OHV vs OHC, difference? Benefits?
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If you could see a modern DOHC V8 on a stand you'd easily see the tremendous width and height is a real packaging issue.
A dry sump pushrod V8 can be amazingly compact and lightweight, which is huge in a real sports car. As an example, there's no way the Corvette could have that low hoodline with a DOHC motor. And VVT is in a lot of pushrod cars now, even cam-in-cam like the new Viper.
Imagining that DOHC is somehow a technical tour-de-force and inherently superior is simply wrong, as they are BOTH competitive technologies that work well in the real world.
A dry sump pushrod V8 can be amazingly compact and lightweight, which is huge in a real sports car. As an example, there's no way the Corvette could have that low hoodline with a DOHC motor. And VVT is in a lot of pushrod cars now, even cam-in-cam like the new Viper.
Imagining that DOHC is somehow a technical tour-de-force and inherently superior is simply wrong, as they are BOTH competitive technologies that work well in the real world.
Originally Posted By: Bamaro
Dont OHV engines generally produce their power at lower RPMs and the OHCs, come on at much higher RPM?
Nope, not at all. My car is very old school design and has a torque peak well north of 4000 rpm. It is also one of the very few V8 American engines you will see with more HP than torque.
Camshaft specs, valve sizes, port configurations and the like are what influence where the power occurs. That's why VVT is such a great thing because you can move the cam timing around to enhance BOTH low speed grunt/torque and high rpm power
Dont OHV engines generally produce their power at lower RPMs and the OHCs, come on at much higher RPM?
Nope, not at all. My car is very old school design and has a torque peak well north of 4000 rpm. It is also one of the very few V8 American engines you will see with more HP than torque.
Camshaft specs, valve sizes, port configurations and the like are what influence where the power occurs. That's why VVT is such a great thing because you can move the cam timing around to enhance BOTH low speed grunt/torque and high rpm power
Originally Posted By: wirelessF
The only reason why people swap Chevy LS engines into Miatas and such.
For sure it's 1955 all over again, Chevy has compact high output OHV engines and is enjoying seeing them swapped in about any chassis you can imagine... Ford's 4.6 OHC V8 is a joke in comparison, as big as a Boss 429 and has all of 281cu in displacement(fat girl that wears A cup bra)... Yeah the new OHC 5.0 is powerful enough but still so large it won't fit many smaller chassis...
As far as a OHV not revving, NASCAR manages to spin their 358cu in V8 engines to 9500+ RPM... Yeah I did forget to mention those are something like $40,000-$50,00 a copy...
The only reason why people swap Chevy LS engines into Miatas and such.
For sure it's 1955 all over again, Chevy has compact high output OHV engines and is enjoying seeing them swapped in about any chassis you can imagine... Ford's 4.6 OHC V8 is a joke in comparison, as big as a Boss 429 and has all of 281cu in displacement(fat girl that wears A cup bra)... Yeah the new OHC 5.0 is powerful enough but still so large it won't fit many smaller chassis...
As far as a OHV not revving, NASCAR manages to spin their 358cu in V8 engines to 9500+ RPM... Yeah I did forget to mention those are something like $40,000-$50,00 a copy...
Out of the 38 vehicles I have owned one was OHC. That was my 97 Mustang GT 4.6. I had a 5.0 in an earlier GT and I was much happier. When I bought my Ranger I made sure I got the OHV engine as they have much fewer problems. The OHC engines have nightmare cam chain set ups.
In the Ford flathead V8 did you ever ask yourself how the exhaust gas got to the exhaust manifold ?
Can you spell HUGE heating system ? Like 24 quarts !
Can you spell HUGE heating system ? Like 24 quarts !
Originally Posted By: SteveSRT8
Originally Posted By: Bamaro
Dont OHV engines generally produce their power at lower RPMs and the OHCs, come on at much higher RPM?
Nope, not at all. My car is very old school design and has a torque peak well north of 4000 rpm. It is also one of the very few V8 American engines you will see with more HP than torque.
Pushrod engines typically have to squeeze the ports between the pushrod centres, so the designer has to factor in casting thicknesses, core shift, etc, and ports tend to suffer in size...which tends to reduce the speed at maximum volumetric efficiency.
An OHC, these constraints are moved to bolt spacings and coolant passages, allowing more freedom in sizes...and maybe higher revs...depending on how the compromises have been made.
Originally Posted By: Bamaro
Dont OHV engines generally produce their power at lower RPMs and the OHCs, come on at much higher RPM?
Nope, not at all. My car is very old school design and has a torque peak well north of 4000 rpm. It is also one of the very few V8 American engines you will see with more HP than torque.
Pushrod engines typically have to squeeze the ports between the pushrod centres, so the designer has to factor in casting thicknesses, core shift, etc, and ports tend to suffer in size...which tends to reduce the speed at maximum volumetric efficiency.
An OHC, these constraints are moved to bolt spacings and coolant passages, allowing more freedom in sizes...and maybe higher revs...depending on how the compromises have been made.
I've noticed that dohc engines will have more hp than torque but ohv engines are opposite. There are some exceptions of course,can anyone tell me why please.
Interestingly, both Honda and BMW have built Very high RPM pushrod engines.
The Honda cx500 and cx650 turbo were both pushrod, 4 valve, short stroke engines.
The Honda cx500 and cx650 turbo were both pushrod, 4 valve, short stroke engines.
Originally Posted By: Clevy
I've noticed that dohc engines will have more hp than torque but ohv engines are opposite. There are some exceptions of course,can anyone tell me why please.
Because 5252 is not a magic number, so torque and horsepower aren't "equal"...if torque was in inch pounds, we wouldn't be having the discussion.
I've noticed that dohc engines will have more hp than torque but ohv engines are opposite. There are some exceptions of course,can anyone tell me why please.
Because 5252 is not a magic number, so torque and horsepower aren't "equal"...if torque was in inch pounds, we wouldn't be having the discussion.
Originally Posted By: Cujet
Interestingly, both Honda and BMW have built Very high RPM pushrod engines.
The Honda cx500 and cx650 turbo were both pushrod, 4 valve, short stroke engines.
Yep, you can really do anything that you set out to design to do...if you design it that way.
The Merceded Indy pushrod V-8 was just such a "design"
Interestingly, both Honda and BMW have built Very high RPM pushrod engines.
The Honda cx500 and cx650 turbo were both pushrod, 4 valve, short stroke engines.
Yep, you can really do anything that you set out to design to do...if you design it that way.
The Merceded Indy pushrod V-8 was just such a "design"
Originally Posted By: Shannow
Originally Posted By: Clevy
I've noticed that dohc engines will have more hp than torque but ohv engines are opposite. There are some exceptions of course,can anyone tell me why please.
Because 5252 is not a magic number, so torque and horsepower aren't "equal"...if torque was in inch pounds, we wouldn't be having the discussion.
Interesting.
So it's the design of the engine that makes the hp/tq lines cross at 5250 or how does that work.
Like Honda vtec engines. They have little tq down low but wake up at higher rpms. Or the motorcycle inline 4s. Those things rev to like 14000 rpms but couldn't get out of their own way at 1000 rpms.
Originally Posted By: Clevy
I've noticed that dohc engines will have more hp than torque but ohv engines are opposite. There are some exceptions of course,can anyone tell me why please.
Because 5252 is not a magic number, so torque and horsepower aren't "equal"...if torque was in inch pounds, we wouldn't be having the discussion.
Interesting.
So it's the design of the engine that makes the hp/tq lines cross at 5250 or how does that work.
Like Honda vtec engines. They have little tq down low but wake up at higher rpms. Or the motorcycle inline 4s. Those things rev to like 14000 rpms but couldn't get out of their own way at 1000 rpms.
Originally Posted By: Shannow
Because 5252 is not a magic number, so torque and horsepower aren't "equal"...if torque was in inch pounds, we wouldn't be having the discussion.
Make it a metric torque/power graph and 5252 just disappears....it doesn't exist.
Pushrod engines are traditionally not high revving because that's the sort of power they wanted in the '50's and '60's. I used to rev my Triumph Daytona engine to over 10,000rpm - stock, max hp was at 7,500, but it just kept revving. My current pushrod BMW R65 has a 7,250rpm rev limit, I often take it to 8,000rpm....I reckon it could go higher, but want to keep it. If a pushrod engine has the ports to do it, it'll rev well enough.
Because 5252 is not a magic number, so torque and horsepower aren't "equal"...if torque was in inch pounds, we wouldn't be having the discussion.
Make it a metric torque/power graph and 5252 just disappears....it doesn't exist.
Pushrod engines are traditionally not high revving because that's the sort of power they wanted in the '50's and '60's. I used to rev my Triumph Daytona engine to over 10,000rpm - stock, max hp was at 7,500, but it just kept revving. My current pushrod BMW R65 has a 7,250rpm rev limit, I often take it to 8,000rpm....I reckon it could go higher, but want to keep it. If a pushrod engine has the ports to do it, it'll rev well enough.
Originally Posted By: Clevy
Interesting.
So it's the design of the engine that makes the hp/tq lines cross at 5250 or how does that work.
Like Honda vtec engines. They have little tq down low but wake up at higher rpms. Or the motorcycle inline 4s. Those things rev to like 14000 rpms but couldn't get out of their own way at 1000 rpms.
IIRC, my Kawasaki ZN1100 LTD idled at about 1000 rpm. It pulled well from just about any rpm (and it needed to because it was so heavy
)
Originally Posted By: Silk
Pushrod engines are traditionally not high revving because that's the sort of power they wanted in the '50's and '60's. I used to rev my Triumph Daytona engine to over 10,000rpm - stock, max hp was at 7,500, but it just kept revving. My current pushrod BMW R65 has a 7,250rpm rev limit, I often take it to 8,000rpm....I reckon it could go higher, but want to keep it. If a pushrod engine has the ports to do it, it'll rev well enough.
The OHV BSA Rocket 3 didn't have a redline on the tach either. Power fell off completely at 8,000rpm but that was pretty high for 1968! The SOHC Honda CB750K redlined at about 8000 rpm.
Interesting.
So it's the design of the engine that makes the hp/tq lines cross at 5250 or how does that work.
Like Honda vtec engines. They have little tq down low but wake up at higher rpms. Or the motorcycle inline 4s. Those things rev to like 14000 rpms but couldn't get out of their own way at 1000 rpms.
IIRC, my Kawasaki ZN1100 LTD idled at about 1000 rpm. It pulled well from just about any rpm (and it needed to because it was so heavy
Originally Posted By: Silk
Pushrod engines are traditionally not high revving because that's the sort of power they wanted in the '50's and '60's. I used to rev my Triumph Daytona engine to over 10,000rpm - stock, max hp was at 7,500, but it just kept revving. My current pushrod BMW R65 has a 7,250rpm rev limit, I often take it to 8,000rpm....I reckon it could go higher, but want to keep it. If a pushrod engine has the ports to do it, it'll rev well enough.
The OHV BSA Rocket 3 didn't have a redline on the tach either. Power fell off completely at 8,000rpm but that was pretty high for 1968! The SOHC Honda CB750K redlined at about 8000 rpm.
Yeah, I was coming down an onramp one day on a Trident, looking for a gap so I could nail it, glanced at the tacho and it was on 8,000rpm. I think a lot of unreliability stories of engines in those days was just over revving - no rev limiter and just rev them until they go flat. I have to watch my tacho in the R65 when I'm riding hard, it sounds pretty good at 8,000rpm. Shifting by ear is not good for an engine.
Originally Posted By: supercity
Ohv pushrod large capacity v8 works. It makes sense. For about every other engine configuration it doesn't. Problem is large capacity v8s are not suitable for all applications
I would have to disagree with you. It worked great on both the Harleys I owned and it works great in my 4L V-6 Ranger too. I would rather have low end torque any day over a high revving OHC.
Ohv pushrod large capacity v8 works. It makes sense. For about every other engine configuration it doesn't. Problem is large capacity v8s are not suitable for all applications
I would have to disagree with you. It worked great on both the Harleys I owned and it works great in my 4L V-6 Ranger too. I would rather have low end torque any day over a high revving OHC.
Originally Posted By: Silk
Yeah, I was coming down an onramp one day on a Trident, looking for a gap so I could nail it, glanced at the tacho and it was on 8,000rpm. I think a lot of unreliability stories of engines in those days was just over revving - no rev limiter and just rev them until they go flat. I have to watch my tacho in the R65 when I'm riding hard, it sounds pretty good at 8,000rpm. Shifting by ear is not good for an engine.
The Beezer I owned didn't have a tach (Starfire OHV 250 single). But it felt like it would rev almost as high as the SOHC Honda CB125 that preceded it. Top speed and acceleration were almost the same, but it was easier to go quickly on the BSA. More torque, it did have twice the displacement...
and it was slightly larger and quite a bit more substantial. Only real problem (other than oil leaking down the shifter and permanently staining your right shoe) was the voltage rectifier. Over-rev at night and you lose bulbs.
Yeah, I was coming down an onramp one day on a Trident, looking for a gap so I could nail it, glanced at the tacho and it was on 8,000rpm. I think a lot of unreliability stories of engines in those days was just over revving - no rev limiter and just rev them until they go flat. I have to watch my tacho in the R65 when I'm riding hard, it sounds pretty good at 8,000rpm. Shifting by ear is not good for an engine.
The Beezer I owned didn't have a tach (Starfire OHV 250 single). But it felt like it would rev almost as high as the SOHC Honda CB125 that preceded it. Top speed and acceleration were almost the same, but it was easier to go quickly on the BSA. More torque, it did have twice the displacement...
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