Torque limiting in 1st/2nd/3rd?

[Graeme4130]

If I've interpreted many previous posts correctly, I'm lead to understand the ECU limits torque in the first three gears so you only get full power in 4th ?
Is there an easy mod to get the ECU to give full power in these earlier gears or will I need to get a full remap done ?
Most of my 'spirited' driving is done in third and sometimes second, so having that extra power in those situations would be useful
Cheers
Graeme

[P_G]

Sadly, it is a remap solution only.

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It's only below 5.5k rpm iirc so if you are really playing it shouldn't make much difference.
Tbh, based on the logs I've seen the difference is marginal at best.
If it were me I wouldn't bother having the limiter removed on its own without any other mods.

[ArthurPE]

It's only below 5.5k rpm iirc so if you are really playing it shouldn't make much difference.
Tbh, based on the logs I've seen the difference is marginal at best.
If it were me I wouldn't bother having the limiter removed on its own without any other mods.

not sure of the rpm, but somewhere around 5000
the throttle is limited to 50%
I don't know if this is to limit torqe as much as to improve the throttling range and throttle modulation/response
at lower rpm's you need less air so perhaps 50% can supply all the air required
isn't torque peak around 5500?

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I just looked at sak's log from a 3rd gear run and you're right - its taking the throttle limiter off around 5100-5300. Not enough resolution to see if it's progressive or just switched.

[Dave_M]

From memory I think it's progressive but over a very short rpm range - I did log throttle position one time just to see.

Dave

[Marten]

Would the car be quicker (or feel) if the torque limiter is switched off?
What could be the reasoning behind Audi using such limiter? Gearbox? Cluctch?

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Would the car be quicker (or feel) if the torque limiter is switched off?
What could be the reasoning behind Audi using such limiter? Gearbox? Cluctch?

Hard to say. However based on Sak's logs you are not going to gain anything noticable by removing the throttle limiter.
If you are doing other modifications that require mapping then sure, go ahead. Just so not worth it on it's own.

[ArthurPE]

Would the car be quicker (or feel) if the torque limiter is switched off?
What could be the reasoning behind Audi using such limiter? Gearbox? Cluctch?

if you read some of the engine designer's comments (the guy used to work for BMW, designed M3 engines, now back at BMW) but throttle response is a big deal
being able to modulate power precisely with the throttle
if you consider the power band to be 2k to 8k, 5k is mid way
below 5k the engine needs ~1/2 the air it does above 5k to make full power at the respective rpm
so there is no need for the whole 0-100% throttle range (the throttle is essentially the engine control valve)
so using the throttle >50% is essentially a dead zone, it has little, if any influence on power, ie, the power ~max's out at 50%
so in order to get better controllability (or throttling range) they limit to exclude the range that has little influence, making it more precise/responsive

it is common to do so in control valve application, either by limiting the range under low flow conditons, or having 2 valves in parallel, a small one for low flow, and a larger sequenced in for high flow

throttling range
The amount of change in the variable being controlled to make the controlled device move through the full length of its stroke.

so if low rpm torque (ie the engine, the controlled device) goes 0-100% with 0-50% of the throttle movement (variable being controlled, by your foot), no need to use the 50-100% portion of the controlled device/throttle...so you limit the range to 0-50 for rpm <5000

[P_G]

Having driven RS4's with and without throttle limiter I can honestly say there is a pronounced difference in bum dyno readings.

[Marten]

Thanks Arthur for the explanation!

[ArthurPE]

the reason can't be to limit driveline shock, that is a function of gearing
in 1st 3.67
3rd 1.52

so the forces would be ~2.5 times as much in 1st as 3rd
let's say the engine makes 300 lb ft at 50%, and if not limited the full 317 (we know this isn't true from dyno's which show peak torque of 317 at 5500 after limitation is removed)
but it makes over 300 <5500 also, but let's say limitation reduces it from 317 to 300 5% reduction

limited
1st 1100
3rd 456

non-limited
1st 1163
3rd 482

minor
besides, if it can handle the limited 1100 in first, no need to limit it in 3rd, it's only 482 un-limited

let's look at the area of the TB and valves
valves, per rpm 4 cyl will intake, or 8 valves at 1" diameter each, area ~ 6.3 sq in (8 valves total), in sequence, not all together, so effectively 1/4th of that at any one instant, or ~1.6 sq in, call it 2 with some overlap

TB
from the manual 90 mm or ~10 sq in, even if limited to 50% ~5 sq in >> 2 in sq, it shouldn't limit required air flow
the manual says the air intake system was designed for maximum airflow control (another reason why the airbox flap is closed below ~5000 rpm, the air is not required)

another thing to consider, with the low gearing (diff is 4.11:1, very low) the car is 'jerky' to drive well at low speed/load in lower gears
by limiting the throttle to a range that excludes the portion that has little if any influence on torque production/output it makes it more controllable/driveable

someone who has the limiter removed, try this
drive in 2nd say, and modulate the throttle >50-100% and see what control you have, see if speed/accel changes much, then try <50%
I'll try the same
I bet mine will be more responsive/controllable, more speed change per % of throttle travel, especially above 5000 rpm

[brn7y]

I now know less of the important stuff I had stored away as it now has been replaced by this!

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Agree with Arthur here.
The engine can only ingest so much air and opening the throttle past that saturation point is not going to give you any extra power. At this point, the limiting factor of getting air into the cylinders is no longer the throttle butterfly.
All that happens is that past that point the throttle is doing nothing. What Audi are doing is dynamically adjusting the pedal sensitivity so that foot to the floor is always 100% of potential power and 50% of pedal travel is always 50%. Without that, you end up with a large dead zone near the end of the pedal.

To show how little effect this has, just look at Sak's log (posted in the S6 vs M5 vs AMG Car and Driver).

Code: Select all

Rev	Throttle%	Maf	g/1k rpm
4760	52.5	91.17	19.15336134
4920	52.5	93.92	19.08943089
5160	52.5	97.17	18.83139535
5360	67.5	107.33	20.02425373
5640	99.6	119.89	21.2570922
5840	99.6	123.78	21.19520548
6040	99.6	126.61	20.96192053

Now there's an awful lot that goes on around 5000-5500 (airbox flap, cam timing, ignition timing) so it's hard to pin down, but the last column is what I think is interesting (the amount of air per 1k rpm so accounts for the engine running faster and naturally drawing in more air) in that the amount of air going into the engine (and therefore engine output) is not dramatically different with 50% throttle or 100%. It certainly isn't anywhere near what you would think - just because you are flowing 91g/s at 50% throttle you are not suddenly going to start flowing 180+g/s at the same speed with 100% throttle.

Is there a gain to be made? Probably if you're willing to compromise on top pedal response but on it's own you are not going to notice it.

The issue with bum dynos is that it's hard to get over perception based on what you think you should feel and that often when "torque limiter"s are removed they are rarely done on their own but usually in conjuction with other tuning and map changes.

[ArthurPE]

I now know less of the important stuff I had stored away as it now has been replaced by this!

as long as you remember where you live you'll be fine
Einstein used to forget