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Old 11-27-2005, 05:32 PM
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OHV vs OHC

Question....
OHV engine has any serious advantages compared with OHC?

(answer "it's cheaper" consider as incorrect)

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Old 11-27-2005, 06:10 PM
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An OHC engine is also a OHV engine. The advantage of the OHC engine over a pushrod one is the absence of all the rods and rockers. Less moving parts sucking up power and losing cam timing
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Old 11-27-2005, 09:37 PM
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just for the record, ohc does not mean absence of rockers and associated parts. for example, the mitsubishi eclipse is an overhead cam engine, yet it still uses cam followers (rocker arms of sort), and "lifters", or more accurately hydraulic plungers that keep the followers running at zero lash against the cam. definately no pushrods though.............some engines do however use "shim buckets" that ride directly on the valve, or a hydraulic version of this. older volvos use shim buckets with replaceable shims for adjusting valve clearance, whereas older saabs used something very similar, except that it was hydraulic, and worked in the same way a hydraulic lifter does. these are just a couple of examples though.......
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Old 11-28-2005, 08:41 AM
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The main advantage of OHC is more precise timing control. There is a little clearance in all the parts between the cam and valve with a push-rod design. All that has to be taken into consideration, and varies with oil pressure and wear. Some of those parts, such as the pushrods, have a little flex under load that has to be considered also. Since a standard passenger car engine doesn't need real precise control, pushrod technology has persisted. Small high power engines, on the other hand, need to squeeze every little bit of power out of each cubic inch (or centimeter). More precise timing helps. As emission regulations and fuel economy needs get tighter, precision in control becomes more important.

Assuming a single OHC in-line, cost is probably less than a comparable push-rod engine due to assembly cost as well as fewer parts. But that's from a manufacturers point of view. I believe that's the main reason GM came out with the new Vortec in-line six a few years ago -- cost of the variable timing configuation (and control of it) would be much greater with two cams in a V configuration.
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Old 11-28-2005, 12:59 PM
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As Nightrider didn't make the ohc/ohv connection I just answered on the kiss principle. You're right about there being ohc engines with lifters, rockers and in one instance that I know of even rods. This was an experimental aircraft engine I saw at Dayton a ton of years ago.
If you want to see a neat motor, they have one there that has no cam or crank. It is an 8 cylinder opposed motor. The pistons run on a swashplate with short rigid conrods. Intake and exhaust duties are carried out by a perforated rotating flat plate that is fixed to the same shaft as the swashplate. Total moving parts, about 16. 300+ hp in a 350lb package using 40s technology. Todays tech would make this a scandalous motor.
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Old 11-28-2005, 02:11 PM
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I would also add that a OHV (non-OHC) makes a more compact engine. If you compare the size of a SOHC/DOHC V8 to a pushrod one, the DOHC is (usually) taller since the cam(s) sit on top.

The new Corvette LS7 is a marvel of pushrod technology, churning out 505hp@6200RPM.
http://www.corvettemuseum.com/specs/2006/LS7.shtml
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Old 11-29-2005, 05:11 AM
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One of the British engine manufacturers (Bristol?) also came up with a pushrod engine with pushrods in series. Instead of a long rocker arm to pick up the exhaust valve with a hemi chamber, they kept the primary pushrods all in a row and used short, horizontal, secondary pushrods and additional rockers to actuate the exhaust valves. Yes, it would be possible to provide an aftermarket hemi cylinder head, using this little trick, for any conventional pushrod wedge engine. The flow could even be reversed and the second rocker used to actuate two intake valves. Ah, the joy of bench racing!
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Old 11-29-2005, 10:52 PM
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Quote:
Originally Posted by BillyShope
One of the British engine manufacturers (Bristol?) also came up with a pushrod engine with pushrods in series. Instead of a long rocker arm to pick up the exhaust valve with a hemi chamber, they kept the primary pushrods all in a row and used short, horizontal, secondary pushrods and additional rockers to actuate the exhaust valves. Yes, it would be possible to provide an aftermarket hemi cylinder head, using this little trick, for any conventional pushrod wedge engine. The flow could even be reversed and the second rocker used to actuate two intake valves. Ah, the joy of bench racing!
Sorry, not quite understand, WHAT YOU SAY???
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Old 11-30-2005, 05:51 PM
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both pushrod and OHC are good. Look at the power the Chevy Gen III engines are producing with pushrods. Most Over head cammers need a huffer to make 400 let alone 500 horse. Then there's Honda's S2000 engine, 120 HP per litre in a production engine!

I guess it's preferance. I like how the DOHC's can alter their LSA without buying a new cam (cams)
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Old 12-01-2005, 12:43 PM
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Most OHC engines need huffers because most OHC engines are smaller than big American V-8s. Even most American OHC engines are smaller than most of their pushrod counterparts.

But you are correct on packaging. If OHC were as compact as pushrod designs the pushrods would have been thrown out long ago. For in-line engines it's not to bad -- the engine can be leaned over ala Chrysler Slant Six and still have plenty accessory room -- just put them all on the "open" side. A V engine is different because of width. Accessories have to be tucked in the V as with the Caddy NorthStar (starter is in the V in back!) or hidden under each bank. Space gets precious fast!
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Old 12-01-2005, 01:07 PM
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THE MAIN ADVANTAGE OF OHC ENGINE TECHNOLOGY;





...I think I am getting misty...sniff...

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Old 12-01-2005, 03:13 PM
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KulTulz

Ahhh.. . . . . . . . I think this is the photo that graced the cover of hot rod magazine back when Ford's SOHC motor was introduced. Mid 60's I think. 600 HP on one carburetor, with gasoline. And a streetable idle. Got my vote for the best V8 motor ever!!

Pat
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Old 12-01-2005, 11:23 PM
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Quote:
Originally Posted by PatM
KulTulz

Ahhh.. . . . . . . . I think this is the photo that graced the cover of hot rod magazine back when Ford's SOHC motor was introduced. Mid 60's I think. 600 HP on one carburetor, with gasoline. And a streetable idle. Got my vote for the best V8 motor ever!!

Pat
Introduced and banned! As I know, banned, because it was unstreetable...although I can mistake.
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Old 12-04-2005, 02:28 PM
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In an earlier post in this thread, I mentioned a six cylinder engine with 18 pushrods. I wasn't certain of the manufacturer, so I did a little "googling" and found the following:


http://www.boc.net/buyers_guide.html

The above will give the full history, for those who are interested. Seems I was right on the Bristol origins, but it was BMW that actually developed the aluminum hemi head with the "extra" pushrods. Bristol re-acquired the engine after the Second World War and ended up churning out 170 horses from two liters for their LeMans version. This would be equivalent to 488 horses from a Chevy 350 on low octane French pump gas! And, this was 50 years ago.
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Old 12-04-2005, 03:25 PM
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Quote:
Originally Posted by smallblocker2
both pushrod and OHC are good. Look at the power the Chevy Gen III engines are producing with pushrods. Most Over head cammers need a huffer to make 400 let alone 500 horse. Then there's Honda's S2000 engine, 120 HP per litre in a production engine!

I guess it's preferance. I like how the DOHC's can alter their LSA without buying a new cam (cams)
You are referring to 346 cubes versus 281 cubes ??????
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