stronger third gear than the Manual. Yet, the Auto beats the Manual by .3 seconds. Why? It can shift faster. The Manual is .1 seconds faster when accelerating, but the auto is .4 seconds faster on the two shifts, giving the Auto a net .3 seconds at the 60 mph point.

Also note the Manual is faster "off the line". Although the Auto carries 3mph more in first gear (which mitigates the time offset at gear shift time), the Manual is shifting to second almost a half second before the Auto shifts. This lead carries through second gear, with the Auto catching up on the last shift.

A last note is the max g. The manual hits a max of .88, while the Auto give you .80. The manual will "feel" faster (and, as noted above, it is faster "when" accelerating), and push you back in the seat with about 10% more force. So, from a pure "fun factor", I believe the manual beats the auto, even though the auto is quicker to 60.

[mbeardsley]

Interesting work...thanks.

I was under the impression that one of the main reasons that the Automatic was faster was that it kept the turbo spooled between shifts.

You seem to be assuming no turbo lag. If that is the case, aren't you ignoring one of the main "benefits" of the Automatic, in that the Auto would suffer less turbo lag between shifts than the manual ?

Or are you assuming that the "faster shift" already includes this ?

[Bogie]

Originally Posted by mbeardsley

Interesting work...thanks.

I was under the impression that one of the main reasons that the Automatic was faster was that it kept the turbo spooled between shifts.

You seem to be assuming no turbo lag. If that is the case, aren't you ignoring one of the main "benefits" of the Automatic, in that the Auto would suffer less turbo lag between shifts than the manual ?

Or are you assuming that the "faster shift" already includes this ?

I don't know the real story is on the turbo. I've heard it explained as you've explained it, but is this just speculation (or perhaps an educated guess) or is there some testing/engineering to back it up?

I'm assuming a 500msec manual shift and a 300msec automatic shift. How much spool does a manual lose in 500msec compared to what an auto loses in 300msec? The torque specified in my virtual dyno, adjusted for gearing, is what is delivered when the vehicle is in gear. If a turbo spool reality exists that affects manual and auto differently, I don't account for it directly.

Perhaps this is a case of ignoring two items that cancel each other out. I've ignored the initial turbo spool up, albeit the 1500RPM launch and the virtual dyno may account for it. If there is additional spooling energized from 1500 to 3000, then the manual (with its stronger first gear) will spool up faster than the auto. Perhaps this boost benefit on the launch is cancelled out on the shifts. Don't know...just speculating.

Also, by linearizing the dyno chart, I may have undercut the initial torque rise. An actual SKY dyno shows the torque rising up and then arching over at the low end peak. My linear values run below the arch, which would make my linear dyno torque values underperform compared to the actual dyno chart. Although not my intent, the underperformance difference could be attributed, ex post facto, as turbo lag.

[Im Fastr]

Here's where the rub is... if second gear was just a little bit taller, there wouldn't be a shift required to get to the 60MPH mark and this would be a "less than 5 second" car. I don't understand why the engineers couldn't make that happen??

[Bogie]

Originally Posted by Im Fastr

Here's where the rub is... if second gear was just a little bit taller, there wouldn't be a shift required to get to the 60MPH mark and this would be a "less than 5 second" car. I don't understand why the engineers couldn't make that happen??

I'll work the numbers and see what comes out. Taller will accelerate less, but can be sustained longer. Also, we need to make sure the drop from a stong first to a weak second doesn't drop below the powerband. Lastly, a quicker 0 to 60 may make for a longer quarter mile.

And then there is the curvy track use. You need second for more than just 0 to 60, and you might not want a weak second coming out of a turn calling for second gear.

[lorennerol]

Originally Posted by Im Fastr

Here's where the rub is... if second gear was just a little bit taller, there wouldn't be a shift required to get to the 60MPH mark and this would be a "less than 5 second" car. I don't understand why the engineers couldn't make that happen??

A couple hundred more RPM before the redline would get us there, too.

Doesn't the BSR tune extend the red line in the first two gears? Is it enough to get to 60? Anyone? Anyone? Bueller?

[Bogie]

Originally Posted by lorennerol

A couple hundred more RPM before the redline would get us there, too.

Doesn't the BSR tune extend the red line in the first two gears? Is it enough to get to 60? Anyone? Anyone? Bueller?

RPM at 60mph for current gear ratio:

Manual: ~6580
Auto: ~6440

Even without a tune, the stock control delivers more torque at the wheels in first at redline than it gets on the shift to second. In other words, simply extending the cutoff will increase performance. I might extrapolate the Dyno fall off to 6500 and see what it delivers.

My numbers are simply the values required given the tire size, loading, and gearing. These are not reflective of BSR tune.

[Bogie]

Originally Posted by Bogie

I'll work the numbers and see what comes out. Taller will accelerate less, but can be sustained longer. Also, we need to make sure the drop from a stong first to a weak second doesn't drop below the powerband. Lastly, a quicker 0 to 60 may make for a longer quarter mile.

And then there is the curvy track use. You need second for more than just 0 to 60, and you might not want a weak second coming out of a turn calling for second gear.

I made 2nd taller (went from 2.26 to 2.12) which keeps you in second to 60mph. The new gear beats the stock by 0.5; gets a 0 to 60 in 5.0.

However, since you shift at 60 (and take the 500msec hit at that point), pulling out of 60 both cars are about dead even. Which goes back to my last comment above. By tuning second gear to meet the 0 to 60 mph spec, it will be less capable in most other second gear applications.

[BlueSkyRL]

These calculations are loosely based on the fact the the driver is very good at shifting a manual. Bogie, I'm sure you know these times have already been calculated and proven in the real world too. So I'm kind of waiting for the punch line or where you might be going with this??

[Bogie]

Originally Posted by BlueSkyRL

These calculations are loosely based on the fact the the driver is very good at shifting a manual. Bogie, I'm sure you know these times have already been calculated and proven in the real world too. So I'm kind of waiting for the punch line or where you might be going with this??

I am an engineer having fun developing equations and crunching numbers. There is no punch line.

[Darkwing]

My real world 0-60:

1. Find an open roadway with no traffic and stop.
2. Place car in 1st gear, release clutch and stall engine. restart car- 6 seconds.
3. Get rolling in first, miss shift to second gear, grind it back into first- 8 seconds.
4. make shift into second, now rolling at 55. Time elapsed- 3 seconds.
5. actually get car in 3rd gear without missing and reach 60 mph.- 1.5 seconds.

Total elapsed time 0-60 18.5 sec.

[Bogie]

Originally Posted by Darkwing

My real world 0-60:

1. Find an open roadway with no traffic and stop.
2. Place car in 1st gear, release clutch and stall engine. restart car- 6 seconds.
3. Get rolling in first, miss shift to second gear, grind it back into first- 8 seconds.
4. make shift into second, now rolling at 55. Time elapsed- 3 seconds.
5. actually get car in 3rd gear without missing and reach 60 mph.- 1.5 seconds.

Total elapsed time 0-60 18.5 sec.

It certainly makes the math easier.

[BLUUSKY]

Originally Posted by Darkwing

My real world 0-60:

1. Find an open roadway with no traffic and stop.
2. Place car in 1st gear, release clutch and stall engine. restart car- 6 seconds.
3. Get rolling in first, miss shift to second gear, grind it back into first- 8 seconds.
4. make shift into second, now rolling at 55. Time elapsed- 3 seconds.
5. actually get car in 3rd gear without missing and reach 60 mph.- 1.5 seconds.

Total elapsed time 0-60 18.5 sec.

Actually did step two yesterday - quite embaressing. Glad the truck behind me was paying attention.