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Thread: Ohv Engine

  1. #1
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    Ohv Engine

    All websites say a disadvantage to a pushrod is, "it's difficult to precisely control the valve timing at high rpm"

    How is this bad? How does this affect me? They all say this is bad, but noone can tell me why.

    Will redlining it once ruin the engine?
    It would be great if one of you could give me a straight answer.

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    At very high speeds, pushrods bend, and sometimes stay bent.
    At somewhat lower speeds, springs surge, and valves bounce.
    None of that is good for an engine.
    Redlining it once in a while is not guaranteed to damage your engine. Some of them have quite a large safety margin; some don't. Nobody will or can tell you exactly how much you can get away with, with your exact engine.
    If you try redlining your engine, you will probably notice that power falls off before you get there anyway, so in a street vehicle, you'll get better performance by shifting a little below the redline anyway.

  3. #3
    Vulture of The Western World Eric's Avatar
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    Quote Originally Posted by Brandonjin View Post
    All websites say a disadvantage to a pushrod is, "it's difficult to precisely control the valve timing at high rpm"

    How is this bad? How does this affect me? They all say this is bad, but noone can tell me why.

    Will redlining it once ruin the engine?
    It would be great if one of you could give me a straight answer.
    What Mike said.

    Plus:

    Some downsides of OHC engines are physical size (V-8s) complexity and expense, relative to pushrod/OHV engines.

    Upsides of OHC engines are they tend to be smoother and have higher RPM capability (though GM has done incredible work with its LS series of OHV V-8s).

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    So if you tend to, "merge" on a daily baisis, It would probably be safer to get an ohc engine then say, the 3800?
    Last edited by Brandonjin; 11-03-2010 at 11:03 PM.

  5. #5
    Vulture of The Western World Eric's Avatar
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    Quote Originally Posted by Brandonjin View Post
    So if you tend to, "merge" on a daily baisis, It would probably be safer to get an ohc engine then say, the 3800?
    Not necessarily!

    OHV engines often have more low-end torque and are set up to produce peak hp at lower RPM.

    The 3.8 V-6 is a good engine; it's also durable and long-lived and simple to fix.

  6. #6
    Senior Member Ken's Avatar
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    Quote Originally Posted by Eric View Post
    Not necessarily!

    OHV engines often have more low-end torque and are set up to produce peak hp at lower RPM.

    The 3.8 V-6 is a good engine; it's also durable and long-lived and simple to fix.
    FWIW my take is this - the OHV engine is old hat, simple but effective, engineering of the old school. OHV engines, like any other can be tuned to produce well over 100 BHP/liter (My 850 mini produced 96 BHP by the time I had finished with it) and, with good lightening and balancing can rev to quite acceptable levels (My mini 9500 rpm against 6500 as stock). The OHC engine is also easily tuned, is generally smoother and generally is capable of producing higher power output at higher revs than the OHV engine.

    But - and it is a big but - unless you drive, on the road, like a racing driver, using all the power that your engine is capable of, redlining at every opportunity, maximising forward motion and using every gap in the traffic, you are hardly likely to notice the difference between a solid OHV engine and a solid OHC engine. Mind you, if you do all those things you probably wouldn't live very long anyway.

    Ken.
    Last edited by Ken; 11-04-2010 at 09:59 AM.
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  7. #7
    Vulture of The Western World Eric's Avatar
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    Quote Originally Posted by Ken View Post
    FWIW my take is this - the OHV engine is old hat, simple but effective, engineering of the old school. OHV engines, like any other can be tuned to produce well over 100 BHP/liter (My 850 mini produced 96 BHP by the time I had finished with it) and, with good lightening and balancing can rev to quite acceptable levels (My mini 9500 rpm against 6500 as stock). The OHC engine is also easily tuned, is generally smoother and generally is capable of producing higher power output at higher revs than the OHV engine.

    But - and it is a big but - unless you drive, on the road, like a racing driver, using all the power that your engine is capable of, redlining at every opportunity, maximising forward motion and using every gap in the traffic used, you are hardly likely to notice the difference between a solid OHV engine and a solid OHC engine. Mind you, if you do all those things you probably wouldn't live very long anyway.

    Ken.

    Yep!

    In my experience, for most normal street driving - even including some fast-paced street driving - a larger displacement/higher torque OHV engine is more useful (and satisfying) than a higher-RPM/lower torque/smaller displacement OHC engine.

    A good example of this is the circa '96-up Mustang GT vs. the same-era Camaro.

    The Ford has a 4.6 liter OHC V-8; the Chevy a 5.7 liter OHV V-8. The Chevy launched much more forcefully; it had superior mid-range and just felt stronger throughout the powerband, but most especially when you floored it off the line.

    Even today, GM has worked miracles with its LS-series of OHV V-8s. They not only have high RPM capability/power that's comparable to OHC designs, they have tremendous low-end punch, too.

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    ^Thats just it^ you spend most of your time on the low end anyway. ohvs are more usefull in daily driving. I was just concerned about the reliability of the thing...

    This all helps everyone. Thanks!
    Last edited by Brandonjin; 11-04-2010 at 06:01 PM.

  9. #9
    Vulture of The Western World Eric's Avatar
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    Quote Originally Posted by Brandonjin View Post
    ^Thats just it^ you spend most of your time on the low end anyway. ohvs are more usefull in daily driving. I was just concerned about the reliability of the thing...

    This all helps everyone. Thanks!
    Oh hell, reliability wise, it is hard to beat a cast iron, two-valve pushrod V-8!

    Not only that, they are easier to work on and cheaper to fix, too.

  10. #10
    Senior Member grouch's Avatar
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    The problem with aujtomotive writers (sorry Eric) is often they have to produce a certain amount of work to fill the magazine or whatever they work for. OHV engines are perfectly servicable. They've been around since the late 40's and only recently are being taken out of production.

    Most of the reason they are being replaced is the same reason the car companies like to build FWD cars over RWD cars. Money. It's cheaper to build an FWD car as all the components can be preassembled. An RWD car has more components added separately. It takes 40% longer to put an engine/transmission assembly, then rear end and drive shaft into the chassis than it does to raise the complete engine/transmission/final drive/half shafts and wheels into the body. Time costs money and Detroit (and Tokyo, Hamburg etc.) try to save a buck anywhere they can. Pintos tended to blow up when hit from behind because of a $1 rubber part not being used.

    One advantage to an OHC engine over an OHV unit is they are generally newer in design and take advantage of advances that have to be retrofitted to an OHV engine. The small block Chevy, especially the 350 (5.7 Liter) goes back in basic design 55 years. GM has done a lot of development over the years and it's still a viable engine. A fresh design can incorporate all the advances in the SB engine and have room for future changes for either power, economy or emissions.

    OHC engines tend to be more complex and can be nightmares to work on. For instance, I had a Lincoln Town Car with the 4.6 engine. Every now and then, it would smoke leaving a light due to worn valve seals. To replace them, you have to remove the timing chain (a pain), remove the camshafts (more of a pain) then remove the valve springs and replace the seals. On a 350 for instance, you remove the rockers and springs then replace the seals. Plus, OHC engines tend to be interference engines so replacing the seals after tear down is more complex. You can use air pressure to hold the valve in place but to use clothesline rope like I do on a 350 might damage the engine. (You feed it in the spark plug hole then rotate the engine for it to press the valve in place.)
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  11. #11
    Vulture of The Western World Eric's Avatar
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    Quote Originally Posted by grouch View Post
    The problem with aujtomotive writers (sorry Eric) is often they have to produce a certain amount of work to fill the magazine or whatever they work for. OHV engines are perfectly servicable. They've been around since the late 40's and only recently are being taken out of production.

    Most of the reason they are being replaced is the same reason the car companies like to build FWD cars over RWD cars. Money. It's cheaper to build an FWD car as all the components can be preassembled. An RWD car has more components added separately. It takes 40% longer to put an engine/transmission assembly, then rear end and drive shaft into the chassis than it does to raise the complete engine/transmission/final drive/half shafts and wheels into the body. Time costs money and Detroit (and Tokyo, Hamburg etc.) try to save a buck anywhere they can. Pintos tended to blow up when hit from behind because of a $1 rubber part not being used.

    One advantage to an OHC engine over an OHV unit is they are generally newer in design and take advantage of advances that have to be retrofitted to an OHV engine. The small block Chevy, especially the 350 (5.7 Liter) goes back in basic design 55 years. GM has done a lot of development over the years and it's still a viable engine. A fresh design can incorporate all the advances in the SB engine and have room for future changes for either power, economy or emissions.

    OHC engines tend to be more complex and can be nightmares to work on. For instance, I had a Lincoln Town Car with the 4.6 engine. Every now and then, it would smoke leaving a light due to worn valve seals. To replace them, you have to remove the timing chain (a pain), remove the camshafts (more of a pain) then remove the valve springs and replace the seals. On a 350 for instance, you remove the rockers and springs then replace the seals. Plus, OHC engines tend to be interference engines so replacing the seals after tear down is more complex. You can use air pressure to hold the valve in place but to use clothesline rope like I do on a 350 might damage the engine. (You feed it in the spark plug hole then rotate the engine for it to press the valve in place.)
    Exactly!

    Another, related reason why OHC designs have supplanted OHV designs is that the majority of OHV designs predate current emissions (and fuel economy) requirements that car companies have to comply with. This is the main reason why Ford, for example, retired the OHV 5.0 V-8 in favor of the "mod" OHC 4.6/5.4 V-8s. The old 5.0 was seen as too much trouble to re-engineer to achieve compliance, so they went with a clean sheet design.

    GM, on the other hand, stayed with the OHV layout but completely re-engineered the design of its LS series V-8s, which do not interchange with the old-style small blocks that first appeared in '55.

    They've worked miracles with this layout, in my opinion!

  12. #12
    Quote Originally Posted by Eric View Post
    Exactly!

    Another, related reason why OHC designs have supplanted OHV designs is that the majority of OHV designs predate current emissions (and fuel economy) requirements that car companies have to comply with. This is the main reason why Ford, for example, retired the OHV 5.0 V-8 in favor of the "mod" OHC 4.6/5.4 V-8s. The old 5.0 was seen as too much trouble to re-engineer to achieve compliance, so they went with a clean sheet design.

    GM, on the other hand, stayed with the OHV layout but completely re-engineered the design of its LS series V-8s, which do not interchange with the old-style small blocks that first appeared in '55.

    They've worked miracles with this layout, in my opinion!
    Oh yes they did..... the current ZR1 Corvette is an OHV engine and it's a masterpiece....

  13. #13
    Vulture of The Western World Eric's Avatar
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    Quote Originally Posted by Mustang_Boy View Post
    Oh yes they did..... the current ZR1 Corvette is an OHV engine and it's a masterpiece....
    It is!

    Hell, the standard LS V-8 is a masterpiece. Effortless 400 hp, with a smooth idle and 30 MPG capability (if you drive it right).

    Back in the Day (muscle car era) anything with 400 hp (or even close to it) was borderline undriveable. Lumpy idle and low vacuum meant things like AC and power brakes were iffy; they were definitely not docile and "wife driveable" like any modern/LS-powered GM car is. Hell, a grandma can easily drive a new Corvette, including the Z06. It's a pussycat - until you hit the gas!

  14. #14
    Quote Originally Posted by Eric View Post
    It is!

    Hell, the standard LS V-8 is a masterpiece. Effortless 400 hp, with a smooth idle and 30 MPG capability (if you drive it right).

    Back in the Day (muscle car era) anything with 400 hp (or even close to it) was borderline undriveable. Lumpy idle and low vacuum meant things like AC and power brakes were iffy; they were definitely not docile and "wife driveable" like any modern/LS-powered GM car is. Hell, a grandma can easily drive a new Corvette, including the Z06. It's a pussycat - until you hit the gas!
    True, but then again there's nothing like the angry roar of a pre-emissions era big block, high compression V8 like a 440 Magnum, 428 Super Cobra Jet, 454 Turbo Jet LS6, SD455...... or my favorite exhaust tones, Steve McQueen's '68 390 Mustang from Bullitt.... why I fell in love with the Mustang, or even though it's technically an emissions era engine, the 440 in Elwood Blue's '74 Dodge Monaco ex-cop car meant business, the part where the Bluesmobile is careening through the elevated subway pylons at 120 MPH wasn't faked, and it had plenty more to give too.... hell even police cars back then were badass, like the '69 Dodge Polara... able to achieve an honest 147 MPH back then..... those cars are the reason why I have a thing about cop cars, simple, low key, no frivolous extras, rugged and reliable and able to kick ass. Sounds like my ideal car.

  15. #15
    Vulture of The Western World Eric's Avatar
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    Quote Originally Posted by Mustang_Boy View Post
    True, but then again there's nothing like the angry roar of a pre-emissions era big block, high compression V8 like a 440 Magnum, 428 Super Cobra Jet, 454 Turbo Jet LS6, SD455...... or my favorite exhaust tones, Steve McQueen's '68 390 Mustang from Bullitt.... why I fell in love with the Mustang, or even though it's technically an emissions era engine, the 440 in Elwood Blue's '74 Dodge Monaco ex-cop car meant business, the part where the Bluesmobile is careening through the elevated subway pylons at 120 MPH wasn't faked, and it had plenty more to give too.... hell even police cars back then were badass, like the '69 Dodge Polara... able to achieve an honest 147 MPH back then..... those cars are the reason why I have a thing about cop cars, simple, low key, no frivolous extras, rugged and reliable and able to kick ass. Sounds like my ideal car.
    That's my attitude, too.

    My old Trans Am is probably easy meat for a new Camaro SS, but I'd never trade.

    The TA has heart.

    The best way I've heard to get the point across is the difference between an old steam locomotive and a modern diesel electric - or between a battleship and modern missile cruiser.

    The rawboned power; the way those things are almost alive and often, a little intimidating - is what makes them so appealing.

    Anyone - literally - can drive a new Corvette Z06. Your mom; my sister - a 12 year old kid.

    That was not true of something like an old AC Cobra or L-88 427 Corvette.

    Even something milder like my '76 Trans-Am has so much more personality...

    Every time I drive it I remember why I love old stuff so much...

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