End user mappable Motronic?

[Verruckt]

I like those K16 hybrids BTW

Where are you located John? If you do go though with the project, I'm good friends with the guy who builds them. He does excellent work and I know I could get you a deal.

[john_banks]

Scotland Nice and cold for charge temperatures

[Verruckt]

Please see my edit. I was mistaken. The fuel pressure varies very linearly with boost pressure.

[john_banks]

Thanks again. A lot of food for thought.

[Verruckt]

Thanks again. A lot of food for thought.

Not a problem John. If you ever make it over to the Germany area, I'd be happy to show you my setup.

[john_banks]

Thanks.

[S2tuner]

Chris (verrückt), whereabouts in Germany are you? I'm in Belgium and I'd definitely be interested in seeing your setup. All this talk has been very interesting and informative for me by the way, thanks for sharing the homebrew secrets with us. I wish I could do the same...

Cheers,

Mihnea

[Diesel]

Hi John

Do you rate the RS4 or/and S4 engine as a strong durable unit that takes a 30% power hike in its stride (when done well of course!)? None of that big end three oil starvation issue as we know of on, ahem, other cars

D

[john_banks]

Appears to be quite a stout engine, why do you think I'm interested ? You're thinking about it too? Main appeal to me is the understated refinement and ride quality. However, I thought the vertical body control of a stock RS4 I tried down roads I know really well was rather suspect - quite a fresh example, and nothing wrong with it, which made me back off because it just wasn't planted over the yumps where I would be flat out in the Scooby with a 50% higher power to weight ratio than a stock RS4. My friend pushed a bit hard behind a 993 on a similar road and that was landing on its undertray at the back as well though, so it isn't in bad company. However, my Scooby is setup just to my tastes for exactly a road like that so unfair comparison - it also weighs a fair bit less I am sure that can be sorted with aftermarket quality suspension, and I have a very good friend who is a suspension engineer. Hopefully the ride quality can be relatively preserved with it.

Another question gents... if I do the fuelling and MAF changes in proportion:

- what do I need to defend? is it the MAP circuit - I saw 12 PSI mentioned as a clamp?
- any links to the boost control setup? I'm happy with MBCs, but usually I REPLACE the stock boost control solenoid and pipework with an MBC

[john_banks]

Reading a bit more it looks like the N75 is just like a 3 port solenoid with a PWM from the ECU. If using an MBC in parallel it looks to me like it would only control spiking but not raise the boost level. Using a MAP voltage clamp at say 12 PSI would stop the ECU seeing higher than 12 PSI so you can run higher boost, and it won't freak out with flow limits because of our frigged MAF in its bigger tube. It may advance the timing as commented because MAP may be an input to engine load and a lookup for the base timing map? I've made huge real world performance gains from an AVC-R because I can get full boost or even higher boost in lower gears. Does the Motronic have per gear boost control?

I've not found reference to the wideband lambda mentioned before on the car as stock? One of the Audiworld theads mentioned what looked to me like narrowband lambda voltages (0.875) rather than this being a lambda ratio - which would be a touch lean, and that he was going to run it on a wideband, but I never found the follow up. Are the Euro cars of different spec and have a wideband?

[Verruckt]

Chris (verrückt), whereabouts in Germany are you? I'm in Belgium and I'd definitely be interested in seeing your setup. All this talk has been very interesting and informative for me by the way, thanks for sharing the homebrew secrets with us. I wish I could do the same...

Cheers,

Mihnea

No problem Mihnea. I live in Köln...probably not too far away from you. Where are you? I have a friend in Brussesls that I visit from time to time.

Appears to be quite a stout engine, why do you think I'm interested ? You're thinking about it too? Main appeal to me is the understated refinement and ride quality. However, I thought the vertical body control of a stock RS4 I tried down roads I know really well was rather suspect - quite a fresh example, and nothing wrong with it, which made me back off because it just wasn't planted over the yumps where I would be flat out in the Scooby with a 50% higher power to weight ratio than a stock RS4. My friend pushed a bit hard behind a 993 on a similar road and that was landing on its undertray at the back as well though, so it isn't in bad company. However, my Scooby is setup just to my tastes for exactly a road like that so unfair comparison - it also weighs a fair bit less I am sure that can be sorted with aftermarket quality suspension, and I have a very good friend who is a suspension engineer. Hopefully the ride quality can be relatively preserved with it.

Another question gents... if I do the fuelling and MAF changes in proportion:

- what do I need to defend? is it the MAP circuit - I saw 12 PSI mentioned as a clamp?
- any links to the boost control setup? I'm happy with MBCs, but usually I REPLACE the stock boost control solenoid and pipework with an MBC

To answer some of your questions...

Here is a quick diagram of my boost control setup.





The MAP clamp is set in a range so that you don't get deviation codes and the car won't cut throttle. I can get you some more specifics on the Zener. I wouldn't suggest replacing the N75 with an MBC. Although it creates a very aggressive boost profile, it can make part throttle response way too jumpy. However, for maximum performance...MBC only is probably the way to go. Keeping the N75 in control gives you very nice part throttle response and preserves the ECU's safety systems as Mihnea has alluded to before.

You are correct in saying the MBC won't raise the boost limit. The ECU software I'm running will always "request" more than 12 psi under full load. When the ECU only sees 12 psi, the N75 will increase duty cycle to meet the requirement. This is why the MBC is ESCENTIAL to controlling the upper end of the boost curve. Right now I'm running a little less boost than I used to. I'm spiking to about 23 psi and tapering to around 19-20 at redline. It's enough for me right now. I'm sure I could go higher. It's easy to switch back to MBC only which would provide a slightly flatter boost curve and quicker wastegate response.

I don't think the Motronic knows what gear the car is in with the 6 speed, but perhaps someone else could shed some light on that question.

The S4 has only narrowband O2's which can be used as a very rough estimate of rich/lean. I wouldn't use it for actual tuning. The car does come with real EGT probes though that have a limited temperature range (945-1035 *C).

[john_banks]

Thanks, I see and understand now

Is the MBC part throttle jerky because:

1.Ball spring MBCs are that way anyway?
or
2.The ECU sees more torque than it requested on part throttle and fights it?

If it is just 1 then an EBC could be quite nice to drive, albeit losing safety functions as noted. I suppose you don't need to litter your car with gauges if you keep the ECU safety control? I'm used to continuous in cabin boost, knock and wideband O2 gauges as I don't trust the ECU. It seems like you can trust the Motronic to some degree without these? Even though there is only a narrowband O2 sensor, does the ECU check it and take corrective action if lean during open loop fuelling? Or does it rely on EGT or knock response to detect if say the fuel pump is tired and the pressure drops on full load?

EGT range sounds quite high compared to what I'm used to, sounds like they are more worried about not melting the turbo than the engine, it takes a stout turbo to enjoy 1000C EGTs, the manifolds appear quite short.

[S2tuner]

The EGTs are measured before the turbine, not after.

About WB O2 sensors, I thought the later S4s had them just the same as the RS4, or do they simply not have them? Heck, gotta check that next week when I do those 2 RS4s to make sure...

1.8T has definitely a WB O2 sensor (5 wire Bosch LSU) after 2001...

HTH,

Mihnea

[Verruckt]

The EGTs are measured before the turbine, not after.

About WB O2 sensors, I thought the later S4s had them just the same as the RS4, or do they simply not have them? Heck, gotta check that next week when I do those 2 RS4s to make sure...

1.8T has definitely a WB O2 sensor (5 wire Bosch LSU) after 2001...

HTH,

Mihnea

It certainly could be that the US spec (which my car is) differs from the EU spec in that respect. Mine are definitely narrow band.

I'd be jealous if you guys had wideband.

To respond to John's questions, here is a description I wrote on another forum...

For the past few months, I've been running an MBC only for boost control and have had the N75 disconnected. This works fairly well and only causes hiccups under a few conditions. This setup will be adequate for most people. The advantage is that the boost response is basically digital. This provides the absolute quickest spoolup and wastegate behavior. The wastegates will stay shut until the desired boost level is met and "should" plateau from there.

The downside is that part throttle (0-20%) response can become too sensitive...especially at higher RPM's. The problem is that at high engine speeds, there is enough exhaust gas energy on tap to spool the turbos rather quickly. This means you can get high levels of boost at relatively low throttle inputs. This can lead to a "surging" behavior which I was never able to completely tune out.

Once the car arrived in Europe, my driving style changed. There are many situations where I will be cruising along at speeds of 120-150 mph. At these speeds, it is very difficult to maintain a steady velocity as the boost level fluctuates very quickly with the slightest change of throttle input. As I stated before, there is enough exhaust gas energy to spool the turbos even at very little throttle. This behavior became unacceptable to me under daily driving conditions.

So today, I hooked the N75 back up in parallel with the MBC. So far, I've left the bleedhole open. It works well, but I may experiment with the bleedhole down the road. Now my part throttle behavior has greatly improved. The jumpiness and surging is gone. Right now I have it set to spike to about 22 psi and taper to about 20 psi. This is a good daily driving setup.

Not a lot has been tried with EBC's to my knowledge. I imagine you could dial it in pretty well though. It would be good to see someone experiment with it.

It is my personal opinion that you can really trust the Motronic system to preserve the motor. In most circles I know, a boost gauge is the only essential gauge you will need. Others are nice, but not necessary. There are so many safety systems in this engine, it's crazy. If your EGT's get above 980 °C, the ECU will run pig rich and reduce boost to cool things down. It has excellent knock protection. If it sees something it doesn't like, it will cut throttle and boost. I don't know of any 2.7T's destroyed by tuning problems.

FWIW, I logged primary O2 sensor temp the other night (not quite as good as EGT's, but better response from the measurment) on the Autobahn...and my setup is running as cool or cooler than data taken from stock turbo'd cars running a chip only.

To clarify, my setup is by no means perfect and certainly isn't for everyone. I would call it 95% complete...meaning 95% of the time it responds as well as you could ask for. There are certain situations where it will react rudely (usualy a hesitation or buck), but it's more of an inconvenience than a hazard to the motor. It's pretty rare I'm also tuning more and more out every day.

I have not driven any of the EU market S4 turbo kits, but mine certainly isn't any worse than any off the shelf product from the US. Our US tuners don't have those totally worked out yet either.

[Dippy]

Well I'm pleased that I've managed to understand this discussion so far. Although it's only academic (I have no intention of 'home brewing' my car), I am still concerned about your previous statement.

Are you saying that there are guys who are making 400 HP at the wheels with just bigger turbos, a zener to limit MAP voltage and an MBC to control boost spikes? What about extra fuelling?