OHV vs SOHC

[Alexcab7]

Ok what is the difference between these I have been wondering for a while? Thanks.

Alex

[Dominic]

OHV = 1 cam, 2 valves per cyl, pushrods are used.
SOHC = 1 cam per bank, 2 valves per cyl, no pushrods.
DOHC = 2 cams per bank, 4+ valves per cyl, no pushrods.

[ April 07, 2003: Message edited by: Dominic ]</p>

[Dojo2000]

http://auto.howstuffworks.com/camshaft.htm

[F1GT]

<blockquote>quote:</font><hr>Originally posted by Dominic:
OHV = 1 cam, 2 valves per cyl, pushrods are used.
SOHC = 1 cam per bank, 2 valves per cyl, no pushrods.
DOHC = 2 cams per bank, 4+ valves per cyl, no pushrods.

[ April 07, 2003: Message edited by: Dominic ]<hr></blockquote>

Correction:
Single OverHead Cam still has 4 valves per cylinder. In fact, any overhead cam has 4 or 5 valves per cylinder.

OverHead Valve just means there is a single camshaft that controls all the valves in the block of the engine, the camshaft lobes pushes the pushrods to move the rocker arms to move the valves open.

Dual or Single Overhead Cams have the camshafts right above the valves, hence "Over Head" camshafts. Either one(single) or two(dual) camshafts above the bank of cylinders. The lobes of the cams are right above the valves, no pushrod needed.

So, if it's a DOHC V6 there are 4 cams. If it's SOHC V6 there are 2 cams. DOHC I-4, there are 2 cams.....etc...

[navyblue2000]

<blockquote>quote:</font><hr>Originally posted by F1GT:


Correction:
Single OverHead Cam still has 4 valves per cylinder. In fact, any overhead cam has 4 or 5 valves per cylinder.

..<hr></blockquote>


uh oh, you better tell those guys running mustang gt's their cars can't run!! they only have 2v/cyl!!!
[img]tongue.gif[/img]

anyway, yeah, refer to the howstuff works link.

[V6Bob]

The cams don't necessarily have anything to do with the number of valves. OHV is _usually_ 2 valves/cylinder, SOHC is usually 2, and DOHC is usually 4.

But not always.

[F1GT]

<blockquote>quote:</font><hr>Originally posted by navyblue2000:



uh oh, you better tell those guys running mustang gt's their cars can't run!! they only have 2v/cyl!!!
[img]tongue.gif[/img]

anyway, yeah, refer to the howstuff works link.<hr></blockquote>

oh yeah, forgot about Cheapo Ford....

Honda Accord 3.0 SOHC 24 Valve V-6,.,.,.,.,and most other manufacturers has at least 4 valves/cylinder for OHC engines.

[ April 09, 2003: Message edited by: F1GT ]</p>

[David Blalock]

I've never heard of a 4 valve SOHC engine before, how do they do this? I saw where Ferd is making all of it's modular (4.6/5.4) engines into SOHC with 3 valves per cylinder so that they could breath better but wouldn't have the added cost of a DOHC to do 4 valves.
David

[F1GT]

Never heard of a 4Valve/cyl SOHC???

Here are some more:
Acura TL Type S 3.2L SOHC 24 Valve V-6
Chrysler 300M/Intrepid 3.5L SOHC 24 Valve V-6
Dodge Neon 2.0L SOHC 16 Valve I-4

These have 3/cyl:
Benz S500 5.0L SOHC 24 Valve V-8
Chrysler Crossfire 3.2L SOHC 18 Valve V-6

[ April 09, 2003: Message edited by: F1GT ]</p>

[Blizzard96]

Sounds like OHC and DOHC are better than OHV. Are there any advantages we have with our OHV engines?

Also, is there a big difference between a OHC and a DOHC engine.

[unleaded]

it is true that sohc have either 4 or 2 valves/cyl.
Ive seen the setup on ripped apart honda motors and it is actually a very simple setup. I cant really explain it without drawing a picture. there has been a lot of people saying that ohv engines are low tech and ohc are high tech however i dont believe either one is ahead of the other in technology. Ohc and ovehead valve engines have been around for over 40 years, so its not like cutting edge technology. They are both better for different purposes. As far as power goes it is impossible to say either way. They have ohv and ohc engines that produce well over 1k horsepower when modified. One advantage of the dohc engine is the ability to change the valve timing(not all can do it though). Allowing then to run smooth at all rpms.

[Shay]

Since were talking about this. I noticed on www.60degreev6.com that there's a guy who is swapping in a FWD 3.4 DOHC v6 into his 3rd gen camaro(obiviously RWD now). :D DOHC 3.4 Camaro

nice to see someone doing something different

[ April 11, 2003: Message edited by: Shay ]</p>

[V6Bob]

"Sounds like OHC and DOHC are better than OHV. Are there any advantages we have with our OHV engines?"

Not much. Maybe manufacturing cost? A little less maintenance (OHC drive belts/chains).

"Also, is there a big difference between a OHC [SOHC] and a DOHC engine."

Again, not much. The advantage, as you go from OHV (requires pushrods and rocker arms) to SOHC (requires rocker arms or less than ideal valve geometry to eliminate them) to DOHC (cams sit directly on top of valves) is that you take something out of the valve train and have more direct contact from cam to valve. That means the valve operation can be faster and more precise.

It's enough of an advantage that no one building a competition engine would ever use something other than DOHC if the rules permit them. On a street car, it's not that big a deal. Mostly DOHC lets you get more power from the same displacement and possibly a bit better fuel economy.

[pvtschultz]

The advantage that OHC engines have over traditional engines is a reduced amount moving mass in the valve train. It takes high spring loads to prevent valve float at high Rs and since most engines are getting smaller, it is taking higher RPMs to get any power out of them. By reducing the reciprocating mass, the valve springs can be lightened up and will require less power to over come them during operation and the efficiency will improve. DOHC engines typically don't have a lot of low end because of the large flow area around the valves, reducing the intake velocity.

OHC engines are more expensive to produce because of the extra head machining and more cam blanks to turn during munufacturing. That's about all that I know.

[Blizzard96]

Thanks guys...

The future GT is supposed to be a 3 valve per cylinder either OHC or DOHC engine. What would it be...2 intake or 2 exhaust valves?

I know more valves means better flow getting air in and out...that much I know. [img]redface.gif[/img]