Web Camshafts Grind #963 VS. Carb Boring *Flattrack*


3 replies to this topic
  • Zaj 243

Posted April 27, 2009 - 08:03 PM

#1

To start, my bike is a '06 YZ450F, JE 12.8:1, full exhaust, Wood intake, and PR2 built head (porting very close to stock). I'm still looking for more top end power, typical '06 with power falling off after 8500-9000 rpms, but an animal before that. If I could get the power to extend farther (not necessarily more peak power) without loosing the brutal power before that i'd be happy. I just picked up USED web camshafts grind #963, their top-performance cams for supermoto and flattrack racing (I am racing flattrack), but still have to buy correct valve springs before installing. They claim a modest increase in HP in upper rpms, but i'm worried about valvetrain reliability and loosing low end. Another option I have been looking at is getting the carb bored (2mm over), which I have heard great things about, and does not affect reliability aside from the slight stress more power would put on the engine. The carb mods would be alot cheaper, cheap enough that I could pick up another used carb to send out and have the option of switching carbs if needed. What limits the YZ head from making power farther? Are the cams a waste without changing porting? Is the stock carb bore choking power at high rpms? Is the ignition not aggressive enough at high rpms? I'm leaning towards boring the carb now, but i'd greatly appreciate any input on either method of HP. Thanks in advance!

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  • harrperf

Posted April 27, 2009 - 08:32 PM

#2

The head flows well enough stock to make some very good hp..

The cam would completely change the character of the bike, but you undoubtedly loose reliability...and of course as you know springs are a must (does that cam require new guides as well? aka shorter?)

The cam is really what dictates the character of the motor...so any time you change it you "feel" the most gain.

The carb mod may be just the ticket your looking for to gain more mid and top...I would think either way to do it. If you don't run the cam, then your gaining more top. If you do the cam, it's a good match for one another.

Reliability is a comprimise with valve train. Open it faster and harder...and close it faster and harder, and you make more power (in general). but doing so stresses the parts more...no way around it.

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  • grayracer513

Posted April 28, 2009 - 09:35 AM

#3

Boring the carb is what you are after, as you describe it, at least at this point. It will obviously not be as helpful without port work and cams aas it would with those mods, but I think if you had to or wanted to do those mods one at a time in the best order, the carb should come first, then the head, then the cams.

With regard to the cams and their effect on the engine, remember that there are two things about the cams that affect the character of the engine's power output. First is the grind, or lobe profile, which determines both how much the cam lifts the valves, and also how long they stay open. This last is called duration. The profile also determines how rapidly they reach their full lift, how rapidly the close, and how much finesse, if any, is involved with opening the valve and returning it to its seat.

Lift by itself only improves airflow without altering the character of the engine, that is, it won't make a low end engine a high end engine, at least not within limits. Duration necessarily does exactly that, because the timing of the opening an closing events is necessarily changed if the valve stays open longer. In general, a cam for shorter tracks where the engine has to pull harder at low speeds or across a wider rpm range will have a greater increase in lift than in duration.

The other important element is timing, and specifically lobe centering. "Lobe center" is the point in crankshaft degrees at which the cam lobe is at the peak center of its lift. Altering the lobe center of either the intake or exhaust, or both, will have an effect on the power character of the engine, and in fact, for some years, this was the only difference between the WR and YZF engines; the lobe center of the exhaust cam was moved closer to TDC on the YZF. Lobe centering is also the major difference in the cams used in the '03-'05, '06, and '07 YZ450's. The grind is otherwise nearly identical. What's cool about this in the case of the YZF is that the cam timing can be altered sleeplessly, and independently, since the intake and exhaust are on different shafts. Several of the aftermarket grinders offer cams with sprockets that can be re-indexed without the need to use a press. Re-centering the cams has long been used by some tuners to "dial-in" the bike for a particular track or track length.

More reading, if you like:

http://www.muzzys.co...be_centers.html

I would recommend anyone really serious about flat track have a talk with Ron Hamp.

  • Zaj 243

Posted April 28, 2009 - 03:30 PM

#4

Thanks for both of your inputs....I'm thinking the carb trick is just what i'm looking for, as I don't really need any more power yet, just extending it further to the limiter is what i need. I think the cams will go on the shelf for now, just gotta find a used 06 carb to send to Ron so I don't have any down time. Thanks for the input again!





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