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post #1 of 11 Old 03-02-2011, 03:34 AM Thread Starter
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DOHC vs SOHC

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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post #2 of 11 Old 03-02-2011, 04:44 AM
 
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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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post #3 of 11 Old 03-02-2011, 05:37 AM
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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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post #4 of 11 Old 03-06-2011, 09:20 PM
 
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Quote:
Originally Posted by Someguy View Post
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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post #5 of 11 Old 03-06-2011, 09:28 PM
 
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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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post #6 of 11 Old 03-07-2011, 01:28 AM Thread Starter
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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??
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post #7 of 11 Old 03-07-2011, 08:16 AM
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Quote:
Originally Posted by 1dmbhonkey View Post
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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post #8 of 11 Old 03-07-2011, 11:26 PM
 
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Quote:
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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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post #9 of 11 Old 03-08-2011, 10:49 AM
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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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post #10 of 11 Old 03-08-2011, 01:08 PM
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Port flow and friction are the key things the DOHC was designed for

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