Inova

Sorry for being such a newbie, I did a serach and found nothing and thought I would post this here.. Anyway, I've read SOHC and DOHC in the magazines and want to learn more about it. I know that it means Single/Double, but what is the big deal between the 2?

PrototypeRacer

Single Over Head Cam.... ^

Dual Over Head Cam.... ^^

Inova

Hhaha, I know THAT much.. what is the difference performance-wise. How does that change the way the engine works etc..

mikersoft

I'm no mechanic, but I'll take a shot a this one... My guess is with DOHC, one cam controls intake valves & the other controls exhaust valves. That allows more differences between intake and exhuast valve lift/duration. Thus, engineers have more ways to fine tune performance when designing an engine. With a SOHC, the one cam controls both intake and exhaust.

OK real mechanics, how close was I?

-Mike

bluetouring350

SOHC has one set of cams controlling intake and exhaust where as DOHC has two pairs controlling intake and exhaust, for a total of 4 cams. Basically it makes for a more efficient motor and more power. But it sucks when oyu want to buy new camshafts cuz you got to buy four insteads of two so instead of $600 it costs us more like $1200.

91na

so SOHC is still really 2 cams in the engine?

My friend went to a rather "illegite" looking auto place to get a "performance cam" for his Rustang. He still hasn't received it (I personally think he lost his money) but even if he didnt he only ordered 1.

Can you just get 1 cam to control either the inlet or exhaust or do you have to get both?

Basically I just wanna know rather I should call him up and tell him he is an idiot or not :-p

bigpickle

Go to howstuffworks.com you will learn more than need.

mikersoft

If your friend has a 5.0 liter mustang, then one cam is all he'd need, since it is a pushrod motor.

-Mike

91na

k, Thank you....
I asked him about it and he said he didnt know if it was SOHC or DOHC. As I am not a Mustang fan really, I didnt know either.

Anyway, I just didnt want him to get F'd by someone.

510dat

91na;
SOHC or DOHC refers to how many cams you have over each bank of cylinders. If you have an SOHC straight-six (or I-6) engine, you only have one cam running over the entire engine. If you have an SOHC V-6, you will have two cams, one over each bank of pistons. The difference being the two cams on the V-6 are (roughly) half as long, and each services 3 pistons instead of one cam serving all six. For DOHC just double those numbers; a straight-six will have two cams running the length of the engine next to each other, and a V-6 will have 4 cams paired up, one pair on each bank of cylinders.

The "OHC" as you know means Over Head Cam; the cam sits on top of the head and the lobes push directly on the valves. Any old american V-8 (chevy 350, Ford 5.0, etc.) has a "pushrod" engine. This is very different: they have only 1 cam which sits between the 2 banks of pistons. Instead of pressing directly on the valves, a "pushrod" sits on the cam lobe, is pushed up by the cam lobe, and in turn pushes on a rocker arm which is on the top of the head (think see-saw; one end goes up, the other end of the rocker arm goes down), and it's the rocker arm that pushes the valve. A pushrod V-8 will have 16 rods and rocker arms, but the cam actually looks like it would work a 4 cyl engine, because each lobe services 2 pistons (one on each bank; ie pistons 1 & 2). This is cheaper to make than an OHC engine; you need only half or 1/4 the number of cams, but isn't nearly as adjustable.

So your friend who only bought one cam for his Mustang should be fine (assuming he gets the part), since it's neither SOHC or DOHC.

I hope this helps you out

D_Nyholm

You have to calm down with the Mustang = Rustang crap. It just shows that you know nothing about them and are just jealous since you most likely got smoked by about 80% of the ones you tried to race...

FLY BY Z

It depends on how many heads you have. If the motor is a V config, you have two heads. Inlines have one. Then the term Dual overhead cam is self explanatory. How many cams above the head(s). The Mustangs after 96 are modular meaning they utilize OHC (overhead cam) technology. The GT's are SOHC and the Cobra's are DOHC. If it is a 95 or earlier it has pushrods and the cam is situated below the heads and between them.

dczoner

iTrader: (1)

Man, is someone cranky this morning?

Desmo

Another benefit with DOHC is the ability to advance or retard the intake and exhaust seperately. Most engines don't have the ability to adjust the cam timing originally, but a set of adjustable cam drive gears will fix that right up. Typically, advancing the timing will shift the power band of the engine to higher revs, thus making more horsepower. Changing the intake and exhaust differently will adjust the overlap and can help you make more power. You really need a dyno to dial them in though, because you are talking maybe 2-5 horsepower, but we'll take all we can get.

Also, today's higher technology engines will vary the timing of the cams automatically. The 350Z fits into that category.

Desmo

SpyVO

*EDIT: Some other stuff came to mind!*

I'm a Rustang guy piping up here, thought I'd lend a hand...

I can't believe none of you guys have pointed out the main reason for having a DOHC motor: more valve area means more airflow. 2 valves (of each type) of a slightly smaller diameter have much more area than a single larger valve. More air in means more power can be made.

Other benefits of having a DOHC head...

-If there are 2 cams above each head, the designer of the head can put them farther apart. This allows the valves to be canted, or tilted. The resulting combustion chamber shape is hemispherical (where the term HEMI comes from). The advantage of this is that the entry angle is greatly reduced which helps out flow a lot. Imagine if the valve faces were parallel to the piston top (assume it's a flat-top piston), and sides of the head (where the intake and exhaust manifold are mounted) were perpandicular to the piston top. The resulting port would come up from the combustion chamber and have to make a sharp 90* bend to get to the intake and exhaust manifolds. That's BAD for flow. Canting the valves straightens out the port. Canting the valves is possible with pushrod engines, but it's kinda tough, and those kinds of heads tend to be W I D E. That's why they had to modify the 69-70 Boss 429 Mustangs. The motor was so wide that the shock towers had to be altered!

-DOHC motors with 4-valves also allow for better spark plug placement (right in the center). This generally allows for better flame propagation, even burning, less detonation and better emissions, if I'm not mistaken.

-More valves allow for greater valve area with less shrouding. That's when a part of the edge of a valve is so close to the cylinder wall or a part of the combustion chamber that the incoming charge doesn't really have an easy path to flow through.

Other stuff: Not all 4-valve motors are DOHC. Some Hondas and Neons have 16 valve SOHC heads. And having 4 valves prevents having quench areas that promote turbulance, better mixture and detonation reduction, although, this was a bigger issue with carburators, where fuel atomization and turbulance were bigger issues.


Once again, all this coming from a Rustang guy. Hope that helps a bit.

FLY BY Z

That's what we get for not reading the entire first post. I thought this thread was about Mustang motors. Oops. Thanks for adding in the good info.