In Part 1 and Part 2 of this series we talked about the basic equipment you need to get your YFZ450 on the racetrack. In this article we're going to show you what we did to Project YFZ to get competitive with the rest of the YFZ450 racers.

Exhaust - Intake - Jetting

In stock form, the YFZ450 is nice and quiet at 92 dB and still a very fast machine. It can be very competitive in any of the Amateur classes and some of the Expert classes.

However, to get this lower sound level, the stock intake and pipe on the YFZ450 are very restrictive and you just aren't going to be fast enough in in the upper-level Expert classes.

The first thing we did to get our YFZ some more speed and power, was put an aftermarket exhaust system on. When looking for a an exhaust system, you may have to compromise depending on your needs. We were looking for a race pipe for competition use, but race pipes are usually loud and may not be legal in many public riding areas.

We looked around at many of the race pipes out there and decided to go with the Rossier Engineering Exhaust system.

Rossier Engineering is not one of the largest names in the ATV world, but they have been building exhaust systems and winning championships for many years. Most of this has been with watercraft but they have also been modifying ATVs. With the advent of the new Yamaha YFZ450, Rossier decided to expand their ATV line and came out with a new YFZ450 system producing, 7 additional HP on the dyno - and that is without cam mods.

The Rossier pipe and jetting will add 5 mph to your top end. The pipe is made completely out of stainless steel with an aluminum silencer and a very trick billet aluminum turn down tip to help the noise levels.

Installation

Rossier Engineering system unboxed and ready for installation.

Rossier does a great job packaging, using lots of bubble wrap around all components. This exhaust is a little bit different than most of the other exhausts out there. First, the end of the pipe is turned down to lower the noise level, and made completely out of billet aluminum.

Second, the pipe comes in three pieces - the subframe of the YFZ flexes a quite a bit and some of the YFZ450 pipes have been known to crack when it does. With the Rossier Engineering design and separate mid-pipe it allows the exhaust to flex with the subframe. instead of cracking.

Remove this clamp then the stock tail pipe can be unbolted and slid off.	Now remove the stock head pipe and you are ready for the new system.

You will need red locktite and some high temp RTV sealant before starting the install.	After installing the head pipe we put RTV on the the end before installing the mid-pipe.

Head Pipe and mid-pipe installed and ready for silencer.	Rossier silencer installed.

The mid-pipe is very close to the rear fender. We adjusted this for awhile and ended up with maybe 1/8" of clearance.	The RE billet end on the silencer is very trick and the turn down is designed to lower noise levels.

With the exhaust system installed we turned to jetting and the air box. We initially installed a UM Performance aluminum air box with the larger 250R filter, but are now looking at installing the Rossier Engineering adapter in the stock airbox. We have had problems with the UM mounting brackets breaking since there is so much flex in the subframe of the YFZ450. (UM is working on a solution to this problem.)

Jetting Rossier supplied a couple main jets a new 45 pilot jet and a new YZ needle, recommending that we go with the 165 main jet. Rejetting may seem intimidating to some but it isn't really that hard.

First step is to remove the airbox snorkel from the carb on the left side. Then go over to the right side and remove the throttle cable cover and take the throttle cable out. Remove the clamp from the front of the snorkel, turn off the gas and remove the fuel line, then all you have to do is very carefully pull the carb out.

There is a plate on top of the carb that says FLAT CR. Remove this to get to the needle. There is a small allen head bolt in there that has to be removed that will allow you to get to the needle.

To get to the jets on the bottom of the carb, the large 17 mm bolt has to be removed. You can then install your new jets and put your carb back in.

With the carb removed we removed the top to access the needle.	We placed the clip on the 4th position on the new YZ needle.

We changed the pilot jet to a 45 (stock is 42).	Now change the main jet - we went with a 165.

Summary

The Rossier Engineering system made the YFZ450 even easier to ride.

With the Rossier exhaust and more air flowing, the YFZ is much better than before - it is like riding a whole new machine again. The first official test ride for the YFZ450 was at the WORCS race in Longview, Washington. The course provided a significant amount of real tight trail, wide open drag-strip sections and of course some time on the motocross track. The YFZ was lacking a little on the bottom end before - now it has GREAT torque down low. On the open drag strip it pulled awesome all the way through the powerband. The additional power provided by the Rossier Engineering pipe made the YFZ450 much easier to ride. As far as sound, the pipe sounds awesome, but it is a little on the loud side. This is to be expected on a race pipe, and the YFZ will be ridden only on private lands or controlled public areas where higher noise levels are allowed. We have not tested it for sound but Rossier says it's right at 100dB. They do make a longer can if you need to keep the sound down but you should expect to lose about 1 HP. The new longer silencer will drop the dB's down to 96. We highly recommend this pipe for those competing on the YFZ450. Enjoy, and we will see you at the racetrack!

• Contact Information

Rossier Engineering
5241 Hardin Avenue Suite B
Plover, WI 54467
(715) 341-9919
www.RossierEngineering.com