and which is better
thanks!
2007-03-26 08:52:31 · 10 answers · asked by Anonymous in Cars & Transportation ➔ Maintenance & Repairs
Valves are the component of the engine that allows air or a fuel/air mix into the engine and exhaust fumes to exit. All valves are placed 'overhead', that is at the top of the engine head, with the exception of 2 stroke engines which I will exclude from this discussion. The valves are pushed open by a 'rocker arm' assembly.
The original design of the engine the cam shaft was placed close to or right on top of the crank shaft. This allows for a very short timing chain or belt to be used. The cam shaft has 'lobes' that are spaced in such a way that as it turns it opens and closes the valves. With the valves placed at the top of the engine and the cam at a midway point the design used 'push rods' as a means to connect the cam to rocker arms and the rocker arms to the valves.
In overhead cam engines the cam shaft is placed on the head(s) next to the vavle and use a longer timing chain/belt to connect it to crank shaft. The cam moves the rocker arms with out the 'push rod' requirement thus eleminating the friction and 'flex delay' they caused. Thus a small horsepower gain as well as the ability to reach higher RPMs.
Dual overhead cams are designed to work with motors with multiple input and/or exhaust valves per cylinder. The original designs had 1 intake and 1 exhaust valve per cylinder. By adding more valves the engine can move fuel/air in and expell exhaust faster. By having dual cams you can have valves that open in stages to better facilitate the higher RPM engines.
As for your question of 'which is better'... well since I pointed out that all engines have overhead valves the real question is which is better single or dual overhead cams. The short answer is dual overhead cams for the reasons stated above.
Hope this answers the question!
2007-03-26 09:12:19 · answer #1 · answered by wrkey 5 · 0⤊ 1⤋
A double overhead cam is two cam's that set on top of the head instead of inside the block. The cam operates the valves, so they too must set on top of he head. The cam lobes press down on what's called a cam follower. This opens and closes the valve. As far as which is better? You'll probably get a lot of opinion's on that. However, the overhead cam eliminates the push rod, and is easier to service.
2007-03-26 16:08:32 · answer #2 · answered by lobo.ranone 1 · 0⤊ 0⤋
Double overhead cams also refured to as DOHC, means it has two cams. One cam controlls the intake valves and another controlls the exhaust.
It this case it is over head
valves. It means the cams push on the valves instede of a push rod.
In a older engine the cam runs down the middle of the engine and pushes on a lifter which pushes on a push rod that pushes on a rocker and the rocker pushes down on the valve.
On a dohc the cam pushes on the valve directorly
2007-03-26 16:04:32 · answer #3 · answered by goldwing127959 6 · 0⤊ 0⤋
DOHC = double over head cam.
This is a component that opens and closes valves by means of an irregular shape that is very accurate. Double cam means that there are two of them as opposed to single over head cam (SOHC). Overhead means that the cam is postioned above the cylinder head. Valves and Cams are distinctly different so what is bettter between a dog and a cat. What is better are DOHC as they operate more valves per cylinder(multivalve) than SOHC, thus producing more power to the engine.
2007-03-26 16:02:09 · answer #4 · answered by Anonymous · 0⤊ 0⤋
Double overhead cam has two camshafts, one for the intake valves and one for the exhaust valves.
Overhead valves has one central mounted in the block camshaft . I would choose the dual overhead cam engine, better performance and economy
2007-03-26 16:03:08 · answer #5 · answered by Anonymous · 0⤊ 0⤋
a double over head cam is when 2 camshafts are OVER the valves and push them open without using push rods. Usually with these, there are 4 cams on certain engine. My opinion is that its just more things to go wrong with the engine, and I don't think any is better, as long as it works.
2007-03-26 15:59:09 · answer #6 · answered by stabnhobo 1 · 0⤊ 1⤋
A double overhead cam means the engine has 2 camshafts.This would contain overhead valves.So you see they work together.Try yahoo and go to www. howstuffworks.com you will see it all explained there hope this helps Mick UK.
2007-03-26 16:01:30 · answer #7 · answered by mick 6 · 0⤊ 0⤋
The overhead cam design is more efficent,less moving parts better high rpm stability,and so on.There is also SOHC (single) the DOHC is mainly used for high performance engines.
2007-03-26 16:02:50 · answer #8 · answered by Bird 2 · 0⤊ 0⤋
Go here......
http://en.wikipedia.org/wiki/DOHC#Double_overhead_camshafts
2007-03-26 15:58:14 · answer #9 · answered by Mr. KnowItAll 7 · 0⤊ 0⤋
natasha campbell is a +++++++`
2007-03-26 16:00:25 · answer #10 · answered by COLTS_MUSTANG_FAN_2008 3 · 0⤊ 0⤋