Computer simulation of vehicle performance
Discussion
Hi Stan
just realised why folk worried about power lines being so different, I was trying to capture concept of speed /power in each gear which shows it is worth stretching revs 2nd to 3rd for a B cos of the daft gap! With the inertia dyno/pau combo I can make the engine work 'properly' in lower gears or with turbo application. The graph above is with no load so engine not being made to work esp in 1st and 2nd. If I get time at some point and I get a similar race B in I'll do a balanced cascade curve for you. It is difficult for folk not used to inertia dynos seeing what is recorded. Maybe good idea to ask why curves different and not just pooh pooh; that way learn and move forward
Peter
just realised why folk worried about power lines being so different, I was trying to capture concept of speed /power in each gear which shows it is worth stretching revs 2nd to 3rd for a B cos of the daft gap! With the inertia dyno/pau combo I can make the engine work 'properly' in lower gears or with turbo application. The graph above is with no load so engine not being made to work esp in 1st and 2nd. If I get time at some point and I get a similar race B in I'll do a balanced cascade curve for you. It is difficult for folk not used to inertia dynos seeing what is recorded. Maybe good idea to ask why curves different and not just pooh pooh; that way learn and move forward
Peter
ivanhoew said:
i wonder if you could do me 3 sims dave,
1) 1/4 mile with some yokos and a lsd ...eg decent grip/launch , say a 1.9 60 ft ?
Even if you had the grip you don't have the power to go that fast. You ideally want a 3.4 diff with the 12" tyres because it's not revving high enough in 4th. However if I put bhp up to 230 at 23 psi, 3.4 diff, no grip limit I get 60ft in 2.0, 1/4 in 12.1 @ 114.4.1) 1/4 mile with some yokos and a lsd ...eg decent grip/launch , say a 1.9 60 ft ?
ivanhoew said:
2)max power top speed with the right gearing , i can run down to a 2.95 diff .
Even that's not really low enough. Depends what your rpm limit is. About 139 mph at 19 psi, 7180 rpm. Maybe 141 mph at 23 psi, 7281 rpm.ivanhoew said:
3) top speed with present 3.1 gearing and 117 bhp at wheels , my normal rd 5psi setting.
122 mph @ 6620 rpm.Stan Weiss said:
Steve,
If that run had been done on a proper drag strip where you had some roll out (I used 11.75 inches) I get the following still using my 242 HP.
60 Foot ET = 2.6765
330 Foot ET = 6.3456
1/8 Mile ET = 9.1775
1/8 Mile MPH = 86.9702
1000 Foot ET = 11.6147
1/4 Mile ET = 13.6606
1/4 Mile MPH = 110.8751
Stan
We have some serious discrepancies. I know we have the same basic maths in there for aero and rolling resistance drag, tractive force at the wheel and net acceleration so it must be in the details which are crucial to simulating a real car. So here is all my data for this car and the times calculated.If that run had been done on a proper drag strip where you had some roll out (I used 11.75 inches) I get the following still using my 242 HP.
60 Foot ET = 2.6765
330 Foot ET = 6.3456
1/8 Mile ET = 9.1775
1/8 Mile MPH = 86.9702
1000 Foot ET = 11.6147
1/4 Mile ET = 13.6606
1/4 Mile MPH = 110.8751
Stan
No rollout
weight with driver 2860 lbs
frontal area 20.24
Cd 0.33
tyre radius 0.9689
diff 3.15
gears 3.72,2.4,1.77,1.26,1.0
Transmission efficiency 0.86 in all gears
Wheel/tyre inertia 125 lbs
Engine inertia 25 lbs at an average radius of gyration of 3.5 inches
Clutch slip rpm 5000
Peak rpm 8000
gearchange time 0.4 seconds
Max grip 0.55g
flywheel power curve
4500 - 155
5000 - 185
5500 - 217
6000 - 235
6500 - 260
7000 - 270
7500 - 280
8000 - 265
60ft - 2.60 @ 31.42
110 yds - 6.33 @ 65.46
220 yds - 9.33 @ 83.72 (82.17 @ 210 yds)
440 yds - 14.03 @ 104.93 (104.22 @ 430 yds)
Top speed 169 @ 7695 rpm in 5th
See how you get on.
Pumaracing said:
ivanhoew said:
i wonder if you could do me 3 sims dave,
1) 1/4 mile with some yokos and a lsd ...eg decent grip/launch , say a 1.9 60 ft ?
Even if you had the grip you don't have the power to go that fast. You ideally want a 3.4 diff with the 12" tyres because it's not revving high enough in 4th. However if I put bhp up to 230 at 23 psi, 3.4 diff, no grip limit I get 60ft in 2.0, 1/4 in 12.1 @ 114.4.1) 1/4 mile with some yokos and a lsd ...eg decent grip/launch , say a 1.9 60 ft ?
ivanhoew said:
2)max power top speed with the right gearing , i can run down to a 2.95 diff .
Even that's not really low enough. Depends what your rpm limit is. About 139 mph at 19 psi, 7180 rpm. Maybe 141 mph at 23 psi, 7281 rpm.ivanhoew said:
3) top speed with present 3.1 gearing and 117 bhp at wheels , my normal rd 5psi setting.
122 mph @ 6620 rpm.over 20 years ago when I had my mini up the strip, I was trapping 101mph, although that was with no real traction the entire 1/4 and crossing the line still in 3rd.
60fts and ET were terrible but just on standard road tyres so to be expected.
brilliant thank you , i know one of our turbo mini chaps ran a 1.9 60 ft , on a 4.11 diff and yoko 32's ,was a bit lighter that my car i think ,
regards
robert
Pumaracing said:
122 mph @ 6620 rpm.
i have had the car at 6700 on that boost , it was just about topped out , so that fits nicely . thank you dave , very interesting .regards
robert
Pumaracing said:
We have some serious discrepancies. I know we have the same basic maths in there for aero and rolling resistance drag, tractive force at the wheel and net acceleration so it must be in the details which are crucial to simulating a real car. So here is all my data for this car and the times calculated.
No rollout
weight with driver 2860 lbs
frontal area 20.24
Cd 0.33
tyre radius 0.9689
diff 3.15
gears 3.72,2.4,1.77,1.26,1.0
Transmission efficiency 0.86 in all gears
Wheel/tyre inertia 125 lbs
Engine inertia 25 lbs at an average radius of gyration of 3.5 inches
Clutch slip rpm 5000
Peak rpm 8000
gearchange time 0.4 seconds
Max grip 0.55g
flywheel power curve
4500 - 155
5000 - 185
5500 - 217
6000 - 235
6500 - 260
7000 - 270
7500 - 280
8000 - 265
60ft - 2.60 @ 31.42
110 yds - 6.33 @ 65.46
220 yds - 9.33 @ 83.72 (82.17 @ 210 yds)
440 yds - 14.03 @ 104.93 (104.22 @ 430 yds)
Top speed 169 @ 7695 rpm in 5th
See how you get on.
Dave,No rollout
weight with driver 2860 lbs
frontal area 20.24
Cd 0.33
tyre radius 0.9689
diff 3.15
gears 3.72,2.4,1.77,1.26,1.0
Transmission efficiency 0.86 in all gears
Wheel/tyre inertia 125 lbs
Engine inertia 25 lbs at an average radius of gyration of 3.5 inches
Clutch slip rpm 5000
Peak rpm 8000
gearchange time 0.4 seconds
Max grip 0.55g
flywheel power curve
4500 - 155
5000 - 185
5500 - 217
6000 - 235
6500 - 260
7000 - 270
7500 - 280
8000 - 265
60ft - 2.60 @ 31.42
110 yds - 6.33 @ 65.46
220 yds - 9.33 @ 83.72 (82.17 @ 210 yds)
440 yds - 14.03 @ 104.93 (104.22 @ 430 yds)
Top speed 169 @ 7695 rpm in 5th
See how you get on.
I maybe out in left field, but this what I used.
Tire Rolling Radius = 11.9 inches
Max G's about 0.553
Shift Time = 0.1 Second
Note these are @ rear wheel so there is no power train loses needed.
RPM Torque
2000 28.86
2125 41.2
2250 53.79
2375 66.46
2500 78.88
2625 91.48
2750 104.06
2875 116.65
3000 126.73
3125 134.05
3250 141.63
3375 149.03
3500 156.42
3625 163.76
3750 171.09
3875 180.25
4000 189.42
4125 197.97
4250 206.53
4375 213.25
4500 219.97
4625 223.64
4750 227.3
4875 229.13
5000 230.97
5125 230.97
5250 230.97
5375 229.13
5500 227.3
5625 224.25
5750 221.19
5875 216.92
6000 212.64
6125 205.3
6250 197.97
6375 190.64
6500 183.31
6625 175.98
6750 168.64
Pumaracing said:
We have some serious discrepancies. I know we have the same basic maths in there for aero and rolling resistance drag, tractive force at the wheel and net acceleration so it must be in the details which are crucial to simulating a real car. So here is all my data for this car and the times calculated.
No rollout
weight with driver 2860 lbs
frontal area 20.24
Cd 0.33
tyre radius 0.9689
diff 3.15
gears 3.72,2.4,1.77,1.26,1.0
Transmission efficiency 0.86 in all gears
Wheel/tyre inertia 125 lbs
Engine inertia 25 lbs at an average radius of gyration of 3.5 inches
Clutch slip rpm 5000
Peak rpm 8000
gearchange time 0.4 seconds
Max grip 0.55g
flywheel power curve
4500 - 155
5000 - 185
5500 - 217
6000 - 235
6500 - 260
7000 - 270
7500 - 280
8000 - 265
60ft - 2.60 @ 31.42
110 yds - 6.33 @ 65.46
220 yds - 9.33 @ 83.72 (82.17 @ 210 yds)
440 yds - 14.03 @ 104.93 (104.22 @ 430 yds)
Top speed 169 @ 7695 rpm in 5th
See how you get on.
Dave,No rollout
weight with driver 2860 lbs
frontal area 20.24
Cd 0.33
tyre radius 0.9689
diff 3.15
gears 3.72,2.4,1.77,1.26,1.0
Transmission efficiency 0.86 in all gears
Wheel/tyre inertia 125 lbs
Engine inertia 25 lbs at an average radius of gyration of 3.5 inches
Clutch slip rpm 5000
Peak rpm 8000
gearchange time 0.4 seconds
Max grip 0.55g
flywheel power curve
4500 - 155
5000 - 185
5500 - 217
6000 - 235
6500 - 260
7000 - 270
7500 - 280
8000 - 265
60ft - 2.60 @ 31.42
110 yds - 6.33 @ 65.46
220 yds - 9.33 @ 83.72 (82.17 @ 210 yds)
440 yds - 14.03 @ 104.93 (104.22 @ 430 yds)
Top speed 169 @ 7695 rpm in 5th
See how you get on.
Using what parameters of yours that I have in my software and making an adjustment to one of them for my software this is what I get.
Stan
................Acceleration.and.Top.Speed.Prediction.Chart.
...................................Force....Aero.....Rolling..Elapsed...........Accele
..RPM......MPH...Velocity..Motor.....@.....dynamic...Resist....Time......Total..ration
..................ft/sec..Torque...Wheel..Drag.-.HP....HP......(ET)....Distance.in.G's
>>>>---.Gear.Change.4.->.5
.6349.3..139.44..204.512...208.8...583.7...123.479...15.985..26.0473..3516.022.....073
.6374.8..140.00..205.334...209.0...584.3...124.973...16.050..26.3998..3588.248.....072
.6400.0..140.55..206.147...209.2...584.9...126.464...16.113..26.7522..3660.764.....071
.6500.0..142.75..209.368...210.1...587.4...132.485...16.365..28.1838..3958.202.....069
.6600.0..144.95..212.589...208.6...583.2...138.694...16.617..29.7038..4278.927.....063
.6602.5..145.00..212.670...208.5...583.1...138.852...16.623..29.7434..4287.346.....063
.6700.0..147.14..215.810...207.1...579.0...145.095...16.869..31.3558..4632.824.....058
.6800.0..149.34..219.031...205.6...574.8...151.689...17.120..33.1668..5026.616.....053
.6830.3..150.00..220.006...205.1...573.5...153.722...17.196..33.7511..5154.883.....051
.6858.5..150.63..220.924...204.7...572.3...155.655...17.268..34.3190..5280.074.....049
.6900.0..151.54..222.252...204.1...570.6...158.480...17.372..35.1730..5469.319.....047
.7000.0..153.73..225.473...202.6...566.4...165.471...17.624..37.4245..5973.418.....042
.7057.8..155.00..227.333...201.8...564.3...169.600...17.769..38.8614..6298.753.....039
.7100.0..155.93..228.694...201.3...562.8...172.664...17.876..39.9868..6555.380.....036
.7101.0..155.96..228.735...201.3...562.7...172.755...17.879..40.0212..6563.236.....036
.7200.0..158.12..231.915...200.0...559.1...180.063...18.127..42.9567....1.3711.....031
.7285.5..160.00..234.669...198.9...556.0...186.554...18.343..45.9386....1.5029.....026
.7300.0..160.32..235.136...198.7...555.5...187.670...18.379..46.4959....1.5277.....026
.7331.0..161.00..236.135...198.3...554.4...190.072...18.457..47.7477....1.5835.....024
.7376.5..162.00..237.601...197.7...552.7...193.633...18.572..49.7560....1.6736.....021
.7400.0..162.52..238.357...197.4...551.9...195.489...18.631..50.8872....1.7246.....020
.7422.3..163.01..239.074...197.1...551.0...197.258...18.687..52.0274....1.7762.....019
.7456.8..163.77..240.193...196.6...549.8...200.041...18.774..53.9659....1.8642.....017
.7467.8..164.00..240.540...196.5...549.4...200.908...18.801..54.6104....1.8935.....016
.7500.0..164.71..241.579...196.1...548.2...203.522...18.883..56.6951....1.9887.....015
.7503.5..164.79..241.699...195.9...547.8...203.827...18.892..56.9551....2.0006.....014
.7513.3..165.00..242.005...195.5...546.6...204.602...18.916..57.6411....2.0320.....013
.7558.8..166.00..243.471...193.5...541.0...208.342...19.031..61.6438....2.2161.....010
.7600.0..166.91..244.800...191.7...535.9...211.772...19.134..67.0786....2.4674.....006
.7602.3..166.96..244.880...191.6...535.5...211.981...19.141..67.5072....2.4873.....006
.7604.3..167.00..244.936...191.5...535.3...212.127...19.145..67.8169....2.5016.....006
.7638.8..167.77..246.056...189.9...531.0...215.049...19.233..76.7919....2.9191.....003
.7643.0..167.86..246.193...189.8...530.5...215.408...19.243..78.5875....3.0028.....002
.7649.8..168.00..246.402...189.5...529.7...215.958...19.260..82.0261....3.1632.....002
.7661.8..168.27..246.797...188.9...528.2...216.997...19.291..94.3346....3.7381.....001
.7664.3..168.33..246.877...188.8...527.9...217.210...19.297.100.0459....4.0051.....000
.7666.3..168.37..246.942...188.7...527.6...217.380...19.302.108.3642....4.3941.....000
.7667.5..168.40..246.982...188.7...527.5...217.486...19.305.120.8732....4.9792.....000
.7667.8..168.40..246.990...188.7...527.5...217.507...19.306.126.5774....5.2460.....000
.7668.0..168.41..246.998...188.6...527.4...217.529...19.306.137.9147....5.7764.....000
.7668.3..168.41..247.006...188.6...527.4...217.550...19.307.1047.8021...48.3415.....000
.7695.3..169.00..247.868...187.4...524.1...219.834...19.374
.7700.0..169.10..248.021...187.2...523.5...220.242...19.386
60 Foot ET = 2.6044
330 Foot ET = 6.3276
1/8 Mile ET = 9.3268
1/8 Mile MPH = 82.2679
1000 Foot ET = 11.8699
1/4 Mile ET = 14.0319
1/4 Mile MPH = 104.6361
1/2 Mile ET = 21.633 -- 1/2 Mile MPH = 130.37
1 KM ET = 24.884 -- 1 KM MPH = 138.00
1 Mile ET = 34.319 -- 1 Mile MPH = 150.63
2 KM ET = 40.014 -- 2 KM MPH = 155.96
3 KM ET = 53.965 -- 3 KM MPH = 163.77
2 Mile ET = 56.942 -- 2 Mile MPH = 164.79
4 KM ET = 67.468 -- 4 KM MPH = 166.96
5 KM ET = 76.758 -- 5 KM MPH = 167.77
3 Mile ET = 78.528 -- 3 Mile MPH = 167.86
6 KM ET = 94.123 -- 6 KM MPH = 168.27
4 Mile ET = 99.936 -- 4 Mile MPH = 168.33
7 KM ET = 107.412 -- 7 KM MPH = 168.37
8 KM ET = 120.697 -- 8 KM MPH = 168.40
5 Mile ET = 121.318 -- 5 Mile MPH = 168.40
9 KM ET = 133.981 -- 9 KM MPH = 168.41
6 Mile ET = 142.710 -- 6 Mile MPH = 168.41
10 KM ET = 147.278 -- 10 KM MPH = 168.41
11 KM ET = 160.560 -- 11 KM MPH = 168.41
7 Mile ET = 164.086 -- 7 Mile MPH = 168.41
12 KM ET = 173.843 -- 12 KM MPH = 168.41
8 Mile ET = 185.462 -- 8 Mile MPH = 168.41
13 KM ET = 187.125 -- 13 KM MPH = 168.41
14 KM ET = 200.408 -- 14 KM MPH = 168.41
9 Mile ET = 206.838 -- 9 Mile MPH = 168.41
15 KM ET = 213.690 -- 15 KM MPH = 168.41
16 KM ET = 226.972 -- 16 KM MPH = 168.41
10 Mile ET = 228.214 -- 10 Mile MPH = 168.41
Stan Weiss said:
Dave,
Using what parameters of yours that I have in my software and making an adjustment to one of them for my software this is what I get.
Much better Using what parameters of yours that I have in my software and making an adjustment to one of them for my software this is what I get.
Makes rather a difference doesn't it having an appropriate power curve rather than something from a Chevy V8 peaking 2000 rpm too low and a gear change time that a human being can't actually achieve. Now you just go right ahead and give yourself a pat on the head and you can open a bag of Maltesers as a special treat.
Computers are great except of course for the proviso that GIGO!
I'll cover rotating inertia briefly.
1) Wheel/tyre inertia can be considered as part of the base vehicle mass as it is independent of gear ratio. Obviously it has to be kept out of any downforce or braking calculations though. After much buggering about with angular momentum and acceleration calculations I concluded that the effective mass add-on is approximately 75% of the total real wheel/tyre mass. I use 125 lbs as an average for road cars and adjust as necessary when I know the wheels will be exceptionally heavy or light.
2) Engine inertia. The equations in each gear with units in lbs and feet are as follows:
(FD ratio x gear ratio x radius of gyration / tyre radius)^2 x effective mass at the specified radius of gyration.
For general car engines I take the average radius of gyration of crank, flywheel and pistons as being 3.5" (0.29167 ft). I adjust this for engines with very small clutches and flywheel, short crank stroke etc like motorbike and F1 engines. Normally down to 2.5".
For effective mass for road type engines I use 25 lbs for 4 cylinder, 30 for 6 and 35 for 8 cylinders. For F1 engines I use 15 lbs.
Therefore for the BMW in question the calculation in 1st gear is (3.15 x 3.72 x 0.29167 / 0.9689)^2 x 25
= 12.44 x 25 = 311 lbs.
The effect drops off rapidly in the higher gears, 2nd 129 lbs, 3rd 70 lbs, 4th 36 lbs, 5th 22 lbs. However it's vital to getting the launch parameters right for the 60 ft and 330 ft times.
So the total effective accelerated mass for the BMW in 1st gear is 2860 lbs (1300 kg) base mass + 125 lbs wheel/tyre inertia + 311 lbs engine inertia = 3296 lbs
ivanhoew said:
brilliant thank you , i know one of our turbo mini chaps ran a 1.9 60 ft , on a 4.11 diff and yoko 32's ,was a bit lighter that my car i think ,
regards
robert
Remember that on a drag strip the 60 ft times can be artificially reduced by up to 0.35 seconds by roll out before the timing light is actually triggered. I have no truck with such foolishness and my program calculates the actual real elapsed times from the instant the clutch bites.Pumaracing said:
122 mph @ 6620 rpm.
i have had the car at 6700 on that boost , it was just about topped out , so that fits nicely . thank you dave , very interesting .regards
robert
So my 2.0 second unlimited grip scenario could be about 1.7s on a strip and it's vanishingly unlikely you'll get anywhere near that without slicks but I used it to give you an idea of the best possible 1/4 mile run you might ever be able to do. Anything within 0.3 or 0.4 seconds of what I calculated would actually be very good going for a real car with the usual homo/mechanical piloting interface
ivanhoew said:
i have had the car at 6700 on that boost , it was just about topped out , so that fits nicely . thank you dave , very interesting .
regards
robert
The actual unlimited distance top speed the computer calculated was 123 mph at 6675 rpm but it took 2 miles to get there. I knocked it back by 1 mph to 122 which was more achievable at about 1.25 miles. Headwinds, tailwinds, slopes can have a massive impact though. My program can allow for those too.regards
robert
Just a 1 degree down slope would add 2 mph to top speed as would a 5 mph tailwind. With both together it would hit 128 mph at 6946 rpm.
So it's a bit of a lottery trying to precisely determine top speed and hence bhp on the road but we appear at least to be very much in the ballpark.
I built in a bunch of other stuff to the program over the years. It can cope with downforce for F1 type cars which of course drastically increases traction at higher speeds. It does braking time and distance calculations based on not just tyre grip but also factoring in aero drag and finally by combining both it can calculate the effect on lap time of bhp or gearing changes by simulating a notional track comprised of given straight lengths and corner entry speeds. It's been fun playing with it and writing it anyway.
Some of you might find this thread on another forum of interest. I used my simulation program to help calculate the power of 2014 F1 cars from the onboard speed display.
http://www.f1technical.net/forum/viewtopic.php?f=4...
We concluded based on not very ideal data that it was somewhere in the region of 700 bhp at the wheels including the 160 bhp hybrid power unit. Maybe 790 flywheel.
http://www.f1technical.net/forum/viewtopic.php?f=4...
We concluded based on not very ideal data that it was somewhere in the region of 700 bhp at the wheels including the 160 bhp hybrid power unit. Maybe 790 flywheel.
Pumaracing said:
Some of you might find this thread on another forum of interest. I used my simulation program to help calculate the power of 2014 F1 cars from the onboard speed display.
http://www.f1technical.net/forum/viewtopic.php?f=4...
We concluded based on not very ideal data that it was somewhere in the region of 700 bhp at the wheels including the 160 bhp hybrid power unit. Maybe 790 flywheel.
Dave,http://www.f1technical.net/forum/viewtopic.php?f=4...
We concluded based on not very ideal data that it was somewhere in the region of 700 bhp at the wheels including the 160 bhp hybrid power unit. Maybe 790 flywheel.
Pumaracing said:
Now you just go right ahead and give yourself a pat on the head and you can open a bag of Maltesers as a special treat.
Stan
Stan,
I think I've found the bug in your program. It's in the rollout section. I input the torque curve you first tried ending at 6750 rpm 168.64 ft lbs, your tyre rolling radius, your gearchange time of 0.1 seconds, took out all the inertia data and still only got a terminal speed of 106 mph at the 1/4. You got 110 mph.
By my calculations a 12" rollout might reduce the 60 ft ET by about 0.3 to 0.35 seconds and the speed at 12" is about 4 mph at 0.5g.
HOWEVER! that 4 mph does not add on to every trap speed up the run. It just means the 1/4 mile is now 1321 ft instead of 1320 ft and the gain in speed is immaterial. The car is hardly accelerating by the end of the run and one extra foot is just a tiny fraction of 1 mph.
Your program seems to be subtracting 0.3s from every trap time and adding 4 mph to every trap speed instead of just adding 1 foot to every trap distance.
I was premature with the Maltesers for you it seems.
I think I've found the bug in your program. It's in the rollout section. I input the torque curve you first tried ending at 6750 rpm 168.64 ft lbs, your tyre rolling radius, your gearchange time of 0.1 seconds, took out all the inertia data and still only got a terminal speed of 106 mph at the 1/4. You got 110 mph.
By my calculations a 12" rollout might reduce the 60 ft ET by about 0.3 to 0.35 seconds and the speed at 12" is about 4 mph at 0.5g.
HOWEVER! that 4 mph does not add on to every trap speed up the run. It just means the 1/4 mile is now 1321 ft instead of 1320 ft and the gain in speed is immaterial. The car is hardly accelerating by the end of the run and one extra foot is just a tiny fraction of 1 mph.
Your program seems to be subtracting 0.3s from every trap time and adding 4 mph to every trap speed instead of just adding 1 foot to every trap distance.
I was premature with the Maltesers for you it seems.
Pumaracing said:
Stan,
I think I've found the bug in your program. It's in the rollout section. I input the torque curve you first tried ending at 6750 rpm 168.64 ft lbs, your tyre rolling radius, your gearchange time of 0.1 seconds, took out all the inertia data and still only got a terminal speed of 106 mph at the 1/4. You got 110 mph.
By my calculations a 12" rollout might reduce the 60 ft ET by about 0.3 to 0.35 seconds and the speed at 12" is about 4 mph at 0.5g.
HOWEVER! that 4 mph does not add on to every trap speed up the run. It just means the 1/4 mile is now 1321 ft instead of 1320 ft and the gain in speed is immaterial. The car is hardly accelerating by the end of the run and one extra foot is just a tiny fraction of 1 mph.
Your program seems to be subtracting 0.3s from every trap time and adding 4 mph to every trap speed instead of just adding 1 foot to every trap distance.
I was premature with the Maltesers for you it seems.
Dave,I think I've found the bug in your program. It's in the rollout section. I input the torque curve you first tried ending at 6750 rpm 168.64 ft lbs, your tyre rolling radius, your gearchange time of 0.1 seconds, took out all the inertia data and still only got a terminal speed of 106 mph at the 1/4. You got 110 mph.
By my calculations a 12" rollout might reduce the 60 ft ET by about 0.3 to 0.35 seconds and the speed at 12" is about 4 mph at 0.5g.
HOWEVER! that 4 mph does not add on to every trap speed up the run. It just means the 1/4 mile is now 1321 ft instead of 1320 ft and the gain in speed is immaterial. The car is hardly accelerating by the end of the run and one extra foot is just a tiny fraction of 1 mph.
Your program seems to be subtracting 0.3s from every trap time and adding 4 mph to every trap speed instead of just adding 1 foot to every trap distance.
I was premature with the Maltesers for you it seems.
I am not sure what you are talking about. If I take MY Data set
No roll out
60 Foot ET = 3.0525
330 Foot ET = 6.7346
1/8 Mile ET = 9.5686
1/8 Mile MPH = 86.9256
1000 Foot ET = 12.0068
1/4 Mile ET = 14.0533
1/4 Mile MPH = 110.8472
12 inches of roll out
60 Foot ET = 2.6727
330 Foot ET = 6.3415
1/8 Mile ET = 9.1733
1/8 Mile MPH = 86.9702
1000 Foot ET = 11.6105
1/4 Mile ET = 13.6564
1/4 Mile MPH = 110.8751
Let no confuse numbers that I posted from MY Data set with numbers I posted using your data set.
No roll out
60 Foot ET = 2.6044
330 Foot ET = 6.3276
1/8 Mile ET = 9.3268
1/8 Mile MPH = 82.2679
1000 Foot ET = 11.8699
1/4 Mile ET = 14.0319
1/4 Mile MPH = 104.6361
12 inches roll out
60 Foot ET = 2.2898
330 Foot ET = 6.0018
1/8 Mile ET = 8.9987
1/8 Mile MPH = 82.3191
1000 Foot ET = 11.5406
1/4 Mile ET = 13.7022
1/4 Mile MPH = 104.6579
Stan
Edited by Stan Weiss on Monday 22 June 16:15
OK. I've had yet another go and think I've answered my own questions.
I don't think you've ever posted results from a single data set before with both roll-out and no roll-out so I assumed this must be something to do with it.
To get the 60 ft time so high I think you've used a very low clutch slip rpm, I match your time using about 2700 rpm. Then the car accelerates quicker again as the revs build up until it hits the grip limit you've used to try and match the 330 ft time and finally the 1/4 mile terminal speed is so high because you've created a power curve that exactly peaks out in 4th as the car hits the 1/4 mile and also because the gear change time is so quick.
If the above is correct then I think we've finally agreed the programming calculations.
I don't think you've ever posted results from a single data set before with both roll-out and no roll-out so I assumed this must be something to do with it.
To get the 60 ft time so high I think you've used a very low clutch slip rpm, I match your time using about 2700 rpm. Then the car accelerates quicker again as the revs build up until it hits the grip limit you've used to try and match the 330 ft time and finally the 1/4 mile terminal speed is so high because you've created a power curve that exactly peaks out in 4th as the car hits the 1/4 mile and also because the gear change time is so quick.
If the above is correct then I think we've finally agreed the programming calculations.
Pumaracing said:
OK. I've had yet another go and think I've answered my own questions.
I don't think you've ever posted results from a single data set before with both roll-out and no roll-out so I assumed this must be something to do with it.
To get the 60 ft time so high I think you've used a very low clutch slip rpm, I match your time using about 2700 rpm. Then the car accelerates quicker again as the revs build up until it hits the grip limit you've used to try and match the 330 ft time and finally the 1/4 mile terminal speed is so high because you've created a power curve that exactly peaks out in 4th as the car hits the 1/4 mile and also because the gear change time is so quick.
If the above is correct then I think we've finally agreed the programming calculations.
Dave,I don't think you've ever posted results from a single data set before with both roll-out and no roll-out so I assumed this must be something to do with it.
To get the 60 ft time so high I think you've used a very low clutch slip rpm, I match your time using about 2700 rpm. Then the car accelerates quicker again as the revs build up until it hits the grip limit you've used to try and match the 330 ft time and finally the 1/4 mile terminal speed is so high because you've created a power curve that exactly peaks out in 4th as the car hits the 1/4 mile and also because the gear change time is so quick.
If the above is correct then I think we've finally agreed the programming calculations.
Yes, I have it set at 2675 and much faster shift times than you do.
Stan
Stan Weiss said:
Dave,
Yes, I have it set at 2675 and much faster shift times than you do.
Stan
Luv a duck Stan. No wonder I had such a job trying to work out what you'd done. This may however deserve some sort of award for the most errrm "creative" juggling with the variables in a simulation to try and match a set of bum speeds and times ever seen.Yes, I have it set at 2675 and much faster shift times than you do.
Stan
As to real gear change times with manual boxes, look at the data Stevieturbo posted. You can see the width of the gaps in the acceleration curve at each change and it's about 0.5 seconds from power off to fully back on again. However some acceleration is still taking place as the tyres and clutch grip again so the total time lost is a bit less than this.
From simulations over the years checking car magazine road tests I reckon the best a professional test driver can do is about 0.25 to 0.3 seconds when it's not his own car and he doesn't care about breaking anything. It's not easy for an owner to be quite so brutal.
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