I have a 98 polaris sport 400l. It has a k&n, jetted approp, hot seat pipe, supertrapp silencer, wiseco forged piston, aggressive clutch, and 12/42 sprockets (stock 12/34). It goes very hard from a dead stop, but it doesn't have much middle end. From 25 to 35 mph it doesn't have much power compared to the aggressive bottom end and pretty good top end that it possesses. What will gain me the better middle end. I use it for mostly trail riding but i would like more even power.

 

it sounds like you have to play w. the clutches more to gain your mid range but you might loose top end in the process.

 

With that pipe you need to be running a brown primary spring with S55 weights the HSP white,HPD violet or Aaen blue secondary spring.
What do you have now.

 

I bought it recently and do not know what the clutch setup is exactly. The previous owner told me it has a different spring setup but i do not know exactly what it is. Would a boyesen rad valve help out?

 

I have bought the quad recently and do not know what the setup is. The previous owner said he had clutch work done to it. I my self do not know much about clutch work as i am new to polaris transmissions. Would i benefit any from a boyesen rad valve?

 

I have bought the quad recently and do not know what the setup is. The previous owner said he had clutch work done to it. I my self do not know much about clutch work as i am new to polaris transmissions. Would i benefit any from a boyesen rad valve?

 

A Rad valve wont hurt.But you need to know exacly what is in your clutch.
The best power mod after a pipe and proper clutching in a port job.

 

I will inquire about my clutch setup. And by porting you mean port the head right?? Also, what does a chain tensioner do, and why would do some people use oil injection block offs on their 400 sports?

 

By porting I mean the cylinder not the head.Head can be milled down .020.
A chain tesioner keeps the slack out of the chain and makes it less likly to snap a chain when jumping.
No reason to block off the oil injection on a Polaris other than dropping a few lbs for drag racing or with a very highly modded engine.This system is better than ones on other brands.

 

That sounds like a big job, i'm assuming you must pull the motor, right? I've never done anything like that before. And how expensive is it?