For a MKIII, V26 is the highest I believe you can go without having problems.
I'm sure someone will chime in to verify. What features are you trying to obtain by going to V27?...........Phil

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2011.5 Dinan ///M3:
SSII DCT
Competition Pkg
Convenience Pkg
Premium Pkg 2
Heated Seats
Enhanced Premium Sound
Black Kidney Grills
BMW M Performance Steering Wheel
BMW Carbon Fiber Performance Spoiler
BMW Aluminum Pedals
Dinan Exhaust
Dinan Mid-Exhaust (x-pipe)
Dinan Carbon Fiber Intake
Dinan Performance Tune
Dinan Pulley Kit
Dinan CH-R Wheels
Dinan Carbon Fiber Strut Tower Braces
Arkym Front Lip
Carbon Reflectors
Lux H8 V3
Brembo 365mm BBK