what is the difference between Over Head Cam and Over Head Valve?
what is the difference between Over Head Cam and Over Head Valve?
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. "
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.Originally Posted by Slicks
WHEN THE POWER OF LOVE OVERCOMES THE LOVE OF POWER, THE WORLD WILL KNOW PEACE!!!!!!!!!!
-Jimi Hendrix
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.
you mean I showed you where to find mad info on different enginesOriginally Posted by car_fiend
well it was megotmeat7 over a year ago actuallyOriginally Posted by Sweeney921
But it's a well known site, hard for any one person to claim it except the owner !!!
"A woman without curves is like a road without bends, you might get to your destination quicker but the ride is boring as hell'
Very good explaination. Also Dual Overhead Camshafts (DOHC) is just like OHC except there is two of them.Originally Posted by derekthetree
arguably DOHC makes for a "better" engine but as i said, its very arguable.
The Datto will rage again...
Depends mostly what you use it for, but yes, DOHC does have its advantagesOriginally Posted by Blue Supra
An it harm none, do as ye will
Approximately 79% of statistics are made up.
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.
Last edited by Shev GTR XU-1; 11-10-2004 at 02:27 PM.
Its a friggin HAMMER!
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.Originally Posted by Shev GTR XU-1
It can be lighter by throwing away the need for rockers and pushrods.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.
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.
Yeah, that was interesting but IIRC it kind of just ended up with the negatives of BOTH layoutsSure 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.
It also depends on how much power per liter is trying to be extracted.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.
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.
"A woman without curves is like a road without bends, you might get to your destination quicker but the ride is boring as hell'
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.Originally Posted by 85RX7
An it harm none, do as ye will
Approximately 79% of statistics are made up.
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
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.Originally Posted by Matra et Alpine
This is a very interesting discussion
Cheers
Its a friggin HAMMER!
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