I just gotta RCR stage 1 kit with a HPD trail pipe. I know I should change my stocker piston to a Wiseco, but I plan on having It trail ported in March, or April. Should I go ahead and get one, or wait till then?

Also when I do get one do I need just the piston, or Rings, Clips, and any gaskets? I can get the stock Wiseco from Rocky Mountain for $78.

Last Question, when I get my piston, I plan on getting a 0.20 over piston, but I don't really know why. what does that do? Is it good to get it, or will it just eat more gasoline? Will I have to have any work done to the cylinder?

Thanks A lot!!!

 

When you send in your cylinder to get ported tell them you want a new piston, they will clean up your bore and size the piston correctly so all you have to do is absolutly nothing but put it back together when you get the pieces back.

 

Let me try to answer your questions one at a time as best I can...
What do you need?
I just did the top end myself, and you will NEED the piston, rings, wrist pin, wrist pin clips, and gaskets for the cylinder to the base, head to cylinder, and reed cage to cylinder. I would also RECOMMEND that you get a new wrist pin bearing, while you are in there. Doesn't cost much, and is always a good idea to mate a new pin to a new bearing.

What does getting a .020 over piston do?
This one is simple. Both the piston and the cylinder will wear from use. If you just put a standard size piston in a cylinder with wear, the piston will start out 'loose' and not last as long as it could, especially considering that the cylinder will not wear evenly. By that I mean it will have more wear towards the top of the stroke, and also will tend to wear egg shaped. By going .020 oversized, you can get the cylinder bored or honed out to eliminate the egg-shape and taper to it. This honing will make the cylinder slightly bigger, hence the need for a bigger piston. A shop that knows what they are doing will measure the piston, and then hone out the bore to get the clearances as close to ideal as possible, for maximum reliability. Too tight, and it can score, or even sieze, too loose and it won't last as long.
This should answer the questions 'is is good to get it?' and 'will I have to get work done to the cylinder?'

Will it just eat more gasoline? No. But don't expect heaps more power, either. Remember, you are going only .02 of an inch in a bore that is something like 3.7 inches, for a gain of about 1/2 of 1%. Any power gains would be a result of a high-compression piston, milling the head, and/or porting.

If it was me, I would wait and swap the piston out when I did the porting (you will have to send the cylinder off anyway, so they might as well bore and port it at the same time). The only reason I would swap the piston now would be if your engine has quite a bit of use on it, or plan to ride a lot this winter, and are afraid of cracking the piston skirt. Otherwise, if you don't ride it much during the winter, it should be OK for a little while if you get it done before you really start riding it this spring.

Also, I would call whoever you are going to have do the porting work to confirm this, but I think they recommend you put a new piston in after a porting job, since the engine will be apart anyway.

What worked for me was to order the piston and a cylinder that had the work I wanted already done to it, with the understanding that when I sent back my original cylinder, they credited me back the cost of the cylinder, only charging me for the work that was done to it. This way I was able to take the engine apart and put it back together right away, while how everything fit was fresh in my mind, and didn't have to worry about any dust or anything getting into my engine while it was apart waiting for the work to be done.

 

Rick Ritter did the porting on my 400. He didn't change the port timing much but enlarged the transfer ports and exhaust port and gave everthing a proper finish. I asked him not to hog out the ports, I wanted to get better mid range and there would be room to change port timing and further enlarge the ports if need be. He also rechambered the stock head for 92 Octane pump gas.

For now, add a small amount of oil to the fuel ( Pre-Mix ) to add to the stock oil injection system. The extra oil will help keep the stock cast piston alive untill you can do the other work.

When you get ready to the modifications, send the cylinder to whomever you decide to have do the work, and let them measure the bore, you may get away with a stock bore piston. That will save you some money in machine work. Boring the cylinder gives a fresh surface for the piston & rings to work and seal against. Honing removes the cutting tool marks from the boring operation, allows very precise control of final bore size and gives the proper crosshatch finish for the rings to seat and seal.

Also, Wiseco does not make a "High Compression" piston for the 400 Polaris. All changes to compression have to be made via the combustion chamber in the head.