Can anyone tell me the pro's and con's of either or both? I'm wanting power and don't want to compromise reliability to much. I know I can't have it all, but if the motor will hold together 2-3 years that will be ok. By then I'll be ready to buy something else anyway. Does anyone make a stock high compression piston and if so will I be wasting time?

'99 400EX, WB R-series, K&N, 152 main

 

It all depends on what kind of power you are looking for. A 440 kit will add gobs and gobs of torque. But, that is as far as you can go. If for some strange reason you blow up the quad, your looking at re-sleaving the cylinder. If you just go with the 416 kit, and a high compresion piston, it will add power all over. It wont be as strong on the bottom end of the power band as the 440 kit, but it will rev alot more. And if you get a tuneable exhaust you will be able to put the power where you want it. (Adding/Subtracting disks) You'll want to add the higher rev limiter, a more aggresive cam, rock hardening the rockers and stiffer valve springs with a triple face valve head job. There are different durations of cams availible too. Some are designed to add top end power, some to add bottom end power, and some will give you a more broader power band. Both kits are reliable. If you go over 11:1 compresion, you won't be able to run pump gas anymore I believe. I'm 90% sure on that one. Gabe would be the one to ask on that one.

It all depends on your riding style. If you want to race the quad, you'll won't want to design the engine to just put out either top or bottom. In woods riding and basic trail riding, you'll wanna add more torque. In the dunes and more open riding you'll wanna add more to the top end.

Good luck,

Jim

 

Currently, I've been sanddragging and I've done pretty well with the minor mods. Thank God for index time. I'm running stock tires and they hook up very good almost to good. A longer swing arm should help keeping the front end down. With that being said, and living in St. Louis I'm finding it kinda hard finding someone I can trust with the mods mentioned above. I'm kinda leaning towards the 416 kit, although I havent heard much about it. It sounds like the higher reving kit would work out better getting those tires spinning off the line. If I could just crank the engine and dump the clutch without flipping over I could add a few more trophies to the collection. Thanks for your help. I just found a new winter project.

Mod Rookie

 

What about the 426 kit? It’s in-between the two extremes.

I think with the 440 even running lower compression you should use race fuel because it runs really hot. That’s just what I’ve heard I could be wrong.