DOHC vs. SOHC

[Kboers]

Now I'm just curious as to what everyone's thoughts were regarding dual overhead cams and single overhead cams. I understand that dohc is considered better but I'm not quite sure why. It has always been my belief that simpler systems work better and last longer and I'd like to assume that a single cam engine would have far fewer parts that could break. The '93 Accord EX f22a6 engine (sohc) has a power output of 140hp while the '91 Prelude Si f22b engine (non-vtec dohc) has a power output of 158hp (Wikipedia). Both have 16 valves, a displacement of 2156cc and the same bore and stroke.The only difference is in compression ratio. Could anyone explain to me why dohc engines typically have more horsepower than sohc? Does it come down to the effort towards performance tuning the manufacturer put into the engine?

[GeoffM]

http://tinyurl.com/4amlsvg

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[pninja82]

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[deevergote]

You can both take 3 days off.
I apologize if you got this behavior from me... but if you're going to post in a thread in this section, you had damn well better be offering some good information. Especially when the question being asked is legitimate.



Kboers,
DOHC is generally regarded as better for cam tuning, as you have control of the intake and exhaust valves separately. With SOHC, you would need to grind a new cam to be able to adjust both separately (as an adjustable cam gear would adjust both equally.)
Also, the DOHC design usually utilizes shorter valves, and therefore shorter valve springs. Shorter springs are less prone to binding.
At least that is the theory.
Also, DOHC is marketed as more "performance oriented"... so it sells cars!


In reality, at least as far as our engines go, the SOHC F22A head is capable of outflowing the almighty H22A head after both heads have been modified. The F22A is one of Honda's finest engines, and is VERY well suited to performance when modified correctly.
You are right, the simple design is condusive to free-flowing ports and a near-ideal valve angle. The valvetrain is lightweight, and quality valve springs have been used time and time again with no binding issues.


So really, the ONLY thing DOHC has over SOHC (in terms of these engines) is better control over the intake and exhaust cams separately. That, and the higher-power engines from the factory (but that's moreso Honda's choice than the engine's actual potential.)

[gloryaccordy]

Now I'm just curious as to what everyone's thoughts were regarding dual overhead cams and single overhead cams. I understand that dohc is considered better but I'm not quite sure why. It has always been my belief that simpler systems work better and last longer and I'd like to assume that a single cam engine would have far fewer parts that could break. The '93 Accord EX f22a6 engine (sohc) has a power output of 140hp while the '91 Prelude Si f22b engine (non-vtec dohc) has a power output of 158hp (Wikipedia). Both have 16 valves, a displacement of 2156cc and the same bore and stroke.The only difference is in compression ratio. Could anyone explain to me why dohc engines typically have more horsepower than sohc? Does it come down to the effort towards performance tuning the manufacturer put into the engine?

Two things

DOHC F22B has a much superior intake manifold (actually just a superior throttle body and plenum which you can swap to your car)

And the F22B has more aggressive cams

I had an F22B in one of my CBs... if your F22A6 is running right, honestly it's not worth the $$$. For the cost of swapping a DOHC F22B you could have a much more monstrous F22A6 (H22/H23 plenum+TB, Bisi cam, chipped ECU, OBX header + 2.5" collector, 2.5" exhaust). For a little more you can get custom pistons and really blow the F22B out of the water. The intake/exhaust cam adjustability deal doesn't mean much as Bisi cams are somewhat optimized anyway.

[pedalpusher90]

I read a book, performance honda and acura engines something or other (great book, don't mean to disrespect the author but i cant remember the title), its been recommended by deev numerous times. It goes in depth on the advantages and disadvantages of sohc and dohc. Sohc is less fine tunable in regards to advancing and retarding exhaust and intake valves individually. It also requires heavier springs and has a faster wear on the parts because of the heavier springs. But, it is also harder to destroy the engine, from pre-detonation due to timing adjustment ignorance. A dohc is lighter, can use lighter springs, longer wear out period, but you need to do more research to fine tune the timing. I believe those are the pros and cons pleae correct me if i am wrong.

[deevergote]

Two things

DOHC F22B has a much superior intake manifold (actually just a superior throttle body and plenum which you can swap to your car)

And the F22B has more aggressive cams

I had an F22B in one of my CBs... if your F22A6 is running right, honestly it's not worth the $$$. For the cost of swapping a DOHC F22B you could have a much more monstrous F22A6 (H22/H23 plenum+TB, Bisi cam, chipped ECU, OBX header + 2.5" collector, 2.5" exhaust). For a little more you can get custom pistons and really blow the F22B out of the water. The intake/exhaust cam adjustability deal doesn't mean much as Bisi cams are somewhat optimized anyway.

All that doesn't really say anything about DOHC being better than SOHC... just that the DOHC was built with more performance in mind.

I read a book, performance honda and acura engines something or other (great book, don't mean to disrespect the author but i cant remember the title), its been recommended by deev numerous times. It goes in depth on the advantages and disadvantages of sohc and dohc. Sohc is less fine tunable in regards to advancing and retarding exhaust and intake valves individually. It also requires heavier springs and has a faster wear on the parts because of the heavier springs. But, it is also harder to destroy the engine, from pre-detonation due to timing adjustment ignorance. A dohc is lighter, can use lighter springs, longer wear out period, but you need to do more research to fine tune the timing. I believe those are the pros and cons pleae correct me if i am wrong.

Honda/Acura Engine Performance by Mike Kojima (and the book DOES have quite a few typos... some blatant misinformation... but overall, it's a fantastic book for a beginner.) Much of what I said above was basically paraphrasing that book, as you did in more detail.

One correction, though... or at least a clarification... the DOHC has lighter individual valvetrain components (smaller valves, shorter springs, etc...) but the overall weight of the valvetrain is greater than that of the SOHC. That's not a big deal to most, but it can come into play in a truly serious build.

[Need4speed]

I never knew that that's what those stood for, it never dawned on me.

[deevergote]

What, Single OverHead Cam and Dual OverHead Cam? Did you think they were just clever names?

Every automotive acronym stands for something technical... well, usually. VTEC does as well (Variable valve Timing and lift Electronic Control.)

[Need4speed]

What, Single OverHead Cam and Dual OverHead Cam? Did you think they were just clever names?

Every automotive acronym stands for something technical... well, usually. VTEC does as well (Variable valve Timing and lift Electronic Control.)

Bro I'm use to working on my 68 vw bug, we didn't have acronyms on our gear. Lol! I'm Learning as I go! Lol