Fit the O2 controller first and feel the difference, then get yourself a Kev mod to start off with. Kev's fuelling mod will do a fine job of adjusting the fuelling to suit stage 1, 2 or 3 air filters and you will notice yet more power and particularly tractability as the usable rev range expands by 1500rpm+. �/bhp there is no cheaper solution than Kev's O2 controller and fuelling mod combo (with DNA filters).

Save your money and get a PCV later on when/if you get bored and fancy another change (which is what I did). The PCV is a more complete solution to fuelling and allows you to better fine tune your setup, but to make the most out of it you do have to fork out another couple of hundred quid for a dyno session. You will easily be able to sell on Kev's two mods and recoup most of your money.

If you fancy it though, and you've got the cash for a PCV and a dyno session, then go for it from the off.

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