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Why was the pushrod page moved and why wasn't the move discussed first? Overhead valve can also be used to describe an overhead camshaft engine, so this page should be moved back or it should be moved to I-head. IJB TA 15:04, 16 April 2007 (UTC)
Should we add the Renesis rotary engine from the RX-8 to the compairison on the bottom of the page? Xboxstrwrs55
I have added some little understood engine technology to this article. Contrary to popular belief, the pushrod engine is more complex than the later OHC style, with more moving parts. It suffers clearance changes due to head-gasket settlement and thermal effects (hence "adjusting the tappets" - though hydraulic lifters avoid this chore in bigger engines). The big advantage of OHV is that it can safely be drip or splash fed with oil (sometimes pushed through hollow pushrods without assistance from the oil pump). The alternative OHC engines have spinning bearings, and are much more sensitive to lubrication. When there is one oil pump feeding both a crankshaft (requiring perhaps 90% of the oil) and an OHC (requiring 10% of the oil, but which must overcome gravity and reach the cylinder head), correct balance between these feeds is vital. Any contamination in the oil feed, or wear in the system, leads to more expensive damage, sooner, in an OHC engine. TomRawlinson 14:39, 5 May 2007 (UTC)
Also oil is fed under pressure to the various parts of the engine so gravity wouldn't cause any problems for an OHC engine. IJB TA 21:37, 5 May 2007 (UTC)
Valvetrain failures are very rare and unusual on any engine type in my experience. I can't find evidence of any valvetrain related reliability problems with OHC engines that don't also apply to pushrod engines. The problems I think you're seeing are a result of timing belt failures where the piston will impact the valves once the cam(s) have stopped turning, this is a result of neglect by the owner not a flaw in the OHC design. Also that type of damage can only happen on interference type engines, most engines are not interference types. Some newer OHC engines have maintenance free timing chains to solve that issue. Last, I have found evidence of cam failure in both pushrod and OHC engines, most failures seem to be a result of improper installation of the cam or a lack of maintenance. Anyway, there isn't nearly enough information here to say one engine type is more reliable than another.
OHC engines of similar configurations have just about always been less complex than pushrod engines. IJB TA 01:37, 7 May 2007 (UTC)
Interference engines are those with valves that will occupy the same space as the top of the piston at some point during the operation of the engine. Obviously the valves wont occupy the same space as the piston at the same time during normal operation. They're usually high performance engines with high compression ratios. I've always maintained all my own vehicles and more recently the vehicles owned by my immediate family, all of them have been OHC vehicles, all of them have been more than 10 or 20 years old and none of them have ever had any kind of valvetrain related problems. I have had a timing belt break once, it's annoying (towing the car and all), but it didn't cause any problems and it's wasn't expensive or very difficult to replace on that vehicle. Yes problems can happen with the OHC system, but they can also happen with pushrod systems, as far as what is more prone to failure, that would probably be pretty difficult to prove. IJB TA 14:49, 10 May 2007 (UTC)
Maybe, but remember that those chains and belts for OHC engines are designed to handle the load of running that specific system. Engineers don't just grab some random chain or belt off of a shelf and pray that it works for their engine. Obviously belts require maintenance but they offer plenty of benefits when compared with chains. Also the drive systems are always improving, better chains, better belts, better tensioners, etc. One example is Honda's newer 4 cylinder engines ( K series, R series), they use a hyvo chain that should never stretch or wear significantly enough to require replacement within an expected engine life (200,000 miles at least). I've seen pushrod engines that needed to have the chain replaced at less than or not much more than 100,000 miles. Newer timing belts generally only require replacement every 100,000 miles, or even more in some cases, that's at least 4 years of use for many people! Anyway, if OHC systems were so unreliable, so expensive and so difficult to maintain there would not be so many 15-20+ year old OHC engines with close to or over 200,000 miles on the road showing no sign of any problems. IJB TA 16:32, 24 June 2007 (UTC)
Most modern production engines are "interference" type engines. http://autorepair.about.com/od/glossary/ss/timin-belt-inf2_8.htm Making an engine "non-interference" isn't usually a good thing. Wouldn't these engines need very low valve lift or low compression? Both of these things make for poor efficiency and power. Plus OHV and OHC are both dependable engines, but how can you say that a chain (moreso a belt) is more dependable than a chain that is 1/3 of the length. It is a trade off, either you put the cam next to the crank inside the block for smaller engine size and short distance for timing at the expense of more valvetrain weight or you put the cams above the heads for less valvetrain weight but longer distance to time the cams across and larger overall engine packaging. And what do brakes have to do with an engine being OHV or OHC? You seem to have personal bias against OHV engines. LrngCrv ( talk) 09:21, 28 December 2007 (UTC)
"Comparing engines is not an exact science. This table shows the comparison of some of the most important features when looking at an engine"
I think it's somewhat misleading to say comparing engines is not an exact science. I would argue that it is an exact science, however I understand what the author was trying to communicate, which is that its not possible to accurately compare engines using only a few figures such as peak power/torque figures and rev limits etc. I would put forward a more accurate phrase such as "There are numerous factors to consider when comparing engines. Some of the key features are described in the following table" —The preceding unsigned comment was added by 60.242.154.34 ( talk) 12:59, 9 May 2007 (UTC).
Removed:
I would like to see proof of this. Pushrod engines have quite a few more parts than an equivalent OHC engine. For example, a 1983 Toyota Camry has a single OHC engine with 8 valves and hydraulic tappets, it has a total of 9 components acting on the valves (1 cam, 8 tappets), not including the drive system. A 1981 Datsun 210 has an 8 valve pushrod engine and has 25 components acting on the valves (1 cam, 8 tappets, 8 pushrods, 8 rocker arms), not including the drive system. Quite a difference wouldn't you say? There are fewer head machining operations but more block machining operations for a pushrod engine, they don't just put cams and tappets in raw block castings. Yes iron engines are less expensive to produce, that does not mean pushrod engines are less expensive to produce. IJB TA 01:06, 29 June 2007 (UTC)
I think I remember reading this article. Then again that isn't proof. —Preceding unsigned comment added by Springee ( talk • contribs) 04:37, 1 April 2008 (UTC)
Removed:
Again this requires proof. Try getting 800 hp from a good old Jeep/AMC 4.0L pushrod engine, then try getting 800 hp from a 3.0 liter Toyota 2JZ-GTE. You can imagine which might be more expensive to achieve that power number with (the Toyota engine will handle that power level with stock internals). There are certain engines that have a large amount of aftermarket support and that does make it less expensive to modify them, but they are not cheap to modify because they are pushrod engines. Also comparing an 800 hp ~1 liter engine to a 800 hp ~6 liter engine is ridiculous, it will be more expensive to produce 800 hp with the ~1 liter engine than the ~6 liter engine no matter what type of valvetrain it may have. IJB TA 01:06, 29 June 2007 (UTC)
I think the Less expensive to produce/modify parts still needs to be there just rewrote and more specifically refering to V and flat engines. Mainly because they only require one camshaft to drive all the valves and the cost of the extra valvetrain parts(the pushrods and rocker arms(although alot of OHC engines have rockers as well)) is usually not more than the cost of another extra long timing chain/belt, tensioners, and gears. Let alone factoring in the cost of an extra camshaft and the requirement to make a stronger head to house the camshafts and the extra machining to do so. Pushrod engines also usually only require one head(further driving down costs due to mass production) to be made as well which can fit on either side of the engine, unlike most OHC engines. The same reasoning could be applied as well when modifying said engines. Planingspeed ( talk) 21:31, 27 July 2008 (UTC)
My point still stands. OHC engines have considerably lower part count when compared to OHV engines in similar configurations. This quote: "which cost less to make largely because they contain fewer parts." is likely referring to a comparison of 2 valve/cylinder pushrod engines and 4 valve/cylinder OHC engines, this always leads to the common misconception that OHV engines are less complex. Just do the math, OHC engines use fewer parts to achieve the same thing. Also GM has been producing OHV engines continuously for decades, that is likely the reason for the lower cost of their OHV engines. Also consider the performance gained with 4 valve OHC engines:
http://media.gm.com/us/powertrain/en/product_services/2009/09car.htm
The GM 3.9 OHV V6 w/VVT available in the G6: OHV 3.9 output
The GM 3.6 DOHC V6 w/VVT also available in the G6: DOHC 3.6 output
The 3.6 in the G8 performs even better: DOHC 3.6 output
Compare these cars: http://www.fueleconomy.gov/
OHC engine = better torque and power output, better fuel economy. You can see a comparison of the 3.9 with a manual transmission (which should have given it an advantage over the 3.6) here: http://en.wikipedia.org/wiki/Talk:Pushrod
This part under the limitations needs sources. It is inaccurate and doesn't describe a limitation of OHV engines. There is no flaw in the OHV engine design that prevents more than two valves per cylinder in the head or prevents variable valve duration. LrngCrv ( talk) 13:18, 18 December 2007 (UTC)
I removed this part. The location of the camshaft in the block instead of in the cylinder heads doesn't prevent variable duration or prevent a certain number of valves. There are plenty of examples of OHV engines that have both. Whether companies want to add these to OHV engines or feel that the benifit isn't there for the operation range of most OHV engines is another story but it isn't a limitation of the camshaft position. Anyone have any other opinions or think it should be reworded? LrngCrv ( talk) 04:23, 11 January 2008 (UTC)
LrngCrv - the whole "Limitations" section could usefully be taken out. Pushrods obviously allow greater flexibility of valve positioning, valve quantity, VVT and all the rest of it. The fact that most of those options (eg moving rocker shafts, sliding cams, wedges etc) have never been used (or, we don't know of them having being used anyway) is neither here nor there. What are we doing comparing older technology directly to the newer stuff anyway? The OHV was around a very long time, in much more inventive times, and there's a vast amount more that could be included. Think of those rotary engines with a single push-pull rod, or a single rod operating the exhaust valve only. Mentioning the fact that some low-tech automobile manufacturers were still using this system long after it was superseded drags down a long and illustrious tradition. TomRawlinson ( talk) 20:34, 29 October 2008 (UTC)
I immediately noticed in this article that when comparing engines, some of the OHC engine benefits/examples were those using pneumatic valve springs, which are decidedly different than the standard coil springs used on the other examples. Can pneumatic valve springs only be implemented in OHC engines, or is it possible for an OHV engine to use them? None of the articles in question give any indication. If pneumatic valves are independent of valvetrain, I suggest the examples be removed from the article. If they are specific to OHC, I suggest that they be listed as a benefit, but set apart from standard coil spring OHC engines. Scott Paeth ( talk) 10:22, 9 February 2008 (UTC)
While it is common to have only one cam in a pushrod motor I think it's worth noting that GM did design a twin cam VVT 3 valve pushrod motor called the XV8. The intent was to maximize the potential benefits of a pushrod motor. That is maximize the displacement you can get in a small total engine package size. The concept is described here: http://www.acarplace.com/brands/gm/xv8-engine.html and here with pictures: http://theautoprophet.blogspot.com/2005/06/redemption-of-pushrod.html —Preceding unsigned comment added by 129.59.246.28 ( talk) 17:43, 28 March 2008 (UTC)
It's not clear what the advantages are from the articles. It might be smaller than the typical 300hp V6 (usually a ~3.5L). It might be cheaper to make. It might have better power delivery. At low RPM displacement generally is better for torque. It may be the benefit is you get a V8 instead of a V6. At least in terms of power delivery adding cylinders usually makes things smoother. As it never made it into production maybe the hoped for benefits didn't pan out. I must say, it is cool looking. —Preceding unsigned comment added by Springee ( talk • contribs) 04:35, 1 April 2008 (UTC)
I can only speculate but when it comes to cost, it’s not always the number of parts but the cost of the parts. Cam shafts are precision machined thus expensive. This is likely part of the reason many motors were SOHC 4 valve setups instead of DOHC 4 valve heads. This motor would also have only 2 cam phasers vs 4 for a DOHC setup (assuming changing both cams).
In the end it’s hard to say. GM certainly thought the design had merit or they wouldn’t have made the prototype. At the same time it’s not in production so it clearly had some limitation (NVH, cost, performance, little need, couldn’t get it in the right shade of red ;) ). I would be great if we could get the inside scope rather than just speculate. —Preceding unsigned comment added by Springee ( talk • contribs) 07:10, 1 April 2008 (UTC)
Why is there a engine comparison chart in the OHV article? This article is about the OHV/pushrod engine not comparing engine specs, although another page/article with these specs would be nice though. Not only that none of the mass produced engines on said chart have proper sources. It also does not specify if the engines are fully dressed or not. For example, if the weight of the engine includes the starter, exhaust, or even engines accessories such as A/C compressor, power steering, etc. Some manufactures even include the weight of the flywheel or a flexplate if said car has automatic which can alter the weight further. Planingspeed ( talk) 19:31, 27 July 2008 (UTC)
OHC engines are capable of making more power from a given displacement, so there is no need to build OHC engines with huge displacements. Fact is: F1 engines would never make even close to their current power output if they weren't OHC engines, so an OHV F1 engine would never have an advantage, no matter how much money you pumped one. Also consider the other two engines I mentioned above, they don't have "hundreds of millions" behind their development (that money also goes into the chassis and things like building huge wind tunnels BTW). And what about the engines in motorcycles like the Yamaha YZF-R1 or the Honda CBR1000RR, etc., how much larger would they be if they were OHV engines? They seem to be pretty inexpensive too considering how they perform. Or how about F1 engines in the mid '80s? They were OHC engines and made nearly 1000 hp per liter, just like top fuel engines. They also lasted for about an hour (though, not while making 1,000 hp/liter) while top fuel engines have the life cycle of a few seconds, IF THEY'RE LUCKY. And one more thing, they weighed around 300 lbs. I don't see the advantage pushrod engines have here. IJB TA ( talk) 23:54, 24 October 2008 (UTC)
Engine name | Displacement ( L) | Configuration | Valvetrain | Car | Engine weight ( lb) | Power ( hp) | RPM power | Torque ( lbf·ft) | RPM torque | Power-weight (hp per lb) |
---|---|---|---|---|---|---|---|---|---|---|
Cosworth RA | 6.5 | V12 | DOHC | 2021 Aston Martin Valkyrie | 454 | 1,000 | 10,500 | 546 | 7,000 | 2.2 |
M18.00 | 4.6 | V8 | DOHC | 2015 Porsche 918 | 298 | 608 | 8,700 | 398 | 6,700 | 2.04 |
F140 HC | 6.5 | V12 | DOHC | 2022 Ferrari Daytona SP3 | 496 | 829 | 9250 | 514 | 7,250 | 1.67 |
Cosworth GMA | 4.0 | V12 | DOHC | 2023 Gordon Murray Automotive T.50 | 392 | 654 | 11,500 | 344 | 9,000 | 1.67 |
L539 | 6.5 | V12 | DOHC | 2021 Lamborghini Aventador LP 780-4 Ultimae | 518 | 769 | 8,500 | 531 | 6,750 | 1.48 |
M159 | 6.2 | V8 | DOHC | 2013 SLS AMG Coupé Black Series | 454 | 622 | 7,400 | 468 | 5,500 | 1.37 |
F140 | 6.0 | V12 | DOHC | 2002 Enzo Ferrari | 496 | 660 | 7,800 | 485 | 5,500 | 1.33 |
M80/01 | 5.7 | V10 | DOHC | 2005 Porsche Carrera GT | 472 | 605 | 8,000 | 435 | 5,750 | 1.28 |
M159 | 6.2 | V8 | DOHC | 2013 SLS AMG GT | 454 | 583 | 6,800 | 479 | 4,750 | 1.28 |
F130 | 4.7 | V12 | DOHC | 1995 Ferrari F50 | 437 | 513 | 8,500 | 347 | 6,500 | 1.17 |
LS7 | 7.0 | V8 | Pushrod | 2006 Corvette Z06 | 458 | 505 | 6,300 | 470 | 4,800 | 1.10 |
M156 | 6.2 | V8 | DOHC | 2007 Mercedes CLK63 AMG | 439 | 475 | 6,800 | 465 | 5,000 | 1.08 |
LT2 | 6.2 | V8 | Pushrod | 2020 Chevrolet Corvette C8 | 472 | 495 | 6,450 | 470 | 5,150 | 1.05 |
SRT-10 | 8.4 | V10 | Pushrod | 2016 Dodge Viper ACR | 625 | 645 | 6,200 | 600 | 6,000 | 1.03 |
LS3 | 6.2 | V8 | Pushrod | 2008 Chevrolet Corvette C6 | 420 | 436 | 5,900 | 428 | 4,400 | 1.02 |
S85 | 5.0 | V10 | DOHC | 2007 BMW M5 & BMW M6 | 529 | 500 | 7,750 | 383 | 6,100 | 0.94 |
SRT-10 | 8.3 | V10 | Pushrod | 2006 Dodge Viper | 550 | 510 | 5,600 | 535 | 4,200 | 0.93 |
S65 | 4.0 | V8 | DOHC | 2007 BMW M3 | 445 | 414 | 8,300 | 295 | 3,900 | 0.93 |
M62 | 5.0 | V8 | DOHC | 2003 BMW M5 | 527 | 396 | 6,600 | 370 | 3,800 | 0.75 |
Comparison of naturally-aspirated engines for race and road legal track day cars
Engine name | Displacement ( L) | Configuration | Valvetrain | Car | Engine weight ( lb) | Power ( hp) | RPM power | Torque ( lbf·ft) | RPM torque | Power-weight (hp per lb) | Reference |
---|---|---|---|---|---|---|---|---|---|---|---|
BMW P84/5 | 3.0 | V10 | DOHC | 2005 Williams FW27 F1 | 203 | 925 | 19,000 | NA | NA | 4.56 | [1] |
Ferrari Tipo 052 | 3.0 | V10 | DOHC | 2003 Ferrari F2003-GA F1 | 203 | 920 | 19,500 | NA | NA | 4.53 | [2] |
Gibson GJ458 | 4.5 | V8 | DOHC | Ginetta-Zytek 09S | 262 | 700 | NA | 435 | NA | 2.67 | [3] |
Judd DB 4.0 | 4.0 | V8 | DOHC | Various | 256 | 670 | 10,000 | NA | NA | 2.62 | [4] |
Powertec RPB V8 | 2.8 | V8 | DOHC | Radical SR9 | 194 | 450 | NA | 250 | NA | 2.32 | [5] |
Motopower RST-V8 | 2.0 | V8 | DOHC | Various | 163 | 340 | 10,250 | 190 | 7,000- 7,800 | 2.09 | [6] |
Powertec RPA V8 | 2.6 | V8 | DOHC | Radical SR8 | 194 | 380 | NA | 215 | NA | 1.96 | [7] |
Chevrolet R07 | 5.8 | V8 | Pushrod | Chevrolet Gen. 6 NASCAR | 525 | 850 | 9,500 (est) | 590 (est) | NA | 1.62 | [8] [9] |
This article is overwhelmed by reference to the later OHC layout. The OHV motor has a long and honorable tradition which it would be interesting and valuable to document. The fact that it's now been (largely) superseded by something more modern is irrelevant - I don't see the horse article filled with references to how much better is the car. TomRawlinson ( talk) 21:22, 9 December 2008 (UTC)
Seconded. Conversely, I don't see much mention of OHV in the overhead cam article. Comparisons of engine types should go within internal combustion engine, or another article should be refactored to hold the comparison. Scott Paeth ( talk) 12:52, 11 December 2008 (UTC)
Wondering why this article is titled "Overhead valve" and not "Overhead valve engine" (which redirects here). The first sentence talks about "overhead valve engine" and not "overhead valve". Facts707 ( talk) 08:22, 30 October 2009 (UTC)
In the introduction it implies that a 1949 engine was the first OHV engine. Well hardly. The curved dashed Oldsmobile produced well before WW1 and almost all Buicks ahd 'valve-in-head' engines. The first Chevrolet 'Stovebolt Six' came out in 1927 and the second in 1939. 203.26.122.12 ( talk) 06:33, 25 November 2009 (UTC)
See Wikipedia:Articles for deletion/Cam-in-block Andy Dingley ( talk) 10:18, 14 April 2012 (UTC)
Maybe somebody can help me to understand the staggered valve arrangement? When I saw a picture of one side of a big block engine a few days ago, I didnt know about the staggered valve arrangement, Now that I know, it might be still not making sense. When you look at an overhead photo of the valves, you see six valves in the center, one valve by itself on one end, and one valve by itself on the other end. In total, eight valves makes sense: four intake valves, and four exhaust valves. But the thing Im not fully fully understanding is the staggered arrangement. It seems really, that of eight valves, only two are staggered. One valve at each end is set at an angle. Am I correct? The valves in the two middle cylinders are closer together, than each valve set in the end cylinders. Am I correct? Or am I missing some facts here? Marc S., Dania Fl 206.192.35.125 ( talk) 13:50, 8 March 2013 (UTC)
I propose that the section "1994 Mercedes/Ilmor Indianapolis 500 engine" be either deleted, or moved to a new page linked to this one. Arrivisto ( talk) 15:01, 29 December 2014 (UTC)
The result of the move request was: Move to overhead valve engine. As noted, this may require some expansion; discussion in that regard can continue below. Cúchullain t/ c 16:04, 1 April 2015 (UTC)
Overhead valve →
OHV engine – 1: The subject is a type of engine, not a type of valve. 2. The subject does not cover all overhead valve engines, just those with valves operated by pushrods. 3. The title "OHV engine" is more in line with "
Flathead engine" and "
IOE engine".
Sincerely, SamBlob (
talk)
00:18, 26 February 2015 (UTC)
This component is broader in scope than a specific kind of engine, should be split off.-- عبد المؤمن ( talk) 13:06, 9 June 2019 (UTC)
This also compromises the spark plug location, since it is not possible to have a centrally located spark plug in an engine with two valves per cylinder.
This is plainly false. While most (possibly all) two-valve engines have the sparkplug offset to allow for maximum valve size, nothing prevents the designer from placing a sparkplug in the center and simply making the valves smaller. Of course, this effectively gives you about half the flow of a four-valve engine, but that's just inefficient, not impossible.
AI0867 ( talk) 13:01, 27 January 2020 (UTC)
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Why was the pushrod page moved and why wasn't the move discussed first? Overhead valve can also be used to describe an overhead camshaft engine, so this page should be moved back or it should be moved to I-head. IJB TA 15:04, 16 April 2007 (UTC)
Should we add the Renesis rotary engine from the RX-8 to the compairison on the bottom of the page? Xboxstrwrs55
I have added some little understood engine technology to this article. Contrary to popular belief, the pushrod engine is more complex than the later OHC style, with more moving parts. It suffers clearance changes due to head-gasket settlement and thermal effects (hence "adjusting the tappets" - though hydraulic lifters avoid this chore in bigger engines). The big advantage of OHV is that it can safely be drip or splash fed with oil (sometimes pushed through hollow pushrods without assistance from the oil pump). The alternative OHC engines have spinning bearings, and are much more sensitive to lubrication. When there is one oil pump feeding both a crankshaft (requiring perhaps 90% of the oil) and an OHC (requiring 10% of the oil, but which must overcome gravity and reach the cylinder head), correct balance between these feeds is vital. Any contamination in the oil feed, or wear in the system, leads to more expensive damage, sooner, in an OHC engine. TomRawlinson 14:39, 5 May 2007 (UTC)
Also oil is fed under pressure to the various parts of the engine so gravity wouldn't cause any problems for an OHC engine. IJB TA 21:37, 5 May 2007 (UTC)
Valvetrain failures are very rare and unusual on any engine type in my experience. I can't find evidence of any valvetrain related reliability problems with OHC engines that don't also apply to pushrod engines. The problems I think you're seeing are a result of timing belt failures where the piston will impact the valves once the cam(s) have stopped turning, this is a result of neglect by the owner not a flaw in the OHC design. Also that type of damage can only happen on interference type engines, most engines are not interference types. Some newer OHC engines have maintenance free timing chains to solve that issue. Last, I have found evidence of cam failure in both pushrod and OHC engines, most failures seem to be a result of improper installation of the cam or a lack of maintenance. Anyway, there isn't nearly enough information here to say one engine type is more reliable than another.
OHC engines of similar configurations have just about always been less complex than pushrod engines. IJB TA 01:37, 7 May 2007 (UTC)
Interference engines are those with valves that will occupy the same space as the top of the piston at some point during the operation of the engine. Obviously the valves wont occupy the same space as the piston at the same time during normal operation. They're usually high performance engines with high compression ratios. I've always maintained all my own vehicles and more recently the vehicles owned by my immediate family, all of them have been OHC vehicles, all of them have been more than 10 or 20 years old and none of them have ever had any kind of valvetrain related problems. I have had a timing belt break once, it's annoying (towing the car and all), but it didn't cause any problems and it's wasn't expensive or very difficult to replace on that vehicle. Yes problems can happen with the OHC system, but they can also happen with pushrod systems, as far as what is more prone to failure, that would probably be pretty difficult to prove. IJB TA 14:49, 10 May 2007 (UTC)
Maybe, but remember that those chains and belts for OHC engines are designed to handle the load of running that specific system. Engineers don't just grab some random chain or belt off of a shelf and pray that it works for their engine. Obviously belts require maintenance but they offer plenty of benefits when compared with chains. Also the drive systems are always improving, better chains, better belts, better tensioners, etc. One example is Honda's newer 4 cylinder engines ( K series, R series), they use a hyvo chain that should never stretch or wear significantly enough to require replacement within an expected engine life (200,000 miles at least). I've seen pushrod engines that needed to have the chain replaced at less than or not much more than 100,000 miles. Newer timing belts generally only require replacement every 100,000 miles, or even more in some cases, that's at least 4 years of use for many people! Anyway, if OHC systems were so unreliable, so expensive and so difficult to maintain there would not be so many 15-20+ year old OHC engines with close to or over 200,000 miles on the road showing no sign of any problems. IJB TA 16:32, 24 June 2007 (UTC)
Most modern production engines are "interference" type engines. http://autorepair.about.com/od/glossary/ss/timin-belt-inf2_8.htm Making an engine "non-interference" isn't usually a good thing. Wouldn't these engines need very low valve lift or low compression? Both of these things make for poor efficiency and power. Plus OHV and OHC are both dependable engines, but how can you say that a chain (moreso a belt) is more dependable than a chain that is 1/3 of the length. It is a trade off, either you put the cam next to the crank inside the block for smaller engine size and short distance for timing at the expense of more valvetrain weight or you put the cams above the heads for less valvetrain weight but longer distance to time the cams across and larger overall engine packaging. And what do brakes have to do with an engine being OHV or OHC? You seem to have personal bias against OHV engines. LrngCrv ( talk) 09:21, 28 December 2007 (UTC)
"Comparing engines is not an exact science. This table shows the comparison of some of the most important features when looking at an engine"
I think it's somewhat misleading to say comparing engines is not an exact science. I would argue that it is an exact science, however I understand what the author was trying to communicate, which is that its not possible to accurately compare engines using only a few figures such as peak power/torque figures and rev limits etc. I would put forward a more accurate phrase such as "There are numerous factors to consider when comparing engines. Some of the key features are described in the following table" —The preceding unsigned comment was added by 60.242.154.34 ( talk) 12:59, 9 May 2007 (UTC).
Removed:
I would like to see proof of this. Pushrod engines have quite a few more parts than an equivalent OHC engine. For example, a 1983 Toyota Camry has a single OHC engine with 8 valves and hydraulic tappets, it has a total of 9 components acting on the valves (1 cam, 8 tappets), not including the drive system. A 1981 Datsun 210 has an 8 valve pushrod engine and has 25 components acting on the valves (1 cam, 8 tappets, 8 pushrods, 8 rocker arms), not including the drive system. Quite a difference wouldn't you say? There are fewer head machining operations but more block machining operations for a pushrod engine, they don't just put cams and tappets in raw block castings. Yes iron engines are less expensive to produce, that does not mean pushrod engines are less expensive to produce. IJB TA 01:06, 29 June 2007 (UTC)
I think I remember reading this article. Then again that isn't proof. —Preceding unsigned comment added by Springee ( talk • contribs) 04:37, 1 April 2008 (UTC)
Removed:
Again this requires proof. Try getting 800 hp from a good old Jeep/AMC 4.0L pushrod engine, then try getting 800 hp from a 3.0 liter Toyota 2JZ-GTE. You can imagine which might be more expensive to achieve that power number with (the Toyota engine will handle that power level with stock internals). There are certain engines that have a large amount of aftermarket support and that does make it less expensive to modify them, but they are not cheap to modify because they are pushrod engines. Also comparing an 800 hp ~1 liter engine to a 800 hp ~6 liter engine is ridiculous, it will be more expensive to produce 800 hp with the ~1 liter engine than the ~6 liter engine no matter what type of valvetrain it may have. IJB TA 01:06, 29 June 2007 (UTC)
I think the Less expensive to produce/modify parts still needs to be there just rewrote and more specifically refering to V and flat engines. Mainly because they only require one camshaft to drive all the valves and the cost of the extra valvetrain parts(the pushrods and rocker arms(although alot of OHC engines have rockers as well)) is usually not more than the cost of another extra long timing chain/belt, tensioners, and gears. Let alone factoring in the cost of an extra camshaft and the requirement to make a stronger head to house the camshafts and the extra machining to do so. Pushrod engines also usually only require one head(further driving down costs due to mass production) to be made as well which can fit on either side of the engine, unlike most OHC engines. The same reasoning could be applied as well when modifying said engines. Planingspeed ( talk) 21:31, 27 July 2008 (UTC)
My point still stands. OHC engines have considerably lower part count when compared to OHV engines in similar configurations. This quote: "which cost less to make largely because they contain fewer parts." is likely referring to a comparison of 2 valve/cylinder pushrod engines and 4 valve/cylinder OHC engines, this always leads to the common misconception that OHV engines are less complex. Just do the math, OHC engines use fewer parts to achieve the same thing. Also GM has been producing OHV engines continuously for decades, that is likely the reason for the lower cost of their OHV engines. Also consider the performance gained with 4 valve OHC engines:
http://media.gm.com/us/powertrain/en/product_services/2009/09car.htm
The GM 3.9 OHV V6 w/VVT available in the G6: OHV 3.9 output
The GM 3.6 DOHC V6 w/VVT also available in the G6: DOHC 3.6 output
The 3.6 in the G8 performs even better: DOHC 3.6 output
Compare these cars: http://www.fueleconomy.gov/
OHC engine = better torque and power output, better fuel economy. You can see a comparison of the 3.9 with a manual transmission (which should have given it an advantage over the 3.6) here: http://en.wikipedia.org/wiki/Talk:Pushrod
This part under the limitations needs sources. It is inaccurate and doesn't describe a limitation of OHV engines. There is no flaw in the OHV engine design that prevents more than two valves per cylinder in the head or prevents variable valve duration. LrngCrv ( talk) 13:18, 18 December 2007 (UTC)
I removed this part. The location of the camshaft in the block instead of in the cylinder heads doesn't prevent variable duration or prevent a certain number of valves. There are plenty of examples of OHV engines that have both. Whether companies want to add these to OHV engines or feel that the benifit isn't there for the operation range of most OHV engines is another story but it isn't a limitation of the camshaft position. Anyone have any other opinions or think it should be reworded? LrngCrv ( talk) 04:23, 11 January 2008 (UTC)
LrngCrv - the whole "Limitations" section could usefully be taken out. Pushrods obviously allow greater flexibility of valve positioning, valve quantity, VVT and all the rest of it. The fact that most of those options (eg moving rocker shafts, sliding cams, wedges etc) have never been used (or, we don't know of them having being used anyway) is neither here nor there. What are we doing comparing older technology directly to the newer stuff anyway? The OHV was around a very long time, in much more inventive times, and there's a vast amount more that could be included. Think of those rotary engines with a single push-pull rod, or a single rod operating the exhaust valve only. Mentioning the fact that some low-tech automobile manufacturers were still using this system long after it was superseded drags down a long and illustrious tradition. TomRawlinson ( talk) 20:34, 29 October 2008 (UTC)
I immediately noticed in this article that when comparing engines, some of the OHC engine benefits/examples were those using pneumatic valve springs, which are decidedly different than the standard coil springs used on the other examples. Can pneumatic valve springs only be implemented in OHC engines, or is it possible for an OHV engine to use them? None of the articles in question give any indication. If pneumatic valves are independent of valvetrain, I suggest the examples be removed from the article. If they are specific to OHC, I suggest that they be listed as a benefit, but set apart from standard coil spring OHC engines. Scott Paeth ( talk) 10:22, 9 February 2008 (UTC)
While it is common to have only one cam in a pushrod motor I think it's worth noting that GM did design a twin cam VVT 3 valve pushrod motor called the XV8. The intent was to maximize the potential benefits of a pushrod motor. That is maximize the displacement you can get in a small total engine package size. The concept is described here: http://www.acarplace.com/brands/gm/xv8-engine.html and here with pictures: http://theautoprophet.blogspot.com/2005/06/redemption-of-pushrod.html —Preceding unsigned comment added by 129.59.246.28 ( talk) 17:43, 28 March 2008 (UTC)
It's not clear what the advantages are from the articles. It might be smaller than the typical 300hp V6 (usually a ~3.5L). It might be cheaper to make. It might have better power delivery. At low RPM displacement generally is better for torque. It may be the benefit is you get a V8 instead of a V6. At least in terms of power delivery adding cylinders usually makes things smoother. As it never made it into production maybe the hoped for benefits didn't pan out. I must say, it is cool looking. —Preceding unsigned comment added by Springee ( talk • contribs) 04:35, 1 April 2008 (UTC)
I can only speculate but when it comes to cost, it’s not always the number of parts but the cost of the parts. Cam shafts are precision machined thus expensive. This is likely part of the reason many motors were SOHC 4 valve setups instead of DOHC 4 valve heads. This motor would also have only 2 cam phasers vs 4 for a DOHC setup (assuming changing both cams).
In the end it’s hard to say. GM certainly thought the design had merit or they wouldn’t have made the prototype. At the same time it’s not in production so it clearly had some limitation (NVH, cost, performance, little need, couldn’t get it in the right shade of red ;) ). I would be great if we could get the inside scope rather than just speculate. —Preceding unsigned comment added by Springee ( talk • contribs) 07:10, 1 April 2008 (UTC)
Why is there a engine comparison chart in the OHV article? This article is about the OHV/pushrod engine not comparing engine specs, although another page/article with these specs would be nice though. Not only that none of the mass produced engines on said chart have proper sources. It also does not specify if the engines are fully dressed or not. For example, if the weight of the engine includes the starter, exhaust, or even engines accessories such as A/C compressor, power steering, etc. Some manufactures even include the weight of the flywheel or a flexplate if said car has automatic which can alter the weight further. Planingspeed ( talk) 19:31, 27 July 2008 (UTC)
OHC engines are capable of making more power from a given displacement, so there is no need to build OHC engines with huge displacements. Fact is: F1 engines would never make even close to their current power output if they weren't OHC engines, so an OHV F1 engine would never have an advantage, no matter how much money you pumped one. Also consider the other two engines I mentioned above, they don't have "hundreds of millions" behind their development (that money also goes into the chassis and things like building huge wind tunnels BTW). And what about the engines in motorcycles like the Yamaha YZF-R1 or the Honda CBR1000RR, etc., how much larger would they be if they were OHV engines? They seem to be pretty inexpensive too considering how they perform. Or how about F1 engines in the mid '80s? They were OHC engines and made nearly 1000 hp per liter, just like top fuel engines. They also lasted for about an hour (though, not while making 1,000 hp/liter) while top fuel engines have the life cycle of a few seconds, IF THEY'RE LUCKY. And one more thing, they weighed around 300 lbs. I don't see the advantage pushrod engines have here. IJB TA ( talk) 23:54, 24 October 2008 (UTC)
Engine name | Displacement ( L) | Configuration | Valvetrain | Car | Engine weight ( lb) | Power ( hp) | RPM power | Torque ( lbf·ft) | RPM torque | Power-weight (hp per lb) |
---|---|---|---|---|---|---|---|---|---|---|
Cosworth RA | 6.5 | V12 | DOHC | 2021 Aston Martin Valkyrie | 454 | 1,000 | 10,500 | 546 | 7,000 | 2.2 |
M18.00 | 4.6 | V8 | DOHC | 2015 Porsche 918 | 298 | 608 | 8,700 | 398 | 6,700 | 2.04 |
F140 HC | 6.5 | V12 | DOHC | 2022 Ferrari Daytona SP3 | 496 | 829 | 9250 | 514 | 7,250 | 1.67 |
Cosworth GMA | 4.0 | V12 | DOHC | 2023 Gordon Murray Automotive T.50 | 392 | 654 | 11,500 | 344 | 9,000 | 1.67 |
L539 | 6.5 | V12 | DOHC | 2021 Lamborghini Aventador LP 780-4 Ultimae | 518 | 769 | 8,500 | 531 | 6,750 | 1.48 |
M159 | 6.2 | V8 | DOHC | 2013 SLS AMG Coupé Black Series | 454 | 622 | 7,400 | 468 | 5,500 | 1.37 |
F140 | 6.0 | V12 | DOHC | 2002 Enzo Ferrari | 496 | 660 | 7,800 | 485 | 5,500 | 1.33 |
M80/01 | 5.7 | V10 | DOHC | 2005 Porsche Carrera GT | 472 | 605 | 8,000 | 435 | 5,750 | 1.28 |
M159 | 6.2 | V8 | DOHC | 2013 SLS AMG GT | 454 | 583 | 6,800 | 479 | 4,750 | 1.28 |
F130 | 4.7 | V12 | DOHC | 1995 Ferrari F50 | 437 | 513 | 8,500 | 347 | 6,500 | 1.17 |
LS7 | 7.0 | V8 | Pushrod | 2006 Corvette Z06 | 458 | 505 | 6,300 | 470 | 4,800 | 1.10 |
M156 | 6.2 | V8 | DOHC | 2007 Mercedes CLK63 AMG | 439 | 475 | 6,800 | 465 | 5,000 | 1.08 |
LT2 | 6.2 | V8 | Pushrod | 2020 Chevrolet Corvette C8 | 472 | 495 | 6,450 | 470 | 5,150 | 1.05 |
SRT-10 | 8.4 | V10 | Pushrod | 2016 Dodge Viper ACR | 625 | 645 | 6,200 | 600 | 6,000 | 1.03 |
LS3 | 6.2 | V8 | Pushrod | 2008 Chevrolet Corvette C6 | 420 | 436 | 5,900 | 428 | 4,400 | 1.02 |
S85 | 5.0 | V10 | DOHC | 2007 BMW M5 & BMW M6 | 529 | 500 | 7,750 | 383 | 6,100 | 0.94 |
SRT-10 | 8.3 | V10 | Pushrod | 2006 Dodge Viper | 550 | 510 | 5,600 | 535 | 4,200 | 0.93 |
S65 | 4.0 | V8 | DOHC | 2007 BMW M3 | 445 | 414 | 8,300 | 295 | 3,900 | 0.93 |
M62 | 5.0 | V8 | DOHC | 2003 BMW M5 | 527 | 396 | 6,600 | 370 | 3,800 | 0.75 |
Comparison of naturally-aspirated engines for race and road legal track day cars
Engine name | Displacement ( L) | Configuration | Valvetrain | Car | Engine weight ( lb) | Power ( hp) | RPM power | Torque ( lbf·ft) | RPM torque | Power-weight (hp per lb) | Reference |
---|---|---|---|---|---|---|---|---|---|---|---|
BMW P84/5 | 3.0 | V10 | DOHC | 2005 Williams FW27 F1 | 203 | 925 | 19,000 | NA | NA | 4.56 | [1] |
Ferrari Tipo 052 | 3.0 | V10 | DOHC | 2003 Ferrari F2003-GA F1 | 203 | 920 | 19,500 | NA | NA | 4.53 | [2] |
Gibson GJ458 | 4.5 | V8 | DOHC | Ginetta-Zytek 09S | 262 | 700 | NA | 435 | NA | 2.67 | [3] |
Judd DB 4.0 | 4.0 | V8 | DOHC | Various | 256 | 670 | 10,000 | NA | NA | 2.62 | [4] |
Powertec RPB V8 | 2.8 | V8 | DOHC | Radical SR9 | 194 | 450 | NA | 250 | NA | 2.32 | [5] |
Motopower RST-V8 | 2.0 | V8 | DOHC | Various | 163 | 340 | 10,250 | 190 | 7,000- 7,800 | 2.09 | [6] |
Powertec RPA V8 | 2.6 | V8 | DOHC | Radical SR8 | 194 | 380 | NA | 215 | NA | 1.96 | [7] |
Chevrolet R07 | 5.8 | V8 | Pushrod | Chevrolet Gen. 6 NASCAR | 525 | 850 | 9,500 (est) | 590 (est) | NA | 1.62 | [8] [9] |
This article is overwhelmed by reference to the later OHC layout. The OHV motor has a long and honorable tradition which it would be interesting and valuable to document. The fact that it's now been (largely) superseded by something more modern is irrelevant - I don't see the horse article filled with references to how much better is the car. TomRawlinson ( talk) 21:22, 9 December 2008 (UTC)
Seconded. Conversely, I don't see much mention of OHV in the overhead cam article. Comparisons of engine types should go within internal combustion engine, or another article should be refactored to hold the comparison. Scott Paeth ( talk) 12:52, 11 December 2008 (UTC)
Wondering why this article is titled "Overhead valve" and not "Overhead valve engine" (which redirects here). The first sentence talks about "overhead valve engine" and not "overhead valve". Facts707 ( talk) 08:22, 30 October 2009 (UTC)
In the introduction it implies that a 1949 engine was the first OHV engine. Well hardly. The curved dashed Oldsmobile produced well before WW1 and almost all Buicks ahd 'valve-in-head' engines. The first Chevrolet 'Stovebolt Six' came out in 1927 and the second in 1939. 203.26.122.12 ( talk) 06:33, 25 November 2009 (UTC)
See Wikipedia:Articles for deletion/Cam-in-block Andy Dingley ( talk) 10:18, 14 April 2012 (UTC)
Maybe somebody can help me to understand the staggered valve arrangement? When I saw a picture of one side of a big block engine a few days ago, I didnt know about the staggered valve arrangement, Now that I know, it might be still not making sense. When you look at an overhead photo of the valves, you see six valves in the center, one valve by itself on one end, and one valve by itself on the other end. In total, eight valves makes sense: four intake valves, and four exhaust valves. But the thing Im not fully fully understanding is the staggered arrangement. It seems really, that of eight valves, only two are staggered. One valve at each end is set at an angle. Am I correct? The valves in the two middle cylinders are closer together, than each valve set in the end cylinders. Am I correct? Or am I missing some facts here? Marc S., Dania Fl 206.192.35.125 ( talk) 13:50, 8 March 2013 (UTC)
I propose that the section "1994 Mercedes/Ilmor Indianapolis 500 engine" be either deleted, or moved to a new page linked to this one. Arrivisto ( talk) 15:01, 29 December 2014 (UTC)
The result of the move request was: Move to overhead valve engine. As noted, this may require some expansion; discussion in that regard can continue below. Cúchullain t/ c 16:04, 1 April 2015 (UTC)
Overhead valve →
OHV engine – 1: The subject is a type of engine, not a type of valve. 2. The subject does not cover all overhead valve engines, just those with valves operated by pushrods. 3. The title "OHV engine" is more in line with "
Flathead engine" and "
IOE engine".
Sincerely, SamBlob (
talk)
00:18, 26 February 2015 (UTC)
This component is broader in scope than a specific kind of engine, should be split off.-- عبد المؤمن ( talk) 13:06, 9 June 2019 (UTC)
This also compromises the spark plug location, since it is not possible to have a centrally located spark plug in an engine with two valves per cylinder.
This is plainly false. While most (possibly all) two-valve engines have the sparkplug offset to allow for maximum valve size, nothing prevents the designer from placing a sparkplug in the center and simply making the valves smaller. Of course, this effectively gives you about half the flow of a four-valve engine, but that's just inefficient, not impossible.
AI0867 ( talk) 13:01, 27 January 2020 (UTC)