SOHC or DOHC?
 

Hi all... Ok.. i don't know much about engines just so ya know... i was comparing my 2000 protege against my bro-in-laws 2002 OZ-Rally Lancer using the info i found autotrader.com. It said the Lancer has a SOHC engine and the protege has a DOHC engine. So whats better? The SOHC or DOHC... and why?

DOHC is usually better, due to its ability to provide better brething for the engine, also it is better to compare that on a same car.

OHC = Over Head Cam; S = single, D = dual.

The cams control the opening and closing of the intake and exhaust valves. On a SOHC engine, a single cam shaft must control all of the intake and exhaust valves. One a DOHC engine, you have one cam for the intake valves and one cam for the exhaust valves.

Having separate cams allows them to be positioned nearer the valves that are being controlled, and they can be configured independently for better valve timing.

This leads to a bit more power being generated from the same engine. It may also mean more fuel consumption and lower gas mileage.

But, as noted, these comparisons make less sense when you're talking about different engines in different cars. I think the Lancer and the Protege both make about 130HP, despite the differences in cams.

DOHC has the added advantage of being able to fit more valves (4 or sometimes 5 per cylinder) in the engine. It allows the manufacturer and the tuner to have more precise control on the intake and exhaust valves and the amount of intake / exhaust flow at a particular moment. Best of all is variable valve timing where the engine can dynamically adjust timing for conditions. That is found on the Corolla, Civic, and Sentra to some degree (and next time around on the Protege). It does not necessarily lower the fuel economy when compared to a SOHC motor, that is a result of the manufacturer's setup.

so pretty much SOHC and DOHC both have their advantages, but generally speaking DOHC would be favorable over SOHC. ...right?

Thanks!

A friend of mine and I both have autos. I have a P5 he has a Lancer. I SMOKED the Lancer, how's that?

That works!

Single or twin cam doesn't make that big of a difference. It's the number/size/position of valves, and the passages to and from them. You can do a little more tuning to a DOHC, and it's a little simpler setup mechanically, but if they're both 4-valve engines, they'll be pretty close.

BTW, DOHC doesn't mean 4-valve, nor does SOHC mean 2. Honda made (and probably still makes) 4-valve engines with a single camshaft. I had an Accord with a 3-valve engine (2 intake 1 exhaust, and a 3bbl carb, weird car). And all the old Alfa Romeos and Fiats were DOHC with 2 valves. And I think Toyota's little Echo has a SOHC engine with variable valve timing.

(edit: good grief, I made a lot of typos! I fixed 'em.)

Me, who cares?

DOHC SOHC PUSHROD FLATHEAD it's all the same. In this case the P5 is faster than an Evo so that helped him in that example. No matter how you move the valves you can make power from it. Go ask a hot rod forum what they think.

PUSHROD, PUSHROD PUSHROD.

Ask a sports car forum...

DOHC, DOHC DOHC.


It's all the same in the long run, hun.