What is the difference between DOHC and SOHC?

[stormcruiser]

I see that our galant uses SOHC except GTZ which uses DOHC....what is the difference between the two? I can see that dohc is somehow related to higher performance but I want to know more......

[QnzMostWanted]

SOHC - Single Over head cam
DOHC - Dual Over Head Cam

[stormcruiser]

https://www.thegalantcenter.org/style_emoticons/default/laugh.gif haha...I know I should of said that...hahaha...I know what it means....I just knowt know how it is related to engine performace~

Could you please tell me the difference in a way it is related to engine performace....

and ya don't tell me DOHC have 2 over head cam and SOHC have 1... https://www.thegalantcenter.org/style_emoticons/default/laugh.gif

Thanks anyway~

[Kain]

Well, it's pretty much one cam vs two

This is done so the intake and exhaust are independent of one another. Really, I've never found much benefit of DOHC over SOHC to be entirely honest. It's just more parts. But they're spread out a little better, and there is slightly less stress on the cams themselves. All else being equal, there is no discernable diffrence between SOHC and DOHC. Though, when talking the Galant DOHC is good for 20 extra hp (assuming all changes are made in accordance. I.E. DIS, ECU, and Intake Manifold)

[IllestGalant]

Well, with one cam, you can't have durations as long as you want, because the same cam is controlling exhaust and intake. If you wanted the cam to have higher lift and more duration you can't get max performance because it can only hold it open for short time because it is controlling 16 valves by itself instead of 8. some may say that dual overhead cams cause more parasitic drain on the motor which is true, but in the long run you can get more performance from dual because it doesn't have to spin as fast and durations and lifts can be maxed out

[stormcruiser]

thanks....haha....Its too technical....but I will take it that DOHC have slightly higher performance... and more parts....

[manybrews]

in the case of mitsu (and most manufacturers), the advantage is a lighter and stronger valvetrain, allowing higher engine speeds before valve "float" occurs.

that, and the valvetrain geometry is closer to what is perfect.


However, thats about it. If a DOHC and a SOHC had the same theoretical lift and duration, the performance would be the same (up until the point of valve "float", which will occur sooner on the SOHC due to the added mass of the massive rocker arms).

[JiP]

uh whats valve "float"?

[Kain]

uh whats valve "float"?

At high RPMs, the vavles don't close completely between cycles, thus "floating" half open, half closed. This is very bad condition, causes backfires, pre combustion, and other nasty things. Can be remidied with stronger vavle springs, though usually rev limiters keep this from hapening on most modern cars. Though, as the car ages and the springs wear out, it can become a worse problem.

[HiperSilver]

Well, it's pretty much one cam vs two

This is done so the intake and exhaust are independent of one another. Really, I've never found much benefit of DOHC over SOHC to be entirely honest. It's just more parts. But they're spread out a little better, and there is slightly less stress on the cams themselves. All else being equal, there is no discernable diffrence between SOHC and DOHC. Though, when talking the Galant DOHC is good for 20 extra hp (assuming all changes are made in accordance. I.E. DIS, ECU, and Intake Manifold)

what do you mean there is no benefit, you have two cams, one controlling intake, another controling exhuast, you can fine tune these to work well together,

[Kain]

what do you mean there is no benefit, you have two cams, one controlling intake, another controling exhuast, you can fine tune these to work well together,

I was referring to the intrinsic benefit as it comes from the factory. I know there is a benefit when tuning for maximum power.

[HiperSilver]

oh ok, thanks for clearnign that.

[98TsiAWD]

And the 94 DOHc 4g64 block has 5 less oil gallies than the SOHC block.

[baadhabit]

DOHC is definatly better. its more than "just" parts.

heres a pic of a SOHC in action
http://static.howstuffworks.com/gif/engine-cam.gif

heres a simple write up on how engines and cams work.

http://auto.howstuffworks.com/camshaft.htm/printable ('http://auto.howstuffworks.com/camshaft.htm/printable')
http://auto.howstuffworks.com/engine.htm/printable ('http://auto.howstuffworks.com/engine.htm/printable')