Why are we going back to SOHC?

Why are we going back to SOHC?

Author
Discussion

hedges88

Original Poster:

639 posts

144 months

Monday 12th September 2016
quotequote all
Why after so many years of thinking that DOHC is "better" than SOHC, why are we going back to it?

I was told that in the case of the VAG 1.2 Turbo it was simply to reduce internal friction, weight and complexity

Was having a look at some new turbocharged motors the other day from various manufacturers and some are SOHC which surprised me

I might be answering my own question but I wanted other opinions, is it simply that the operating range of turbochargers means that DOHC designs with higher rev limits are now deemed unnecessary?

I kind of thought that efficiency and emissions being at the top of the tables when designing a new motor would still be better to go with DOHC

Have the engineers really reached a stage where they are seeing significant gains from reducing engine resistance and weight?

stevieturbo

17,229 posts

246 months

Monday 12th September 2016
quotequote all
Probably cheaper and if using various rocker arrangements etc....could well allow engines to be physically smaller so they can cram them into smaller spaces to make maintenance an even bigger ballache than it already is

Although a manufacturer claiming they're trying to reduce complexity when you see some of the massively over-complicated bundles of st they produce...is hard to believe.

Penelope Stopit

11,209 posts

108 months

Monday 12th September 2016
quotequote all
stevieturbo said:
Probably cheaper and if using various rocker arrangements etc....could well allow engines to be physically smaller so they can cram them into smaller spaces to make maintenance an even bigger ballache than it already is

Although a manufacturer claiming they're trying to reduce complexity when you see some of the massively over-complicated bundles of st they produce...is hard to believe.
Nice one, very nice

V40Vinnie

863 posts

118 months

Monday 12th September 2016
quotequote all
might be a motoring myth but aren't SOHC engine meant to be a bit more torquey at low revs therefore it could make a better city car?

stevieturbo

17,229 posts

246 months

Monday 12th September 2016
quotequote all
V40Vinnie said:
might be a motoring myth but aren't SOHC engine meant to be a bit more torquey at low revs therefore it could make a better city car?
No, you're referring to older 2v per cylinder engines.

That isnt the same as SOHC.

Although with the odd fascination many car makers have with variable valve timing, I cant see that SOHC is an easy way to achieve that, unless they've found some other way of manipulating valve timing over adjusting the cam position.

stevesingo

4,848 posts

221 months

Monday 12th September 2016
quotequote all
hedges88 said:
Why after so many years of thinking that DOHC is "better" than SOHC, why are we going back to it?

I was told that in the case of the VAG 1.2 Turbo it was simply to reduce internal friction, weight and complexity

Was having a look at some new turbocharged motors the other day from various manufacturers and some are SOHC which surprised me

I might be answering my own question but I wanted other opinions, is it simply that the operating range of turbochargers means that DOHC designs with higher rev limits are now deemed unnecessary?

I kind of thought that efficiency and emissions being at the top of the tables when designing a new motor would still be better to go with DOHC

Have the engineers really reached a stage where they are seeing significant gains from reducing engine resistance and weight?
Can you provide examples of these latest SOHC engines, I'd be interested to do some reading.

Inline__engine

195 posts

135 months

Tuesday 13th September 2016
quotequote all
i doubt its going to be a trend that catches on. its hard to have variable valve timing with a sohc while being able to vary inlet and exhaust independantly

annodomini2

6,860 posts

250 months

Tuesday 13th September 2016
quotequote all
Inline__engine said:
i doubt its going to be a trend that catches on. its hard to have variable valve timing with a sohc while being able to vary inlet and exhaust independantly
Variable timing and lift benefits NA engines much more than turbocharged, which much of the current crop are sporting.

It will be for a combination of cost, weight and mechanical drag. In that order.

Due to the ever stringent emissions regulations, the cost of the systems to meet these new regulations is ever increasing. They have to scrape some cost back somewhere.

CrutyRammers

13,735 posts

197 months

Tuesday 13th September 2016
quotequote all
stevieturbo said:
V40Vinnie said:
might be a motoring myth but aren't SOHC engine meant to be a bit more torquey at low revs therefore it could make a better city car?
No, you're referring to older 2v per cylinder engines.

That isnt the same as SOHC.
...And I've never actually seen an example where there was a 2v and 4v version of the engine, and the 2v made more torque. Made peak torque at lower revs, yes, but not more torque. Seems to have been one of those "bloke down the pub things" as a way of justifying having an older, less powerful engine wink

I guess SOHC with a variable rocker system like the fiat multiair or similar might have some friction and cost advantages, if you can package it all. I suppose also with the move to turbo engines, high revs are less important so the flexing of rockers and pushrods and things become less of an issue?

Kitchski

6,514 posts

230 months

Tuesday 13th September 2016
quotequote all
V40Vinnie said:
might be a motoring myth but aren't SOHC engine meant to be a bit more torquey at low revs therefore it could make a better city car?
They weren't 'more' torquey, that was the common misconception. What torque they did produce was lower down in the rev range though, compared with the DOHC multivalve stuff.

It was a common battle cry of the Golf mk2 GTI 8v driver who couldn't find that extra £1500 to afford the 16v hehe

But as matey said, SOHC doesn't mean only 2 valves per cylinder. Honda and Toyota were making 16v 4-pots with SOHC in the late 80's. They were always the economy option.

And Ford, bless 'em, were making DOHC engines with 8 valves at the same time.

stevesingo

4,848 posts

221 months

Tuesday 13th September 2016
quotequote all
Hell, even Triumph made a SOHC 4 valve engine in 1972!

Evoluzione

10,345 posts

242 months

Tuesday 13th September 2016
quotequote all
annodomini2 said:
Variable timing and lift benefits NA engines much more than turbocharged, which much of the current crop are sporting.
No it benefits both just as much.

KiaDiseasel

83 posts

90 months

Tuesday 13th September 2016
quotequote all
Evoluzione said:
No it benefits both just as much.
Hmmmm. On the basis that most turbo engines will have a very mild cam and N/A ones will have more duration then it benefits the N/A engine much more than the turbo one.

chuntington101

5,733 posts

235 months

Tuesday 13th September 2016
quotequote all
KiaDiseasel said:
Evoluzione said:
No it benefits both just as much.
Hmmmm. On the basis that most turbo engines will have a very mild cam and N/A ones will have more duration then it benefits the N/A engine much more than the turbo one.
Isn't it more about getting the valve event at the right time? Hence why it will help a turbo engine just as much as an NA unit. The valve event, is duration, will remain the same, but the start and end points will change I guess as rpms change.

KiaDiseasel

83 posts

90 months

Tuesday 13th September 2016
quotequote all
chuntington101 said:
Isn't it more about getting the valve event at the right time? Hence why it will help a turbo engine just as much as an NA unit. The valve event, is duration, will remain the same, but the start and end points will change I guess as rpms change.
No. The whole point of VVT is to allow the use of long duration cams for high rpm power but without suffering too much low rpm torque loss. If the cam is mild enough it pulls down to three fifths of F/A rpm anyway. Meddling with the high rpm timing of a short duration cam makes much less difference to the engine than meddling with the low rpm timing of a long duration one.

Evoluzione

10,345 posts

242 months

Tuesday 13th September 2016
quotequote all
KiaDiseasel said:
Evoluzione said:
No it benefits both just as much.
Hmmmm. On the basis that most turbo engines will have a very mild cam and N/A ones will have more duration then it benefits the N/A engine much more than the turbo one.
No it doesn't, more lift, duration and overlap will benefit both N/A and turbo engines. Infact in some situations a cam change will bring about a bigger % increase on a turbo than on an N/A.

You cannot really enter a debate with 'most engines', you need to be a bit more specific.

Edited by Evoluzione on Tuesday 13th September 17:24

KiaDiseasel

83 posts

90 months

Tuesday 13th September 2016
quotequote all
Evoluzione said:
You cannot really enter a debate with 'most engines', you need to be a bit more specific.
Your assertion that it benefits both types of engine just as much would appear to include all of them regardless of other factors. I'm not sure it's me that needs to be more specific here.

Evoluzione

10,345 posts

242 months

Tuesday 13th September 2016
quotequote all
KiaDiseasel said:
Evoluzione said:
You cannot really enter a debate with 'most engines', you need to be a bit more specific.
Your assertion that it benefits both types of engine just as much would appear to include all of them regardless of other factors. I'm not sure it's me that needs to be more specific here.
If you want to disprove what I wrote then post up a scenario or some evidence that suggests so, then we'll have something to debate about.

KiaDiseasel

83 posts

90 months

Tuesday 13th September 2016
quotequote all
Evoluzione said:
If you want to disprove what I wrote then post up a scenario or some evidence that suggests so, then we'll have something to debate about.
I think I can see rather too much scope for a "can of worms" scenario here so I'll pass this time.

stevesingo

4,848 posts

221 months

Tuesday 13th September 2016
quotequote all
BMW could be argued as the makers of some fairly cutting edge engines, now mainly turbo charged of course.

N54 DOHC VVC Turbo
http://www.e90post.com/forums/attachment.php?attac...
http://www.e90post.com/forums/attachment.php?attac...
http://www.e90post.com/forums/attachment.php?attac...
http://www.e90post.com/forums/attachment.php?attac...

N55 DOHC VVC Turbo
http://www.bimmerpost.com/goodiesforyou/N55-guide-...

B58 DOHC VVC Valvetronic variable lift Turbo.
http://s3.bimmerfile.com.s3.amazonaws.com/wp-conte...

Still waiting for an example of a modern SOHC Turbo.

On the subject of VVC on turbo engines, why when all forced induction does is increase intake air density, would the engine behave any differently in relation to cam timing than a NA engine?