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Discussion Starter · #1 ·
I had a thought when I was doing my hotcam install.......why would you even want a DOHC?? What are the adavantages of having a dual cam motor vs a single?? I couldn't really come up with a good anwser on my own. Any of you guys at EHS or White Knuckle got any input on the subject
 

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DOHC offers more Precise valve timing because typically 1 cam is for intake and one cam is for exhaust valves. From everything I have been taught though SOHC offers better low end torque. I could be Wrong and I am sure someone else will Chime in with additional Info.
 

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Its more so for a lighter valvetrain going to a DOHC(for the most part). SOHC(for the most part) has a rocker arm and that adds weight(which some DOHC setups do too) compared to most DOHCs.
Its more a question of what would complement the port layout and overall flow capacity of the cylinder head than a question of simply DOHC vs SOHC. Most DOHC setups are limited to lobe shape and size compared to a SOHC(like I said, most) so in most applications were a DOHC is used the ports in that cylinder head dont flow well in higher lift ranges.
 

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DOHC offers more Precise valve timing because typically 1 cam is for intake and one cam is for exhaust valves. From everything I have been taught though SOHC offers better low end torque. I could be Wrong and I am sure someone else will Chime in with additional Info.
In no way to call you out but the cam profile would dictate torque output not it being SOHC or DOHC.
 

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As Bo pointed out weight savings in the valve train is one benefit. Another is less valve train deflection from not having push rods.
Lower weight, Lower Spring Pressure More Powa!
 

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Discussion Starter · #6 ·
Push rods?? I thought we were talking about over head cam engines....lol. Its hard for me to accept that two cams weighs less than one cam and rocker arms..... port layout knida makes sense I guess, but the cams are above the ports, so you would think you could pretty much do what you want with the ports unless engine highth is a concern or something. Maybe it has something to do with combustion chamber layout??
 

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Push rods?? I thought we were talking about over head cam engines....lol. Its hard for me to accept that two cams weighs less than one cam and rocker arms..... port layout knida makes sense I guess, but the cams are above the ports, so you would think you could pretty much do what you want with the ports unless engine highth is a concern or something. Maybe it has something to do with combustion chamber layout??
when they say less weigh they mean the amount of weight the valve spring have to push back and rocker arms add to that weight. but dohc head is biger and heavier overall. best way to see this is too look at a yfz head and comparer to a trx450 head
 

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Push rods?? I thought we were talking about over head cam engines....lol. Its hard for me to accept that two cams weighs less than one cam and rocker arms..... port layout knida makes sense I guess, but the cams are above the ports, so you would think you could pretty much do what you want with the ports unless engine highth is a concern or something. Maybe it has something to do with combustion chamber layout??
Your correct, my mind wondered off subject with the pushrods. It's an advantage SOHC/DOHC has over a conventional engine.

The OP's question is pretty tough to answer, There are many variables. DOHC would offer you greater valve angle options to suit port designs and create better flow. I'd think that would be one of the top reasonings.
 

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is also has alot to do with power loss due to friction, more parts normally in a sohc engine, dohc is a more direct way normally of opening valves, a dohc engine will rev higher make more power, and be more efficient, its like when you put roller rockers on a push rod motor
 

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Port flow and friction are the key things the DOHC was designed for
 

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Yes, flow on most 450s are limited past .400 lift because of this. DOHC setups on these heads are limited to .400" lift because there are limitations on geometry to go more than that on the lobe design were a SOHC has rocker arms that can alter ratios of pivot to give more lift to the valves.
 
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