الموضوع: SOHC vs. DOHC engines

A SOHC engine will produce more torque at lower RPM but less top end power

A DOHC engine will produce less torque in the mid range but it will have more top end power


So a SOHC will feel quicker than a DOHC for daily driving because it is better in the mid range RPM levels

But a SOHC will start to feel like nothing is there when you get up around 4500 RPM

The DOHC will feel gutless in mid RPM but pick up quickly as you pass 4000 RPM


In a race it's most likely the DOHC would win because you would run it up near redline then shift (bringing it down to 4500 RPM ) then run it up near redline and shift.

So the SOHC would pull ahead in 1st gear due to it's supperior low end torque it would have less power at high RPM (4500 RPM ) so the DOHC would quickly catch it as you moved into 2nd and 3rd gear.


So it's a trade off..... better torque in mid RPM levels with the SOHC where you are on daily driving versus the power of a DOHC at high RPM.


The difference between the two engines is not so much the cams ( two versus one ) as it is the valves.

The SOHC will have two valves and the DOHC will have four valves.

At lower RPM the SOHC will have a better efficency than the DOHC but as the RPM rises the DOHC will become more efficent than the SOHC.

The best engines (like my Mazdaspeed 2.3L DISI turbo ) have a shutter valve to make maximum power.

Basicly at lower RPM the engine shuts a valve and completely closes off one of the ports in the DOHC head so that it's more efficent and makes more power

Then at higher RPM the valve opens and the engine intakes air through both ports which again makes it more efficent and makes more power.


So... a DOHC that blocks one valve path at low RPM will be the most efficent and therefore fastest engine.

Hope that helps.

Chris

From Daewootech.com forum

MMamdouh