Roadracing a WR426 - need tuning advice
Posted September 04, 2003 - 12:27 PM
Posted September 04, 2003 - 01:21 PM
The low oil capacity of these motors could certainly become an issue in longer road races. Keeping the oil changed and new filters installed often should keep things running smoothly. My motor has been bullet-proof for over 2,500 miles of motocross and high-speed trail riding.
To answer one of your questions directly with regard to being unsure of the power of the WR in comparison to the YZ, they are basically the same motor. The WR can be made to run just as strongly as the YZ's with very minor mods(exhaust, jetting, grey wire removal, throttle stop mods). There are a gazillion posts about uncorking the WR's.
I honestly don't think getting a "YZ cam" would be a good move for a road racing bike. Linear power delivery and the resulting better throttle control is usually more conducive to faster lap times than getting a big "hit" off the bottom that the "hot" cams deliver. I am sure that there are some aftermarket companies making cams that would suit the applications you are shooting for than a motocross cam.
There is a ton of information on uncorking the WR series in here (just do a quick search) and getting it jetted correctly. Run fatter jetting if you are going to be running road racing speeds.
If I were you, I would venture into the supermotard and dirttracker forums within this site to look for more complete information on making your motor a top end missle. Those folks will have alot of info on the direction you should go.
It sounds like a good project. Keep the site informed of your progress.
Posted September 04, 2003 - 02:05 PM
Posted September 04, 2003 - 06:40 PM
I too come from a roadracing back ground and remember back a while when steve crevia was racing f2 and some guy came from back east with a rotax 600 in a spondan frame and gave him a hard time untill the rotax puked it's guts out on the back straitaway. I think the 4 stroke would do nice on the track. what year is your tz frame?
Posted September 04, 2003 - 08:33 PM
Posted September 05, 2003 - 04:49 AM
Photo of TZ250 here
Posted September 05, 2003 - 12:59 PM
Posted September 05, 2003 - 01:51 PM
With my WR426 YZ timed, the thing flys. With a much lighter chassis from the TZ, you should have some decent top end. Get a good YZ exhaust for maximum airflow since noise probably isn't an issue.
The new YZ450 is only a 4-speed. Basically a wide ratio 4-speed so that won't work very well for your application.
Do we get pictures when you are finished?
Posted September 06, 2003 - 09:20 AM
Carbonbody, you did say you were new to the site and with these motors, so what is obvious to all of the riders of these bikes may not be apparent to you. I am going to try to clear something up; I hope it helps you in your decisions.
The '03 and '04 YZ450's have 4 speed tranny's and are geared
for motocross. People do use them to ride trails but usually are compromised with gearing in some situations. Yamaha left the fifth gear out and lowered the oil capacity as a weight savings measure.
The '03 and '04 WR450's have 5 speed tranny's and are geared for a wider variety of off-road riding. First gear is able to deal with tight single track(down to walking speed) and 5th is much like an overdrive, usually for wide open desert riding.
When I race motocross with my '03 WR450, I am easily able to do second gear starts and am able to ride the whole track in 2nd and 3rd, rarely tapping into 4th. The broad powerband or torque curve of these motors and the way they make usable power throughout the rev range is remarkable. They can lug down at low rpm's, pull hard off the bottom and rev to the moon. They make really good power on top and have lots of over-rev.
The engine was originally designed for motocross. The main difference between the motors is the transmission. To sum it up, neither of them have a six speed.
I realize it will be very difficult to find a 450 motor and the 426 will probably be a better choice. The older 400 motors had some cooling issues, so do your research.
You have created alot of interest with this idea.