[Kazudon]

wat does dohc mean??

[小凱]

Double overhead cams
雙凸輪軸

[NTG P5]

Dual Over Head Cams
same as LittleKai's answer la...haha...

while we are at it:

SOHC - Single Over Head Cam
OHV - Over Head Valve

so...basically...with DOHC, you have 1 cam controlling the opening and closing of your exhaust valve(s) and the other cam controlling your intake valves

*notice that I used valve, not valves? cuz some of MB's engines have only 3 valves (was it 2 intake and 1 exhaust...or the other way around?) anywayz

Honda's 3.0L V6 is of SOHC design, so it has 2 cams in total, one cam on each cylinder bank controlling both exhaust and intake

Toyota's 3.0L V6 is DOHC, so it has 4 cams in total, 2 cams on each bank

for 4 cylinder cars, there are 2 cams for DOHC and 1 cam for SOHC cuz the cylinder are oriented in a straight line

(the same goes for Toyota's I-6 and Nissan's I-6 and Volvo's I-5)
(exclude boxer engines; horizontally opposed)

:biglaugh:

[Kazudon]

sory
i am stupid wats cams??

[Zeta]

最初由 kazu 發表
sory
i am stupid wats cams??

camshaft..... the rod used to control the valves

[turbos86]

While we're doing Q&A, can someone tell me how backpressure effects the power-train, mainly the engine in producing power. Thanks~

MB has 2 intake valves and 1 exhaust valve.
MB use it for Torque and Emission advantages.

Most other have 2 intake valves and 2 exhaust valves.
Covers a good chunk of cylinder head and is best compromise.

Audi has 3 intake valves and 2 exhaust valves.
Audi use it for high rpm Breathing advantages.

[NTG P5]

thanx Initial-D...hehe...yeh...makes sense...more intake valve than exhaust valves...

backpressure...hmm...gotta go look up more info on dat...

but basically you want your engine to "inhale" and "exhale" as efficiently as possible, therefore, for performance's sake backpressure can be reduced by swapping out the often pretty restrictive factory exhaust systems

exhaust gas goes through your headers -> downpipes -> cat -> muffler -> exhaust pipe -> atmosphere (BAD BAD BAD!!! )

during the path, these components will slow down the exhaust gas flowing through, thus creating back pressure

*** correct me if I'm wrong with any of these points, cuz I'm just putting whatever that comes to mind***

[turbos86]

But ok, I'm confused on one thing. Some people say back pressure is bad, other says you need it. And what's it got to do with torque/power lost.

awww, screw it, do I/H/E and get a straight pipe, who needs back pressure anyways! LOL

[NTG P5]

actually...I've heard of the same thing b4...having "some" backpressure is good...but donno what it's for

still gotta look it up...hah....