Dyno Dynamics - Shoot out modes

Dyno Dynamics - Shoot out modes

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Discussion

GregK2

Original Poster:

1,651 posts

145 months

Friday 16th November 2018
quotequote all
Mignon said:
My bad. I missed that the pedal position was 100% and the throttle is drive by wire so that only opens as much as needed. Assuming that was a flat road I obtained a perfect acceleration curve matching actual to calculated 10 mph increments to within 0.01 seconds for every increment. I've never actually obtained a curve as perfect as that right the way through a gear.

At the flywheel you have peak torque of 417 ft lbs at about 3000 to 3500 rpm and peak power is 357 at about 5000 to 5250. That's 303 bhp at the wheels.

From the intergoogles I obtained curb weight of 3420 lbs so plus driver I used 3600. Final drive 3.08, 3rd gear 1.58, rear tyres 245/35/18. MPH per 1000 rpm in 3rd is 14.53. Frontal area 22.4 sq ft, cD 0.33. Spec sheet is here.

http://media.caranddriver.com/files/2008-bmw-135i-...

The car is very traction limited, it'll light the tyres up without even trying so acceleration off the line depends on tyres and launch but on very good road tyres I get 0-60 mph in 4.7s. 1/4 mile is 13.26 @ 110 mph. Top speed is 171.
This is fascinating stuff and you got exactly the kind of figures I would have expected to see.

AW111 thanks for taking the time to run that. there is very little difference in the simulated power outputs between modes. But would wheel spin issues be more likely as a result of the slower than desired ramp rate? I think we can deduce that the heat soak from failed runs had more of an adverse affect than the shootout mode now?

Mignon

1,018 posts

88 months

Friday 16th November 2018
quotequote all
AW111 said:
It's better than it used to be : the current standards basically require the engine to be tested "as fitted", so with all accessories, equivalent exhaust, etc.

Back when we started this flywheel power malarkey, we kept getting low fly power figures for one particular model car, compared to the brochure figure. An unofficial chat with a couple of the manufacturer's engineers revealed that they couldn't get the official power figure on their engine dyno either...
but things are better now.
Jaguar.

AW111

9,455 posts

132 months

Friday 16th November 2018
quotequote all
GregK2 said:
This is fascinating stuff and you got exactly the kind of figures I would have expected to see.

AW111 thanks for taking the time to run that. there is very little difference in the simulated power outputs between modes. But would wheel spin issues be more likely as a result of the slower than desired ramp rate? I think we can deduce that the heat soak from failed runs had more of an adverse affect than the shootout mode now?
I setup the tacho ratio to the same as the original graph : that gives peak power @ 5500 rpm, 103 kph.
That means that peak torque will be produced at around 50 kph (2750). I would expect tying it down to be problematic.
What gear was it run in previously?

But sight unseen, from the other side of the planet wink - if you think it was suffering from heat soak (which would be exacerbated by a slower than ideal ramp rate) that's definitely what I'd suspect first.

Mignon

1,018 posts

88 months

Friday 16th November 2018
quotequote all
AW111 said:
I setup the tacho ratio to the same as the original graph : that gives peak power @ 5500 rpm, 103 kph
That opens up another metallic container of vermicular entities then. The tacho ratio photographed is 53.19 rpm / kph. That calculates to 11.68 mph / 1000 rpm. I've just run a simulation based on the stated gearing and tyre sizes of the car I found online and it's 14.53 mph / 1000 rpm in 3rd. For reference the mph / 1000 rpm in each gear is

1st 5.65
2nd 9.56
3rd 14.53
4th 19.29
5th 22.95
6th 26.38

I suggest the car owner check this next time he's out for a drive. Most car speedos read a bit high but those flashing slow down signs with built in speed detector are pretty accurate and a good way to check it.

Mignon

1,018 posts

88 months

Friday 16th November 2018
quotequote all
More questions are being raised than answered. Spitfire's dyno is showing huge differences between the various shootout modes. AW111's simulator isn't. What's going on? Spitfire's dyno has inertia as a linear (flywheel mass) default of 100 kg which calculates a moment of inertia value of 1.19 kg m^2. Other printouts are showing a TN value of 3.4 or whatever. What's the difference? What does 3.4 actually mean in standard units? Is there a software difference issue here and maybe Spitfire's dyno needs updating?

GregK2

Original Poster:

1,651 posts

145 months

Friday 16th November 2018
quotequote all
Mignon said:
I suggest the car owner check this next time he's out for a drive. Most car speedos read a bit high but those flashing slow down signs with built in speed detector are pretty accurate and a good way to check it.
I have added speed to the logging software I use so will get a 3rd gear log with it.

Mignon

1,018 posts

88 months

Friday 16th November 2018
quotequote all
GregK2 said:
I have added speed to the logging software I use so will get a 3rd gear log with it.
Jaysus. Just see how fast the car is going at 3000 rpm like we had to do in the stone age. Not everything needs a bloody computer.

PeterBurgess

775 posts

145 months

Friday 16th November 2018
quotequote all
I'll check mph per 1000 on my rollers for you Dave smile

Mignon

1,018 posts

88 months

Friday 16th November 2018
quotequote all
PeterBurgess said:
I'll check mph per 1000 on my rollers for you Dave smile
I think you should. Then you might work out what's wrong with your 1.9 race MGB power curve with 82 ft lbs per litre at the wheels.

GregK2

Original Poster:

1,651 posts

145 months

Friday 16th November 2018
quotequote all
Mignon said:
GregK2 said:
I have added speed to the logging software I use so will get a 3rd gear log with it.
Jaysus. Just see how fast the car is going at 3000 rpm like we had to do in the stone age. Not everything needs a bloody computer.
biggrin

https://datazap.me/u/gregk2/speed?log=0&data=6...

Mignon

1,018 posts

88 months

Friday 16th November 2018
quotequote all
GregK2 said:
Exactly as I calculated from the spec gearing. 14.5 mph / 1000 rpm. Your dyno run got well screwed up then. One of the first things I check for when I'm analysing a dyno graph is whether the rpm is correct for the wheel speed and/or the expected power points of the engine type in question. If not it screws up all the numbers. Sadly most of the people who run dynos are neither mathematicians nor often very bright, or at least pedantically careful which can often compensate for the former. It helps to be both with a dash of OCD thrown in.

I have no idea what this did to your power figures if anything because the dyno was obviously taking the correct rpm from an inductive pickup rather than calculating it from roller speed. I suspect it made no difference but I'm still not sure what mathematical shenanigans are going on under the hood on those things. Your low rpm torque was exactly what my simulation calculated so I suspect the power curve only went wrong at high rpm due to heat soak or lack of boost. Next time you would be well advised to log boost during each run!

Mignon

1,018 posts

88 months

Friday 16th November 2018
quotequote all
Mignon said:
AW111 said:
It's better than it used to be : the current standards basically require the engine to be tested "as fitted", so with all accessories, equivalent exhaust, etc.

Back when we started this flywheel power malarkey, we kept getting low fly power figures for one particular model car, compared to the brochure figure. An unofficial chat with a couple of the manufacturer's engineers revealed that they couldn't get the official power figure on their engine dyno either...
but things are better now.
Jaguar.
25 or more years ago when I first wrote my vehicle simulation program I was modelling every car I could find in a Motor or Autocar test to verify the software and equations and dial in on things like moments of inertia. Most cars came out pretty much like the claimed flywheel power suggested. Then one day I did a Jaguar. I can't remember which model. It clearly had nowhere near the claimed power unless the testers had forgotten about the boot full of sacks of cement. More in hope than expectation I phoned up Jaguar's technical department and actually got put through to a very interesting guy in the dyno department and he told me a fascinating story.

It is the marketing guys there who decide what each new model ought to be like to compete with other manufacturers. They specify engine size, bhp etc and then the R&D guys get to try and design this. The marketing guys are not engineers so they often decide their desired engine is going to produce far more power than is realistically possible and the poor sods in the dyno shop try and get as close as possible but often just have to admit defeat. Getting more power is easy but not without compromising other things like reliability and low rpm driveability. So they do their best and the car still gets marketed as what the marketing guys wanted in the first place.

Go and look at the Rototest site and examine the Jaguar graphs.

http://www.rri.se/

There are only 6 of them tested. As I said in another thread the hub dyno bhp should be about 91% of the flywheel power for a rwd car. Every one of the 6 jags is only between 81% to 84%, even the 2.5 V6 manual gearbox model. They are all about 10% shy of the claimed flywheel power. Now you all know why.

Stan Weiss

260 posts

147 months

Friday 16th November 2018
quotequote all
Mignon said:
Exactly as I calculated from the spec gearing. 14.5 mph / 1000 rpm. Your dyno run got well screwed up then. One of the first things I check for when I'm analysing a dyno graph is whether the rpm is correct for the wheel speed and/or the expected power points of the engine type in question. If not it screws up all the numbers. Sadly most of the people who run dynos are neither mathematicians nor often very bright, or at least pedantically careful which can often compensate for the former. It helps to be both with a dash of OCD thrown in.

I have no idea what this did to your power figures if anything because the dyno was obviously taking the correct rpm from an inductive pickup rather than calculating it from roller speed. I suspect it made no difference but I'm still not sure what mathematical shenanigans are going on under the hood on those things. Your low rpm torque was exactly what my simulation calculated so I suspect the power curve only went wrong at high rpm due to heat soak or lack of boost. Next time you would be well advised to log boost during each run!
Dave,

Using a 1.58:1 3.08:1 I get 15.13 MPH per 1000 RPM. Using a 245-35-18 tire I get a tire diameter of 24.752 inches. What are you using for a tire diameter?

I have also posted a new raw data simulation using all of the new information.

Stan


Weight = 3600.0# Radius = 12.37599 Inches

Rear Aero Rolling Rear W Accele Time Rate
RPM MPH Velocity Wheel dynamic Resist. Elapsed Horse ration Differ Rev Per
ft/sec Torque Drag - HP HP Time Power in G's ential Sec

2434.0 36.831 54.018 0.00 2.519 5.304 .0000 0.00 0.0000 0.0000 0.0
2446.0 37.012 54.284 79.46 2.556 5.330 .1010 37.01 .0820 0.1010 118.8
2458.0 37.194 54.551 74.40 2.594 5.356 .2110 34.82 .0752 0.1100 109.1
2474.0 37.436 54.906 92.24 2.645 5.391 .3230 43.45 .0985 0.1120 142.9
2484.0 37.587 55.128 65.39 2.677 5.413 .4320 30.93 .0633 0.1090 91.7
2500.0 37.829 55.483 95.14 2.729 5.447 .5400 45.29 .1022 0.1080 148.1
2514.0 38.041 55.794 83.03 2.775 5.478 .6520 39.74 .0862 0.1120 125.0
2525.0 38.208 56.038 70.89 2.812 5.502 .7600 34.08 .0703 0.1080 101.9
2538.0 38.404 56.326 79.55 2.856 5.530 .8700 38.44 .0815 0.1100 118.2
2554.0 38.646 56.681 99.98 2.910 5.565 .9720 48.62 .1082 0.1020 156.9
2568.0 38.858 56.992 85.71 2.958 5.596 1.0800 41.91 .0894 0.1080 129.6
2586.0 39.131 57.392 102.92 3.021 5.635 1.1910 50.68 .1119 0.1110 162.2
2602.0 39.373 57.747 94.20 3.077 5.670 1.3010 46.67 .1003 0.1100 145.5
2636.0 39.887 58.501 198.56 3.199 5.744 1.4000 99.66 .2369 0.0990 343.4
2654.0 40.160 58.901 70.53 3.265 5.783 1.5800 35.64 .0690 0.1800 100.0
2710.0 41.007 60.143 286.10 3.476 5.905 1.6900 147.63 .3512 0.1100 509.1
2747.0 41.567 60.965 213.09 3.621 5.986 1.7900 111.45 .2552 0.1000 370.0
2806.0 42.460 62.274 295.90 3.859 6.114 1.9020 158.09 .3634 0.1120 526.8
2855.0 43.201 63.362 282.06 4.065 6.221 2.0000 153.33 .3449 0.0980 500.0
2881.0 43.594 63.939 144.59 4.177 6.278 2.1090 79.32 .1645 0.1090 238.5
2979.0 45.077 66.113 484.22 4.618 6.491 2.2200 274.65 .6090 0.1110 882.9
3055.0 46.227 67.800 383.61 4.980 6.657 2.3300 223.14 .4766 0.1100 690.9
3106.0 46.999 68.932 264.29 5.234 6.768 2.4400 156.30 .3198 0.1100 463.6
3164.0 47.877 70.219 295.61 5.533 6.894 2.5510 178.09 .3604 0.1110 522.5
3229.0 48.860 71.662 366.54 5.881 7.036 2.6500 225.35 .4529 0.0990 656.6
3312.0 50.116 73.504 458.31 6.346 7.217 2.7500 289.02 .5725 0.1000 830.0
3382.0 51.175 75.057 386.68 6.757 7.369 2.8510 249.00 .4781 0.1010 693.1
3423.0 51.796 75.967 261.94 7.005 7.459 2.9410 170.72 .3142 0.0900 455.6
3500.0 52.961 77.676 427.91 7.489 7.626 3.0410 285.16 .5311 0.1000 770.0
3578.0 54.141 79.407 399.78 8.001 7.796 3.1500 272.36 .4936 0.1090 715.6
3648.0 55.200 80.961 355.53 8.480 7.949 3.2610 246.95 .4350 0.1110 630.6
3730.0 56.441 82.781 455.75 9.065 8.128 3.3610 323.67 .5656 0.1000 820.0
3769.0 57.031 83.646 211.06 9.352 8.213 3.4710 151.46 .2446 0.1100 354.5
3854.0 58.318 85.532 463.63 9.999 8.398 3.5730 340.22 .5748 0.1020 833.3
3929.0 59.452 87.197 428.36 10.594 8.561 3.6710 320.46 .5279 0.0980 765.3
3967.0 60.027 88.040 225.86 10.904 8.644 3.7710 170.60 .2621 0.1000 380.0
4031.0 60.996 89.461 329.78 11.441 8.783 3.8820 253.11 .3977 0.1110 576.6
4114.0 62.252 91.303 427.71 12.162 8.964 3.9910 335.03 .5252 0.1090 761.5
4169.0 63.084 92.523 316.84 12.656 9.084 4.0910 251.50 .3794 0.1000 550.0
4246.0 64.249 94.232 429.20 13.371 9.252 4.1920 346.99 .5259 0.1010 762.4
4302.0 65.097 95.475 323.13 13.907 9.374 4.2920 264.68 .3863 0.1000 560.0
4354.0 65.883 96.629 305.26 14.417 9.487 4.3910 253.06 .3623 0.0990 525.3
4420.0 66.882 98.094 373.26 15.083 9.631 4.4920 314.13 .4508 0.1010 653.5
4480.0 67.790 99.425 348.81 15.705 9.762 4.5910 297.53 .4181 0.0990 606.1
4554.0 68.910 101.068 384.50 16.497 9.923 4.7010 333.40 .4640 0.1100 672.7
4604.0 69.666 102.177 267.95 17.046 10.032 4.8120 234.89 .3107 0.1110 450.5
4672.0 70.695 103.686 359.78 17.813 10.180 4.9210 320.05 .4303 0.1090 623.9
4740.0 71.724 105.196 354.45 18.602 10.328 5.0320 319.90 .4226 0.1110 612.6
4806.0 72.723 106.660 348.39 19.390 10.472 5.1420 318.81 .4139 0.1100 600.0
4861.0 73.555 107.881 319.70 20.063 10.592 5.2430 295.90 .3756 0.1010 544.6
4912.0 74.327 109.013 282.09 20.701 10.703 5.3510 263.83 .3257 0.1080 472.2
4974.0 75.265 110.389 360.43 21.495 10.838 5.4510 341.35 .4277 0.1000 620.0
5042.0 76.294 111.898 357.16 22.389 10.986 5.5620 342.88 .4226 0.1110 612.6
5110.0 77.323 113.407 393.26 23.307 11.135 5.6620 382.63 .4691 0.1000 680.0
5134.0 77.686 113.940 160.68 23.637 11.187 5.7630 157.07 .1639 0.1010 237.6
5194.0 78.594 115.271 323.25 24.475 11.318 5.8730 319.68 .3762 0.1100 545.5
5262.0 79.623 116.780 368.20 25.449 11.466 5.9810 368.90 .4343 0.1080 629.6
5323.0 80.546 118.134 326.65 26.344 11.599 6.0920 331.06 .3791 0.1110 549.5
5376.0 81.348 119.310 314.12 27.139 11.714 6.1930 321.53 .3620 0.1010 524.8
5415.0 81.938 120.176 247.78 27.734 11.799 6.2910 255.47 .2745 0.0980 398.0
5470.0 82.770 121.397 297.33 28.588 11.919 6.4030 309.67 .3387 0.1120 491.1
5534.0 83.739 122.817 345.73 29.603 12.058 6.5130 364.29 .4013 0.1100 581.8
5570.0 84.284 123.616 233.23 30.184 12.137 6.6110 247.35 .2534 0.0980 367.3
5610.0 84.889 124.504 250.82 30.839 12.224 6.7110 267.92 .2759 0.1000 400.0
5690.0 86.099 126.279 423.89 32.178 12.398 6.8210 459.24 .5017 0.1100 727.3
5710.0 86.402 126.723 135.33 32.518 12.442 6.9330 147.13 .1232 0.1120 178.6
5780.0 87.461 128.277 414.20 33.729 12.594 7.0320 455.84 .4877 0.0990 707.1
5849.0 88.505 129.808 409.62 34.951 12.745 7.1310 456.18 .4808 0.0990 697.0
5854.0 88.581 129.919 66.59 35.041 12.756 7.2420 74.22 .0311 0.1110 45.0
5912.0 89.459 131.206 318.49 36.093 12.882 7.3530 358.52 .3604 0.1110 522.5
5982.0 90.518 132.760 379.17 37.390 13.035 7.4630 431.87 .4390 0.1100 636.4
6014.0 91.002 133.470 187.34 37.993 13.104 7.5810 214.52 .1871 0.1180 271.2
6058.0 91.668 134.446 257.55 38.833 13.200 7.6900 297.07 .2784 0.1090 403.7
6099.0 92.288 135.356 239.96 39.627 13.290 7.8010 278.65 .2548 0.1110 369.4

Averages 278.96 229.31 0.1069 476.3

Smoothed
Torque
79.459
79.459
74.397
81.250
80.556
81.626
82.019
82.040
85.397
88.785
98.032
106.161
123.738
147.829
171.843
210.026
227.916
255.321
282.125
294.598
325.355
331.810
337.453
351.855
354.713
368.762
374.484
370.610
380.954
373.910
374.514
381.616
362.238
363.832
359.191
343.028
353.941
357.019
354.688
362.854
353.288
347.973
347.979
343.616
344.630
339.551
340.039
336.515
333.010
332.311
332.974
330.905
326.138
321.513
308.127
311.920
313.319
309.599
311.236
298.226
290.125
294.362
284.256
290.517
306.513
292.267
302.620
299.472
272.506
279.807
270.752
187.340
257.549
239.955
.000

Mignon

1,018 posts

88 months

Friday 16th November 2018
quotequote all
Stan Weiss said:
Dave,

Using a 1.58:1 3.08:1 I get 15.13 MPH per 1000 RPM. Using a 245-35-18 tire I get a tire diameter of 24.752 inches. What are you using for a tire diameter?
Stan you know how pedantic and OCD I am smile

You're not calculating it right. The rolling circumference of the average brand new radial with about 8mm tread is only 97% of the calculated figure. I checked manufacturers catalogues listing actual rolling radii and worked out the equations. For a worn out tyre with only 1.6 mm of tread left it would be 95% so I take part worn as being 96% as the best possible average.

245 x 0.35 = 85.75 mm x 2 / 25.4 = 6.75" plus the 18" = 24.75" x 0.96 = 23.76"

The reason of course is that tyres compress under vehicle weight and the distance from the axle centre to the ground is less than the nominal inflated value. The tread then sort of shuffles round as it compresses and expands again as it goes over the top of the wheel and that's where much of the rolling friction comes from.


Edited by Mignon on Friday 16th November 20:39

Mignon

1,018 posts

88 months

Friday 16th November 2018
quotequote all
Stan, here's a selection of tyre sizes and the actual manufacturer measured rolling circumference in cm for you.

205/40/17 1818
245/40/17 1915
285/40/17 2013
205/45/16 1800
225/45/17 1934
255/45/18 2095
205/50/15 1790
255/50/16 2019
225/60/15 1986
195/50/15 1760

AW111

9,455 posts

132 months

Friday 16th November 2018
quotequote all
As noted above, the dyno measures roller speed and torque, so the tacho ratio being out won't affect the power reading. It also uses roller speed for the tyre losses.

It will effect the torque reading, as that is calculated from power / engine revs.

Inline__engine

195 posts

135 months

Saturday 17th November 2018
quotequote all
i find dyno dynamics very sensitive to tyres setup (pressure, size, compound, strapdown) in part due to the twin roller design and screwed up double contact patch that changes as a function of load. some operators loosely restrain them to get them to ride on the front roller only as its "more consistent" more likely they read higher and people like that.....but then if you do coast down the car sits back on both so i would competently ignore the bhp values and use rwhp. i always thought the DD coastdown was based on a fixed % for each of the shootout modes but this may have been in the old days.

i'm generally somewhat skeptical of results if the car has been removed and then re setup and always make sure that tyre pressures are the same and the vehicle is strapped down identically. anytime the wheels and tyres are changed of course it all goes out he window but i always reestablish a baseline if its not just a tuning session

i dont know how true it is but i was told shootout 6 inertia and so forth were based on a holden VL commodore which has an Rb30 engine i believe

Edited by Inline__engine on Saturday 17th November 01:46

Mignon

1,018 posts

88 months

Saturday 17th November 2018
quotequote all
AW111 said:
As noted above, the dyno measures roller speed and torque, so the tacho ratio being out won't affect the power reading. It also uses roller speed for the tyre losses.

It will effect the torque reading, as that is calculated from power / engine revs.
Except clearly this didn't happen. The revs were correct despite the tacho ratio and so were the torque figures at least at 3000 rpm.

Mignon

1,018 posts

88 months

Saturday 17th November 2018
quotequote all
More googling suggests kerb weight of Euro spec 135i is only 1485 kg, 3267 lbs so about 200lbs less than American spec. If so bhp is down to 345.

Running these simulations is f'ing time consuming. If you want to get your car weighed and do another datalog from 1500 rpm all the way to 7000 rpm I'll do one more for you and nail the bhp and power curve properly. To get a car weighed try scrap dealers, local authority tips or if you google your local council will have a list of public weighbridges.

GregK2

Original Poster:

1,651 posts

145 months

Saturday 17th November 2018
quotequote all