Is there an AC App to display actual power output?

[Celtic Pharaoh]

Hi everyone,

Something that has annoyed me about trying to BoP cars is that if I apply 10% BoP, I don't know how much power it takes away. I was told by a friend that it doesn't simply mean its 10% less power and that if it went up to 20%, it isn't 20% but 20% of 10% (i.e.: 2%) etc.

So to try and demystify how it all works, I was wondering if anyone knows of an app that can output the engine power and torque in realtime so that I can see for myself how much power and torque certain cars have (911 RSR, Audi R18 etc.) and see how much different percentages affect the total overall power output.

 

[RasmusP]

Hi everyone,

Something that has annoyed me about trying to BoP cars is that if I apply 10% BoP, I don't know how much power it takes away. I was told by a friend that it doesn't simply mean its 10% less power and that if it went up to 20%, it isn't 20% but 20% of 10% (i.e.: 2%) etc.

So to try and demystify how it all works, I was wondering if anyone knows of an app that can output the engine power and torque in realtime so that I can see for myself how much power and torque certain cars have (911 RSR, Audi R18 etc.) and see how much different percentages affect the total overall power output.

Motec with acti shows max power & torque. Sadly no graph or anything... In theory you could calculate it though with a custom maths!
@Neilski knows a bit more about it
We should probably come together and figure it out! At least you could see it in detail, but not in real time... I don't know of an app.

Only app there is would be a little one that measures different acceleration speeds like 0-100, 80-120 etc. Maybe that would help too?

 

[Guillaume Francois]

If you have the DEV APPS enabled you could give a look at the car status app i guess. Not 100% sure tho.

 

[dud]

I have a static Python app that grovels the data/ folder and prints things like actual power (after turbos etc).

Computing live without the data/ folder will be difficult as long as the CD aero values are not available.

 

[Neilski]

I've been playing about with power calcs for a while, but don't yet have an app that can do the calc in real time.
Some of my results are on the AC forum - e.g. http://www.assettocorsa.net/forum/i...-restrictor-research.48632/page-2#post-949793 and other posts in the same thread.

My current power calc uses: mass, acceleration, slip ratio, and a simple air-resistance estimate (tuned to make the data in high gears match the other gears reasonably well). It works pretty well on a straight-line acceleration test (which is how I got the data shown in that link). In principle, I could calculate all of that stuff on the fly but it might be a bit messy. I might give it a go for fun!
I don't have rolling resistance in there yet, but should probably add it.
It would be fairly easy to handle the effect of going up or down hills, but cornering would be pretty tricky so I'd probably have to stick to data gathered while the car is more or less moving in a straight line.
NB: as other people have pointed out in various discussions of BoP in general, even if you know precisely how much power you will lose, it's non-trivial to work out how to balance any given pair or cars.

Btw, be aware that the restrictor in AC (like in real life I guess) affects the top end much more than the bottom end; this moves the power peak and shift points (more in some cars than others).

EDIT: I have been looking at the power curve for the M235i. This is THE car that Aris said needed really early upshifts, during at least one of his Youtube videos. I didn't believe him at the time, because the power curve in the ui_car.json file (which AC itself displays within the GUI, and which Sidekick uses to work out the shiftpoints) says he's wrong - the power peak and curve after the peak combine to mean the shift points should be really close to the red line.
HOWEVER, that file appears to be pretty badly wrong. I've attached an image which shows the acceleration in each gear, starting from 1st. (Pink is 7th gear, which is pretty pointless in this car on most tracks (!!), and 8th is entirely pointless for racing - it's the tiny grey blip at 254 kph.) Apologies for the lack of a legend on the graph - it was created for my personal consumption and I can't rebuild it right now cos my main machine is poorly.
The important bit is the crossover points - 4th and 5th cross at about 153 kph for example. This is when Sidekick should be telling you to change up, but it doesn't, because the power curve it's using is wrong. (PS: I decided to also upload the power and torque curves with and without 100% restrictor, and the ratio of the curves with and w/o restrictor... )

 

[dud]

Another big problem here is the "wheel power" versus "engine power" issue. In most real-world cases 85% "drivetrain efficiency" is assumed, in AC it seems 90% is more common.

That's a bunch of hogwash. No way that all those different drivetrains are anywhere close to each other. And that rule of thumb people pull out of thin air to account for AWD doesn't make it much better.

And no way that the same drivetrain has the same efficiency over the entire spectrum of input rpm (from engine) and wheel rpm. I suspect this is the major reason why car manufacturers specify engine power, not wheel power. I bet it varies like mad badger on caffeine.

 

[dud]

I've been playing about with power calcs for a while, but don't yet have an app that can do the calc in real time.
Some of my results are on the AC forum - e.g. http://www.assettocorsa.net/forum/i...-restrictor-research.48632/page-2#post-949793 and other posts in the same thread.

My current power calc uses: mass, acceleration, slip ratio, and a simple air-resistance estimate (tuned to make the data in high gears match the other gears reasonably well). It works pretty well on a straight-line acceleration test (which is how I got the data shown in that link). In principle, I could calculate all of that stuff on the fly but it might be a bit messy. I might give it a go for fun!
I don't have rolling resistance in there yet, but should probably add it.
It would be fairly easy to handle the effect of going up or down hills, but cornering would be pretty tricky so I'd probably have to stick to data gathered while the car is more or less moving in a straight line.
NB: as other people have pointed out in various discussions of BoP in general, even if you know precisely how much power you will lose, it's non-trivial to work out how to balance any given pair or cars.

Btw, be aware that the restrictor in AC (like in real life I guess) affects the top end much more than the bottom end; this moves the power peak and shift points (more in some cars than others).

I suppose you could make that work as follows:

• Change data to have zero roll resistance (leaving wind resistance)
• Accelerate to speed <s>, then measure via telemetry what the slowdown is. That will give you total drag, easily divided by front surface to get to the drag coefficient
• Change data to statically place all active aero in their different positions, repeat measurement
• While at it, you could put in a temporary, braindead suspension that allows you to figure downforce via suspension height
• Couple other things like avoiding gearshift (set clutch to open while measuring)

 

[Neilski]

In most real-world cases 85% "drivetrain efficiency" is assumed, in AC it seems 90% is more common.

Interesting that you should say that
I just calculated 283/333 (M235i actual power to the wheels, by my calcs, vs. nominal) and it comes out at 0.8498

 

[Neilski]

I suppose you could make that work as follows:

• Change data to have zero roll resistance (leaving wind resistance)
• Accelerate to speed <s>, then measure via telemetry what the slowdown is. That will give you total drag, easily divided by front surface to get to the drag coefficient
• Change data to statically place all active aero in their different positions, repeat measurement
• While at it, you could put in a temporary, braindead suspension that allows you to figure downforce via suspension height
• Couple other things like avoiding gearshift (set clutch to open while measuring)

Well, I haven't given much thought to cars with serious aero yet. I think I can probably use the real-time data to work out the drag and rolling resistance without having to muck about with the car data though. As for downforce, I can work it out on the fly (by using wheel loads) but I don't think I need it for anything (?).

 

[Neilski]

(Btw, turns out that the 333 bhp figure for the M235i is wrong for a few different reasons, so at present I have no idea what the drivetrain efficiency is!)

 

[Nico Major]

Maybe it does not fit perfectly to the initial request. I was interestedly reading all posts and you mentioned shift points and engine power output vs. "final push the car actually receives".

Once I was interested in finding the shift points for the BMW M235i I used a small app that logs some information into a csv file and recorded data by accelerating full throttle from low to maximum revs in every gear on a loooong straight (test track).

Then I put longitudinal G over speed (see attached image) and figured out the shift points (roughly). I like this approach very much, because it tells me the final truth since all relevant factors are already "included" (drive train losses, drag at certain speeds, etc).
What I'm trying to say - maybe G-foce can help judging the effect of (BOP) changes.
It's probably hard to read as a live number cause it's changeing quickly but I guess the same holds true for live HP data. Maybe recorded data from comparable test runs can provide some insight.

 

[Neilski]

What I'm trying to say - maybe G-foce can help judging the effect of (BOP) changes.

Yes indeed.
You may have missed my post above which has some graphs which I made using the same approach as you (the graphs are tiny until you click on them which makes them a little to easy to miss I'm afraid):

I've been playing about with power calcs for a while [snip]

 

[Andy-R]

Maybe it does not fit perfectly to the initial request. I was interestedly reading all posts and you mentioned shift points and engine power output vs. "final push the car actually receives".

Once I was interested in finding the shift points for the BMW M235i I used a small app that logs some information into a csv file and recorded data by accelerating full throttle from low to maximum revs in every gear on a loooong straight (test track).

Then I put longitudinal G over speed (see attached image) and figured out the shift points (roughly). I like this approach very much, because it tells me the final truth since all relevant factors are already "included" (drive train losses, drag at certain speeds, etc).
What I'm trying to say - maybe G-foce can help judging the effect of (BOP) changes.
It's probably hard to read as a live number cause it's changeing quickly but I guess the same holds true for live HP data. Maybe recorded data from comparable test runs can provide some insight.

What RPM did you come up with for the M235i if you don't mind sharing? I always shift at somewhere between 6.5K and 6.7K which seemed about right to me based on just the delta app but I don't drive the car that often (I quite like it though) and would be interested to know how far off I am.

With regards to BoP I am a server admin and use it fairly regularly but have always used the trial and error method and alternate between restrictor and ballast depending on where the faster car is OP (straight line speed, cornering/braking.) It would be really interesting to see the numbers with an app although I don't think it would help me with BoP. I'd much rather see an auto assign ballast app to make success ballast feasible in MP (I think it would just need to see grid position and spit out server commands assigning the required ballast for each position.)

 

[RasmusP]

What RPM did you come up with for the M235i if you don't mind sharing? I always shift at somewhere between 6.5K and 6.7K which seemed about right to me based on just the delta app but I don't drive the car that often (I quite like it though) and would be interested to know how far off I am.

With regards to BoP I am a server admin and use it fairly regularly but have always used the trial and error method and alternate between restrictor and ballast depending on where the faster car is OP (straight line speed, cornering/braking.) It would be really interesting to see the numbers with an app although I don't think it would help me with BoP. I'd much rather see an auto assign ballast app to make success ballast feasible in MP (I think it would just need to see grid position and spit out server commands assigning the required ballast for each position.)

May the sandbagging begin then!
Just kidding, would be awesome!

Shifting points: they basically start at 7k for 1st and 2nd gear and then drop the faster you get with a little notch in 3rd.
So 6.4k for 3rd, 6.5k for 4th and 5th and 6.3k for 6th. Quite important though is that going a bit too high is not as bad as shifting too early!
Probably easier to just go red line for 1st/2nd and then 6.5k all the way up

 

[Andy-R]

May the sandbagging begin then!
Just kidding, would be awesome!

Shifting points: they basically start at 7k for 1st and 2nd gear and then drop the faster you get with a little notch in 3rd.
So 6.4k for 3rd, 6.5k for 4th and 5th and 6.3k for 6th. Quite important though is that going a bit too high is not as bad as shifting too early!
Probably easier to just go red line for 1st/2nd and then 6.5k all the way up

Thanks I'll try maxing 1st and 2nd next time I drive the car.

I think track position is better anyway (rather than sand bagging) for sprint races.

We tested BTCC rules success ballast (or maybe we halved it I cant remember) at RBR National with the MX5 Cup and Abarth 500 AC and it worked really well IMO. I had to set a 5min wait time after Q and Race 1 to adjust the ballast manually though and it was a real struggle with people chatting which kept removing the player ID stuff from admin app in the chat. I might try posting it as a mod suggestion again. It would be quite a basic app to make I think.

 

[Nico Major]

You may have missed my post above which has some graphs which I made using the same approach as you (the graphs are tiny until you click on them which makes them a little to easy to miss I'm afraid):

Thx for pointing this out again. Actually I looked at them but did not read everything carefully enough. "Accel" is clearly written there but my brain somehow constructed "wheel torque" or something like that because in the past I also constructed such a graph from pure data (torque/power graph, gearing, wheel size) and because the discussion was about HP and power graph I got on that path probably .

@Andy-R I dont know the RPMs right now. Had to look into my spreadsheet at home, but I think RasmusP is spot on with his advise. I personally did not look at the RPMs but at the speeds (as written in my graph) for shifting 3-4, 4-5, 5-6. If you get theese roughly right, than that's good enough.

 

[007DBR9]

Another big problem here is the "wheel power" versus "engine power" issue. In most real-world cases 85% "drivetrain efficiency" is assumed, in AC it seems 90% is more common.

That's a bunch of hogwash. No way that all those different drivetrains are anywhere close to each other. And that rule of thumb people pull out of thin air to account for AWD doesn't make it much better.

And no way that the same drivetrain has the same efficiency over the entire spectrum of input rpm (from engine) and wheel rpm. I suspect this is the major reason why car manufacturers specify engine power, not wheel power. I bet it varies like mad badger on caffeine.

From a modding perspective drivetrain loss is just how power is displayed, you can literally move around a slider and choose what you want it to be. Obviously there's more to it than just that value, but most modded cars are manual sequential, or at least most race cars are, which are a good bit more efficient than any roadcar transmission.
Usually I'll do 8-14% for racecars and 13-20% for roadcars, but I prefer to just balance them with kunos cars, or well made modded cars like rss or vrc.

If manufatures put out dyno results without anything applied to make it look like crank bhp that'd be ideal, but usually they just say peak power is this peak torque is this, and you're lucky to get corresponding rpm.