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New KTM XC/EXC Spied

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From the April 2007 Dirt Rider Magazine:

Although it looks like an SX model, with handguards and a headlight, closer inspection reveals an all-new motor! Mated to the latest generation bottom end, now with electric start, the top end is a single-cam design like all the former SX models (pre-2007 450/525) and current EXC/XC bikes.

Expect a weight reduction and a higher power output. The water pump is now located on the case instead of off the camshaft. We suspect the transmission will continue to be a six-speed. When will we see it? Not sure, as KTM wouldn't comment on the bike but did mention that any homologation in the U.S. is a timely process. Could be '08 or '09.

Although the DOHC KTM is using is proving to be very reliable I'm not real suprised at with the use of a SOHC on the off-road bikes. What does suprise me is their (DR Mag) expectation of more power from a single cam. I'm no engine designer/builder but I'm pretty sure that a DOHC will always have more HP potential than a SOHC.

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I agree. Maybe they have come up with some new configuration that will give DOHC power with SOHC simplicity. If ever there was a manufacture willing to try something new and radical it would be KTM.

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Am I missing something? Isn't the CRF450R a "Unicam" motor? as are the rest of the MX based Honda dirt bikes. Honda's make good power obviously.

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Yep, the Honda is SOHC design and it makes good power. There are those that believe the Hondas eat valves because of the high side loads on the valves (due to the Unicam design).

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From the April 2007 Dirt Rider Magazine:

Although the DOHC KTM is using is proving to be very reliable I'm not real suprised at with the use of a SOHC on the off-road bikes. What does suprise me is their (DR Mag) expectation of more power from a single cam. I'm no engine designer/builder but I'm pretty sure that a DOHC will always have more HP potential than a SOHC.

Im curious,why would a sohc deliver less power than a dohc...???

may be a fundamental question to some...educate me,why is dohc better..??

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Im curious,why would a sohc deliver less power than a dohc...???

may be a fundamental question to some...educate me,why is dohc better..??

I think he's got something really confused. SOHC (SINGLE over head cam aka Honda Unicam) DOHC (Dual over head cam or other bikes). Honda uses one cam and people use that against them with their valve problems. It's a good question though, what's the point of using one cam vs two?

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Until the Honda Unicam came along ALL Single Over Head Cams (SOHC) motorcycle engines were at a disadvantage to DOHC. A conventional SOHC has lower RPM limitations than a DOHC has. There is a more complicated valvetrain arrangement and cam lobe shapes, both of which lessen the RPM ceiling of a SOHC design. Spark plugs were place where they could instead of the optimum. RPM x Torque = Horse Power. The higher you can spin it the more HP you can make. The Unicam re-wrote the book on SOHC engines. Until then DOHC always won the HP war due to being able to spin the engine faster.

Basically a DOHC design allows for a flatter combustion chamber shape and the use of flat top pistons with high compression. There is also valve angle, spark plug placement and combustion chamber shape. Most DOHC engines (except KTM and Husky) have the cams mounted directly above the valve arrangement (valve stem, shim, bucket). The cam directly actuates the valve via cam lobe on bucket. There are no rocker arms and such. Machining is more complicated and it has more parts (which are lighter and allow for a higher RPM ceiling). DOHC engine cost more to make due to the complexity, weigh more and take up more space (engine height). That is how a YZF is configured.

At least this is how I understand it.

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From the April 2007 Dirt Rider Magazine:

Although the DOHC KTM is using is proving to be very reliable I'm not real suprised at with the use of a SOHC on the off-road bikes. What does suprise me is their (DR Mag) expectation of more power from a single cam. I'm no engine designer/builder but I'm pretty sure that a DOHC will always have more HP potential than a SOHC.

When they say less weight and more power they are talking about the current RFS, not the SX-F. I am sure the new engines will be heavier and less powerful than the SX-F, but a huge improvement on the RFS.

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