Naughty but nice
Car: Z4 sDrive35is
Join Date: 28th September 2007
Thanked 103 Times in 102 Posts
The HKS racing suction kit is the next best alternative if you don't want to shell out for the GruppeM, followed by the K&N Apollo. It all depends on how much you really want to spend and how your going to be using the car. Are you going for a ECU upgrade to and or a new exhaust system? All these things together will give gains.
Until there is some real figures for the GruppeM then I cannot comment on how good it actually is as the gains could be very similar to the HKS at half the price, but hype and price always make people think that something is better than it actually is. Your basically paying for the carbon fiber with that one.