I am trying to raise the compression on my 95 Bayou 400 and was wondering what the bore and stroke were on a Prairie 400 and also the compression.The problem I am having is noone makes aftermarket pistons for these 4wheelers.The bayo is no longer in production but if the pistons are the same between the 2 models I may persuade a piston company to put one in production.I just have recieved a piston work sheet and will be filling it out soon.Any info will be appreciated.This will not be a race piston but a piston specifacally for sport utility 4 wheelers.My stock compression is 9 to 1 so looking to raise it to 10.5 to 1 so as to help low end torque.Still will be able to run pump gas .I have found in cars that one point of compression is worth about 10 % more torque.The extra power is really needed on my machine because of the tires.We stay in nothing but mud.Sometimes so deep and sticky it will stop your tires from turning.

 

While I'm not sure you've picked the right horse to ride in this race (candidate engine for a hop-up), if higher compression is your goal, why not mill the head? No problem if there's no valve-piston interference; you can flycut the piston top for clearance if necessary.

A simple calculation will tell you how much you need to shave to raise the compression to the desired ratio.

If that's not enough, you can overbore to the largest oversize piston available, install it with matching rings, and away you go.

These approaches combined would cost less than a custom piston, I'd think.

Tree Farmer

 

The only problem with milling is the timing chain.When milling the head it also retards the camshaft which hurts low end.I have thought of the larger size stock piston but then I might not be able to re bore if something drastic happens.This motor makes more horsepower than any other brands in this same type atv.Mine with stock tires would make mince meat of Foremans and big bears in a drag race.With the pipe filter and carb mods I have already performed it is bacjk almost to the same speed it was before the big tires.The key to good mudding is tire speed.2nd gear is a must.With these big Vampires it is hard for me to keep them spinning.Your insight is 100 percent correct and would be cheaper and probally accomplish the same thing.But I was also in fear of running out of tension on my timing chain if it wore any.Well we will se what they have to say at the piston manufacture next week hoprfully good news.