why are dohc better?

why are doch so much better as opposed to a single cam?

[2ndGenTeg]

By using two separate camshafts, you can do a myriad of things.

1. You can use different grinds- lift, duration, etc. When looking at aftermarket cam specs, the intake and exhaust numbers are usually different, i.e. Jun Stage 2s- intake lift is 12mm, exhaust is 11.5mm.

2. It allows you to individually time the intake and exhaust valves. When tuning, you can advance one while retarding the other, advance and retard different amounts, etc. If you were restricted to the same camshaft in charge of both, what ecer you did to one you would have to do to the other, and in the same amount.

3. The big one- overlap. By using two separate cams, you can time the intake and exhaust valves so that there is a little bit of overlap, or time where both the intake and exhaust valves are open. By doing this, exiting exhaust gases leave a vacuum inside the cylinder, drawing in fresh air fuel mix. In a SOHC, only one side can be open at a time.

Making sense?

[ebpda9]

damn that was a great explanation.

yes that is a bad ass explanation.

2ndGenTeg, thanks alot for the great explanation

[ShEaNy]

is there any good things about SOHC? i heard in an article about how they can actually be just AS good as DOHC...Am i wrong? I"ll find the magazine I was reading and post some of it..if i can..

[ebpda9]

well some of the good points of sohc:

a quieter engine,
less burned up gas
cheaper to make

Whether they're just as good or not would depend on how you want the car tuned. For any way that an engine can be tuned with SOHC, it can be done with DOHC as well, thus making them equal in those situations. As has been explained, though, DOHC gives much more flexibility in tuning and a car can be tuned in ways with DOHC that it cannot with SOHC.

Or at least that's how I see it, correct me if I'm wrong.

b

[ebpda9]

Originally posted by spoogenet
Whether they're just as good or not would depend on how you want the car tuned. For any way that an engine can be tuned with SOHC, it can be done with DOHC as well, thus making them equal in those situations. As has been explained, though, DOHC gives much more flexibility in tuning and a car can be tuned in ways with DOHC that it cannot with SOHC.

Or at least that's how I see it, correct me if I'm wrong.

b

ditto

[2ndGenTeg]

Well, SOHC engines will never be as good in an all motor setup, because of the overlap issue. They simply are not capable of ingesting as much air/fuel as a DOHC is.

However...

In an FI setup, overlap is a bad thing. When the air/fuel is under pressure and both sides are open, you get blow by, which is exactly what it sounds like- the air/fuel passes right through the combustion chamber and out the exhaust, with out ever being ignited. Now you know why most turbo cams have a shorter duration than all motor cams- it's much easier to tune that way.

So if you're planning on doing a "moderate" FI setup, a SOHC engine can be just as good as a DOHC. However, you still lose the flexibility in specs and timing.

Originally posted by 2ndGenTeg
Well, SOHC engines will never be as good in an all motor setup, because of the overlap issue. They simply are not capable of ingesting as much air/fuel as a DOHC is.

However...

In an FI setup, overlap is a bad thing. When the air/fuel is under pressure and both sides are open, you get blow by, which is exactly what it sounds like- the air/fuel passes right through the combustion chamber and out the exhaust, with out ever being ignited. Now you know why most turbo cams have a shorter duration than all motor cams- it's much easier to tune that way.

So if you're planning on doing a "moderate" FI setup, a SOHC engine can be just as good as a DOHC. However, you still lose the flexibility in specs and timing.

Just to elaborate, in case someone isn't following. As long as you don't need overlap, SOHC can be just as good. But if you want to change the intake vs. exhaust timing....you'd need a new cam for SOHC, whereas with DOHC you can change them relative to one another.

b

[2ndGenTeg]

Don't confuse people.

In an all motor setup where overlap is key, a DOHC is a must.

In an FI setup where overlap is undesirable, a SOHC can function just as well. However, you still lose the versatility in tuning a DOHC provides.

[ShEaNy]

Yup... I was lost When u said well... lol I''ll just buy a newer cam (AEM) and move on...

I didn't find it confusing.

What I said is basically what you just said, except I didn't make specific reference to FI or all motor.

Was it really that confusing?

b

[ChrisCantSkate]

well, dohc is always gonna beat sohc in every performance aspect. stock engines have valve overlap of some sort. none seal perfectly. with dohc it is possible to elimiate all overlap. with a sohc it may not be quite as feasable. a h22 is gonna produce better numbers than a f22 (dohc and sohc 2.2 motors) same with a b16 and d16. while you can get by with sohc remember you have a smaller head. the dohc motors made by honda are built more for performance and have more "options" such as oil squirters in the cylender walls and better geared trannies.

which is the singe cam and which is the two cam motor in the all mighty preludes?

[ChrisCantSkate]

the prelude comes with 3 engines in the 4th generation body style.

h22- dohc 190hp 158lb/ft this is the monster
h23 dohc 160hp 156lb/ft still a nice engine
f22 sohc accord engine