MTM Chipping...Help

Post by **tartan_rob** » Wed Jun 16, 2004 4:35 pm

Just done it. Trying to refine it now to get a decent stretch of road that I can use 4th gear from 1000rpm to redline. I intend on mapping rpm, actual boost, req/d boost, torque, road speed and load. Give me a few days.

Early results look like with N75 opened up there is more boost given at higher revs but lower end responsiveness seems have diminshed a little.

Post by **Golich** » Wed Jun 16, 2004 7:26 pm

SimonS4MTM wrote:Has anyone done any VAG-COM logs to prove that adjusting the N75 actually increases boost.

I am thinking that if boost pressure is monitored by the ecu and cotrolled via the N75 to open the wastegates, the ecu will simply put more demand on the N75 to reduce the actual boost back to meet same level as the demand boost.

I'm with you on that - anyone care to expand?

Post by **KayGee** » Wed Jun 16, 2004 7:36 pm

N75 is a motorised valve. ECU controls the boost curve, tweaky screw (technical term

) contols max the boost level. Turn it up or down too far and you get pos/neg boost deviation logged. Also get a big boost spike if you go too far and possibly throttle cut (sustained positive deviation). The purpose is to keep the turbo in it's optimum boost map for any given volume of gas. In the US the guys seem to fit a Manual Boost Contoller (MBC or three way bleed valve) in parallel. This is then adjusted to open at required max pressure and effectively take care of the boost spike, but still allow the N75 to manage the boost curve meaning less stress on the turbos and a smoother curve. From the logs on AW it seems quite effective.

Post by **KayGee** » Wed Jun 16, 2004 7:40 pm

Doh, mean't to post a thread to the link....

http://forums.audiworld.com/s4/msgs/1584336.phtml

Post by **Golich** » Wed Jun 16, 2004 8:04 pm

Post by **tartan_rob** » Thu Jun 17, 2004 10:06 am

The N75 valve has a spring in it, using the small screw for manual adjustment you can alter the force required to open the spring thus making it open more or less. As long as the boost does not exceed the pre-set upper limit the ECU will happily increase fuelling accordingly. Lets face it, its no different to the ECU having to sort out the fuelling on a very cold day running RS4 intercoolers instead of std jobs. If the ECU recognised a preoblem, it would shut down. It knows what boost it is after and what it is getting from that (+ other params) it knows exactly what is going on.

Post by **Nige_RS4** » Thu Jun 17, 2004 11:38 am

I adjusted my N75 last year to reduce surging (I'm running APR s/w and saw spikes of 18-19psi). I have been running max boost of 16psi for a while now, but I decided to return it to the std position on Tues night to see what would happen.

Feels much stronger when on boost now - no low-end or pickup problems (as Rob commented on).

Incidentaly, after fitting the RS4 IC's, the boost raised from 16psi peak (which settled to 14psi) to 17psi peak (which now settles to around 15psi) - which confirms that the std IC's drop at least 1psi - this is well documented by tuners.

Post by **Dippy** » Mon Jun 21, 2004 12:56 pm

I may be a bit rusty on my 2.7 biturbo technical knowledge now, but this is what I remember:

The ECU operates on a closed loop boost control. This means that it uses the boost sensor fitted at the TBB to determine when demanded boost has been achieved, and then uses pneumatic control to open the turbo wastegates to limit the boost at this level.

The N75 valve is part of this pneumatic control, and is calibrated so that the control loop operates efficiently. If you adjust it, you are only adjusting the way that the ECU controls the boost, not the max boost itself. I can see how the boost can be increased by the 'failure' of the loop to control it, and this may be rather exciting, but not really healthy for the engine.

For anyone who knows anything about control theory (I only know a little), this is a very complex area. When control involves the risk of turbo surge, it is not only complex but dangerous (for the turbos & engine). I don't recommend that anyone 'suck and see' using the N75.

Post by **tartan_rob** » Fri Jun 25, 2004 9:55 am

I have done the two runs and have the charts on my PC but not sure how to upload them, anyone any ideas?

The post N75 change run shows a significant increase in torque

(amongst other things) and ECU Requested boost is acheived quicker and maintained longer. drop me a line at robbie_beaton@dell.com for a copy of the excel sheet.

Post by **eric_mok** » Sun Jun 27, 2004 5:33 am

The time has come for me to upgrade to an MTM ECU mod, and I'm stuck with the following question: Should I stick with my modded N75 and continue to trick out the ECU for that extra 1-3 psi, or should I revert to stock N75 under the assumption that any reconfigured boost will have been optimized by the MTM programme, hence no further tricking needed?

FYI, i recently reverted back to a stock setting N75 from a 'tuned' setting and added the MTM ECU mod. I feel that turbo spool up is almost identical (if not slightly slower) at below 2500 revs compared to before. But once the revs build, the car simply takes off. Since the effects of the modded N75 setting is supposed to benefit low end pickup and gradually reverts back to mean when revs build up, I'm wondering if i should give the modded setting another try with the modded ECU to push the low end a bit more.....after i have a boost gauge installed that is.

Post by **eric_mok** » Sun Jun 27, 2004 5:34 am

The time has come for me to upgrade to an MTM ECU mod, and I'm stuck with the following question: Should I stick with my modded N75 and continue to trick out the ECU for that extra 1-3 psi, or should I revert to stock N75 under the assumption that any reconfigured boost will have been optimized by the MTM programme, hence no further tricking needed?

FYI, i recently reverted back to a stock setting N75 from a 'tuned' setting and added the MTM ECU mod. I feel that turbo spool up is almost identical (if not slightly slower) at below 2500 revs compared to before. But once the revs build, the car simply takes off. Since the effects of the modded N75 setting is supposed to benefit low end pickup and gradually reverts back to mean when revs build up, I'm wondering if i should give the modded setting another try with the modded ECU to push the low end a bit more.....after i have a boost gauge installed that is.

Post by **Druggie** » Wed Jul 21, 2004 4:12 am

What is factory boost levels on s4s
What boost levels do chpped ecu run at?

Post by **Dippy** » Wed Jul 21, 2004 12:55 pm

UK stock 0.8 bar, US stock 0.7 bar (approximate peaks).

Typical tune is 1.0 to 1.1 bar with 1.3 bar overboost.
I believe that the K03's are in severe danger much above 1.3 bar but don't quote me on that.

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