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I have a 2006 Z4 E85 2.5i with 175 BHP, 169 lbft torque, and want to bring it to Si engine spec with 215 BHP, 184 lbft torque.
From what I can see the only engine difference is a different intake manifold, additional DISA valve and remap. The 2.5i has a two-stage manifold that is tuned to maximise power and torque in the low and middle RPM ranges, the 2.5Si manifold adds a third stage that makes more power at higher RPM. Low and middle RPM torque are unchanged.
I have purchases a secondhand E90 325i N52 manifold part no 11617559525 and a new smaller DISA valve part no. 11617560538. Apparently the 2.5i wiring harness already has the connection for the second DISA valve, and the same throttle body should be ok. The larger DISA valve part no 11617579114 can be reused. (The 2.5i manifold part no is 11617559526) It is also recommended to fit a new 90 degree elbow crankase vent/heater, as the old one was subject to a BMW recall.
The set up should enable more efficient cylinder filling above 3,500 RPM, and should be a straight forward swap, however it wont yield the extra power without a remap.
Has anyone carried out this or a similar change, and if so can they recommend where I can get the ECU remaped/flashed. I have seen options in the US, but would appreciate any info for the UK and in particular Northern Ireland. If not possible is anyone selling a 2.5 Si ECU?
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