I will be doing mostly mountain trail riding. Looking at 400 4x4 automatic. What is the difference in full independent rear suspension and ACT rear suspension? I heard the full independent tends to role a bit more in turns. Is the 400 a strong enough engine given the weight of the atv?

 

I have an '02 400 4x4 with the Act. First, the 400 is more than strong enough to pull the weight. The '03 400's have an even better engine and weigh less, so it only gets better with them. I've not ridden an IRS enough to make a good judgement (they weren't out when I bought mine) but by all accounts, they're pretty good in the turns. I believe the difference in price is only about $200 and for the extra clearance it's well worth the price.

The Act suspension performs wonderfully, however. Nearly as well as the IRS and better than some competitor's IRS machines (since they have sway bars that restrict the IRS function). Be advised that the claimed clearance is measured at the center of the ATV, and not at the rear "pumpkin" which is a little lower. I've never had a clearance problem with it, but there aren't too many mountains in Minnesnowta.

 

The 400 motor is strong enough to go anywhere you want to.
Second the differences between the ACT and IRS:
The ACT will Articulate more than the IRS. This means the suspension is allowed to flex more before the opposite wheel is lifted off the ground. The ACT is a solid axle with trailing arms to allow the flexability. Unless you are going through a slide area where you are crawling over boulders you won't notice the difference between the two setups. Second, when you put weight on the rear rack and the suspension compresses you don't loose ground clearence with the ACT. When you load up the IRS it looses ground clearence. However the IRS will give a smoother ride when you are just trail ridng. Each wheel acts independently when hitting an obsticale. It doens't transfer the jolt to the other side like the solid axle would.
Both setups are great but they are different. If you are just trail riding you won't be disappointed with either one. I really don't think that one is better than the other its just what do you feel would best suit your needs.

 

Since Cat has added adjustable shocks to the ACT models it should cure the body roll issues. I'm planning on adding the 03 shocks just for this reason. The ACT performs almost as well as an IRS except in the most challenging situations. The biggest reason to buy an ACT is for the simpler setup (no CV boots or joints to worry about). Yet, $200 isn't a huge amount... It all boils down to personal preference, try out both.