This is info from a previous thread that is very relevant to this new eurospec subforum:

BACKGROUND:
A member here has a Group N euro S50 B32 3.2L crate motor installed in his 99 M3. He purchased the car after the previous owner had the engine rebuilt by a well respected engine builder. The rebuild consisted of custom forged pistons, rings and maybe a thinner (1.6mm GrpN vs 1.74mm stock) GrpN head gasket.

He does not know if he has the GrpN 57deg thermostat installed instead of the stock 80deg tstat.

He purchased the M3 with the GrpN ECU installed, and he acquired a stock ECU from the UK a few months ago. He is unsure of the cams installed (GrpN or stock?) but research suggests that GrpN cams are the same as stock cams, just that GrpN cams have been blueprinted. The GrpN catalog confirms that the duration of the GrpN cams (260/260) is the same as stock cams, but lift is not provided. If this is the case, then for the purpose of the comparison below you can conclude that software tuning should be the same for GrpN and stock ECU......right?

Well, we were quite surprised by the results of his dyno with the stock ECU installed.

Below is a dyno comparison of the GrpN ECU (DYNORUN_009) versus stock ECU (DYNORUN_012);

http://img.photobucket.com/albums/v420/trailerparkboy/GrpN_vs_Stock_ECU_DBooth.jpg

These runs were done 2 weeks apart. Details of the conditions are listed below...

DYNORUN_009:
- Group N ECU installed
- 5th gear
- 78.8 degrees F; 29.6 in-Hg; Humidity 14%; SAE 0.99

DYNORUN_012:
- Stock ECU installed
- 5th gear
- 70.5 degrees F; 29.5 in-Hg; Humidity 28%; SAE 0.99

He installed (and aligned) the stock ECU for the first time after dyno'ing the car with the GrpN ECU installed. He allowed approximately 2 weeks to allow for the stock ECU to adapt to his motor and driving style. It is not a daily driver, but he drove the M3 hard for many days prior to the dyno runs.

After installing the stock ECU, he noticed an immediate bump in low-end torque, which has been confirmed on the dyno. However, torque has dropped significantly between 4k and 6k RPM.

By switching to the stock ECU, the previously ideal AFR is now running much richer throughout the RPM range, with a very large drop in AFR around 3k RPM.

Based on this info, it appears as if the ECU's have different vanos maps. This is just a FYI...

thats pretty suprising that the afr's are so different yet the both the hp/tq graphs are very similar throughout the entire rev band.

i wouldve expected the GrpN to gain alot more top end, and lose in the mid range.

GrpN is still appears to be more desirable with the larger increase in power from 4k-5.5k, but i dont know if i could justify the cost.

I can't make any sense of the AFR's so I blame it on the fact that they were taken at the tailpipe so they're likely not very accurate. :dunno

With the Gp N DME:

PLUS:
- has no EWS
- no rev limiter
- no vmax limiter

MINUS:
- engine idles at 1k rather than 700 rpm
- hunts for idle when coming to a stop

the groupN seem to have more fuel to service its greater VE from better cam/compression/induction???.

Its more agressive timing is prob cancelled out by its over rich mixture when the DME is on the stocker..

Interesting they run in the 260-270rwhp mark. thats where mine is also, but on the dyno dynamics. My mixtures are just over the 13:1 A/F

I have the Group-N Cams and software in my race car. The engine came from a 1997 Euro M3. We did have problems getting the timing set right but once set, the thing is a rocket. A lot faster than the stock 3.2L euro.

Part of the problems is that the Group-N cams (at least the ones I have) are really 3.0L cams. As such the index mark is off substantially for a 3.2L. We figured this out by comparing a set of Stock 3L cams with a set of stock 3.2L cams. So when you set them up you have to compensate for the location of the index mark.

I know they are not stock because when we were having this trouble we swapped the DME for one with the stock software. The car would not run at all with the stock DME.