M50 Vanos Switching RPM's

[wrs 118]

My Vanos is buggered so I'm going to do a rebuild. At the same time I'll get the oil pump rebuilt because the sump has to come off to fix an oil leak and will replace all timing chains and guides etc. This is because all the timing gear and oil pump is of unknown age and condition.

The engine was a M50B25nv converted into a M50B30 with S50US cams (and Vanos). My old ECU was from a M50B25nv and not compatible with a Vanos engine + because of the S50US cams I decided to by a Link G4+ Plugin for better tuning flexibility. Tuning was done by Graham Neal at WRC in Napier. Graham used the standard basemap Vanos On/Off RPM settings of 2500 On, 4500 Off. It would have been better to lock the Vanos off and do a full tune then do a second tune with the Vanos locked on. Then the two torque curves could be overlaid to see where they cross and those RPMs would be the best on/off points.

Considering the basemap for the Link is for a M50B25TU with everything stock there could be some differences in cam switching points considering I'm using S50US cams. I'm also using the S50 Euro headers and M50 inlet manifold. I'm not using the MAF with the Link only using MAP, TPS, IAT and engine temp. The current tune is based on this configuration but it was found the engine was running out of air and fuel starting from about 5700 rpm. I have new injectors and a bored throttle body (18% bigger) which will go on at the same time the maintenance is done. After this it will get a re-tune.

I briefly considered deleting the Vanos and locking the cams in full advance but think that will end up giving good midrange torque but nothing down low or up high - could be a disaster.

As already stated, the best method to find the optimum cam on/off RPMs is to do a dual tune but I'm hoping there might be someone who has experience with a similar setup who already knows what the best values would be and would be prepared to tell me. A dual tune is pretty expensive and I'm trying to avoid the extra cost.

At present when the Vanos turns on at 2500 you can feel a big change - I've been wondering how much lower the rpm value could be dropped to get the torque boost earlier. There's no noticeable change at 4500 when the Vanos switches off so this point could already be about right.

Any thoughts??

I have also read the maximum RPM should be limited if locking the Vanos on to avoid high RPM valve clearance issues. If the dual tune approach is taken and this is a real issue then does anyone know what the safe maximum RPM with Vanos on is? I suspect you could limit it to the point where the torque is less than the Vanos locked off RPM crossover - no point going past there anyway.