My latest chiptuning. Full report

[Pisobiker]

By the way, Mark, if I remember correctly I think I've read from Mihnea himself or Paul N. that when at WOT ECU doesn't use Lambda values to correct fuel mixtures but a "inbuilt" fuel map.

Marco

[KramRS2]

Oh yes, I know.
This information is only to myself.

Like I sad, after the peak boost was achieved, it drops and I can sense some kind wrong. A rispid thing, its difficult to put in words, but looking to the Voltmeter in the lambda sensor, I can see it lean, lean until below stoichometric, which could be dangerous at WOT with boost. But the boost the engine has no power to drive the boost.

Without the hose I could sense the timing retard because the engine doesn't want to rev any more, it stop to accelerate the car with a little load (like a little uphill in third).
The peak boost was something like 1,7bar. Putting the hose back it boost 2,2bar again at peak. I think that is something with the boost chip, may be checksum or something, and the ecu goes in emergency mode after some point in the map.


The faults stored are something like "time adjust exceeded", "fuel adjust exceeded", "leak in some breather"?? and things like that.


Now with the stock chip no problems stored but I think that it is running a little lean yet.

Fuel pressure is ok, flow is ok, injectors are ok, lambda sensor new...

[]
MArk

[KramRS2]

Hi Marco,
I was surfing at RS246 and saw some Dyno statement that some RS4 supposed to has 460hp at flywheel has only 325hp at the wheels, on a RR. So, in the 100octane mode of your car, you are running something like 309whp. Moreover, summing a little drag power....Putting that in perspective, and from a lot of testimonials saying that the Quattro system + tyres consumes about 25% of the power, Your flywheel power should be something like >400hp!!

What is wrong, and where?

[Pisobiker]

Both mechanical and aerodynamical losses increase more than linearly with speed.
Then saying a transmission has 25% or whatever percentage mechanical absorbtion of delivered power is wrong (or at least not correct) for two main reasons:
1) Power losses depend on speed, and only very little of power delivered by engine;
2) Power losses are not a fixed percentage through the rpm but increase with speed.

Statement n°1 mean that a given car with 100 hp and running at 100km/h, will have lets say a 30hp of power losses. If same car @ same speed gets a 200hp engine on it power losses will be the same as before or very close to the same.
If you would have applyed the "fixed percentage" rule to the second example using data of the first one, you would have guessed 30% losses which would have been 60hp....

Statement n°2 mean that the car of example 1 would have power losses that increase while increasing speed but with a parabolical curve, totally different from its engine power curve.

The right statement would than be:
"car has 25% power losses at peak power rpm and whatever speed"


Going then to my specific case, my runs are 3th gear runs, unlike most of RR tests that are done using 4th gear. This means my "end of test" speed is ~165km/h @ 7.000 rpm, while would have been ~190km/h @ same rpm if done using 4th gear.
That's why my asorbtions seem too small compared to others.
I've roughly calculated that on a 4th gear on the road run, if my engine really delivers 360/370hp at flywheel, I then wouldn't have more than 240hp at wheels left with all mechanical + aerodynamical absorbtions I would have at those higher speeds.


Marco

[S2central.net]

@Mark - are you 100% certain the problem is not an air leak of some sort ?

In my experience with chipped ABY the lambda o/p at WOT ranges from 700-800mV. Any higher than 800 is probably just a waste of fuel. Much lower than 700 and you might be too lean. Unfortunately the lambda probe is really accurate enough for this kind of measurement - its better done with a WB-O2 probe or an EGT probe.

Cheers,

Paul

[porkkis]

Re: My latest chiptuning. Full report

Originally posted by Pisobiker

Sorry for picture quality, but coldn't find a better way for them to stay whitin the 100k!

You might want to use GIF format for such images. Jpeg is good for photos, gif for "unnatural" images.

[Pisobiker]

Tanks Porkkis,

will check this out immediatly .


Marco

[Pisobiker]

Originally posted by S2central.net
@Mark

....... its better done with a WB-O2 probe or an EGT probe.

Cheers,

Paul

Agree with that. Use a EGT gauge, Mark. If you pick out temps after the turbine (like I did for more practical use), make sure your temps don't raise over 830-850°C (950°C before turbine). This will let you have a wider overall data on engine load and functioning.

Marco

[Pisobiker]

OK, got some readings from boost gauge.
They're not very accurate, but it's not easy to keep an aye on boost gauge, one on tacho, and another one on the street simultaniously.... (could it just be because I only have "TWO" eyes? )

Anyway:

~1,70 bar from 3500 to 5000 rpm;
~1,55 bar @ 5.500;
~1.40 bar @ 6.000;
~1.20 bar @ 7.000;
~1.10 @ redline.

[KramRS2]

Thanks Marco, Paul and Porkkis!!

I’ll install a EGT as soon as possible. Thanks for your information.

Marco, about your boost behavior, it is exactly what though. Exploiting all the compressor capabilities as you sent to me.

About the power calculation, I still have some doubts.
The rolling resistance is almost linear with speed. In RR there is no air drag. So I did a little simple math and find a 1550Kg car (S2) with normal tires Cr=0,015 travelling at 140km/h loss 12hp through the tires and a 1750kg car (the damm RS4) with normal tires, a bit fatter Cr=0,016 travelling (on top of rollers) at 190km/h loss no more than 20hp. The difference between testing a RS4 at 190km/h and a S2 testing at 140km/h is no more than 8hp to flywheel.:confused:

You could see here :

http://forums.rs246.com/forums/showflat.php?Cat=&Board=RS4&Number=27473&Forum=RS4&Words=dyno%20wheel&Match=And&Searchpage=0&Limit=25&Old=allposts&Main=27473&Search=true#Post27473

They have no more than 270hp at wheels:nana: !!! So if you have more than 300hp to the wheels on your high boost setting, I think you have more than 380hp or maybe the RS4 are weaker than I Though. :nana: (and my car weaker than I wish :wacked: ops: )

Right?

[]

[Pisobiker]

Mark, I don't think those numbers are credible.
I can just make a couple of "real" examples to proove this.

A car like an S2, about same weight, frontal area and CX, would need not less than 130 hp to reach 200 "real" Km/h on the road.
The meaning of this is that if sucha car have a 130 hp engine ALL the power produced at that speed is TOTALLY absorbed by drag forces.
These of course are the sum of aerodynamical drag (that increases with a cubic ratio vs. speed) and transmission + wheel and tyres drag which increase with a square ratio vs. speed (as any other form of dissipating force is not linear with speed).
If these weren't the facts we would have had "Fiat Panda 30" running at 200 km/h all around :eek2:

While surfing in the net I found some dyno runs of Dahlback monsters which demonstrate that drivetrain+transmission losses are way higher than the numbers you found:

This is an S2: at 200 km/h drag on a RR is ~50Kw = ~ 68 Hp

[Pisobiker]

This one is another S2:

same stuff as the other: ~50 Kw @ 200 km/h

[Pisobiker]

Same for an RS4:

[Pisobiker]

And almost the same even for the Golf RS1 (but should have the "quattro" transmission, though )

[Pisobiker]

Of course drag is the "negative" line that sits on bottom of the charts.
As you can see it is not linear.

I may try to write down a "formula" for computing exact power consumption for all the drag forces vs. speed.
Unfortunatly any formula will need some data I don't have and have no idea were to find (like exact Cx, exact front area of car, transmission efficiency, wheels and tyres drag...).


Marco