Hi there,i've got a 260z with roundtops on, and it idles like a bag of spanners, and emits a ridiculous amount of white smoke out the back. Normally you would think this would be a blown headgasket, but it is a brand new headgasket, torqued down correctly. I have even tried draining all the water from the system and starting it with absolutely no coolant in for a short period, but with the same cloud of white smoke. What else could this be? a warped head maybe, or vacuum leak? Really getting to my wits end with it now.