OHC(also DOHC) and OHV, whats the difference

[targa]

what is the difference between Over Head Cam and Over Head Valve?

[derekthetree]

found this on automotive learning online

"Overhead Camshaft (OHC)
Some engines have the camshaft mounted above, or over, the cylinder head instead of inside the block (OHC "overhead camshaft" engines). This arrangement has the advantage of eliminating the added weight of the rocker arms and push rods; this weight can sometimes make the valves "float" when you are moving at high speeds. The rocker arm setup is operated by the camshaft lobe rubbing directly on the rocker. Stem to rocker clearance is maintained with a hydraulic valve lash adjuster for "zero" clearance. The overhead camshaft is also something that we think of as a relatively new development, but it's not. In 1898 the Wilkinson Motor Car Company introduced the same feature on a car. "

"Overhead Valve (OHV)
In an overhead valve (OHV) engine, the valves are mounted in the cylinder head, above the combustion chamber. Usually this type of engine has the camshaft mounted in the cylinder block, and the valves are opened and closed by push rods. "

[Slicks]

search http://www.howstuffworks.com/ youll find alot of stuff there.

[car_fiend]

Originally Posted by Slicks

search http://www.howstuffworks.com/ youll find alot of stuff there.

i was gonna suggest the same site, thaz where i found mad info on different engines.

[Smokescreen]

And when talking about older cars, you'll hear flat heads. They have a cam in the block like a puchrod engine, but minus the rockers. WHen the valves are opened, they are pushed up next to the cylinder and the air/fuel & exhaust flow in and out through the side of the cylinder, so the engine doesn't have real heads.

[Sweeney921]

Originally Posted by car_fiend

i was gonna suggest the same site, thaz where i found mad info on different engines.

you mean I showed you where to find mad info on different engines

[Matra et Alpine]

Originally Posted by Sweeney921

you mean I showed you where to find mad info on different engines

well it was megotmeat7 over a year ago actually
But it's a well known site, hard for any one person to claim it except the owner !!!

[aNOBLEman]

Originally Posted by derekthetree

found this on automotive learning online

"Overhead Camshaft (OHC)
Some engines have the camshaft mounted above, or over, the cylinder head instead of inside the block (OHC "overhead camshaft" engines). This arrangement has the advantage of eliminating the added weight of the rocker arms and push rods; this weight can sometimes make the valves "float" when you are moving at high speeds. The rocker arm setup is operated by the camshaft lobe rubbing directly on the rocker. Stem to rocker clearance is maintained with a hydraulic valve lash adjuster for "zero" clearance. The overhead camshaft is also something that we think of as a relatively new development, but it's not. In 1898 the Wilkinson Motor Car Company introduced the same feature on a car. "

"Overhead Valve (OHV)
In an overhead valve (OHV) engine, the valves are mounted in the cylinder head, above the combustion chamber. Usually this type of engine has the camshaft mounted in the cylinder block, and the valves are opened and closed by push rods. "

Very good explaination. Also Dual Overhead Camshafts (DOHC) is just like OHC except there is two of them.

[Blue Supra]

arguably DOHC makes for a "better" engine but as i said, its very arguable.

[jcp123]

Originally Posted by Blue Supra

arguably DOHC makes for a "better" engine but as i said, its very arguable.

Depends mostly what you use it for, but yes, DOHC does have its advantages

[Shev GTR XU-1]

Only advantages DOHC engines would have is the easier availability of having devices that can vary the timing of the camshafts as well as having more valves per cylinder. Hence they are a couple of the main reasons for been considered more cutting edge technologically. A drawback of DOHC is a much heavier cylinder head, and all this heavier weight is higher up as well, which is a drawback for cornering and acceleration performance.
Sure pushrod, OHV are 'dinosaurs' in terms of mechanical technology, but GM have proven time and again pushrod engines aren't as outdated as most perceive.As they had shown with their twin cam (Gen IV concept a couple of years ago) pushrod V8. Both cams were still deep down in the block. 3 valves per cylinder, 1 cam had variable timing (can't remember if it was for inlet/exhaust), as well as been able to cruise on 4 cylinders to save fuel.

This is why in my opinion the quad cam Ford BOSS V8 is over-rated, the extra weight over the front hoops is all that is holding it back from been a commodore killer. Commodore is still pushrod single cam 2 valves per cylinder.

[Matra et Alpine]

Originally Posted by Shev GTR XU-1

Only advantages DOHC engines would have is the easier availability of having devices that can vary the timing of the camshafts as well as having more valves per cylinder.

Both critical in the extracting peak performance across a wide range of conditions. Were you thinking dynamic valve timing variation ? VVT can be achieved with either.

A drawback of DOHC is a much heavier cylinder head, and all this heavier weight is higher up as well, which is a drawback for cornering and acceleration performance.

It can be lighter by throwing away the need for rockers and pushrods.
Hence why DOHC is common on full-on race engines.
It's NOT the cylinder head per-se that's heavier. But that the cam is higher and there tends to be more of them than in a pushrod.
But more cams gives more tunability during track/race/rally setup for each day/event.
The weight differential is hugely over-rated
Especially in performance when rockers and rods need to be heavier to handle the stresses.

Sure pushrod, OHV are 'dinosaurs' in terms of mechanical technology, but GM have proven time and again pushrod engines aren't as outdated as most perceive.As they had shown with their twin cam (Gen IV concept a couple of years ago) pushrod V8. Both cams were still deep down in the block. 3 valves per cylinder, 1 cam had variable timing (can't remember if it was for inlet/exhaust), as well as been able to cruise on 4 cylinders to save fuel.

Yeah, that was interesting but IIRC it kind of just ended up with the negatives of BOTH layouts

This is why in my opinion the quad cam Ford BOSS V8 is over-rated, the extra weight over the front hoops is all that is holding it back from been a commodore killer. Commodore is still pushrod single cam 2 valves per cylinder.

It also depends on how much power per liter is trying to be extracted.
More bhp/litre means LOTS more fuel/air mixture in and exhaust gas out. TAHT needs larger valves, larger valve opening and for wide power band FASTER valve opening. That's when the OHC comes into it's own. If a solution can give power without needing to go that route it will be easier.

[85RX7]

Then you can get the quad cam's on the V formation engines which is basically just two DOHC's on two rows of cylinders.

[jcp123]

Originally Posted by 85RX7

Then you can get the quad cam's on the V formation engines which is basically just two DOHC's on two rows of cylinders.

Not to confuse anyone, but that's just called DOHC here too.

[Shev GTR XU-1]

Originally Posted by Matra et Alpine

Both critical in the extracting peak performance across a wide range of conditions. Were you thinking dynamic valve timing variation ? VVT can be achieved with either.

VVT, VCT, VTEC, its all very similar, ultimately varying the timing of when the valves open and close. Either by varying the cam, or somehow varying the valves in relation to the lobes on the cam, which I'm guessing is thru the system of 'dynamic vavle timing'.

Originally Posted by Matra et Alpine

It can be lighter by throwing away the need for rockers and pushrods.
Hence why DOHC is common on full-on race engines.
It's NOT the cylinder head per-se that's heavier. But that the cam is higher and there tends to be more of them than in a pushrod.
But more cams gives more tunability during track/race/rally setup for each day/event.

I'm pretty sure OHC type setups still use rockers, while I agree its way better to have the lobe in direct contact with the valve (ie, no rocker), and also agree yes they would use that on more full house race engines, as it should be able to rev higher. Also when I mention cylinder head been heavier, I mean when it is assembled with valve train components including cams. So on a DOHC 'V' configuration engine there a 3 extra camshafts that add significant weight.

This is a very interesting discussion
Cheers