singlecam/doublecam theory

[PunkAlex]

Ive been thinking about this for quite a while...anyways

Ok, so lets take two engines...same block, internals, compression ratio, all the little details the same on the bottom end. Same for the intake mani, injectors and all that stuff. One has a single cam cam head and one has a double cam head. Same lift cam/cams on both engines, same port sizes/shapes, same fuel maps, same everything cept one has one cam and one has two. Both set to 0 degrees adv/ret. Will one engine make more power than the other?

[CivicSpoon]

Hard to say I'd think DOHC, except maybe between a jdm d15b vtec vs. a DOHC ZC; in that case it'd be too damn close.

[b16a3sol]

if everything is exactly the same, except for the number of camshafts, then i would have to say the SOHC, simply because the motor has to rotate that much less mass. there is one less camshaft, pulley, many springs, valves, resistance from friction for all the parts, etc. the whole point of adding another camshaft, is to allow the entire head and manifolds to be restructured to allow more air into and out of the cylinders. if thats not taken advantage of by changing just about everything, then adding more parts is not really beneficial.

thats my take on it anyways, could be wrong...

[jcrx]

Originally Posted by b16a3sol

the whole point of adding another camshaft, is to allow the entire head and manifolds to be restructured to allow more air into and out of the cylinders. if thats not taken advantage of by changing just about everything, then adding more parts is not really beneficial.

thats my take on it anyways, could be wrong...

Right o, the point is to effect airflow both in and out in relation to each other.

[seniorbigs]

I think the main advantage of DOHC is valve placement in the head, which will dictate combustion chamber shape to some degree. Cam followers can be made smaller and lighter with the valve stem closer to the cam lobes.

[unusualcivic]

fact is, parasitic drag would make the DOHC slower.

[jcrx]

Originally Posted by unusualcivic

fact is, parasitic drag would make the DOHC slower.

maybe if everyhing else was exactly the same you'd lose 1 hp, but FACT is DOHC are faster. Reason being that the intake and exhaust cams are set to maximize flow, and that is the whole point of have two cams. The weakest DOHC is the first ZC at 124hp and it was quite a few Hp faster than it's peers.

[PunkAlex]

ok then, real world application. Say we were to take a d16z6, give it the beefed up internals similar to that of a b16, cam w/ same profile, same fuel map, same revs (however the hell you would be able to do that ), same compression etc. would it make the same power as a b16?

[snowman2005]

on vtec sohc there is no agressive lobe for the exhaust(not enough space).i think they would make the same power.

[unusualcivic]

Originally Posted by jcrx

maybe if everyhing else was exactly the same you'd lose 1 hp, but FACT is DOHC are faster. Reason being that the intake and exhaust cams are set to maximize flow, and that is the whole point of have two cams. The weakest DOHC is the first ZC at 124hp and it was quite a few Hp faster than it's peers.

if everything was perfectly equal between the SOHC and DOHC? i would think that, while minor, the drag created by the extra rotating assembly would cause the engine to be just a hair less powerful. in real world applications, you are absolutely correct, but what he said was everything is identical except the number of cams..

[jcrx]

In that case, what if there was no gravity and we could all fly? It's retarded, you're trying to turn an apple into an orange. Or what if, what if, what if, we made the second cam out of superduper light titanium alloy composite fibers, and it could just be there, and not weight anything, what if, what if, what if...


Point is, there's no use trying to compare the effieciency of two different motors in a vacuum.

He asked with all things the same, which is faster, and that's going to be the DOHC because you can tune the intake exhaust for better effiecency. Since you can't tune a SOHC this way, you can't say all things equal, or exclude this as a factor.

[PunkAlex]

Yeah i know ability of tune will always be a plus for DOHC....and in the real world a b16 will always make more power mod for mod than a d16. I wsa just wondering if there were any more advantages to DOHC over SOHC besides plug placement and tuning

[unusualcivic]

jcrx, i wasnt arguing with you, you are right, a dohc is more efficient, period. i was mistaken at first and trying to figure it out, thats all