I just baught a polaris 400 4x4. ok i was wondering about the following things......

i want to bored out the psiton, what should i bored it to?

also i want to put diffrent sprockets with more teeth on them, how many teeth should i get on the sprocket( remember im doing this all for speed)

also is there anything else i can do to get better acceleration/top speed?

thank you to everyone who can help me out.

 

I don't know much about the 400, but I do know changing sprocket sizes goes one way or the other on the top speed/acceleration. So if you change your sprocket for top speed you lose acceleration and vise versa...

Rick Ritter can definitely make your 400 faster!

Glenn.

 

Before doing the mods you listed, ptu in an HPD clutch kit, pipe, and reeds. You won't need the other mods after you see what it will do.

 

Buy some extra brake pads and keep them on hand.

 

If it is a 4x4 my dealer recommended against changing sprocket ratios. It will/should screw up your 4x4 system. Rear wheels turning faster than front.

Just a thought. Like someone said, call HPD or RCR for a pipe or other mods.

 

Don't worry about boring it out. Spend the money on a clutch kit, pipe, reeds, a high flow air filter & make sure it is jetted right. If you STILL need more power, then consider a high compression piston or head, and porting. The first 4 items you can bolt-on yourself, so you can buy more stuff since you won't have to pay labor. Jetting isn't that tough to do, but is important to get it right.
I am betting it will be a while before you feel the need to open the engine up and do any internal mods.

 

A word of warning about polaris pistons: They are not of the highest quality, above about 50 HP ( stock is 36-38 HP ) they become the weak link in the engine. If the engine has lots of hours, has been ridden hard, or if you're planning some serious modifications, invest in a Wiseco Piston. If you feel confident to pull and replace the parts yourself, the cost should be about $200.00 to bore, hone, purchase the piston, gaskets, coolant and a new upper rod bearing.
I scuffed a piston with about 30 hard hours on my 2000 that was pushing about 50HP at the time.
A 50:1 pre-mix in the fuel tank will help longevity.

 

How fast does your polaris go with the 50 hp??
also with some sand tires how do you think it will run in the dunes?

 

With 50+ HP on an uphill paved road the Scrambler ran just over 70 MPH ( 70.4 MPH to be exact ) Clocked with a 12 channel Garmin GPS 48. That run was with a new piston and very rich jetting for break in. The fuel was mixed 3 oz of Polaris Gold Synthetic per gallon of 92 octane pump gas in addition to the oil injection. There's still some power left to be found in jetting and cutting back slightly on the pre mix. That run was in late July / early August, temp about 95, humidity about 90%, about 400 feet elevation. In colder, drier air with the proper jetting, I would guess another 2 to 4 MPH would be possible.
As for the paddles, a good set should help you keep up with the piped banshees and ahead of the 400ex's
I clocked the 300 honda with the same GPS later in the year 40 MPH was max speed.
I am 5'11" 230 lbs and a commercial diver by trade, so I'm not a fat slob... A lighter, smaller rider would reach higher speeds than I did.
For Reference, here's the modification sheet:
HPD Trail Pipe w/ stock silencer/spark arrestor ( Yes, it fits with no modifications. Trying to keep it reasonably quiet )
HPD Aggresive clutch kit
V-Force Delta 2 Reeds
HPD Reed Cage spacer
RCR Air Box Mod
K & N Air Filter w/ Outerware
RCR Porting ( I wasn't willing to lose much bottom end, so Rick didn't alter port timing very much. But it does make a bunch more power in the mid range than when it was stock. The engine has a wide powerband and is very easy to ride. My wife and my father both ride it too. )
RCR Modified stock cylinder head for 92 octane gas
Wiseco Piston 0.040 oversize
Renthal Handlebars and diamond grips ( honda 400 ex bend, a BIG improvement over stock. )
There's still a lot of power to be found in this combination, ie. bigger carb, lower restriction silencer, more aggressive porting, etc.