cam specs

I have a sumo 09 yz450f with athena big bore + aftermarket exhaust. This bike works really well on low and mid end but miss a lot of power on top. On quick straight track all the others 450 toast me. The difference is huge. I compared with a friend 06 yz450f also with athena big bore and the same exhaust as me + bored carb, ported head and hotcam intake. This bike works really well. It works as mine on low and mid end but has a lot of power on top end.

I was looking for yz camshaft specs and I found this topic

http://www.thumpertalk.com/topic/936760-cam-differences-between-wr-and-yz/

Based on these values and on webcam explanations, it seems that yz 08/09 should have more low and mid and compared to 06. But Gray always says that 08/09 yz450f have 2 horsepower more than 06 yz on top. What is the thruth?

What could explained this difference between my bike and that of my friend? I think that dored carb, cam spec and ported head all together explained this, but what is the most important factor?

Sorry for my English. I hope that you undestood my question.

If you just look at the cam numbers, you would conclude that the '06 would have more top end, if for no other reason than the greater overlap with the '06 cam set. Dyno sheets, however, repeatedly show the '08-'09 models at 50-52 peak horsepower, and the '06 at 49-50.5. Obviously, there are other factors like the ignition advance curves and the exhausts, and I don't know of a comprehensive, truly scientific comparison having been done between only the cams on a bike where other factors were equal. It would be interesting to try the '06 cams as a set and see what came of it. Remember that it is the torque curve that makes the bike accelerate, not the ultimate power numbers.

But regardless of which one turns out best, if you want really significant gains, I would pursue a set of aftermarket cams. You'll get much more gain from them. To fully utilize them, have the carb bored or switch to a 41mm from a CRF, add a tunable ignition box, and get a good port job done.

Ok. So the difference at peak horsepower between 06 and 08/09 could be explained by the difference in cdi or the head channel.

My bike has excellente acceleration but it miss power on top. I only have problem in long straight part of the track.

I agree with you to do all the mods. Maybe do cam and bore the carb and see how it works. Do you have a preference for cam? Stage 2 should be better for top end power.

I understand, but the issue is one of acceleration if it won't accelerate from say 110 to 130 km/h as it should. Using a tach at least for a test would help you to know where it's actually falling off.

No preference, really. I haven't got a good reason to modify my engines that way. The only time I come up short on top end is by running out of gears.

Stage 2 cams will produce more top end, yes. You might want to look at the GYT-R cams as well as some of the others.

I am not out of gear. It seems that the engine does not rev in 4 or 5th speed. Maybe the main jet is to big? It is a 170.

I will try to measure speed with a gps to determine when I miss power

For the moment, the engine is split in half for a complete rebuilt

170 is on the big side, alright, but not way over. Might even be right at the low elevations you have in most of Belgium. Try a 165 and see what happens.

Thank you. I will try this when the rebuilt will be finished.

On any big bores I have done you had to lean them out some.

Yes I know that. The bike was jetted by the previous owner of the bike.

I try to find a jetting base on the forum, but I saw some people ride with 145 main jet from and others with 185.

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