How many hours on your 450 before rings?

Oh wait I replaced my piston at about 60 hours,it had quite abit more wear on it than I thought it should running mobil1 at 5hr oil change intervals.There back on topic again :-)

Since were off subject abit ill add my 1.5 cents.I have an 07 and I was pretty happy with it(pro moto end cap stock exhaust) untill I bought my son an 06 yz450f and rode that.I loved the bottom end hit it had.
Put an '06 exhaust cam in it. :worthy:

I have a 07 and I am very happy with the power and the delivery. With that said, it has 42 hrs on it and I am going to keep it one more year. If I need to replace the piston, any suggestions? Stock, aftermarket, and/or high compression? I dont want to change anything, I just want to freshen it up if it needs it.

Even though i like the strong hit of some of the other bikes,i think that with the rekluse clutch and an exhaust the 07 is going to be a great woods racer,that is if i can get it to turn:bonk:

It's the ignition advance map in the CDI. To some extent, it's the cam timing, too, as the cams on the '06, '07' and '08 are each recentered to have a greater bias toward top end power. An eye-opening comparison is an '03/4 vs. an '05. They all use the same cams, but you'd never know it.

Ah, see, you're onto something. The truth is that anyone who rides both would say that the '03 has more power, based on the huge hit it has, but the '06 produces about 49.5-50 hp, and an '07 produces about a half horse more, while the '03 cranks out only 47.

I ran my '03 against my first '06 from a rolling start on asphalt, and it was dead even 'til we got close to top gear, and the '06 started pulling away.

The thing is "butt dynos" aren't very accurate.

Kind of like a home, location is everything (location of the power band that is.)

power curve moved lower in band = "butt dyno" false reading of peak output!

I had exactly 709 hours on the bike (03 yz450) before replacing the piston and rings. The only reason I actually replaced them was because the crank bearings were getting slightly loose. So since I had the engine apart I replaced a lot of things that werent actually wore out. The bike still ran perfect when I tore it apart. And about 60% of the hours were racing. I did however replace the cam chain about every 75 hours.

How is the head looking after all of those hours? Anyone checking the valves and guides?

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