but i still dont understand the big difference between these newer 450's and our 700. sorry i know im being a pain.lol
There are a bunch of factors. The main ones are cam choice and ignition timing. More timing, the more octane you need. (This is set at the factory, so it is what it is.) Can choice comes into play as Velociraptor noted. The more "overlap" a cam has, the more it bleeds off compression, basically one of the valves is still open as the piston starts to come up on the compression stroke, compression does not start untill all the valves are closed. So if you install a 12:1 piston with a high overlap cam, your true compression may only be 11.5:1.
Another factor could be load on the engine. Higher the load, the more it will want to detonate. Lets say your quad is right at the edge for 91 when you are just riding the trails. Works just fine on the trails, but take it to the dunes, and the 91 octane will not be enough. Sand puts more of a load on the engine.
Can't speak on any 450 other then the TRX450R. Most people that run a 13:1 piston on pump fuel are using a high overlap cam. Again, load on the engine has alot to do with it. I bet with a 13:1 piston in a 450R with pump gas, it would detonate big time if you took it to the dunes on a hot day. I run 12.5:1 compression piston in my race 450R and I use a 50/50 mix of 91/100 octane in it whenever I race. I will sometimes run straight 91 if I go out play riding, but I feel it is right on the edge and I don't do it very often. I would never run 13:1 piston in my 450R with pump gas, not in the "high load" areas I ride in.
Not even close to a expert on this kind of stuff, this is just what I have learned over the years. Hope it helps. I am sure Velciraptor can expand more if needed.
Doug
