DOHC vs SOHC

[badkuk]

is one really better than the other? what benefit does having two camshafts working the intake/exhaust valves have?

[ian_rex]

ok, basically DOHC is a lot powerful than SOHC counterpart. this is due to the fact that DOHC has separate camshaft for both intake and exhaust valves. because there is less slippage for the camshaft on DOHC, especially at high RPMs, thus, no power loss.

[badkuk]

ic...napansin ko lang kasi ung mga ford suvs e usually SOHC lang. is it because the larger displacement more than makes up for the slippage?

[ulolin]

mas malakas dohc

[benchph1]

my opinion on this is DOHC engines produce abundant power and torque while returning a not so satisfying fuel mileage...while SOHC engines return a good fuel mileage while producing marginal power and torque ( given that they have both the same displacements)

[empy]

the big advantage of sohc is that it costs less for an automaker to produce.

[ian_rex]

yep. production cost, is considered. SOHC is fairly easy to manufacture and less complicated than DOHC

[ebbfolls]

Both DOHC and SOHC should be the same, all things being equal (same # of valves, same valve actuation, displacement, etc.).

Theoretically, DOHC's should have an inertial disadvantage by reason of the greater moment of inertia resulting from 2 instead of one camshaft/gear. But the difference is very slight because the crankshaft has a 2:1 mechanical advantage over the camshaft. However, since combustion is so much better with a centrally located spark plug (consider Dodge/Chrysler's "Hemi" design), a DOHC will usually be used for engines designed more for Horsepower than Torque. Another reason is with DOHC, there no longer is a need for tappets as the valves are directly acted upon by the cams. Less moving parts, less inertia and inertial loads, the higher the rpm capacity of the engine, the greater the power output. Thus, more powerful engines are usually found with DOHC rather than SOHC, but that's not to say a DOHC setup is more superior to the SOHC design.

There's more to an engine's power characteristics than the valve train, though that may be a crucial part.

[gearspeed]

mas malakas dohc

I agree mas malakas talaga ang DOHC kaya nga nakakapagtaka na napakalakas ng SIR stock pa lang at malaki ang difference when it comes to ps or hp ng DOHC sa SOHC yun nga lang sa honda...

Meron pa ngang OHV nabasa ko dati ito sa car magazine..Ford pa nga yun eh..:D

[empy]

Originally posted by ebbfolls
Both DOHC and SOHC should be the same, all things being equal (same # of valves, same valve actuation, displacement, etc.).

Theoretically, DOHC's should have an inertial disadvantage by reason of the greater moment of inertia resulting from 2 instead of one camshaft/gear. But the difference is very slight because the crankshaft has a 2:1 mechanical advantage over the camshaft. However, since combustion is so much better with a centrally located spark plug (consider Dodge/Chrysler's "Hemi" design), a DOHC will usually be used for engines designed more for Horsepower than Torque. Another reason is with DOHC, there no longer is a need for tappets as the valves are directly acted upon by the cams. Less moving parts, less inertia and inertial loads, the higher the rpm capacity of the engine, the greater the power output. Thus, more powerful engines are usually found with DOHC rather than SOHC, but that's not to say a DOHC setup is more superior to the SOHC design.

There's more to an engine's power characteristics than the valve train, though that may be a crucial part.

good analysis.

in practical terms, DOHC is superior to SOHC because it's easier to design and package a 4 or 5 valve-per-cylinder setup with an intake and an exhaust cam than a single cam doing double duty. this is why people tend to think DOHC > SOHC...because most DOHC engines are 4v/cylinder and SOHC are 2v/cylinder. the advantage really comes from 4v/cyl > 2v/cyl, not the camshaft design.

it's also more practical to have a DOHC engine if you want to do variable valve timing (VVT-i, VTEC, Vanos) because you can dynamically and independently adjust intake and exhaust timing with two cams. so chalk that up as another advantage of DOHC.

[pepengtom]

the advantage really comes from 4v/cyl > 2v/cyl, not the camshaft design.

how come?
e ang DOHC = double overhead cam
SOHC = single overhead cam?
so why not its depending on the 4v/cyl not on the camshaft?

[rukawa]

i have no idea here hehe

[empy]

Originally posted by pepengtom
how come?
e ang DOHC = double overhead cam
SOHC = single overhead cam?
so why not its depending on the 4v/cyl not on the camshaft?

let me rephrase:

1. four valves per cylinder is always better than 2 valves per cylinder because the engine 'breathes' and burns gas more efficiently.

2. most 4 valve per cylinder engines are DOHC because it's easier to design them that way. SOHC engines tend to be 2 valves per cylinder. of course, there are exceptions to both.

3. therefore, people tend to think that DOHC is better than SOHC, when in reality DOHC engines tend to be the better engines because they have two more valves per cylinder - not necessarily because they have another camshaft.

[pajerokid]

DOHCs usually have an advantage because they allow the valves to be positioned at a wider angle than SOHCs ever could. This allows the air to rush into the cylinders faster. More air allows better combustion.

FYI lang, there are DOHCs with 2 valves per cylinder, so i see no relation with double camshafts being associated with 4 valve setups.

[pajerokid]

Prime example of these would be the Toyota engines...

Yung nasa Gen1 RAV4 and Corona na 3SFE, double overhead cams pero narrow angle ("F") = nasa 120+ hp.

A higher performance model, the 3SGE ("G" stands for wide angle in toyota speak) of the same engine manages more or less 180hp. DOHC po pareho yan.

My point here is that DOHC configurations in itself provides only small advantages over SOHC, mainly timing accuracy. But when placed in a wide angle valve config (which cant be done with SOHC afaik), the freer airflow shows you how much more power can be generated given that everything else is the same.

[the_wildthing]

Originally posted by M54 Powered
let me rephrase:

...

2. most 4 valve per cylinder engines are DOHC because it's easier to design them that way. SOHC engines tend to be 2 valves per cylinder. of course, there are exceptions to both.

Tama po ito. DOHC is said to be more practical esp in 4v/cyl. Because if you had just one camshaft, there will be so many cam lobes on a single shaft that'll make it heavy or just too bulky. Here's a good link: http://auto.howstuffworks.com/camshaft4.htm

[pepengtom]

2. most 4 valve per cylinder engines are DOHC because it's easier to design them that way. SOHC engines tend to be 2 valves per cylinder. of course, there are exceptions to both.

ang DOHC ba ay 4v/cyl = 16valve
and ang SOHC, 2v/cyl = 8 valve?

hindi bat 16valve na mga lumalabas ngayon ng SOHC?
e san naman napupunta ung ibang 8 valve?

[the_wildthing]

The way I understand it, the 4G-92 sa Lancer pizza ay SOHC pero 16V. Ang 4A-FE ay DOHC na 16V. So the cam lobes on a 4G-92 are pushing arms that push the valves... Please correct me if I'm wrong. I haven't seen an open a 4G-92.

[pajerokid]

pepengtom, please read all the posts carefully coz all the answers to your questions are there already.

[pepengtom]

e san napupunta ung ibang valves? ndi ko din kasi maintindihan to e...