Team-BHP - Which engine is better? SOHC vs DOHC

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Can you tell me whats the difference between the engines.

here's the short version...

a SOHC or single overhead camshaft engine uses a single camshaft on the head to lift all the valves, whereas in a DOHC or double overhead camshaft head, two camshafts are used to lift the valves (a camshaft each for intake and exhaust valves) ; normally, SOHCs are used in both 16 valve or 8 valve configurations (for a four cylinder engine), but DOHCs are used in 16 valve configurations (or more) only. some exceptions are there, like the vRS, which has DOHC layout and 20 valves (5 valves per cylinder).

a DOHC layout is better than a SOHC layout in many ways- in DOHCs, the valve timing is more precise, and better valve lift is achieved. also, a DOHC setup eliminates the need for rocker arms, hence creating better timing, and valve contact is more direct too. but of course, these are all in stock form. a SOHC layout, when tuned, can be as efficient as a DOHC, but under proper tuning, DOHCs always achieve more power than SOHCs...

Found a Good thread!

Now, ANHC engine is SOHC while Fiesta 1.6 is a DOHC. So, as per the logic given by members in the above posts Fiesta's engine should be better, but ANHC engine is believed to be futuristic ( due to H... factor)!

If DOHC is better, why didn't HONDA offer on this car (ANHC) ?:Shockked:

Couldn't find much about CIVIC engines on HONDA site ( IMO, 1.8L is SOHC & 2.0L is DOHC)

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Originally Posted by abhibh (Post 120269)

Can you tell me whats the difference between the engines.

When you are resting or just lazing around or even going for a short walk you could close one of your nostrils with your finger and still not feel any discomfort but without doubt you would need both of your nostrils open if you are doing some exercise. Now GOD was so clever that he had the inlet and exhaust coming through the same exit pipe and the change over valve he made it closer to the exchange area; but occasionally we use the mouth too for exhaling which is similar to the 5 valve design where there are two inlet valves and 3 exhaust valves. Making a 5 valve design witha sohc design is near impossible and inefficient too.

In engines more the valves more are the possibles ways to extract power.
In engines the 2 valve design is well suited for city driving where instant throttle response is expected but on the highway power at higher rpm is expected and hence the 4 valve design is better sited.

The dohc design gives more precise control of these valves while the sohc is with more number of linkages. Its similar to the difference between a direct linked gear lever and one thats connected to the gear box through many linkages.

DOHCs offer 2 advantages over SOHCs, that of central spark plug placement and implementation of variable valve control on the exhaust side as well. Other than that, there's not much for the layman. In fact, due to the valvetrain package being heavier on DOHCs, their low-end torque might suffer, making the SOHC a better traffic/daily-drive bet.

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Originally Posted by drpullockaran (Post 1194186)

5 valve design where there are two inlet valves and 3 exhaust valves. Making a 5 valve design witha sohc design is near impossible and inefficient too.

I don't know about God, but most 5 valve engines have 3 intake valves and 2 exhaust valves. All other things being equal, 5v also does not make a significant difference compared to 4v. In fact, Yamaha has gone back to 4v per cylinder for its flagship R1.

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Originally Posted by drpullockaran

In engines more the valves more are the possibles ways to extract power.
In engines the 2 valve design is well suited for city driving where instant throttle response is expected but on the highway power at higher rpm is expected and hence the 4 valve design is better sited.

I think there are arguments for it to be the other way round as well. 2v would mean the valves are larger, thus mass -- valves, springs etc -- would be higher. This means more power sapped at lower rpms. Addedly, charge intake speeds would be lower, because valve dia is bigger. This will also lead to lower torque and power in low-end scenarios. Which is why supercharged V8s in dragsters use 2v heads.

with dohc, you have dedicated cams for each intake and exhaust valves.
its convenient to use dohc for a three, four or five valve engine.

the torque of an engine is decided by slightly different parameters at different operating ranges.
at low revs, it is decided by the velocity of the intake charge usually defined by swirl. this is where two valve engines are good. they have higher swirl values and therefore make good torque at the bottom operating range.
as the engine gathers speed, its torque is dependent on the sheer volume of charge entering the cylinder, thus giving two valve engines a disadvantege. thats where four valve engines engines are better.

to quote an example, there are two vehicles which are famous and have five valves per cylinder. the pre 2004 yamaha R1 and the ferrari 355. both have excellent breathing at top end but little low down grunt. thus, anybody who drove these vehicles was afraid of the way the power shoots up as the revs build. this can also be conpared with the RD 350 HT & LT versions. hts rev out easier due to the port durations. lts have better torque at the bottom end.
yamaha has published a paper about this which elaborates their understanding about number of valves and power production. that was sometime in 1990s... anybody have it?

in that they have mentioned that 4 valve is the best compromise they have got. dohc is ideal for this.
with double cams, the valve angles can be a little more flexible. with single cam, the design of the finger followers gets a little cramped and thus limits the flexibility with the valve opening angles.

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Originally Posted by v1p3r (Post 1194258)

I don't know about God, but most 5 valve engines have 3 intake valves and 2 exhaust valves.

Thats was a :Frustratibig screw up by me. I stand corrected. A slip in typing. God was circumspect in the design too. He designed us to use all three external respiratory orifices but here too I made a mistake. For inlet we can use the nose or mouth for inhaling but not both of them together simultaneously and the same goes for exhaling.

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Originally Posted by breezydrive (Post 1194051)

Found a Good thread!

Couldn't find much about CIVIC engines on HONDA site ( IMO, 1.8L is SOHC & 2.0L is DOHC)

The current Civic has a 1.8L SOHC in the LX to DX variants (140bhp) and a 2.0L DOHC in the Si and Si Mugen variants (197bhp). The DOHC is way more powerful and awesome fun to drive. Even the i-Vtec system benefits in a DOHC as both inlet and exhaust valves can have multiple timing profiles. As a drivers car, the DOHC Si is way better!