a little while back, i looked at trading my honda 450r for a suzuki z-400 with a gsxr 600 engine in it. The kid who built is was 18 and did an excellent job to say the least. This quad was TRAIL ridden only for over a year, and had absolutely no problems. No rebuilds, great on gas, and you cant beat the sound of a gixxer engine revving up. The quad radared at 134mph and got there quick. When i rode it, it didnt feel very heavy, felt just right. Now i weigh 160, and with the added weight of the gixxer engine, it probably equalled out to a 200lb rider on a stock z400. Not much of a difference there.
I seriously looked into this quad. If you can get a rolling chassis for a quad, a complete engine and computer/dash from a bike can be had for around $700. look around. Now your into a sick quad for about $1500+a ton of labor hours. But get a few cold ones and the job gets fun. Another expensive piece is the fuel cell that needs tobe made. On the z400 i looked at, and rode, the fuel cell was in the place under the seat where the airbox would normally be and the intake(4 k&N filters) was where the gas tank would normally be. All that needed tobe done on the frame was cut the two top supports and make them wider. Other than that, the rest of the quad was stock geometry. The plastics and seat fit real good, no ugly gaps. The chain and rear sprocket need to be swapped out for a bigger size, but other than that, the quad was perfect. The pipes hung down under the frame and came up above the rear axle to a jardine slipon. If you can fab the motor into the chassis, then you should be able to make a skidplate for the engine/pipes. The pipes dont hang lower than the rear axle anyways so no worries about bottoming out on rocks.
The best add on to the quad was a steering stabilizer, much needed now that it was so much faster than stock. Quad was real comfortable and easy to ride. felt as good as stock, just sounded better and much faster. Im looking to build one myself now, the kid sold it before i could trade. Ive seen cbr engines in banshees, but i know for a fact that a gixxer 600 can be put into a z400 frame and look/run great.
