Push Rod Vs Overhead Cam
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When talking about Mustang’s and V8 motors, they break down into two categories – pushrod or modular. Starting with the 289 back in 1964 and finishing with the 5.0L in 1996, every V8 Mustang between those years was equipped with some form or another of a pushrod engine. OHC vs OHC - Pro's and Con's. Overhead valves and a single overhead cam can have very similar results. If you add in DOHC you will get into another world of comparison. Here is an excellent post regarding the delta between DOHC and OHC. What is difference between DOHC and SOHC?
It's about as high tech as a pushrod V-8 can get. Revs very freely and depending on computer programing 350 to 450 HP. Yes I voted for an overhead cam engine, but in the real world that LS-1 fits nicely, a touch expensive, but an enviable package. My next step.
Try, or.Tint questions and advice?.Tire reviews? Tires questions?.Car trouble? Your title must include year/make/model and a short description of the problem.Please do not delete your threads.Our.For information on content removal, user warnings, and bans, please see the page.Forget the trunk monkey, check out.Sticky Schedule(weekly)Car Buying AssistanceTuesTune-Up: Repair AssistancePrevious AMAs.Banner Image/Car InfoCar: Ford GT350Photographer. OHCPros:. Less reciprocating weight, which allows for higher rev limits and/or more aggressive cam profiles.
The ability to adjust intake and exhaust can timing separately when using vvt, allowing for a broader power curve. Allows for four or more valves per cylinder, improving power by allowing for greater airflow and higher revs.Cons:. Heavier, with the weight of the cam(s) higher up, raising the cg of the car.
Potentially costlier. Makes for a significantly larger engine. (See of a DOHC Ford 4.6 (left) and an OHV 302W.)Pushrods (OHV)Pros:. Cheaper. Significantly lighter and more compact. (You want to know why the SBC and LS motors get swapped in everything? This is partly why.)Cons:.
More reciprocating mass, meaning lower max revs (Not that they can't be made to rev. It's just harder.). Generally limited to two valves per cylinder. The LOLstoneagetech jokes. Everyone has already said a lot of things, and I'd like to add another.OHC's generally have an advantage where they can flow more air per liter. This is better if you're limited to smaller engines, like in a racing series that limits displacement.For street cars, airflow generally isn't an issue at all. As other people have mentioned, OHV engines are physically smaller by design, and this allows engineers to get away with using significantly larger displacements.So a 5.0L Coyote, for example, might flow more air per liter, but a 6.2L LS3 can still match it because of its increased displacement, which GM engineers were allowed to take advantage of because it's physically smaller than the Coyote.
For the Coyote to have superior airflow (not on a per liter basis, but superior at the total amount of flow), you'd have to scale up it's displacement. But doing so would increase its physical size, and it's already a pretty big engine going by external dimensions.The Aventador engine is one that can easily out-flow an LS3 (and even the LS7), but it's physically fucking massive. Like, ridiculously huge. But it makes nearly 700hp.Another example of a large displacement DOHC engine would be the V12 in the Speed 12. Go look at pictures of that thing. Talk about a huge engine.TL;DR - When it comes to airflow, OHC's are generally superior in a regulated racing environment with displacement limits. In an unregulated street environment, where you're allowed to have 7.0L engines and such, airflow no longer becomes a huge issue (literally nobody ever complains about their LS3's and LS7's not being able to flow enough air, lol).
OHC can do faster more precise valve openings, both due to the aggresiveness of the lobe shape ('hot cams'), and the absence of dynamics in the actual pushrod (cause everything in the world is a spring).This is more useful when you want to get more hp out of the engine through RPM (which requires fast valve openings and closings), rather than torque, which is better for racing cause it allows you to stay in a lower gear longer. Also variable valve timing as well, but that is not usually done at racing because you will be sitting at the top of the rev range most of the time. If you ever hear the growl of a race engine at idle, its because it has aggressive cams which at lower RPMS introduce more interference waves and introduce rachety tones in the exhaust.On the contrary, at lower RPM's you want slower valve openings, which is why the Vette's torque peak is low in the RPM curve. This is usefull for the street and allows the car to cruise in high gear low revs, or not have to downshift to pass.
Generally speaking, overhead cam engines allow higher rev operation, and thus are better for peak power output. They're found in many different exotic car and racing applications (Ferrari, IRL, etc) where high rpms are desirable.Pushrods are generally cheaper to make for V engines than OHC, OHC is sometimes cheaper for inline engines.Using two cams instead of one (DOHC vs SOHC) can give you a bit more flexibility when designing lift profiles, as you'll have less contact stress, and you may be able to achieve higher speeds. DOHC is a logical choice if you have a variable cam phasing mechanism, as you can put your intake and exhaust lobes on separate shafts.Both OHC and pushrod valvetrains can use timing chains or timing belts, but timing chains are more common on pushrod engines, and timing belts are more common on OHC engines. The advantage of a chain is that it lasts longer; belts are quieter, easier to package, and offer better high-rev performance if the drive load requirements aren't too high. OHC and pushrod configurations can both use hydraulic lash adjustment, which almost eliminates the need for periodic manual lash adjustments.Valvetrain friction can go either way. For reduced valvetrain friction, it is preferable to use a rolling follower, and it is preferable to use manual lash adjustment.
Either of those can be done on a pushrod engine, but they seem to be more common on OHC engines. An OHC valvetrain will generally have less mass to control (hence the potential for higher operating speed), which translates to lower spring forces for a given operating speed, and lower friction. Pushrod engines are easily capable of keeping up with multivalve OHC engines mustang, but they're hardly 'better'. For smaller engines OHC is the way to go, you need to rev then to use the gearing necessary for fast acceleration. For larger engines it's not as much of a problem IMO since you're going to produce alot of torque anyway there's no need for high RPMs and short gearing.If you aren't revving high then OHVs valvetrain issues won't come into play anyway, the LS6 can already rev to 7000 without any float, it doesn't need to go any higher and its head flows more air then it needs. If you are revving high then you use OHC, unlike ass-i mean NASCAR the general public doesn't know how to set the lash on their solid roller pushrod motors and hydraulic lifters haven't seen duty much above 7-7500 RPM to my knowledge. 4 valve DOHC heads have also showed that they can be used in high power engines without giving too bad exhaust emissions too.For maximum power the best head configuration is a 4 valve pentroof type head with valves angled around 20 degrees.
The combustion chamber should have the spark plug raised in the center and the smaller exhaust valves should be placed close to eachother, and there shall be a raise between the valve looking something like a + and the squish zone should be angled. The valves shall be actuated by twin cams (per cylinder bank) and fingerfollowers (preferbly).This type of head can be found in F1, CART, touringcars and so on.
Fingerfollowers and angled squishzones are however not always used since they are quite 'new'. If a cylinderhead is modified this also sets some limitations.
Here is a pic of a pentroof combustion chamber with a central spark plug.the valves angle at a very steep 48 degrees howeverand i would like to agree that the DOHC setup is by far the better one even on high displacement engines.the 6.0 in enzo for example or the 5.7 in the carrera GTanother advantage of DOHC engines that IMO is crucial is the fact that you can adjust the lift and timing of the exaust and intake valves independetly from each other.this raises the tuning posibilities to a new levelthe only advantages of pushrod that i can see are:1. Smaller head. Lower weight and less complexity as well, assuming you can meet your airflow needs with an OHV head (and since most pushrod designs dont rev high airflow need is decreased) and don't wish to rev over 7500 it's a fine choice. The lower and lighter engine has many handling benefits as well, a dry sump OHV engine is extremely short, supposedly the new corvette will have a high perf. Model utilizing that.There are concept 2 cam OHV engines, 1 for intake 1 for the exhaust, with that working an OHV engine with VVT is possible, you can run as many valves off of that as you like too. Pushrod weight and flex is always going to be a problem, but new metals have already fixed much of that, chromemoly rods are very light and stiff and for the enthusiast solid lifters will fix any valve float issues at high RPMs.
Pushrod race engines:Top fuel dragsters 7-8000 hpNascar 700 hpformula ford 170 hp (only 1600 cc w/ 2 barrel carb)some LeMans cars (viper, vette)DOHC is used in the IRL however. With 650 hp.and toyota atlantic (cart) uses the 4age. DOHCMany of the engines you mentioned are limited to push rods, they don't use it because they are somehow better.DOHC is used in almost all motorsports with a few exceptions. DOHC is for example used in F1, CART, IRL, most GT racing cars (Corvette, Panoz and Viper being the exceptions), WRC and touring cars (like BTCC). Some of the highest brake mean effective pressures of NA engines have been measured in touring cars like BTCC. OHV is certainly not superior, among other things already mentioned the pushrod intrusion through the cylinder head limits port design and shape.
Of course more of the airflow differences between domestic and import cylinder head flow is due to the Big 3's reliance on displacement to make airflow rather than brilliant cylinder head design and RPM, but then either approach can work extremely well.' Rather then brilliant cylinder head design' I don't know why you would say that, to be able to do what GM's done with only 2 valves is fairly impressive in my book, and tuners have found alot of room left in them as well. Yup saabjohan please try to pay attention to the conversation. Push rod engines are generally refered to as ohv. As for the comment from mustang I'm not sure what you are baseing your oppinion on camless engines on.
In theory they will blow everything else out of the water I'm interesting why you think they are that great especially seeing how I doubt you have diven one as they haven't been released yet. And acually ohc can be traced back to at least the 1920's so yes the both have been around a simalar amount of time. Yup saabjohan please try to pay attention to the conversation. Push rod engines are generally refered to as ohv.
As for the comment from mustang I'm not sure what you are baseing your oppinion on camless engines on. In theory they will blow everything else out of the water I'm interesting why you think they are that great especially seeing how I doubt you have diven one as they haven't been released yet. And acually ohc can be traced back to at least the 1920's so yes the both have been around a simalar amount of timeUse the correct terms instead, it avoids misunderstanding. Over Head Valve refers to nothing more than that the valves are placed in the cylinder head, which is usually the case for both push rod and OHC. Well its a little bit hard to show proof seeing how they haven't been mass produced yet how even in theory a camless engines should be able to alter the lift and duration for peek performance at any rpm and driving condition. It will be like vtec only 100 times better very good hp numbers should be able to be produced from even very small engines with exelent drivablity. Now of cource there will be teathing problems as with any new tecnology and I probably wouldn't want to buy one till they get it perfected but it should be quite amazing once they get it right.
I'll have to side with SJ.And Ill have to Ditto that.Enginers have spent hundreds of years developing special terms and word usages to avoid confusion and allow the easy and efficant transfer of ideas, so when discussing things of a technical nature it pays to adhere to those terms.And since OHV Hondas have entered the conversation Im wondering if Ferrari, BMW and Honda have ever made a pushrod engine?They are generaly regarded as the three best engine builders in the world, proven by thier F1 success. (Note, Im excluding low production manufactors like Cosworth, as they normaly start with a mass produced engine design).
I believe alot of companies are running with the concept at the moment I know for sure gm is working on it and plans to have some engines using it in the not to distant future how ever it will require going to a higher voltage electrical systems for sure to supply the soliniods that will be used to open the valvesassuming you use electric solenoids to open the valves. That's not the only option for a 'camless' engine. You can also use lower-power solenoids if you pressure balance the valve, or use a force multiplier of some sort (hydraulic, pneumatic, etc).I say 'blame canada!' What are the advantages and disadvantages, performance wise, of Pushrod engines vs SOHC and DOHC engines? Also what are easier to maintain?valve actuation does not really have much bearing on power output as racing has shown.however, if you need a small engine to make the hp of a large engine, you need to force feed it, OR increase the RPMs. When you increase rpms, xOHC designs allow more consistent valve actuation at higher rpms (chevy 350s run over 9000rpm in nascar so pushrods can move quickly)the problem with xOHC designs is the increased size, noise and rotational moment of the moment.For example, a SOHC 4.6 or 5.4 ford engine, is larger than the IH 444 block diesel.
Kinda interferes with aerodynamic body designs.Plus, take a cam for a V8, has 5 bearings to oil. The same v8, if only a SOHC has 10, if dOHC it has 20. This means increased demand on the oiling system to deliver high pressure oil to the very top of the motor - not an easy feat.
(the most common failure of xOHC motors is in fact damage due to top end oil starvation)Also, OHV motors are usually chain driven for the cam, nice and quiet and reliable - chains RARELY break. XOHC designs use external belts, which break often if not changed often and add a lot of noise.Lastly, you now have cams and pulleys rotating at the outer extremes of the motor, making it a bear to hold still in the engine bay.So, xOHC engines have advantages, but they have disadvantages. Changed often? As in once every 5-7 years?well the average american drives appx 15K miles a year, making each change on average every 4 years, and, the average american trades in his car at appx 58K miles so if the impending large labor bill was one of the reasons why he traded the car, the next buyer has a nice surprise to add to his total.And who ever told you that chains were quieter than belts?My ears.
An oiled chain buried inside the motor is far quieter than a kevlar reinforced rubber belt with cogs no less running on at least 2 pulleys behind a thin plastic cover. Well the average american drives appx 15K miles a year, making each change on average every 4 years, and, the average american trades in his car at appx 58K miles so if the impending large labor bill was one of the reasons why he traded the car, the next buyer has a nice surprise to add to his total.Why change the belt at 60k, when the mfr likely recommends 90k-120k miles, or 7 years (whichever comes sooner)?My ears.
An oiled chain buried inside the motor is far quieter than a kevlar reinforced rubber belt with cogs no less running on at least 2 pulleys behind a thin plastic cover.Well measurements don't support what your ears are telling you, except in very special circumstances (where someone went to a great deal of trouble to make a particularly quiet chain and a noise-attenuating cover to go over it).some info on the subject:'Noisy chain drives can often be replaced directly with quieter timing belts. Within the range of timing belts available, there are also quiet designs that use different tooth profiles to minimise noise. There is also a very new design of belt for applications where noise is critical whichuses a chevron tooth pattern to provide very quiet running. Noise reductions in the range of 6 - 20 dB are often possible using this approach.' 'Even if timing belts are generally considered as silent transmissions, when compared to mechanical chains, nevertheless a large interest is devoted to further enhancement of the vibrational behaviour under operating conditions.' 'Play in a gear or chain style cam drive can cause noise, retarded valve timing and/or ignition timing depending on the engine design and application.
With rubber timing belts, noise is seldom a problem even at high mileages. Valve timing and ignition timing (if it reads off the camshaft) also remain steady because timing belts don’t stretch.'
'The Browning HPT synchronous drive line from Emerson EPT combines the timing action of gears with the speed and noise level of belts. Why change the belt at 60k, when the mfr likely recommends 90k-120k miles, or 7 years (whichever comes sooner)?Well measurements don't support what your ears are telling you, except in very special circumstances (where someone went to a great deal of trouble to make a particularly quiet chain and a noise-attenuating cover to go over it).some info on the subject:'Noisy chain drives can often be replaced directly with quieter timing belts. Within the range of timing belts available, there are also quiet designs that use different tooth profiles to minimise noise. There is also a very new design of belt for applications where noise is critical whichuses a chevron tooth pattern to provide very quiet running.
Noise reductions in the range of 6 - 20 dB are often possible using this approach.' 'Even if timing belts are generally considered as silent transmissions, when compared to mechanical chains, nevertheless a large interest is devoted to further enhancement of the vibrational behaviour under operating conditions.'
'Play in a gear or chain style cam drive can cause noise, retarded valve timing and/or ignition timing depending on the engine design and application. With rubber timing belts, noise is seldom a problem even at high mileages. Valve timing and ignition timing (if it reads off the camshaft) also remain steady because timing belts don’t stretch.'
'The Browning HPT synchronous drive line from Emerson EPT combines the timing action of gears with the speed and noise level of belts. 'well if we beleive stats, honda and toyota are the most popular cars sold in the USA, and they recommend 60K.so.at any rate it does not matter. A belt needs changed. A chain does not until end of engine life - period.and I notice not one of the links was from an auto manu or testing magazine (like cd, rt, MT, aw, SC, ff, mm &c) who actually measure noise with a meter and report coincidently the same findings I do;-)PS - I defy you to stand outside a GM 3800 and find ANY xOHC engine that makes less noise. I stand on my position.
You are free to argue the minority position as long as you desire. Chains are used in both push rod and OHC engines (BMW and Saab are examples on the latter). Chains tend to make more noise, especially when they become worn.
(basic engineering)Many high revving motorcycles use chains for the cams, but at high performance applications gears are common. This introduces however more noise.The service interval on belts have become a lot better lately, 60k is very low. But the cost of a belt is low and many people can do it theirself if they want (not that much more complex than to change waterpump/generator/servopump/AC belt). Yup honda for 1 and many others recomend timing belt repacement at 60k or 100,000km how ever there are cases when they even break before this time.
On an interferance engine as many ohc's are this results in at least a few bent valves.What recommendations are you guys referring to? I have a Honda service manual in front of me right now, for 1996-2000 Civics, all models, recommending timing belt replacement at 105,000 miles for severe service, excluding where outdoor temps are frequently in excess of 110degF or colder than -20degF, in which case they say 60,000 miles.I notice not one of the links was from an auto manu or testing magazine (like cd, rt, MT, aw, SC, ff, mm &c) who actually measure noise with a meter and report coincidently the same findings I doI notice that you don't have any such findings to show us either. Not that I'd be impressed with NVH results measured by people working for a magazine - these people are english majors first, mechanics second, engineers 'not at all,' remember? NVH measurement is difficult to do right in a proper lab setting, let alone in some backyard dyno.If the GM 3800 is your 'gold standard' of engine refinement, then I know what sort of person I'm speaking to, and that it's pointless to continue this discussion of automotive technology.I leave it to you to pursue an education in automotive design; it's not my job or desire to educate you (nor am I confident that it would be possible).
Yup honda for 1 and many others recomend timing belt repacement at 60k or 100,000km how ever there are cases when they even break before this time. On an interferance engine as many ohc's are this results in at least a few bent valves.90k miles is the recommended timing belt change for every Honda I've seen in the US. And I have never heard of one breaking before 90k unless someone went and screwed with it, the gears or the cover at an earlier point.The difference in size of a push rod and DOHC engine is very small, the increase in performance more than compensate for this.While some manufacturers are getting better at making DOHC heads short, there is a very sizeable difference between your typical V configured engine in cam-in-block vs. Though you are definitely correct that for basically any application the OHC has enough basic airflow advantage to compensate for this. What recommendations are you guys referring to? I have a Honda service manual in front of me right now, for 1996-2000 Civics, all models, recommending timing belt replacement at 105,000 miles for severe service, excluding where outdoor temps are frequently in excess of 110degF or colder than -20degF, in which case they say 60,000 miles.In other words, as I said, Honda recommends a 60K interval.
At least you now admit that. Sidebar: what interval does ANY manufacturer recommend for a chain driven cam? We could not hear you say the word 'None' clearly.Score: xOHC motors have cam driving mechanisms that require inspection, service and replacement on a frequent basis over the life of the car. OHV motors have cam driving mechanisms that require nothing and last the life of motor.
Push Rod Vs Overhead Cam Video
Advantage OHV as originally stated.I notice that you don't have any such findings to show us either. Not that I'd be impressed with NVH results measured by people working for a magazine - these people are english majors first, mechanics second, engineers 'not at all,' remember? NVH measurement is difficult to do right in a proper lab setting, let alone in some backyard dyno.Well, managing editor of C&D Csaba Csere has an engineering degree which is more than you do, and he himself has conducted such tests AND he has an online presence - feel free to contact him and inform him how useless his findings are.
Its not all that hard to measure the noise output from the engine bay at any RPM. Why, I even hear the measuring devices are simple enough be used by high school students such as yourself! Aint modern progress grand?If the GM 3800 is your 'gold standard' of engine refinement,Actually, its the SAE who has named the 3800 from GM 'best', criteria being a number of factors not limited to power output, economy, emissions, reliability, noise, smoothness, service ease, and so forth.
Please note, in the last few years it has supplanted even the SBC. An astute reader will notice a certain 'on topic commonality' between the two motors.then I know what sort of person I'm speaking to,Hmm, forgive but Im not all that confident that you are all that intuitive, or even all that bright.and that it's pointless to continue this discussion of automotive technology.Especially when you are not contributing any.I leave it to you to pursue an education in automotive design;You are so funny mikey.you want me to do what you have not.but suffice to say, I am satisfied with my college education and degrees earned. I think I'll stand pat.however, when you do graduate high school, I highly recommend a college education if you can swing it. Very beneficial.it's not my job or desire to educate you (nor am I confident that it would be possible).Perhaps the most accurate thing you have said to date in all of your posts.we (the reading public) agree, it would not be possible for you to educate myself, or anyone else reading here for that matter.btw - that fact that you do have a chilton book for your car is admirable, many people fly blind. But please tell us you didnt 'rice it out', take if from someone much older and more experienced: it does NOT look cool that way. In other words, as I said, Honda recommends a 60K interval.Sure, in perhaps 5% of cases they recommend an interval that short.
I don't think that's a very strong basis for your assertion that they must be changed frequently.Score: xOHC motors have cam driving mechanisms that require inspection, service and replacement on a frequent basis over the life of the car. OHV motors have cam driving mechanisms that require nothing and last the life of motor.
Advantage OHV as originally stated.These 'frequent' replacements of the timing belt that you keep harping on still amount to a single replacement in the entire life of the vehicle, in the vast majority of cases.Well, managing editor of C&D Csaba Csere has an engineering degree which is more than you do, and he himself has conducted such tests AND he has an online presence - feel free to contact him and inform him how useless his findings are. Its not all that hard to measure the noise output from the engine bay at any RPM.
Why, I even hear the measuring devices are simple enough be used by high school students such as yourself! Aint modern progress grand?How about if you post a link to a site where this guy actually makes the claims that you attribute to him (belts are noisier than chains, in case you forgot what you're talking about). Alternatively, since you insist that he's making these claims, you contact him, then tell us what he says. That's the responsibility of the person making the ridiculous claims (you), not the person who says that something smells (me). You clearly haven't a clue about NVH measurement practice, nor about the equipment required.
Not surprisingly, you have no idea what my credentials are either.Actually, its the SAE who has named the 3800 from GM 'best', criteria being a number of factors not limited to power output, economy, emissions, reliability, noise, smoothness, service ease, and so forth.References? I gather you're not a fan of supporting your blathering with anything credible.You are so funny mikey.you want me to do what you have not.but suffice to say, I am satisfied with my college education and degrees earned.Perhaps you should reassess that level of satisfaction.
I think that my college education and present field of work put me on pretty firm ground here. And I can tell you don't have a clue.I think I'll stand pat.however, when you do graduate high school, I highly recommend a college education if you can swing it. Very beneficial.or so you've heard, right?btw - that fact that you do have a chilton book for your car is admirable, many people fly blind.btw, it's not a chilton book, and it's not for my car. It's a factory service manual for a Honda Civic, which I keep on my desk for the occasional reference or diagram.
It's great for occasional client questions like 'can you give me any examples of a lost-motion device that is used in the valvetrain of a current production engine?' Take if from someone much older and more experiencedYou may be older, but based on your statements thus far, you're clearly not more experienced in the field of automotive design. Chains are used in both push rod and OHC engines (BMW and Saab are examples on the latter). Chains tend to make more noise, especially when they become worn. (basic engineering)Many high revving motorcycles use chains for the cams, but at high performance applications gears are common.
This introduces however more noise.The service interval on belts have become a lot better lately, 60k is very low. But the cost of a belt is low and many people can do it theirself if they want (not that much more complex than to change waterpump/generator/servopump/AC belt).
You have no idea what my credentials are either.Correct, I have no idea what you may be imagining.I think that my college education and present field of work put me on pretty firm ground here. And I can tell you don't have a clue.well, you did open the door.so lets procede with the facts:you dont have a degree in 'automotive design'you dont work for any automobile or motorcycle manufactureryou dont simply design automobiles nor any of the components. Like it or not, those are the fact that you have now exposed. So you have attacked me ad hominem claiming 'expert status' why?You may be older, but based on your statements thus far, you're clearly not more experienced in the field of automotive design.and this exposes more facts.you are not engaged in employment in any matter dealing with anything automotive on a technical level.
If you were, you would not have asked for the reference on the SAEs stance on the 3800, simply because you would have HAD it on your desk (for future reference, when you commit such blunders, especially in an online environment, your credibility is shot forever. Shall we examine the other 713 posts you have made?)Furthermore, you would know who Mr Csere is and have read him quite often.
I am not going to do for you the homework you should have already done.Ps - it is of light humor that we note you have not to date challenged any point in any of my posts on a technical level, merely the timing of suggested timing belt changes (all the while, on a grander level of humor noting that you skirted the issue that they in fact need changed, whereas chains do not, as I originally stated) I believe my correct stance at this point should be (in your vernacular): Bwahahahahahahah. You dont have a degree in 'automotive design'That's correct, my degree is in mechanical engineering.you dont work for any automobile or motorcycle manufacturer. You dont simply design automobiles nor any of the components.That is wrong. In fact, I have been involved in the design of valvetrain hardware for some recent US automobile engines that you are probably very familiar with, and some that you will no doubt become familiar with within a year or two.So you have attacked me ad hominem claiming 'expert status' why?Because you clearly don't know what you're talking about when it comes to the relative noise levels of different timing drive schemes.
You do seem to have plenty of experience with the 'I may not be an expert, but I play one on the internet' routine.you are not engaged in employment in any matter dealing with anything automotive on a technical level. If you were, you would not have asked for the reference on the SAEs stance on the 3800, simply because you would have HAD it on your desk(for future reference, when you commit such blunders, especially in an online environment, your credibility is shot forever. Shall we examine the other 713 posts you have made?)You really don't know what you're talking about.
I am an SAE member (since 1996), and I have several of their publications on my desk currently, mainly dealing with piston and ring lubrication, oil consumption, and recent developments in low-friction coatings. I also read their monthly magazine, Automotive Engineering, and I get the sectional newsletter. I get the idea that you really have no idea what automotive engineers do during the day (work), or what they have on their bookshelves (Roark's formulas for stress and strain, Shigley's Mechanical Engineering Design, and/or Heywood, typically, with a smattering of Timoshenko or Hartog texts as well). Do you have any idea how many papers come out of SAE in a year? I get abstracts from about 20 per month, specific to the areas of design that I'm responsible for. You try reading all that sometime (I usually don't).Furthermore, you would know who Mr Csere is and have read him quite often. I am not going to do for you the homework you should have already done.Yeah, like engineers have time to sit around reading car and driver.
Now you want me to write a letter to him and ask 'some kid on the internet says that timing belts are noisier than timing chains. Should I abandon my several years of experience in the design of timing drive systems and adopt his bizarre and ill-formed viewpoint?'
Ps - it is of light humor that we note you have not to date challenged any point in any of my posts on a technical level, merely the timing of suggested timing belt changes (all the while, on a grander level of humor noting that you skirted the issue that they in fact need changed, whereas chains do not, as I originally stated) I believe my correct stance at this point should be (in your vernacular): BwahahahahahahahWell, since you clearly need things spelled out for you, let me say it plainly. Your statement that chain drives are quieter than belt drives is absolute rubbish. Technically speaking, you don't have a clue. Read some of the articles I linked to above, or go get a real education!(as I, and several of the other people posting to this thread, have done)If you read this thread from the start, you might have noticed that in the fourth paragraph of my first post, I made the following statement: The advantage of a chain is that it lasts longer; belts are quieter, easier to package, and offer better high-rev performance if the drive load requirements aren't too high. I stand by that statement.
I don't need to 'skirt' the subject of timing belt changes. You seem to be intent on misrepresenting the frequency with which they must be performed, which is not entirely surpising, given that you seem to be prone to grandstanding and make-believe.eh, sorta.OHV motors really only need a smidgen of oil to lube the ball/rocker assembly, pushrod end and cool the springs.since the cams in an xOHC motor are held in aluminum, in most cases without benefit of a bearing shell, forming a hydrodynamic wedge is critical - and maintaining same across the cam. On a DOHC V, there are 4 steel cams that can wipe out the aluminum bosses in MINUTES, not miles. In the old days, OHV engine had a simple 'x lbs per y rpm' oil pressure requirement.today, the xOHC motors tend to require much more oil rpessure at much lower rpms to ensure all the cams are oiled at idle.As for your valvetrain comments.you're all wet. Hydraulic cam followers are what EVERY manu has went to. Now note, save geometry, the parts and use of are the same - with a solid setup, you must set the clearance correctly - just having said clearance leads to a LOT of noise (just ask anyone with an older honda;car or bike; or toyota) and it accelerates wear.
With hydraulic lash, the tension on the plunger is measured in inch-lbs, whereas the seat pressure on the valve is measured in ft-lbs. In solid designs, the lobe must whack the follower which deforms the iron or in some cases steel slowly but surely.
In hydraulic designs, the cams are offset ground (in OHV applicatins) to rotate the follower/lifter - wear is negligible. Whereas solid deisgns require readjustment every 15Kish miles due to wear, hydraulic designs last forever. But please note, the loss of oil pressure on either will cause negative results. I have seen cam lobes wiped clean, but the vast majority as any professional will tell you will be incorrectly set solid designs - once the clearance is gone, the cam lobe is ALWAYS against seat pressure, (as opposed to plunger pressure in a hydraulic setup) Do hydraulic lifters collapse? Yep, but it is so rare as to not require mention.Of note is the use of roller followers today, I and many others have taken roller lifters out of 200K mile motors and reused them after inspection on a fresh cam. They just dont wear out.Unfortunately, HLA-equipped pushrod engines (OHV is not an adequate description) typically rely on oil feed through an orifice in the HLA to the pushrod to get lube oil to the over-head area. Oil flow through that orifice is restricted to something in the neighborhood of several grams per minute (say 24gm/min @ 100degC).
Cams in the head often get oil drillings, and a much healthier oil supply. Not all overhead cam engines use aluminum heads (see Deere). Idle lubrication is the primary design factor for the oil pump for almost all engine configurations. Aluminum makes a pretty good journal bearing material.Honda still uses mechanical lash adjustment, with a recommended adjustment frequency of about 60k miles.
Mechanical lash adjustment is also used in a number of high-perf applications, and on a very large number of heavy duty diesels. Wear is definitely not neglible at the cam-follower interface on pushrod engines. Ask a mechanic. Pressure is never measured in ft-lbs (duh).
With a hydraulic lash adjuster, the expansion spring preload is not very large (say 40N or so), but the force that the lash adjuster exerts against the cam & pushrod on the base circle when the engine is running is much higher (say 150N). If you'd like, I can explain to you how a typical HLA works. There are often collase and pump-up issues with HLAs during development, usually they're sorted out by the likes of me before the likes of you get an engine.
A properly adjusted mechanical system will have less force on the cam-follower interface over the base circle than a HLA valvetrain (close to zero).Roller followers are used on both overhead and in-block cam valvetrain configurations (as noted in my MUCH earlier post). :lol::lol::lol::lol::lol::lol::lol::lol:quaddriver do you seriously expect anyone here to take your comments sersiously?Not only are you attacking one of the most knowledgable enginers I know, but you are doing it with no surporting evidence and incorrect use of terminology already clearly defined in this thread.You are of course welcome to give and provide your opinions in the forums, but please stick to topics you know something about, unless your asking questions, and please refrain from flaming other members. It would be a shame to have to ban you before you make a complete fool of yourself. :lol::lol::lol::lol::lol::lol::lol::lol:quaddriver do you seriously expect anyone here to take your comments sersiously?Not only are you attacking one of the most knowledgable enginers I know, but you are doing it with no surporting evidence and incorrect use of terminology already clearly defined in this thread.You are of course welcome to give and provide your opinions in the forums, but please stick to topics you know something about, unless your asking questions, and please refrain from flaming other members. It would be a shame to have to ban you before you make a complete fool of yourself.yes as a matter of fact I do. In my initial post I centered on 3 disadvantages of the xOHC engine.
'Mikey' jumped on one, and only incorrectly. He has obviously pulled a bit of wool over your eyes but I repeat, he has not coherently or accurately challenged any of the facts presented, in fact, in a bizarre form of transferrence, his last post(s) confirm what I said in my first, but he still ignores the third because the one thing I can assure you of, he is not whom he claims to be.Ban if you must, but the attacks have only come from him.
That's correct, my degree is in mechanical engineering.I do not believe that.That is wrong. In fact, I have been involved in the design of valvetrain hardware for some recent US automobile engines that you are probably very familiar with, and some that you will no doubt become familiar with within a year or two.name one. Its put up or shut up time. Since you and you alone have claimed to be THE expert, its time to prove it.Because you clearly don't know what you're talking about when it comes to the relative noise levels of different timing drive schemes.I have already stated that an OHV (which will perfectly suffice for a defn here, only a field mouse would not know what is being discussed) is quieter than any xOHC in same application. If you are sooooo sure of yourself and have done sooo much research, you will simply post sound measurements of the engine bay.
Or are you now claiming that xOHC engines are soooo quiet that the manus use noisier alternators and PS pumps because they can?I am an SAE member (since 1996), and I have several of their publications on my desk currently, mainly dealing with piston and ring lubrication, oil consumption, and recent developments in low-friction coatings. I also read their monthly magazine, Automotive Engineering, and I get the sectional newsletter. I get the idea that you really have no idea what automotive engineers do during the day (work), or what they have on their bookshelves (Roark's formulas for stress and strain, Shigley's Mechanical Engineering Design, and/or Heywood, typically, with a smattering of Timoshenko or Hartog texts as well). Do you have any idea how many papers come out of SAE in a year? I get abstracts from about 20 per month, specific to the areas of design that I'm responsible for. You try reading all that sometime (I usually don't).Again, I do not believe this. Comments you have made here and in other threads do not belie this.I don't need to 'skirt' the subject of timing belt changes.
You seem to be intent on misrepresenting the frequency with which they must be performed,yes you do need to skirt it. As I am saying now for the forth? Time, one needs changed, one does not. I even listed (correctly) which design that is an advantage to and I did not misprepresent the frequency, I.GAVE. the frequency and you later confirmed it. If we assume, as the 'industry' does, that a cars primary and secondary life is 10 years, and if we gather up all the models sold in 10 years (1994-2004) and averaged the timing belt change frequency, who is more correct?
(hint: I would not bet on yourself)Unfortunately, HLA-equipped pushrod engines (OHV is not an adequate description) typically rely on oil feed through an orifice in the HLA to the pushrod to get lube oil to the over-head area.Besides being off topic, so? As I said and you have learned in the last 2 hours, the oil needed in the OHV heads' area is small.Oil flow through that orifice is restricted to something in the neighborhood of several grams per minute (say 24gm/min @ 100degC).No mikey, it is spec'd as a volume.sidebar: I have to ask, because the answer I fear is apparent: you have never actually SEEN any of these systems in component form have you?
Just ask and I will photo any of the components and upload them and explain to YOU how they work. The fact that oil travels up the pushrod is apparent. But how the flow is triggered you got wrong. Way wrong.Cams in the head often get oil drillings, and a much healthier oil supply.I believe I mentioned that the oil system is different. And I beleive I mentioned that the supply requirements are higher.
So you agree with me finally.Not all overhead cam engines use aluminum heads (see Deere).I didnt say they did, in fact I think I used the word 'most'. So aside from clouding the fact that I was, once again, not surprisingly right your point is? Ps - iron on iron cam/boss contact is just as undesirableIdle lubrication is the primary design factor for the oil pump for almost all engine configurations.So? This was not the topic, other than the fact that I and I alone mentioned that xOHC have a greater need at idle than OHV designs and you have agreed with now twice.Aluminum makes a pretty good journal bearing material.Once again I ask not so rhetorically if you have ever seen the component pieces.
I dont believe I mentioned any preference in bearing material (but I would prefer trimetal designs if asked), however, without, as I and I alone mentioned, ANY bearing between the cam and boss, loss of material is catastrophic. Unless of course you think it is a good design to have the cylinder head itself literally eaten away.its not the most bizarre thing I have heard.Honda still uses mechanical lash adjustment, with a recommended adjustment frequency of about 60k miles. Mechanical lash adjustment is also used in a number of high-perf applications, and on a very large number of heavy duty diesels.I didnt say there wasnt, for this other off topic presentation. I did say however that manus have moved away from mechanical systems, which I notice you do not dispute.Wear is definitely not neglible at the cam-follower interface on pushrod engines.
Ask a mechanic.LOL, you get funny, OK, I asked one, myself. What is the wear then mikey? How much have you measured? On engines without oiling problems using hydraulic systems cams usually only need polished and the lifter bottoms reground.
On mechanical systems, the lobes are ALWAYS deformed and the cam itself needs reground, IF it can be saved, often however with a smaller base circle. Again, it is hideously apparent that you have never observed first hand the components.Pressure is never measured in ft-lbs (duh).yes, I should have just said lbs. Well ivy mike they cirtianly didn't teach you any modesty or maturity at university.And they didn't teach you guys when to quit.Ivymike's been posting here for years, dutifully answering engineering questions for the masses and without having to piss on anyone's parade. Now some people are waltzing in and after a few days on the board want to question his integrity, knowledge and honesty without even knowing who he is, what he does or where he's coming from (though some of you have made plenty of INCORRECT assumptions throughout this thread). Quit before I have to close the thread, and learn to be a little more respectful of the guys who regularly help others and just might be able to do the same for you.
If you'd chill out and listen to them. And they didn't teach you guys when to quit.Ivymike's been posting here for years, dutifully answering engineering questions for the masses and without having to piss on anyone's parade. Now some people are waltzing in and after a few days on the board want to question his integrity, knowledge and honesty without even knowing who he is, what he does or where he's coming from (though some of you have made plenty of INCORRECT assumptions throughout this thread). Quit before I have to close the thread, and learn to be a little more respectful of the guys who regularly help others and just might be able to do the same for you. If you'd chill out and listen to them.this is good advice, however, lets be totally honest with history.
I made one post, which as you note was challenged soley on the frequency of timing belt changes. A quick review of the posts shows that HE and he alone attacked. I have made no claims as to expertise - the unchallenged technical facts I post speaks for themselves. I feel no need to slam 'dicks' on the table.
But, he has claimed:In fact, I have been involved in the design of valvetrain hardware for some recent US automobile enginesNow please note, this statement is meant to give weight to his posts, however the statement can be true if he is the guy who sweeps the floors in said engineering building up to and including the project lead. This statement can even mean that he works for a sinterer manufacturing rocker arms. I know 30 or so people in St Marys PA making control arms for GM, does that mean I am gonna ask suspension tuning questions of them??? So yea, since he presented himself as THE expert in the US of A, Im gonna challenge him. In short, his statement was meant to confuse and support a damaged argument, nothing more. Why nothing more specific? I am close friends with design engineers for Powertrain, Motorsports, Shelby as well as people on the joint GM/chrysler design council.
Many people know this from elsewhere and know I will find out a BS-er in a heartbeat. And when I say close friends I dont mean exchanging emails, I mean at my table, on my boat kind of close friends.And texan, with all due respect, read his other posts in other threads, I took a few moments to do so after his first attack. His 'Im smarter than thou' additude is duplicated in each thread he contributes to.
If that is help, then so be it, but my experience has found that people asking for help do not like smart azz answers. Anyways what is the simpler design OHV(Cam in block?) or OHC(Cam in head?)?I'd have to say belts create less noise than chains if we consider there application to an OHC design, and a chain that long would be heavy, we also have to consider the HP of the engine and how much stronger the transfer medium to the cams has to be, which reflects the size and weigh increase.Discuss amongst your selves:)Simpler is a term neither layout lends itself to. Valve actuation is still a complex process, involing many rotating, reciprocating and sometimes heavy componentry (some of which requires VERY close production tolerances and high grade materials). Both have relative complexities in design, though all things considered I believe pushrod actuation through an in-block cam is mechanically simpler (it is after all a later invention). It's certainly more space efficient, but then again block design is significantly more complex, and cylinder head ports are flow compromised (though this could be minimized further than today's designs).Whether or not chains or belts create the most noise isn't of much importance IMO. With either layout there is a combustion event regularly taking place just inches away that produces far more noise than either drive system, but it is also well suppressed with something as simple as a muffler. Chain driving Honda's S2000 motor doesn't seem to create any great underhood noise, and it's actually got a reasonably complex variable cam timing device thrown into this drive system.
On the other hand my belt drive system seems nearly transparent underhood, but both have enclosures that are designed to supress their respective noise generating properties. In other words, it's how well you supress the noise coming off each that will matter to the end consumer, because both can be noisy or nearly silent depending upon how good a job the NVH crew does.Lastly, there's also that intangible difference between noise and sound that will always muddle this argument. For example the quitest exhaust system isn't often the best appreciated, it's the 'quality' of sound that matters more than it's quantity in these types of discussions. I prefer the metallic goings on of a double roller timing chain to a cogged belt drive, but that's just me.
Well ivy mike they cirtianly didn't teach you any modesty or maturity at university.No, you're generally expected to learn that sort of thing on your own. I must not quite be there yet, since I keep letting myself get dragged into these silly 'discussions' on the internet, where 'yeah, well I know a guy who knows an editor at a magazine who once said this, and his cousin knew my grandpa' gives as much weight to a position as 'here are five published documents on the subject, by people who are familiar with the topic.' I certainly get a whole lot more respect around the office than I do around the internet, which I suppose is a great deal more important in the end.and the latest VVT mechanism that I've seen from GM, which is mentioned here , uses a hydraulically actuated vane-type phaser (as opposed to a spline-type phaser) on each cam (OHC). It also uses three separate chains (hydraulically tensioned) to drive the cams.more info.