low power !

[42tt]

Since SKIWI mentioned the N75. I have read on a few sites relating to the S4/RS4 2.7TT that owners have had good results by running a MBC in parrallel to the N75 which reduces the spiking, others have used the N75 to log boost and then removed the N75 (vacum connections only) and replaced it with a MBC set to the max. req boost and found more stable boost control. Not sure how this would work on a chipped RS6 anyone tried this?

42tt

[Fen]

I'm not an engine mapper, but I do know that the boost characteristics can be altered by fuelling and ignition timing, just like the performance of an NA car can be. More usually I have seen it used to aid quicker spool of a turbo to get more low down torque, but if something can be adjusted one way then it can be adjusted the other. I don't know how big a difference could be achieved on the RS6, but the original question was only looking for a small difference.

I wasn't personally advocating the knock protection as a means of control, but again knock protection can work by pulling ignition and upping fuelling which is possible based on rpm range and would reduce torque in those ranges. In fact you make a good point in that we also are only interested in torque rather than boost. There's a range of acceptable fuelling for any given engine condition and using the richer end of that range with less aggressive ignition will not maximise the torque potential and will also have the effect of cooling the cylinders and reducing EGT (which in turn will reduce boost slightly).

How did Audi get the extra 30bhp out of the Plus without increasing peak torque? I assume that came by changing the higher rpm range performance without touching the lower.

[S2tuner]

skiwi: if your job/hobby is tuning, I think you'd better stay away from Audi ECUs That's just friendly advice.

[42tt]

S2tuner - Sorry to be a pain but I would like to know your opinions on the use of a MBC either replacing or in-line with the N75

42tt

[S2tuner]

42tt: the only people I've heard about using MBC in parallel were all GIAC customers. AFAIK no one else has ever needed to use an MBC on any car to get it running right. So the tuning is either done properly or it's not and it needs bandaids like MBC.

HTH,

Mihnea

[skiwi]

skiwi: if your job/hobby is tuning, I think you'd better stay away from Audi ECUs That's just friendly advice.

nope it's not - and i don't have anything to sell. and lemme guess, yours is, and you do??

[S2tuner]

Yes, in case you haven't noticed, my business is also one of the sponsors of this website. And yes, tuning is my hobby and my job

[grizz]

As he says ,it's his hobby but, he's very very good at it.

[42tt]

S2tuner - What i was referring to was this use of the MBC

http://forums.audiworld.com/s4/msgs/1584287.phtml

Ideally we would like the boost curve of the Blue line shown but as the turbos loose efficency in the high rpm's they will drop off but i thought they would stay on longer due to the the MBC as opposed to the ECU controlled N75

Just a thought, assuming you have a remap already this is to just hold a more stable boost curve at the remaps max requested boost not to increase boost in any way

42tt

[S2tuner]

to me at least, an MBC has never been necessary. make up your own mind, if people need it with GIAC sw (and most do), it only means GIAC don't really do a good job, but that's old news to me...

[42tt]

S2Tuner - I think i will stop asking you q's as you seem to think that i am somehow assosciated with GIAC which i am not so thanks for your input upto now

42tt

[S2tuner]

42tt: sorry, I didn't mean you were associated with GIAC, the only thing I meant is that if the software is tuned correctly, there shouldn't ever be any needs for an MBC. An MBC does exactly the same job as an ECU with the N75 if it's programmed correctly.

[42tt]

S2Tuner - Thats cool I understand where you come from regarding GIAC as I tried their program and wasnt impressed.

But I have read alot of people use the MBC to smooth the boost response out as the N75 doesnt allow for as smooth boost response as a MBC will unless the system was improved on for the RS6 but from watching the boost gauge I can say even at stock i have an initial boost spike and then the taper off towards redline but this i believe is due to the ECU and N75.

42tt

[Fen]

I'll preface this by saying that I'm new to the RS6, but in my experience MBCs result in more boost spiking than less.

Much of my turbo tuning experience comes from the 944 Turbo where the standard boost control is a slow reacting "cycling valve" (doing what I imagine the N75 does) linked to a poorly designed wastegate - a good wastegate would probably grenade the engine due to the cycling valve's poor response. Stage 1 of improving that is to fit a proper wastegate and an MBC, but cars equipped like that spike quite badly. Next stage is to fit an EBC and solenoid to actively manage the boost in close to real-time which smoothes things out dramatically. Finally some cars have a standalone aftermarket management system with integrated boost control - I use an Autronic SM4.

I don't really understand the N75 fully beyond that in basic terms it allows the ECU to control boost, but surely it can't be worse than the mid-Eighties cycling valve the 944T uses? Are we saying it's perfectly adequate with the right ECU software or just that it's better than an MBC with the right software?

[42tt]

Fen - I know what you mean by the older MBC's and spiking but the new ones are good or even an electronic boost controller replacing the N75 would be better i think

42tt