Any Way To Figure 1/4 Times Using EFILIVE

[WeathermanShawn]

In a log where your frames are 1 second apart. With all the normal PIDS being logged, in addition I am logging VSS, G-Force, Power at Read Wheels.

Using finding a nice flat road and following all safety precautions and local laws:grin:, I am logging a run through gears 1-4. I am particularly interested in my change in speed per frame (second). Anybody have a PID handy or an easy math calculation to figure distance especially a set distance like 1/4 mile?

While I do have a "G-Tech Pass RR" that can do it, it is a little difficult to use. I am trying to figure out if I can successfully do it using my EFILive Software.

Any ideas?

[joecar]

Shawn,

You would need to integrate VSS over time (i.e. find the area under the VSS curve)...

convert VSS[mph] to VSS[mile/s] or VSS[m/s] (i.e. time units must be consistent), and then add the area under the curve from t=0 to t=T where T is when you notice the integral is close to 1/4 mile (in whatever distance units you're using)...

however, the scantool does not have an integrate() function, so you can only do this offline.

[WeathermanShawn]

Joecar, could I do this through Excel, or am I going to have to break out my Calculus books to compute?

[joecar]

v[mile/s] = VSS[mile/hr]/3600

Plot v[mile/s] and then compute the area under that curve... I am not sure if Excel does that...

[joecar]

The other problem is that 10 Samples/second is insufficient...

40 S/s is better but only barely insufficient (if sufficient)...

The G-Tech samples at 100+ S/s.

I tried a quick/crude plot of going from 3.6 to 36.0 mph in 6.5 s, see attached graph (using DPlot)...

in that 6.5 s time the distance traveled was 0.039 mile (206 ft).

[WeathermanShawn]

Thanks Joecar.

Roger that on the frames per second. I guess I could try G-Tech again while simultaneously logging via EFIlive. It is just that the Gtech requires level road, no tire spin, and use of 3rd gear. By that time the State Troopers will be chasing me.

So, I guess it all comes down to simply figuring how much distance you can cover in one second..then adding up all the frames?

I know the simple answer is to find a marked 1/4 distance. We only have one track in the area, it is almost 6000' feet, so I am trying to 'improvise' without breaking too many speed limits.

I have also been logging the Calculated.Power Pid. It appears to be similar to G-Tech is that it looks like it comes close to a 'Net Horsepower' calculation.

If you come up with any other insights, I would be interested. It might be a worthwhile function (if possible) for the masses. Sounds like a good way to further market EFILive's capabilities...:grin:

[joecar]

...

So, I guess it all comes down to simply figuring how much distance you can cover in one second..then adding up all the frames?

...Not necessarily 1 second... the shorter the time delta the more accurate it becomes...
e.g. for LS1B the sample period is approx 0.1 second (but watch out, it varies...)...

the time deltas can all be different...

You convert mph to mile/s, then for each time delta you calculate it's area (time_delta[s] * v[mile/s]), and then you pick a starting point (say time zero) and you successively accumulate all the areas...

Algorithms:
http://en.wikipedia.org/wiki/Rectangle_method
http://en.wikipedia.org/wiki/Trapezoidal_rule

[WeathermanShawn]

Thanks.

I'll do some experimenting.:cheers:

[joecar]

Here's another example I did while waiting for dinner...

0.0 to 63.4 mile/hr in a leisurely 7.5 s

.csv.txt file contains the data points (log time [s], vss [mph]) taken from log,
.chart.png file shows log (the vss slope to the left of the cursor),
.graph.png file shows s [mile] graphically integrated from v [mile/s],

I got DPlot to divide vss [mph] by 3600 to obtain v [mile/s],
then I got it to graphically integrate to obtain s [mile].

At the end of the graph, the distance covered is 0.070 mile (370 ft).

The time axis is absolute log time [s].

If you convert the units so that all curves will have consistent units, then it becomes relatively easy...;)

[WeathermanShawn]

Outstanding work. Thanks a lot.
It is pretty intriguing, so I will run a few tests/logs myself.:cheers:

[nathans1987]

is it possible to use vss counts per second then the tyre diamiter etc to get distance?

[joecar]

is it possible to use vss counts per second then the tyre diamiter etc to get distance?If you graph vss counts per second vs time, you still have to integrate (find the area under the curve) and to get total counts...

and then divide this by counts per distance (which is scaled by axle ratio and tire circumference) to get the elapsed distance in inches, feet, or miles.

VSS in mph already has all the count/distance or distance/counts scaling already in it... so then all you have to do is find the area under the VSS mph curve.

i.e. both methods are doing the same thing, one mothod has the PCM doing the scaling math for you...

You could make a calc pid for VSS in miles/second... this would eliminate some math.

[nathans1987]

ok so that pid does not show total counts just the rate.

[joecar]

Which pid...?

[nathans1987]

the vss counts one? i'm sure i saw somthing like that. there is atleast a place in the tune where you place counts per km or somthing like that maybe thats what i have seen.

[joecar]

Shawn,

Here's a quarter mile ET and TS graph from post #40 (http://forum.efilive.com/showpost.php?p=105451&postcount=40) of this thread: showthread.php?t=11749 (http://forum.efilive.com/showthread.php?t=11749)

The logged data is courtesy of forum member projectblackbird (http://forum.efilive.com/member.php?u=9393).


http://usera.imagecave.com/joecar/lucas%20pass%201.png

[joecar]

I didn't even have to filter out the wheelspin.


Edit: when I tried to filter/smooth out wheelspin, I was getting 13.8-14.0 seconds, which disagreed with his timeslip.

i.e. the raw data seems to work best.

:)

[WeathermanShawn]

Joecar:

Hey thanks. Impressive work. I think I am almost there on my own plot. I think I can even do some extrapolating from the slope of the curve vs time to estimate a 1/4 mile without actually having to run it.

Of course that would entail a number of assumptions as obviously the acceleration slope changes with increasing aerodynamic drag, rolling resistance, etc, with increasing VSS.

I will try to duplicate something similar to see if I have it down. If I can equate EFILive's Calculated HP PID to a general 1/4 mile performance it will give me a general comparison. The trick for me is to keep the distance and speed within reason. If nothing else gives you a sanity check on 'street dyno' performance.

[joecar]

The CALC.RWHP can be used to roughly compare the more substantial mods by repeating acceleration tests over the same road under the same conditions, and comparing graphs/data...


The CALC.RWHP pid gives the power left over after balancing friction that is accelerating the vehicle (i.e. Newton's laws).


You can do this to roughly estimate FWHP:
a. on stretch of road, accelerate from 0 to X mph, gives positive RWHP data,
b. on same stretch of road going in the same direction, in neutral coast down from X to 0 mph (or almost 0), gives negative RWHP data;

Then make a chart sorted by mph, and at each mph point add the absolute values of CALC.RWHP to estimate FWHP... (i.e. do a. minus b.)...

using gear/axle ratio and tire diameter, you can correlate mph to rpm:

RPM = MPH * 336 * GR / TD

where: GR = overall gear ratio, TD = tire diameter inches.

Joe :)

[joecar]

the vss counts one? i'm sure i saw somthing like that. there is atleast a place in the tune where you place counts per km or somthing like that maybe thats what i have seen.Nathan,

Sorry, I somehow missed your question...:doh2:

I don't see a pid for raw VSS counts (i.e. a count of the reluctor pulses)... if you had this you would have distance (since you know the pulse count per mile from your tune file)...

If you try to convert VSS in mile/hr to VSS pulse counts, you are effectively performing an integration (i.e. converting velocity to distance) since you would be relating time to distance.

:)