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Old 16th April 2007, 22:54   #16
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Originally Posted by raajks View Post
Do we need a different driving for DOHC and SOHC?
For DOHC's, the engine comes to life at higher RPMs, so we would need to rev the higher than what we would normally do for a SOHC before shifting up.
DOHC/SOHC arrangement has got nothing to do with your RPM.
its your cam profile which will decide, I can have a DOHC for low end torque and a SOHC for hi rpm range torque depending on my cams..

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Originally Posted by raajks View Post
SOHC, delivers an excellent low end torque and flattens out at higher RPMs.
depends on your cam profile..you cannot generallise that SOHC= good torque at low revs.

by the way FYI.. cam profile decide how high and how much your valves open and how much they overlap with each other... etc etc etc

I hope you are not getting confused with single pattern and dual pattern cams instead of SOHC and DOHC,but then again its the lobe profile which will decide your torque curves...
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Old 16th April 2007, 23:03   #17
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Originally Posted by sbasak View Post
One's driving style should not be changed whether it is DOHC or SOHC.
To drive any engine optimally, all you need to know is the power torqure characteristics (ie. at what RPM what torque is produced) - so that you can get max. fuel efficiency.
You have said exact opposite.
If you want max fuel efficency dont drive where you get max torque.
If you are on a racetrack then drive at your RPM where you get max torque..if u want to blast out of corners etc..
if you want mileage drive at the tallest gear possible at the lowest rpm possible without making the engine knock or get loaded for that speed.

e.g. some engine makes max torque @ 6000 RPM , driving at 6000 wont give you any mileage as compared to driving at 2500 RPM in overdrive.
If the engine can take the load otherwise shift down and move to 3500 RPM etc .. just an example, see what Im trying to say.
basically lower the rpm better the mileage.

Last edited by chetanhanda : 16th April 2007 at 23:20.
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Old 16th April 2007, 23:07   #18
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Chetan it would be really helpful if you could club all the posts in one .. Makes reading easier .. Besides you have a 15min limit , kindly try to make use of it ..
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Old 16th April 2007, 23:09   #19
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Originally Posted by mclaren1885 View Post
Chetan it would be really helpful if you could club all the posts in one .. Makes reading easier .. Besides you have a 15min limit , kindly try to make use of it ..
... yes sir I forgot that.
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Old 17th April 2007, 22:55   #20
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Quote:
By Chetanhanda:
DOHC/SOHC arrangement has got nothing to do with your RPM.
Well while i understand you are saying that its the cams that decide your torque and power characteristics, I would like to say here that for a higher rpm engine, DOHC is preferable because in a SOHC there would be more reciprocating components - rocker arms - and hence forces which would not allow as accurate control of the valves at high speeds where there is less margin for error.

One more thing. You were mentioning its all about keeping the rpms of your engine low to get good mileage, while sbasak was talking about mileage at peak torque rpms. The point of max torque is usually where peak volumetric efficiencys are obtained and we get the maximum combustion pressure at that rpm, hence the max torque. I guess sbasak was trying to point this out, especially considering the cars we drive are the types where torque is made at the lower rpms. To sum it up, the point is, power is being produced the most efficiently at this rpm right. In an idealistic situation if we had an engine having high torque at really low rpms and gear the car such that it runs at low speeds in top gear at the high torque speed range(which would be much more possible considering the engine would give out more torque here in this case), it should be possible to get higher mileage, becuase the engine will possibly run leaner on account of good volumetric efficiency, due to which even more complete combustion will take place. So I am not sure its completely fair to say that he was saying the complete opposite.

@Raajks: Though your intention was to share the video, it brought out a lot more than that! One thing here, when you were talking about SOHC and DOHC engine characteristics, it seemed like you were mistaking it with 2-valves and 4-valve heads. Yes i guess you know the difference, but the confusion could be because, DOHCs are generally employed on 4V heads and 2V heads usually use SOHC's, and what would you have read or heard could have been based on such a case.
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Old 18th April 2007, 10:48   #21
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A good sumup of the points Sparkie.

Chetan,
"basically you have got everything completely wrong" -- That was an interesting comment.

For SOHC's the timing belt is the key... that ensures that Outlet Valve and Inlet valve timing is synchronized. It is not about timing belt as a component that mattered but how it was deployed that made all the difference.
DOHC's inlet and outlet valves reach a higher state of synchronization at higher RPMs (Does this mean, you will have to redline everytime you shift - Ofcourse not) Higher is a relative term and it set differently for different conditions and for different engines. Also, this does not mean that they are not synchronized at lower RPMs.

Any movement of a component requires energy, A component that is heavier requires more energy simple physics. (Does that affect driveability? Ofcourse not)

My point, never to categorize that SOHC is better or DOHC is better.
Intention - Highlight how DOHC's and SOHC's are different and how different manufactures employ.
Observation - Rally cars predominantly use DOHC and I have seen the Jap manufactures (for India) placing their SOHC engines for production cars. T

They are amazing machines no doubt (Personal favorites being OHC and Lancer) but their primary reason was for good FE in addition to good drivability as that is what Indian market was looking at.

Do I have document evidence for all those - May be..maybe not....
Source -- It comes from the time I have spent with cars

As sbasak, stated
"To drive any engine optimally, all you need to know is the power torqure characteristics (ie. at what RPM what torque is produced) - so that you can get max. fuel efficiency."
If you know your engine and how it works you can extract better performance and even better fuel efficiency.

AND finally

Whereas European "AND" driver or race oriented car were DOHC. - Do I need to explain this????
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Old 18th April 2007, 12:39   #22
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Quote:
Well while i understand you are saying that its the cams that decide your torque and power characteristics, I would like to say here that for a higher rpm engine, DOHC is preferable because in a SOHC there would be more reciprocating components - rocker arms - and hence forces which would not allow as accurate control of the valves at high speeds where there is less margin for error.
The OHC Vtec produced it's power at 6800rpm (highest among any Indian car) and it was an SOHC. So, it's not that SOHC engines can't be made to perform at high rpms. Engine technology has come a long way.

Shan2nu
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Old 18th April 2007, 15:28   #23
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Quote:
Originally Posted by raajks View Post
If you know your engine and how it works you can extract better performance and even better fuel efficiency.
Ohhh....so all you wanted to say was that! The thread title and initial posts made us think something else.
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Old 18th April 2007, 20:51   #24
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Quote:
Originally Posted by Shan2nu View Post
The OHC Vtec produced it's power at 6800rpm (highest among any Indian car) and it was an SOHC. So, it's not that SOHC engines can't be made to perform at high rpms. Engine technology has come a long way.

Shan2nu
Yup, you sure are right, SOHC's can be designed to perform too no doubt! But generally, as i was saying before, higher the rpm's DOHCs are preferable for the reason I was mentioning. As somebody else was mentioning too, engines used at higher rpms like the rally cars use DOHCs.
And not to oppose what you are saying, but its more of an afterthought, that I don't think that the max power is produced at that engine speed in the Vtec because its a SOHC. It's becuase they run two different cam profiles for the lower and higher engine speeds which enables optimal design for the second cam to produce more power at the higher engine speed.

Another thing why SOHC's might be used is that they are cheaper too produce than DOHC.

Doubt: On the Vtec, SOHC might be used because there might not be enough space to include the Vtec gadgetry and two cam profiles together. Can anybody crosscheck that? Because I have never seen its engine head. Or is there just a cost reasoning here again?


Quote:
Raajks: For SOHC's the timing belt is the key... that ensures that Outlet Valve and Inlet valve timing is synchronized. It is not about timing belt as a component that mattered but how it was deployed that made all the difference.
I don't completely agree here. Outlet & inlet valve timing is based on the cam. The only way the timing belt affects this is the way it is mounted, because at that time it has to be made sure that the crankshaft and camshaft have correct relative postions with respect to each other. Do tell me if I am missing something else you are saying here.

Quote:
Raajks: DOHC's inlet and outlet valves reach a higher state of synchronization at higher RPMs (Does this mean, you will have to redline everytime you shift - Ofcourse not) Higher is a relative term and it set differently for different conditions and for different engines. Also, this does not mean that they are not synchronized at lower RPMs.
I don't understand how they are more synchronized at higher rpms. If you compare a DOHC with a SOHC, then at higher rpms the DOHC will be more synchronized. But otherwise, slower the rpms, more synchronized the valves on either setup. Another situation, are you saying that the cam is designed optimally for higher rpms such that the design takes into consideration the probable delay of valves to come back to their closed position due to the valve springs not acting in time?

Cheers
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Old 26th May 2007, 04:29   #25
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Quote:
Originally Posted by raajks View Post
A good sumup of the points Sparkie.
Chetan,
"basically you have got everything completely wrong" -- That was an interesting comment.
ok ..


Quote:
Originally Posted by raajks View Post
For SOHC's the timing belt is the key... that ensures that Outlet Valve and Inlet valve timing is synchronized. It is not about timing belt as a component that mattered but how it was deployed that made all the difference.

What do you mean timing belt is the key ? are you joking dude ? are you serious ?
its the CAM profile which is the key..
are you implying that choice of timing belt is going to alter the characteristics ?

Quote:
Originally Posted by raajks View Post
DOHC's inlet and outlet valves reach a higher state of synchronization at higher RPMs
what do u mean higher rate of synchronization in DOHC ?
both SOHC and DOHC have to be synchronizing perfectly at all RPM's

Quote:
Originally Posted by raajks View Post
Any movement of a component requires energy, A component that is heavier requires more energy simple physics. (Does that affect driveability? Ofcourse not)
Ok

Quote:
Originally Posted by raajks View Post
My point, never to categorize that SOHC is better or DOHC is better.
Why not ?, DOHC is always better than SOHC for everything.
SOHC engine is always cheaper to make for a manufacturer than a DOHC engine for a model

Quote:
Originally Posted by raajks View Post
Intention - Highlight how DOHC's and SOHC's are different and how different manufactures employ.
Observation - Rally cars predominantly use DOHC and I have seen the Jap manufactures (for India) placing their SOHC engines for production cars. T
yes .. becoz SOHC is cheaper

Quote:
Originally Posted by raajks View Post
As sbasak, stated
"To drive any engine optimally, all you need to know is the power torqure characteristics (ie. at what RPM what torque is produced) - so that you can get max. fuel efficiency."
If you know your engine and how it works you can extract better performance and even better fuel efficiency.
very WRONG dude ... you got it exactly wrong dude.
If you drive a car where the max torque comes you wont get any mileage... you will good performance but no mileage
Simply drive at the lowest RPM possible in the tallest gear without loading the engine or making it knock.. why do you need max torque for max mileage.. u just minimum torque to keep the car sedately coasting along for mileage..

Quote:
Originally Posted by raajks View Post
If you notice, most of the JAP's employ SOHC's
Whereas European and driver or race oriented car were DOHC.
Not all JAP's employ SOHC's.. the race oriented JAps are DOHC and the mileage oriented ones are SOHC..
Quote:
Originally Posted by raajks View Post
AND finally
Whereas European "AND" driver or race oriented car were DOHC. - Do I need to explain this????
Yes you need to explain If you are saying JAP cars are not race oriented becoz they are SOHC...

Last edited by chetanhanda : 26th May 2007 at 04:31.
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Old 26th May 2007, 15:30   #26
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bull-bull-bull. none of yo have answered the question correctly.

driving style -sohc : pedal to the metal& flat out

driving style -dohc : pedal to the metal& flat out
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Old 27th May 2007, 09:42   #27
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Originally Posted by Revvhead View Post
bull-bull-bull
So you are calling this bull ... either u are joking or u have no idea what we are talking about.
Wish I could write my reply to your post here but I dont want another infraction.
Nothing more to say.
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Old 27th May 2007, 23:11   #28
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Quote:
Originally Posted by chetanhanda View Post
So you are calling this bull ... either u are joking or u have no idea what we are talking about.
Relax Chetan, he's just joking!
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Old 27th May 2007, 23:28   #29
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Folks. Majorly OT here. But is not the word, 'Jap' or 'Japs' considered as derogatory term for Japanese? I see lot of people using it. I am sure it is unintentional though.
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Old 19th June 2007, 23:12   #30
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Quote:
Originally Posted by iraghava View Post
Relax Chetan, he's just joking!
.. ok cool..
flooring a DOHC Vtec is definately fun..
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