So I am starting to move into performance mods now. I have milltek cat back high flow exhaust, and a 15% reduction pulley. I just recently purchased ddm works CAI with an Alta inlet tube and a craven 17% reduction pulley. My question is...
Would I have to tune my ECU to run these mods?
Would these mods mess with fuel/ air mixture?

I almost forgot. I have an 05 mcs.

Thanks,
Steve

 

I have been reading up on this too. From what I understand you do not have to have a tune for these although it will help

 

All your mods will lean things out....
it should run ok...
But will pretty lean at high rpm's....even a 17% with just a cai is leaner than optimum...
will it blow up...probably not....will you burn a valve...prob not...I think it depends on how you drive...injectors and tune WILL help you make more power...heck bang for the $$, the switch from a 15% to a 17% is pretty minor...you will feel it....maybe..if you live in an cool area, have good fuel, and run sparkplugs one step cooler than stock....the same plugs as the JCW.
IMO if no tune is planed, jcw 380's would be good....just a bit more fuel, no tune needed...but if you plan a tune, you could easily use bigger ones, but they MUST be tuned at time or install (or very close).

 

I ran my '05 S with a 17% + cai for a bit....then got 380's...then got a tune...the car ran better, and smoother, with more power at each step...
many folks run 17% with a cai and exaust a-ok....