DOHC vs SOHC

[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...