Whats a "cam" (DOHC, single cam, that stuff...)

[driftflow]

Yeah so whats a cam in a car, cos after watching videos on youtube i see comments talking about single cam cars and DOHC, i learned a while ago that DOHC stands for dual overhead cam, but what is that supposed to mean? Thanks for the replies.

[MagicRat]

Excellent, simple description of the principles and configurations:
http://auto.howstuffworks.com/camshaft1.htm

[Moppie]

First person to claim one is better than the other gets banned for a day.

[UncleBob]

reed valves are best *neener*

[Moppie]

Originally Posted by UncleBob

reed valves are best *neener*

Thats a mighty big pair of brass balls your carrying tonight Uncle.

[J-Ri]

Originally Posted by Moppie

First person to claim one is better than the other gets banned for a day.

What if we say OHV is better?

[Moppie]

Originally Posted by J-Ri

What if we say OHV is better?

You can get away with it, only because I know you know what your talking about

[KiwiBacon]

Originally Posted by Moppie

First person to claim one is better than the other gets banned for a day.

Can I vote for pushrods?
Simply so you can fit a bigger engine in a smaller place.

[Nereth]

Two stroke FTW.

What will your gods do now?

[driftflow]

Ok im still completely confused. But ill explain what i grasped and you tell me if im correct.

There are valves that take in air/fuel mixture, from previous knowledge i remembered that there are at least 2 valves per cylinder, intake and exhaust valve. So a cam is what makes the valves take in mixture and exhaust it. So a single cam is only 1 cam working to take in air/fuel and exhaust it. And the DOHC has 2 instead of one, and the reason 2 is makes it faster is because the faster the car goes the more air/fuel it needs, and DOHC does the job faster allowing air/fuel to be taken in a exhausted out.

Am i right?

[KiwiBacon]

Originally Posted by driftflow

Ok im still completely confused. But ill explain what i grasped and you tell me if im correct.

There are valves that take in air/fuel mixture, from previous knowledge i remembered that there are at least 2 valves per cylinder, intake and exhaust valve. So a cam is what makes the valves take in mixture and exhaust it. So a single cam is only 1 cam working to take in air/fuel and exhaust it. And the DOHC has 2 instead of one, and the reason 2 is makes it faster is because the faster the car goes the more air/fuel it needs, and DOHC does the job faster allowing air/fuel to be taken in a exhausted out.

Am i right?

The advantage of twin cams (DOHC) is that you can put the valves on vastly different angles, it gives a lot more freedom in how you want to shape the combustion chamber.
It can also make it easier to change intake timing without affecting exhaust or vice-versa.

[slideways...]

two over head cams also allows an easier and cheaper packaging route for variable valve timing and lift mechanisms. basically your statement is based on good information, but you kind of got the wrong conclusion from it. every part in a car is a comprimise. the most powerful engines also are the most complicated and expensive. thats why people still modify stone age two valve pushrod engines. because you cant get a 350+ hp DOHC 4 valve variable valve timing engine without spending easily twice as much if not much more. and sacrificing reliability to a degree. (more parts always = more broken parts at some point).

so yes as a purely theoretical measure, DOHC is better. but in reality, each engine is better for some people.

[Moppie]

Originally Posted by slideways...

two over head cams also allows an easier and cheaper packaging route for variable valve timing and lift mechanisms.

Honda would disagree.
The vast majority of their VTEC engines are single cam.

Originally Posted by slideways...

so yes as a purely theoretical measure, DOHC is better.

Bob, Curtis, what do you reckon, 1 day ban or not?

[slideways...]

oh cmon. you know im right.

oh but i didnt mean to say dohc is better for VVT. i meant over head cam engines are better for VVT, as opposed to under head cam engines.

[Moppie]

Originally Posted by slideways...

oh cmon. you know im right.

Only if you can justify it.

Originally Posted by slideways...

oh but i didnt mean to say dohc is better for VVT. i meant over head cam engines are better for VVT, as opposed to under head cam engines.

I would disagree with that.
I think it is simply that more and more modern engines are overhead cam, and it is the same modern engines that also have VVT systems fitted.
But they are not built as over head cam engines just so they can be fitted with VVT systems.