Can someone explain the difference between single overhead cam and dual overhead cams to me? I'm not just talking about the fact that there is one cam in sohc and 2 in dohc. How is dohc better? What differences are there other than the number of cams? Thanks.

 

dohc one cam runs the intake and one runs the exhaust with sohc one cam does it all. not sure one is superior over the other, 2 cams makes timing drive and setting it a lot harder.

 

because they say that with 4 valves you can get more air flow


whatever..................unless your going to give me a ZR1's LT5, i'll keep my OHV thank you

 

2 cams allow more precise valve timing which leads to better breathing. DOHC design also allows more valves per cylinder. More air in+more air out=more power. I'm a tech at a Saturn dealer and Saturn offers the S-Series in either SOHC or DOHC design on the same 1.9 liter engine. Go to a Saturn dealer and test drive both. You will easliy feel a difference. SOHC hp is 100. DOHC hp is 124. The only difference is 1 or 2 cams, everything else is the same.

 

the early 90's z24 lumina has 4 cams...i guess thats the DOHC then right?

 

Ya, its the number of cams per head.

 

So, lemme get this straight...

Two camshafts for 124 HP is BETTER than one camshaft and 850 HP, right? O.K. What did I miss? I'll have to make a note of that the next time I'm shopping for a... (ready for this?) ...SATURN! :sillylol:

(Sorry, but I just HAD to...))

 

Sorry to put my clueless nose in here, but let me try & post something to discuss...

Okay, here's what the reasoning behind this is (my stupid self thinks):

Europeans and Asians are stuck with super-expensive gasoline (~$4/gallon in Croatia, where gasoline is the cheapest in Europe). These countries don't have nearly as much power over the oil-delivering countries as USA does, so they can't force the prices down by much more.

Besides, people in Europe earn, at best, half as much as Americans do, so every mile per gallon counts...Just imagine paying $8/gallon (I calculated the living standard differences in) and you'll see what I mean. Croatia, where I used to live permanently, has 1/8th of U.S. living standard...

Thus, traditionally, Europe went with small displacement engines trying then to maximize the efficiency of the combustion process to win back some of those horsies that wandered away because of reduction in volume. Later, EFI came in and things changed significantly in both OHV and SOHC/DOHC area regarding consumption, etc...Still, OHC designs often win in high-performance area when you talk about fuel consumption. However, who cares about mileage when you are talking about high-performance.....I don't know, some do, especially when you get into that shady area of family-sportsy cars like most BMW and Mercedes cars are..

Little rice engines, as well as little Italian and French engines, compensate for their lack in volume by increasing RPMs... Approximately:
HP(current_torque,current_RPM) = current_torque*current_RPM

... Low volume engines produce puny torque altogether, so they have to rev really high to produce the horsepower they later bravely advertise... The truth is, for example, unless you rev your 2nd gen Integra really high you are going to see only a very very small fraction of the advertised # of ponies...

Example:
A 1.4L OHV engine would, I think, just be funny....funny, funny, funny...
It's tricky to try and make OHV engines endure high RPMs and even trickier putting the valves at an optimal angle for the max. airflow...I think, and don't trust me much on this because I couldn't tell a camshaft from a crankshaft half a year ago. Such an engine would have crappy airflow and couldn't even rev high enough---you would barely push such a car... I think some 50 HP is what you could get out of it -- tops...
OverHead Cams have no rocker arms, and no pushrods....hint: very very light. Can fly at high RPMs...As the name implies, the cam is pretty much over the head..

Dual OverHead Cam designs are made I GUESS because the intake and exhaust valves are angled in such a way (I guess) that they would be hard to physically reach with other setups... Again, lightness reigns here, as well as the ability to go to insanely high RPMs...

Besides, some claim that SOHC and especially DOHC allow for superior timing, i.e. the mechanical error whilst opening/closing at high RPMs is drastically smaller...

As everyone knows, more efficient burn = more ponies...

Example.. A 5.0L TBI Camaro like mine achieves 170HP stock..
It is a very simple OHV design which brings tons of advantages I very well know because I happen to have one of those -- one of them being it's very easy to work on and it's very easy to squeeze more power out of it if you want to...

A 1.8L Fiat Tipo, which has been around for almost as much as the setup above achieves 130 HP. How? It's N/A, but it's DOHC and has 4 valves per cylinder.

Keep in mind that this is peak horsepower and is achieved at something like 7000 RPM and if you think ricers are loud and annoying, you should hear these cars, the engine sounds like it's going to explode any moment..you have to have a very powerful stereo not to get inhibited by the sound and lift your foot off the pedal

So, while mileage is not something you would prefer one car over the other in U.S., in Europe, it is often the main reason why you bought, say, an Opel instead of an Alfa Romeo, which, although DOHC, spends more than my Camaro with its 1.8L super-agressively tuned engine..

I know 1.8L and super-agressive shouldn't be in the same sentence, but from the perspective of a tuner, some of these cars had pretty much everything done to them there is to be done..

This should have been a shorter post, sorry guys, but here's a short summary:

SOHC/DOHC = trickier, but sustain much higher revs and have significantly better airflow. Probably more expensive, more prone to eventual malfunction (interference designs are common..cam chain gets messed up and a valve rams into a piston.. bye-bye valvetrain... many cars need a preventative chain replacement every 30000 miles)

OHV = simpler, cheaper, can't sustain high revs, imprecise. robust, hard to mess up. goofy valve positioning...

My opinion is that Europeans and Asians sometimes force the OHC designs simply because they have little experience in the OHV department...

Does this make any sense?

What TICKLES my imagination is how a 305cid DOHC engine would perform like... Imagine revving your Camaro to 8000 RPM like it's a *****

Maybe it would perform like a V10 DOHC Bugatti which whoops some 650HP N/A..

Comments welcome, especially from 10x more knowledgable people like Vader & co...

 

Doesnt one of the saleen mustangs come with a V8 that has OHC ?? I remember seeing it in car and driver or something, the numbers didnt seem all that much more than the regular one.

 

The difference is I wouldnt own either!

 

ford v8s are now all ohc except maybe the diesel.

marin: it's funny you mention a 1.4 liter ohv engine. i race a 1969 triumph spitfire with an 1147 cc motor (that's about 1.2 liters after we bore it). spitfire motors are ohv and I rev ours to 8000-8500 rpms. you're right about trying to make one live, there's just a whole lot of valvetrain to screw up compared to ohc. Nascar motors are small block chevys, fords, and chryslers and they hang at 9000 plus rpms for 5 or 600 miles, amazing.

ohv motors usually make more lowend torque than a dohc and i think this is due to one large valve opening up on the ohv versus two small valves opening up on the dohc. sort of like opening a floodgate.

 

Hm, yeah, 4.6L SOHC V-8 = 235 hp.. 4.6L DOHC V-8 = 300 HP..
20% difference...I wonder if it was worth it..

OTOH, I just browsed for Ford DOHC engines and came upon:

http://members.tripod.com/lyc_42/fordv8/foyt/foyt.htm

It's a DOHC, producing 825 HP at 9600 RPM (!!!!) It's just funny...
I still wonder if it's justifiable...

 

Oops, sorry Tom, you replied while I was sending out a reply to PonyKiller....
9000 rpms in an OHV engine..makes me dizzy... I wonder how they do it...

I think, oh wow, that must be some expensive valvetrain, but on the other hand when you see what kind of barely justifiable extremes rest-of-the-world designers go into today, it's hard for me to say that there is a better alternative.

Your explanation of torque difference between an OHV and DOHC makes perfect sense...and matches my personal experience

I can just imagine the cost of producing a 1.8 twin-spark (2 sparkplugs per cyl.) Alfa Romeo engine.. or putting super-volatile Turbos that provide a barely noticable boost (Volvo, Maserati, etc.) or a boost that makes a difference between a useless and a sort-of usable or nervous engine (Audi, Lancia Delta)

With SFI, I don't think there's mileage problems anymore... however that level of sophistication --- OBD2 computers, tons of sensors, many of them useless is where hotrodding stops for me and consumer-driven engineering begins....

So I guess your example proves the point that today there is no significant advantage of any of the designs if price of the engine is a concern... otherwise I guess something like a 32V DOHC Northstar design would win? or a 16V SOHC if you want more low-end power? or a VTEC (?) Ah... can't make up my mind about these..

 

just to add one thing....

ohv engines are generally much more durable than ohc engines.

i can't stand the timing belts on ohc engines, you have to replace them about 100,000 miles....and it is one of the worst pains you'll ever go through. it wouldnt be so bad if the belts werent covered completly by about 1,000 different things. but if you dont change them....then bye-bye pistons....

 

In reference to needing to change the timing belt, I remember a brief description of a guy who had a porsche, and let the belt changing go by it's interval.

the belt broke, the cam stopped, piston smacked valves that were hanging down.

the guy ended payin $4000 or so in repairs, oh yeah, and 1 $32.20 belt.

EDIT--- If only I could type....

 

btw, the DOHC ford also has a better cam profile, better intake manifold, and better exhaust...im not saying that DOHC isnt better. but those factors make up for alot of the difference.

 

cool ol german engineering, effiecent as hell, but *** help you when it breaks.

My buddies got a 944, he has 220,000 miles on it. Does the timing belt every 6 months. He let the clutch go and it wrecked the tranny, which wrecked the diff, which cost him 3k, as its all one unit.

 

RJR99, robert -- yes, exactly as I mentioned in that excruciatingly long post the timing chain actually needs preventative replacement every 30000 miles in most cars...

Designs like 1984 Volvo's 2.3L SOHC won't collapse if the timing chain breaks because their design is non-interference, i.e. when the piston is at TDC and the valve is all the way open there is still about 1mm gap between them...

However, most of designs are interference... If you open the hood of a Honda Civic (for some strange strange reason ), you might see a label with a warning that this is an interference design engine, the same thing shows up in their owner's manuals....

I wouldn't put "german efficiency" and Porsche in the same sentence... I'd say Porsche has many strange solutions and I haven't yet heard from any person who owned it who didn't need almost constant repairs.. After a certain time period almost everything starts to go I heard of blown heads after only 6 months of driving, cracked piston rings, broken tranny, broken diffs, cooling system leaks, etc. etc. Wouldn't touch it unless if it were someone elses

If you want to see efficient german engines, check out BMW series 3 and series 5 engines... nothing to complain about there...(or is it?)

 

Marin,

You've obviously done some research, and bring some good information to the forum. Personally, I'm glad you're here and out of Croatia. It can't very comfortable over there right now.

One thing to remember about peak RPM capability, however, is that it is less dependent on the valve train design and more dependent on stroke length and balance. Chevy used to offer a 302 CID V-8 with a single camshaft and pushrods that would turn 7,600 RPM from the factory, and make plenty of power in the process - in the neighborhood of 400 HP if tweaked. With a little balancing and valve train work, 8,500 RPM was a safe red line.

The 209 CID Chevy Indy V-8 would turn at 12,000 RPM and make over 900HP at that speed. As you mentioned, there are some details that need special attention to be able to achieve that RPM and hold together.

And NASCAR crews are limited to 358 cubes, and have to breathe through four 7/8" diameter holes (restrictor plate) but still manage to turn their single cam, pushrod engines to 8,500 RPM for hours on end while making 800 HP.

- - - - - - - - - - - - - - - - - - - - - - - -

On German Engineering

First, anyone who has had to work with German products outside the automotive industry will already understand that the "superior" German engineering is simply a myth, likely a result of an American advertising campaign for cars. I'll cite the Siemens group as my proof, but could provide numerous other examples.

The biggest difference between German "engineering" and North American designs is not even really in the engineering. It's more in the attention to details abroad, versus the mass-produced mediocrity of North American engines.

Restricted by fuel prices and with severe displacement taxes, the Germans MUST squeeze everything they can get from a small engine. You typically won't find large chunks of extra cast iron in German engine ports, or factory balanced rods that are not within 25 grams, mismatch in the openings, etc. North Americans can build to "middle-of-the-road" tolerances and bolt things together without worry over displacement. The efficiency is typically made with the control of the fuel systems and ingnitions. Ports and castings can be sloppy, balance can be mrginal, components can be oversized and too heavy for high RPM. Engines here aren't built to run on the ragged edge all the time just to make acceptable power, unlike their counterparts from abroad.

The moderate loads for a given displacement and heavy components are what make North American designs more durable. That is also why a lot more power can be squeezed out of an American V-8 than a German V-8. The Germans left very little to play with, while almost any of us with a good reference book can double the output of a Chevy, Ford, or Dodge V-8 over the factory ratings. All we have to do is pay more attention to the details than the factory mass-production standards would allow. Try getting 1,400 HP from a BMW or Daimler V-8 (or Toyota, for that matter) and you'll be left scrathcing your head. With a larger North American/Australian V-8, all one has to do is the same things the Germans have done to their little engines, and enjoy the power. There's a guy named "Lingenfelter" that has drawn a roadmap to power and reliability, following in the footsteps of Smokey, Kiekhaffer, and many others. It really isn't that difficult.

The last time the Germans' piston engine engineering was really put to the test was WWII. The Daimler-Benz inlines that powered the Me's and Bf's weren't even equal to the rather tame Packard/Allison V-16 in the P-51s, and the British Rolls-Royce Merlins were just plain massive overkill. Most commercial jets of today still can't outrun a P-51/Merlin that is stripped for speed instead of strafing. The Republic P-47s, British Hawker Typhoons/Tempests, and Australian Sea Fury (no joke - the Aussie engine actually rotated backward, opposite the normal rotation) just thoroughly outclass anything the "premier" German engineering could dcliver.

Dig in to their cars (like the Posches as cited above) and you'll find that they really aren't "all that"... I'll hang onto my "fat, slow, American V-8 cars" for now, thanks. When the Beat My Weenie sets a land speed record, I'll be a little more attentive, thanks.

Oh, yeah - one more thing. It's that same kind of North American MUSCLE that is the primary reason we are paying 1/3 the price for fuel, even with our ridiculous fuel taxes. That is just as Marin stated.

 

No surprise there, since their toilets flush in an opposite rotation compared to ours. Must be something to do with the earth rotation and hemishpere location.....

 

The latest 4.6 SOHC Ford engine puts out a bit more than 235 in stock form, more like 265. Apples to apples.

 

my grandpa has one of those "dz 302's" and that things runs like a raped ape on steroids..it still amazes me how he can turn that thing to 8 grand...and he has it tweaked a little its a little over 425 horse....

and about the nascar motors...they only use the restrictor plate at talledega and daytona..if they didnt the car would run 220mph+ so they use the 7/8 plate to limit the motors to about 450 horse...on all the other tracks there isnt a plate so without the plate a good motor lik a rick hendrick motor (jeff gordon) or richard childress (kevin harvick) theyll make 800+ horse and at tracks like atlanta michigan et they hang 9000 rpm's for 500 miles...now with this years one engine rule they have to use the same motor for practice qualifying practice happy hour and the race so in a weekend there puttin 800 miles on one of um...thats a stout peice....
when you guys get a chance go to www.musclemotorsports.com
its a page were u can buy winston cup parts..

im very much into nascar and i can tell you everything anyone wants to know about this =))

 

Vader, thanks for all the input dude, I was wondering if you are going to post here..

You may remember my first post on thirdgen in February when my injectors got clogged and at that time I was really really clueless about engines and cars

Actually, I happen to be in Croatia right now, I come over here every summer, mostly because of beatiful nature (read: women), sun, sea and all that..typical mediterannean stuff and I'm trying to enjoy it before it gets swamped with hundreds of thousands of tourists.. You must have reffered to war that was going on until some 5 years ago..Unfortunately, I was 'lucky' enough to be in Croatia during the whole 7 years of war.. but you're right, going abroad was definitely an eye opener in every sort of way and I sure got comfy in Chicago.

Anyway, I am going to use that post of yours in my arguments over American vs. ROTW, it's crystal clear what's up. Not to mention that Japan limits its production cars to 280 bhp..heh..heh.. but they are a whole different story.

Obviously I still have vast amounts to learn, and I was wondering if you could elaborate some more on how stroke length affects peak RPM and what kind of balance needs most attention (balancing the crank??)..

 

madmax: the newest SOHC must've finally gotten the improvements in cam, intake & exhaust that the DOHC got according to cobrakiller's post... from which it follows that DOHC really doesn't pay (at least in this case) considering how much more expensive it is to maintain, etc.

 

Started in 99, with PI heads, intake and different cams. I think they squeezed out another 5 last year with exhaust changes. There have been some bumps over the years, the 96 was overrated at a pathetic 215 (it was probably more like 180-190) and its been going up since then. The DOHC motors seem to make a fair amount more power when boosted though.