I've been doing alot of reading these days within the forums and looking at the websites of different mod manufacturers to try and understand the benefits and interworkings of these modifications. So far I am only getting vague ideas. What I would really like to find is a manufacture nuetral book on tuning snowmobiles. I want to learn more about the raw engineering behind these modifiactions. People talk about things like porting and head exchanges and clutching and I don't have a complete understanding. Can anyone recommend a good book or set of readings that will shine more light on the subject? I'm a heating and cooling equipment engineer and am a fast learner but I admit I know what I consider to be little about snowmobile mechanics. Could someone please point me in the right direction? I am currently running a stock 09 m1000 162 spring order with powder pros as my only modification and have an 03 1m 900 I let my sledless friends ride. I really want to open the 1000 up with some mods over the summer. I intend to add a full new exhaust system, the PCV controller, intake, and do some hood/chassis venting. I am concerned with making the requisite clutching changes and what my real options are here. I am interested in maybe changing the porting and cylinder heads but again I do not feel educated enough to make these decisions and desire further definition and comprehension. Please help!