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Here is a topic. SOHC or DOHC? What would you rather have? What are the advantages and disadvantages?

Here is what I think.
"The cam mod" is the yfz way of saying " advancing or retarding the cam timing". Having 2 cams, you are able to make simple adjustments to the "cam timing"(when the cam starts to move the valve). For examp. on "Jap Cars" (twin cam cars) tuners/engine builders are able to "dial in" or adjust the "cam timing" using "adjustable cam sprokets". For anyone who has done "The Cam Mod", if our yfz was equiped with "adjustable cam sprokets" the cam mod would have been as easy as loosen 3 nuts, and tighten 3 nuts. This is a feature would be awsome if you were to have the bike on a dyno because you can make a quik adjustment and see the results right away. Maybe not on a stock engine, but when strokers and overbore kits become popular( and I bet they will) adjustable cam sprokets would definately be an advantege the twin cam has over the single cam. This allows you to "tinker" with the one side and it wont affect the other. With a single cam, what ever you do to the exh. (as far as advancing or retarding the cam timing) is also done to the intake. So the only way to "tinker" with a sohc (the TRX) is by changing or regrinding the factory cam and when it is changed or reground it better be right,,or ya gotta regrind.
 

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You already answered your own question. DOHC is the only way to go! There are NO advantages to SOHC other than being a simpler motor.
 

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IMO it's 6 of one and half dozen of the other. DOHC does allow for cam timing adjustment and that, in and of itself, can be a great feature. However, DOHC does increase weight and complexity which could lead to potential problems. I'm not saying it will be problematic but could be.

SOHC reduces weight and complexity but reduces cam timing options. In the case of the TRX head the intake valves are actuated directly off the cam lobes and the exhaust valves are actuated off a forked roller rocker. This is what has my mind wandering. A trick in car engines for years was messing with rocker arm ratios. When you change rocker arm ratios you change lift and duration specs. I can only speak for small block Chevy heads but your run-of-the-mill Chevy 350 heads didn't flow all that great, especially on the exhaust side. Rather than tearing the top of the motor off to port the heads guys would throw a set of 1.6 rockers on the exhaust side to pick up some flow. While this wasn't a huge horsepower builder it did help a stock motor and milder cam combo. I'm wondering what effect a different ratio rocker would have on the TRX? In theory, if it worked on car engines than it should work in this engine. But, I don't know flow specs on the CRF head so I can't say for certain. SOHC cam engines utilizing rocker arms can effectively change their cam timing as well, albeit a little more limited.

One advantage to DOHC is that you can change cam timing without changing lift/duration. If that's what you're seeking than that's great. If you do want to change lift/duration than you're buying new a new cam(s). On a rocker arm system you can change lift/duration using the stock cam by simply replacing the rocker arm. Again, if that's what you're looking at doing than that's great. And when I say you're changing cam duration I don't mean you're changing how long the valve is staying open, simply the time at which the valve opens and closes changes respective to whether you increased or decreased arm ratio.

Both systems have their advantages and disadvantages. In both DOHC and SOHC you'll still have to buy a new cam (or cams) if you want to change lift and duration specs independantly of each other. While cam timing might gain you some horsepower, changing the actual cam profile is where the real meat and potatoes is. In order to do this both Honda and Yamaha owners are buying cams so in the end it's a wash.

I could type much more than this but my fingers are beginning to numb and this topic could drag on for pages. Just offering my opinion but trying to keep it relatively short ;)
 
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