14 wr450 for motocross

The engine is still a five-titanium-valve unit that Yamaha says it prefers to stick with rather than a four-valve configuration because it offers superior reliability. Who are we to argue? The record stands for itself on that one.

Straight from Yamaha via dirt action website. You can call Yamaha and they will tell you straight up maintence and reliability of the WR is far superior. Its meant to be riden every day of the year. Once you pass a certain power level on a 450 jug you stress out the working parts, hints the 5 valves.

 

All the new YZ's are now 4 valve heads.

 

Yamaha always had a big problem with flow restriction and cavitation with the 5 valve head, as the center port was tuned differently that the other intake ports

 

The 5 valve was very reliable and very restrictive.

If you ever saw the 2009 YZ GYTR head, it had 5 OUNCES of aluminum removed for porting, to make it fast enough to match the KX450f

 

My '08 head has MASSIVE porting done to the center port and Medium Masive to the other two intake. 

 

I don't even have to use 1st the power is so massive down low, even geared 13/50

Im geared 13/40 and could leave in 2nd no problem if i had to. All anyone has said is the wr is not as powerful of a motor. No one ever doubted the yz was faster, but ridden in similar conditions the wr will go 10,000-20,000 miles without needing any top end repair. A yz cannot do that no matter how you want to spin it.

Im geared 13/40 and could leave in 2nd no problem if i had to. All anyone has said is the wr is not as powerful of a motor. No one ever doubted the yz was faster, but ridden in similar conditions the wr will go 10,000-20,000 miles without needing any top end repair. A yz cannot do that no matter how you want to spin it.

Don't be sure sonny boy. There is no observable difference. I already have close to 20,000 miles on my Hopped up YZ'd WR450 and many times it is revved to pi-s and ridden very hard. All the new WR450's will likley end up with the backwards motor. It will have more power than the previous fuel injected WR due to the better port design.

K gotcha. Your saying your wr has gone 20,000 miles, and that in the "future" their gonna change motor design. Luckily im refering to now, and the motors in the bikes currently. Even in the owners manual the wr's service intervals far out stretch the yz. Its cool you dont have anything to prove. I know the 5 valve motor is better for longevity. It doesnt matter to me what you believe will be its replacment. Until it happens your pissing in the wind "sonny boy".

K gotcha. Your saying your wr has gone 20,000 miles, and that in the "future" their gonna change motor design. Luckily im refering to now, and the motors in the bikes currently. Even in the owners manual the wr's service intervals far out stretch the yz. Its cool you dont have anything to prove. I know the 5 valve motor is better for longevity. It doesnt matter to me what you believe will be its replacment. Until it happens your pissing in the wind "sonny boy".

The owners manuals always say stupid stuff as though you own a race team like JGR. My old CR500 owners manual used to say to replace the throttle cable every three races. Never did.

I'm curious as to what a jr. considers will break in a four valve motor. I believe they will be just as reliable. It's not a KTM or a Honda.

Well think I dropped a valve today, only 34 hours. Find out the damage next week

Well think I dropped a valve today, only 34 hours. Find out the damage next week

That sucks

Well think I dropped a valve today, only 34 hours. Find out the damage next week

 

Pretty rare but anything can happen.

That would have NEVER happened on a KTM! [insert smiley that indicates sarcasm here]

I was riding this new track Saturday, fairly well up it down a straight n on deceleration I heard to loud pops, so did my mate riding behind me, n it jus died, could kickstart or roll start. But still had compression,Changed spark plug. What else could it be, don't think it's valves anymore, having it looked at next week. Any ideas?

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