Afternoon guys, ive been meaning to post this for a while, but have only just got around to finding the time to think about it properly. before i start, i hope this doesnt come across as the typical 'can i fit this to my car and get 30bhp' question. ive heard an awful lot of bad things about mbc's, and was wondering why they are thought of so badly.... i know on many non VAG cars its possible to turn the boost too far up, causing the engine to run lean, things to get hot, and things to start melting.... from what ive been able to find out so far: The 1.8 T standard ECU is able to maintain factory Air/Fuel ratios up to 15psi of boost (im assuming this is through sensors in the MAF and the Lambda) i also believe the ECU will go into soft limp mode at 14.7psi (1 Bar) if what i have read is correct. now, are mbc's so frowned upon because people tend to increase boost too much, causing continous hitting of limp mode? or is there another reason? i ask, because a friend of mine has recently fitted an mbc to his mk4 golf gti T. he has fitted the mbc, in place of the N75 completely, leaving the n75 doing nothing, and increased the boost to a mild 13psi, clearly well below the limp mode at 14.7. he has been running the car like this for around 2 months now, with no problems whatso ever. the car is a fair bit faster than it was, whilst still being totally driveable, and still very smooth, and if what ive read about the ECU's ability to maintain air/fuel ratios is correct, it wont be running lean at all, and thus will be completely safe. so- in this case, running only a small increase, and seeming to be able to hold boost for longer, what is the problem with running an mbc? ive noticed many people over in the USA are now fitting mbc's to the 20vt engines, with seemingly good results, provided the boost isnt upped to a silly level. ive read all the articles about fitting the zenner diode to clamp the volate the ecu reads, and im not too fussed about that stuff, im just talking about adding an mbc alone, and upping the boost a small amount, like my friend bill has. so-whats so bad about it?