realisticly 7mm. Technically you could probably do 14 but would need spacer welded to tops of cylinders and new sleeves for the setup. not cost effective and wouldnt perform as well as a aftermarket cylinder. this would not be an off the shelf type thing. doubt many builders would even do it nowadays. but you asked.you can do a 14mm wampus if your trying to look stock but anyone with half a clue would know whats up