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Author Topic: Tutorial: recalculating drivetrain data in Carp.txt with RealTuner assistance  (Read 1314 times)


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For those who are familiar with Carp.txt editing, this might be not new to you, as well as some might not agree with the method or calculation I use.

I am just trying to explain (in a more or less simple way) how to re-calculate particular gearing/engine entries (in the Carp.txt) in NFSWizard with the assistance of RealTuner and somewhat realistic data from web resources.

The base for a realistic drivetrain calculation in any cases is a suitable torque curve of the particular car's engine.

The web source I mostly use is automobile-catalogue.com. As you can imagine, saving 'real' torque curve measurements tabs on a web server would cost a lot disk space as well as not every engine's torque curves were being measured or recorded as well. As a matter of fact, the website uses a calculator to generate a torque curve by the basic engine's and drivetrain factory data. As a result, this only a CALCULATED torque curve (and power curve, too), but since NFS HS anyway uses theoretical data it might fit quite well in most of the cases. The website also points out to that fact:

'The Horsepower / Torque Curve below was generated by ... software, based on the factory data'

All I furthermore do is a kind of 'calculating' the given data 'backwards' for NFS' Carp.txt gearing/engine tab entries.

So now to torque curves in general: As I noticed so far, torque curves in many cars are simply wrong.
It seems to me as if some (and as I have to assume, as if some of the NFS' developers, too ..) mistake 'torque' by 'power', 'horsepower'. An average combustion engine produces its maximum torque earlier (depending on) than its power peak (sometimes it is really just a 'peak')

If you compare the different curves (wykres_power.php.jpg): the Countach's torque curve (in red) compared to the power curve (white) it may become clear. The torque curve reaches its maximum earlier than the power curve which really culminates into a 'peak' in the end. (This is just an example folks, other car's engines might or will definetely look different, of course ...)

If now you want to edit the torque curve in NFSWizard, remember the gradual steps' entries of the tab/the picture.

>>Step one: Understanding the curves' differences

In Carp.txt by default the stepping (when '20' is the highest x-axis entry) is 500rpm, have a look at 'torque curve -> curve editor'
In the picture stepping is identically, but you have to multiply the values by 2 and divide by 1000 since the Carp.txt values are just plain numbers.

For example: Maximum torque (pic) is at 5000rpm, this means: Carp.txt value: multiply by 2 divided by 1000 = 10 (x-axis value)
Too complicated? You'll get used to it. Carp.txt (as said, by default resolution, 20 x-axis values: 1 = 500, 2 = 1000, 3 = 1500rpm and so on)

>>Step two: Transferring a 'real' curve into Carp.txt

It is not necessary to produce a more or less 'clean' curve, even if it looks better, the more important things are the curve's maximum, its slope or 'steepness' and the 'cut-off' rpm.

Now RealTuner becomes somewhat important: According to your edited torque curve (export -> Carp.txt to the car's folder, be sure to 'dublicate' the existing Carp.txt in NFSWizard!) and navigate RealTuner to the desired folder. RealTuner now calculates an Idle rpm as well as a new redline -> save new Carp.txt

Now import the new Carp.txt and you can see a new idling as well as a new redline rpm RealTuner has calculated based upon the new torque curve you had created.

If the redline rpm doesn't correspond to the 'real' data found, alter the 3 or 4 torque values after the maximum torque value in Carp.txt, either lower or raise all values a bit or just lower the cut-off rpm.

<<Remark: if, like in the Countach's case, no redline is given (in the powertrain tab) please read my little tutorial 'Car specification web resources' (or read the additional explanation at the end of this tutorial), it explains how to calculate a redline by certain gear (gearspeed) values>>

Export again, let RealTuner recalculate (You may also notice the gearspeed values changing), save, import and see if the redline has changed to your desired value.

Repeat that again if the result still isn't satisfying, you'll get a feeling for it after several trials.
Same with the idling rpm, raise the torque values a bit (as said, the 3 or 4 values -here- BELOW the max torque value) if idling seems to high, lower it if it may seem to low to you.

>>Step three: entering the gearspeed values from existing specification data

That is, if a somewhat correct redline is being recognized (calculated) by RealTuner, quite easy.
Transfer the maximum gearspeed data ('Speed range') into RealTuner and save it! (pic 'drivetrain')
RealTuner now calculates new 'Velocity to RPM' values, 'automatic' as well as 'manually' shifted in both tabs.
That is very important since now the car knows when to shift gears at which rpm.

You can now transfer the gear values into the gear ratios tab, although NFS cares little about that, since RealTuner by default enters '1.0,1.0,1.0,1.0' .. and so on, same with the final gear entry.

>> Step three (and a half): Calculating the reverse gear 'Velocity to RPM' value

Much more important becomes a small calculation you have to do still for the reverse gear:
By default, RealTuner enters the same 'Velocity to RPM' value for the first as well as the reverse gear.

Start Windows' Calculator and do the following:

.. as you can see in the gear values (as you transferred them into Carp.txt.), either divide the reverse gears' value if it is higher (in most cases) by the first gear value, or vice versa.

Multiply the result (this is your factor) with the first gears' 'Velocity to RPM' value, copy and paste the result into the 'Velocity to RPM' tab, just before the '0.0000' (neutral gear) entry, make sure the minus (-) is STILL before the pasted-in value, otherwise your car will go forward when in reverse gear instead of moving backwards.

>>Step four: 'gear efficiency' tab in NFSWizard ..
Well, that's more or less a matter of personal taste or preferences, but if you entered an appropriate acceleration value (which can also be found in the car's 'full specification' data of the website) in RealTuner (X.XX sec) , I would recommend to leave RealTuner's values unchanged or alter them as said by personal preferences ...

Add.: Explanation: Calculating a redline rpm by certain given gear specification data:
If a car's engine has no given redline (in the 'drivetrain' tab of 'full specification' -> pic 'powertrain') simply divide the 'theoretical top gear speed' of the car's highest gear by the 1000rpm gearspeed value of the same gear, multiply the value by 1000 and you get the approximate redline value.

For example the 1978 Lamborghini Countach LP400 S:
No redline given, top (5th) gearspeed (theoretically): 315 km/h, 1000rpm value (5th gear also): 37 km/h
-> 315/37 = 8.5135 x 1000 ~ 8.500 rpm, that's your redline.

Ok that's all so far folks ..

« Last Edit: October 14, 2016, 10:18:45 PM by FranknFurter »


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Back in 2002 we did not have automobile-catalogue.com so it could be a herculean task to find correct data... Cars not available in the US were the worst, unless they were new or relatively well-known (like the M3 CSL). Most people didn't care and just released the car with a random fast CARP but, let's be honest, the whole fun of playing classic NFS was in the different strengths and weaknesses of each car. In HS you had between the absolute bottom of the barrel (Mercedes SLK) to the absolute top (McLaren F1 was overall the best except on really fast tracks), and the rest in the middle, some of them almost breaking through a higher class than where they were placed (Corvette for example).

Erick's tool was more than the community deserved at the time, especially the likes of Kremit.

I didn't know RealTuner would calculate efficiency based on acceleration times, that's really cool! Although you should try to get press times whenever possible. The Germans always understate their cars. :D


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Small addition from me, that can be useful, I think.
In case where you stuck on step three, calculations on gearspeeds could be done in more or less simplified way knowing wheel size, redline, gear ratios/final gear.
At least I tried that with data on SD-455 1973, knowing 455 HO torque data (covering 2400-5500 rpm), redline, wheels and having info on that 4-speed manual Muncie M20. Using similar tools I got absolutely the same results, which themselves quite close to the real car data.
So far I found two instances of such applications:
Like it had been said, these provide similar results (at least in all 5 cases I tried so far), so no difference in them.


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Except the fact that I didn't think anyone would ever understand this calculation tutorial let alone use it then =D it's nice to see that some further information can be found, thx Rider ^-^

For German cars, especially Volkswagen of recent times you often really get spoiled for choice for there is too many information found .. too many gearboxes and drivetrain data that makes it sometimes hard to decide which powertrain (engine) data used which gearbox (with what final gear) etc ..

Had that on the T4: '.. this particular engine was used until that day with the choice of these gearboxes as follow: ..', but two years later completely different engines were introduced again with different gearboxes .. :o
« Last Edit: May 21, 2017, 06:52:43 AM by FranknFurter »


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Yep, agreed. Some of the cars gives too much info, some just have bits literally. As for the first ones, I remember doing carp for Reight's Hudson 7B Club Coupe 2 days ago, which had manual 3-speed, manual with overdrive and automatic trannies. Did 1+3, but these options giving completely different feeling of the very same car. Too bad I had never drove real Hornet in my life to compare calculations with the thing :)