Talk:Overhead camshaft

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Removed the following (speculative and subjective without references):

"This arrangement is less complex, usually has fewer parts and requires less engine power to operate. It relies on a timing belt or chain to drive the cam(s), and allows for greater valvetrain flexibility."

Discuss? CJ DUB 16:34, 8 May 2006 (UTC)

When compared directly between two valve cam in block engines (OHV) and two valve overhead cam (OHC) engines the OHC system will be less complex. An OHC system only requires a drive system such as a belt, chain, or gear drive, a cam shaft and some type of cam follower. An OHV system requires all of the components of the OHC system but would also require the addition of pushrods and tappets. The same can also be said for four valve OHV systems compared to four valve OHC systems. In engines with more than one bank of cylinders the OHC system becomes slightly more complex but still requires fewer parts. An edit was made to include those instances. IJB TA

  • Not good enough I'm afraid. You know the pushrod page says exactly the same thing? I would say for sure OHC is more flexible, for VVT and multivalves, even intake geometry, but "less parts" is pure speculation. Even the section about higher engine speeds; speculation and hearsay. Some modern pushrods in cars can spin up to 8000 rpm. In race applications they can reach 10,000 rpm. I'm gonna edit the pushrod page too. CJ DUB 16:02, 11 May 2006 (UTC)

I have not read through the pushrod page but if it is written by the same person it is also very likely wrong. I understand the capabilities of pushrod engines but the maximum speed of the engine does nothing to determine the number of parts in the valve system. If you want to argue the engine speed capabilities consider that the rotational speeds of an OHC F1 engine approach 20,000 rpm. If you consider what I have said to be speculation then you are clearly not qualified to edit these pages. IJB TA

  • Nice. This is a discussion not a dictatorship. "I heard of engine that does 20,00 rpm, if you haven't heard of that then you shouldn't be editing." Gimme a freaking break. Anything is open to discussion. You haven't presented one single reference yet. There are several facts in the list of the abilities of the OHC that are speculation, but not ALL. My biggest issue is the less parts and the less engine power statement. You said it yourself, it's more complex=more parts. Maybe OHC does spin faster. But thinking of these things in your head and quoting some F1 number does not make a strong argument. Cite it. If you can't cite then you shouldn't be editing. 8-) My opinion is that you should discuss the advanteges and disadvantages of OHC like is done in pushrod engine. CJ DUB 13:36, 12 May 2006 (UTC)

This article is NOT a discussion. I am listing fact only. Do the research yourself, I will not be teaching you things you should already know if you are going to be editing these articles. Concerning the number of RECIPROCATING parts, just look at any OHC engine and OHV engine and count the number of major reciprocating parts. As far as references, here are some links I happen to have already. I am getting a second opinion on the "less power to operate" subject, I did not include that statement in my last edit. http://www.hondaracingf1.com/loband/car_engine.php - Most if not all F1 teams have engines that rev to the 18,0000 rpm to 19,0000+ rpm range. http://www.exvitermini.com/r33specs.htm - Here is a Skyline GTR that can rev to 13,000+ rpm. Just about all OHC Super Sport motorcycles will rev to 12,000+ rpm. IJB TA

  • K, I'm gonna try this one more time. THIS is the DISCUSSION relating to the CONTENT of the ARTICLE. I can discuss whatever I choose. You'll also note I haven't done any changes without consulting. I kept the edit on the discussion page. for future. When we come to a decision about something, then we change the article. Hopefully with more than 2 of us. I removed the material that was unreferenced staright away, however. You, on the other hand don't even have a frigging login other than your IP address. Now lets see some references for more power & less parts. Also, you may want to think about reading the pushrod page as there are good arguments for OHC on there. CJ DUB 22:59, 12 May 2006 (UTC)

There is nothing to discuss, these are the facts and nothing more. I am not responsible for your ignorance on this subject, it is your responsibility to make sure YOUR facts are correct. If you question the facts that I have given then it is your responsibility to do the research to determine the validity of the statements I have made. THIS IS NOT AN OPINION PAGE, so keep them to yourself. Also this site does not require me to register, that is my choice. Lastly I am not going to dig up every book I have ever read just because one person has an OPINION about this subject. Like I said before, do the research yourself, I have done mine. IJB TA

I have not said "more power" anywhere in this article, this is the last time I will say that. The cam-in-block page does not have any credible reference either, how can you say with any certainty that it is correct? IJB TA

  • Haha. All you have to do is read it and realize it was written by somebody with automotive experience and first hand technical knowledge. We need somebody like that to read this page and decide. This page was written by somebody who read something on OHC, once, basically. I suspect that neither you nor I are qualified to provide definative answers on the properties of OHC.

Contents

[edit] Poor engineering on display.

Several obvious faults in this article, and I don't know where to start correcting them.

  • OHC is not more complex than OHV, quite the reverse. It's "relative fragility" comes about because of the difficulty of keeping it lubricated, nothing to do with number of parts.
  • Article refers to "I-Head" engine instead of OHV - it's near enough impossible to find "I-head" elsewhere in the encyclopaedia, the article diverts to OHV. (Though it also appears under "Cam-in-Block"). It's use seems intended to confuse.
  • No mention needs to be made of there being two SOHC or 4 DOHC in a V8, it's plain confusing to readers.
  • I'm surprised to learn it was Fiat who first rushed into DOHC engines. Even if true, it's unencyclopaedic. TomRawlinson 15:21, 5 May 2007 (UTC)
Re:"obvious faults"
  • The drive system for an OHC valvetrain is more complex, the rest is less complex.
  • I'm not really sure what to do about the whole I-head/pushrod/OHV thing. Every piece of material I have ever read on the subject has named the pushrod engine as an I-head, no one seems to call it that anymore. Then some people seem to not want to call it a pushrod engine while others don't want it to be called an OHV engine. When I find the time I'm just going change it all to I-head and see what happens.
  • I will simplify the explanation of the number of cams.
  • The mention of the first production DOHC systems seems plenty encyclopedic to me, it is in the history section. IJB TA 07:31, 15 May 2007 (UTC)

[edit] Limitations

I noticed all the "limitations" listed under the pushrod article, but that section wasn't listed. There really are no limitations? I always figured more complexity would render a better chance for wear and tear, at least I always thought cams wore down over time. Huh, guess I was wrong, there isn't such a thing as "cam wear". Oh well. Zchris87v 15:37, 29 May 2007 (UTC)

Oh, I almost forgot - don't OHC engines require higher RPMs to produce optimal power? This is at comparison with an OHV, obviously, because they produce optimal power at lower RPMs. Keep reading...
These pages [1] at fueleconomy.gov compare two cars - one mine, one belonging to a friend of mine. Mine is an automatic 1992 Chevy S-10 Blazer, his is a 5-speed 1999 VW Jetta. Mine's producing just over 200 HP (195 stock), and his 115. Engines are, respectively, a pushrod 4.3L Central Port Injected (injects fuel to each cylinder all the time, not efficient), and a 2.0L overhead cam engine (standard injection I assume). So, that's a difference of 2.3L on the engine size. Now, stock gas mileages have his car getting 21 MPG in the city and 28 on the highway, whereas mine is listed as 14 city and 20 highway. Now my only argument is that these numbers aren't 100% accurate for the style of driver or anything. I'll give you that his Jetta is more efficient, but for having over half the engine size and 80 HP less, it probably wouldn't move anything remotely the size of what I drive. For him to realistically drive, he has to shift much higher than normal, whereas my engine shifts at 2000-2500 RPM. His is about 3500-4000 to drive in traffic. On the highway, I can cruise at 60 MPH and be sitting around 1250-1500 RPM, and his is a good bit higher, high 2000's to around 3000. Now at 45 I'm resting comfortably at 1000RPM, where he doesn't like to let his engine get below 2500RPM in any gear. Why? The engine bogs down and won't power it below that. But I can still manage to drive the same stretch of interstate and manage a decent 20-something MPG (with an air intake system I made) and he gets somewhere around the stock estimate.
I don't know how you can compare this all, but all I really mean by it is that there ARE limitations to the OHC engine. Great, the engine can have a high redline, but the peak HP/TQ is at a high RPM. So to drive around in a vehicle with this engine would require a higher RPM to cruise, correct? That's all I'm trying to say, these things aren't absolutely flawless. In fact, don't most of the vehicles on this [2] list use OHC engines? And as far as reliability is concerned, my engine's at 210,000 miles and it hasn't had any valve adjustment or anything. In fact, just semi-regular oil changes and that's it. I know Hondas can see some high mileage, but most that I've seen need valve adjustments at least. Even so, you can't dismiss the venerable Chevy 350 as being "crap" by any means, it's a true testament to the pushrod engine. Zchris87v 15:37, 29 May 2007 (UTC)

OHC engines are less complex, they almost always have fewer moving parts. OHC engines do not have to run at higher rpm to produce optimal power, but most are tuned to produce peak power at a high rpm. There are plenty of OHC engines that produce more power at lower rpm than many pushrod engines. Cam lobe wear? From what? Pushrod engines have greater loads on the cam lobes due to the much greater mass of the valvetrain. I drive an OHC vehicle and the engine very rarely exceeds 2500-3000 rpm under normal driving. Comparing two vehicles simply does not provide nearly enough information to back up what you are implying. Please read the discussion here. IJB TA 21:35, 1 June 2007 (UTC)

[edit] twin cam and dohc

is there any difference at all between twin cam and DOHC engine configurations? or are those merely two different names for the exact same thing? —Preceding unsigned comment added by Cirilobeto (talk • contribs) 15:14, 3 April 2008 (UTC)

Yes there can be difference, twin cam doesnt tell where the camshafts are and dohc tells they are overhead. --— Typ932T | C  15:23, 3 April 2008 (UTC)
Ok, so location could be different. how about the cam themselves? is there any difference in them as to size, valve opening or anything like that? Cirilobeto (talk) 17:12, 3 April 2008 (UTC)

[edit] Honda CRX picture

Please pardon my ignorance, but isn`t that picture claiming to show an SOHC head really a DOHC? Aren´t there two cams visible? If I am mistaken, please correct me. --328cia (talk) 18:27, 15 April 2008 (UTC)

No, the photo is in fact of a 12 valve SOHC head. The 2 shafts which you are mistaking for camshafts are rocker shafts. The camshaft is connected to the centre of the cam sprocket, and is obscured and not visible in the photo. Also notice there is only a single cam sprocket, meaning there is only a single cam.219.90.153.215 (talk) 10:46, 23 April 2008 (UTC)