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

[Dave_M]

I guess the other question is for people who've had the throttle remapped - do you still get a kick at c.5,500rpm? I know as Adsgreen says, several things change at that point - but assuming the remap didn't change the base map cam timing / air box flap / tumble flaps operation, then all things being equal removing the throttle limit shouldn't remove the kick at 5,500rpm, If it does, surely that implies the limited throttle opening was restricting power?

Or am I missing something?

Dave

[P_G]

Difficult to tell though Artheur because I would suggest with 95+% of remaps, they not only will remove the torque limiter but also adjust throttle aggression and fuelling so the overall affect gained is a combination of the three rather than just the one you want to test.

[adsgreen]

The "kick" is a funny thing. Personally, I can't stand it as with an N/A engine power should be relatively linear especially with a complex variable valve system (as an aside, not sure if the RS4 has variable lift but I digress).

The worst case of this I found was on performance Toyota cars such as the Celica and later Lotus Elises. The jump from "economy cam" to "power cam" was so aggressive it felt identical to turbo lag. Sure, you get a shove in the back but that just means the mapping was off. Interestingly Lotus revised the map to move the cam change over 500 rpm lower which smoothed things out. According to engine dynos the effect was hardly noticable but there was no kick and the car felt better to drive.

Any tuner worth their reputation should be able to tune out the kick (assuming they have access to valve and timing parameters). Again, Sak's data showed to me that the cam change point of 5.5k rpm is fractionally to high and should be 4800-5000. There's many reasons why car companies do this and I suspect it was possibly a nod to B5 drivers or some arcane EU rule on emissions.

[Dave_M]

I agree the kick is a funny thing - it does however give the impression of the car being quicker than it would with a nice smooth, linear power curve. I've owned several turbo cars in the past (and one currently) - the RS4 feels slower generally than the turbo cars until you look at the speedo and realise just how quickly you're gaining speed! Then you appreciate just how quick the RS4 is.

One thing the kick does do for me is give the impression I'm missing out on something below the point of the kick - which is where a good remap should be able to reap rewards.

Dave

[ArthurPE]

very good example and explanation
although the mass increases with rpm >50% throttle, it does so linearly, just as you would expect, no discrete step

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.

[sakimano]

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.

It makes a pretty big difference, but as was mentioned by adsgreen, not if you're ripping WOT through the gears as you ought not to be in the sub 5500 RPM range too often once you shift. Of course at a track day this could be significant because you'll dip down to 3000-4000 a bunch.

Here's a log of my car. This was 3rd gear. As you can see it is quite restricted up until about 5500 RPM where it goes 100%.
The change starts somewhere after 5160 and is fully implemented somewhere before 5640 (so less than 480 RPMs for the change to happen)
The restriction here was at 52.5% (nice cold day around 0 celsius with good conditions for making power), HOWEVER I am sure I have logged my car other times where the restriction was more like 70%. Maybe when it's warmer it allows more throttle to compensate for density (or a lack thereof).

here's the direct link to allow you to see it full resolution. http://audirevolution.net/addons/albums ... 968961.jpg

[ArthurPE]

his point is that the mass/krpm is not a large change
when you ratio rpm's x mass it is almost linear, maybe 10% difference
for example
4920 rpm/52.5%/97.17 g/sec
5640 rpm/99.6/120

5640/4920 x 97.17 ~ 111 gm, or 7.5% less than you would expect 120 vs 111) due to rpm change
but cam timing has changed, air box flaps open, tumble flap position, etc.
and most importantly these have improved vol eff...so what portion of the 7.5% is due to the throttle? much less than 7.5%, if any

if the throttle was the limiting factor you would expect this much more air going from 52.5 to 99,6% ~ sqrt(99.6/52.5) ~ 1.38 or 38% more for the same system
the throttle is not much of the total system restriction: intake, air filter, hoses, throttle, manifold, tumble flaps, valves, etc.

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.

It makes a pretty big difference, but as was mentioned by adsgreen, not if you're ripping WOT through the gears as you ought not to be in the sub 5500 RPM range too often once you shift. Of course at a track day this could be significant because you'll dip down to 3000-4000 a bunch.

Here's a log of my car. This was 3rd gear. As you can see it is quite restricted up until about 5500 RPM where it goes 100%.
The change starts somewhere after 5160 and is fully implemented somewhere before 5640 (so less than 480 RPMs for the change to happen)
The restriction here was at 52.5% (nice cold day around 0 celsius with good conditions for making power), HOWEVER I am sure I have logged my car other times where the restriction was more like 70%. Maybe when it's warmer it allows more throttle to compensate for density (or a lack thereof).

here's the direct link to allow you to see it full resolution. http://audirevolution.net/addons/albums ... 968961.jpg

[ArthurPE]

I did not notice that torque was logged
the avg of the 5 52.5% values before and after change over (using the 67.5 value as the changeover)
before 382.2
after 395.7 (starts off high, then tapers off, probably an inrush when it opos open)
a 3.4% increase for the total of throttle, filter box flap, cam timing, manifold flaps, vol eff and rpm increase...

It makes a pretty big difference, but as was mentioned by adsgreen, not if you're ripping WOT through the gears as you ought not to be in the sub 5500 RPM range too often once you shift. Of course at a track day this could be significant because you'll dip down to 3000-4000 a bunch.

Here's a log of my car. This was 3rd gear. As you can see it is quite restricted up until about 5500 RPM where it goes 100%.
The change starts somewhere after 5160 and is fully implemented somewhere before 5640 (so less than 480 RPMs for the change to happen)
The restriction here was at 52.5% (nice cold day around 0 celsius with good conditions for making power), HOWEVER I am sure I have logged my car other times where the restriction was more like 70%. Maybe when it's warmer it allows more throttle to compensate for density (or a lack thereof).

here's the direct link to allow you to see it full resolution. http://audirevolution.net/addons/albums ... 968961.jpg

[sakimano]

good eye, I didn't notice that. I was looking at the change in RPMs / second which were pretty consistent for the 1000 or so rpm before and after.

[adsgreen]

In 3rd it is very roughly 12mph/1k rpm (actual, not indicated) so 4k rpm is about 48 mph and at those speeds aero is starting to have a noticeable affect.
Go to 6k rpm so 1.5 times faster but aero is now 1.5^2 or 2.25 times as much - makes comparing rpm/sec difficult when evaluating the engine (however it is useful when looking at the car as a whole).
Thats why I went with the maf reading as I would expect this to be largely more consistent with road speed and I'm imagine the logged torque is based on the airflow values.