I did a few mods to my 400EX that have really improved its' performance in the dunes. Last year I ran my '00 400EX pretty much stock at Siver Lake. It did OK for the most part but there were a couple problems: it was easy to bog the engine down and it didn't rev out well in top gear.

This past weekend I went out there with a few mods I did over the winter. I added a 10:1 85mm piston with stock cam. One less tooth on front sprocket. And 8 paddle 20X10X10 Haulers on Douglas Ultimate Billets. Stock rev limiter.
Right away I notice a difference. At first I ran on the stock tires to compare the engine to last year's performance. Very little bogging now and rev's out easily in top gear. In fact, it pulls fairly strong in fifth now.

Next I put the Haulers on. I didn't notice a big improvement in acceleration from a stop- it was better, but not dramatic. The biggest difference was in the power transfer at speed. Once I was moving things really started to hook up well. Instead of waiting for the stock tires to stop spinning and hook up I was shifting into the next gear. It also seemed more stable at speed and turned nearly as easily as stock.

Without a speedo and considering the smaller front sprocket, I figured I was probably losing a little speed on the top end (although it actually felt a little faster). While back at my truck two guys with Banshee's who were parked next to me, said they had rolled up behind me and had a hard time catching me. I didn't know they were after me, if I had, I could have pushed it harder. I'm not saying that my 400EX is a Banshee beater- but it is a lot better dunner now.

 

Cool...

 

Sounds killer TrailMix, sounds to me like the biggest bang for the buck was the front sprocket. Would you recommend it? Also, is it something i could do at home or would i have to take it to a shop? Anything else im misssing (stock chain?)? Thanks for the help.

 

2k400EX, I originally got the smaller front sprocket because I wanted more low end. I mostly ride in the woods and need to torque through tight corners and pop the front end up with a stab of throttle. I think the sprocket is ideal for those low speed conditions. However, I didn't expect it to work so well in the dunes. I was basically lazy and didn't feel like changing back to the orginal sprocket. Next time I go to the dunes I'm gonna put the stock sprocket on for comparison.

As far as installation goes, it is easy to change and you use the stock chain. I bought a Sidewinder sprocket (about $30) but I bet you could get a Renthal for less. Just take the case saver/chain guard off, then take two small bolts out of the small plate that retains the sprocket on the splined countershaft. Loosen the rear axle carrier and take the tension out of the chain. Once the chain is slack you can slide the sprocket off the countershaft shaft. Put the new sprocket in the slack chain and slide onto the shaft. Take the slack out of the chain and compare chain tension on top and bottom. If the bottom chain is not equal in tension to or just a little looser than the top chain, take sprocket back off and adjust its' position in the chain. Then secure axle carrier, reassemble retainer plate to sprocket and finally install the chain guard.

 

Well I finnaly got around to adding my Renthal drive Train last night... Did the whole thing. Looks Sweet... As for people saying it is hard to take off the rear sprocket, I thought it was a snap.

 

Skunky, so what exactly did you get and how do you like now?

 

At the Glamis dunes in California a fatter (richer) main jet should be used to prevent bogging down. I don't remember what jet I used last April but my quad ran great. Since then I've replaced the stock 15 tooth counter shaft sprocket with a 14 tooth which made a great difference here in the pine forrests. I'm looking forward to seeing how well the different gearing works at the dunes this winter.

 

azrob, keep us posted, im definately intrested in the results. Thanks.