VTEC (not really), and DOHC

[Auto_newb]

I know what V-TEC is, but my question is, what are the benefits of having the valves open up only a bit, compared to having it opening up the valves all the way, Why can't I just set the VTEC to kick in at like say 1000 RPMS so I get power right when I touch the throttle? Wouldn't it make the engine "breath better"?

Or does it have something to do with the "exhaust scavenging" from that exhaust thread?

My other question is: What is DOHC? I know it stands for dual overhead cams, but how does it control the valves any better than SOHC? What exactly is "Dual Overhead Cams?" is it like 2 camshafts? Or 2 pairs of cam lobes on one shaft?

Oh and one more thing, my friend says that a 3 stage VTEC would give a civic si engine as much HP as 160. Is this true?

[Neutrino]

Originally Posted by Auto_newb

My other question is: What is DOHC? I know it stands for dual overhead cams, but how does it control the valves any better than SOHC? What exactly is "Dual Overhead Cams?" is it like 2 camshafts? Or 2 pairs of cam lobes on one shaft?

Oh and one more thing, my friend says that a 3 stage VTEC would give a civic si engine as much HP as 160. Is this true?

DOHC engines have two camshafts one controling the exaust valves and another controling the intake valves.


DOHC engines have 4 or sometimes 5 valves while SOHC engines regularly have only 2 valves due mainly to clearance purposes I presume (In an SOHC engine the valves have to be in line)

also in an DOHC engine you can fully control the timing of the intake and exaust valves independently from one another

for your second question "stage 3" means nothing in itself, it is just a term that some aftermarket companies use to separate their upgrade kits so without further info we cannot say if your frined is wrong or not

[Auto_newb]

"for your second question "stage 3" means nothing in itself, it is just a term that some aftermarket companies use to separate their upgrade kits so without further info we cannot say if your frined is wrong or not"

No... I mean this http://www.leecao.com/honda/vtec/3stagevtec.html

[Auto_newb]

"DOHC engines have two camshafts one controling the exaust valves and another controling the intake valves."

So... DOHC can handle more valves easier because the valves don't have to be inline?

[Neutrino]

Originally Posted by Auto_newb

"DOHC engines have two camshafts one controling the exaust valves and another controling the intake valves."

So... DOHC can handle more valves easier because the valves don't have to be inline?

well its a whole lot easier to fit in a circle a

1 2
3 4

than a

1 2 3 4

[Auto_newb]

What about the SOHC engines with 4 valves per cylinder?

[-Jayson-]

i dont think SOHC can have 4 valves per cylinder.

[Auto_newb]

Examples, D15, C30

[Evil Result]

Depending on how far the valve open depend on how well the A/F mixture will swirl as it drawn through the opening....

So for a low RPM engine a low opening valve will keep intake velocities high and help keep the fuel atomized and distributed more evenly inside the combustion chamber, thus equaling more powerfor less usage of fuel...

But, this dosen't work and higher rpms because you would be choking the engine for air, so you have the valve open a bit more to allow the engine to breath better but still keep intake and exhaust velocities high.

VTEC has 2 sometimes 3 cam stages which improve power through each of their own RPM ranges; Intake/exhaust velocities, Valve overlap, torque, fuel efficiency.

[timberdoodle]

Originally Posted by Auto_newb

I know what V-TEC is, but my question is, what are the benefits of having the valves open up only a bit, compared to having it opening up the valves all the way, Why can't I just set the VTEC to kick in at like say 1000 RPMS so I get power right when I touch the throttle? Wouldn't it make the engine "breath better"?

Or does it have something to do with the "exhaust scavenging" from that exhaust thread?

My other question is: What is DOHC? I know it stands for dual overhead cams, but how does it control the valves any better than SOHC? What exactly is "Dual Overhead Cams?" is it like 2 camshafts? Or 2 pairs of cam lobes on one shaft?

Oh and one more thing, my friend says that a 3 stage VTEC would give a civic si engine as much HP as 160. Is this true?

Vtec kicks in at higher rpms because you need to feed the engine more fuel in that higher range. If it kicked in at 1000, your engine would be choking with gas and oxygen making it not very efficient and not running very well.

[Auto_newb]

Depending on how far the valve open depend on how well the A/F mixture will swirl as it drawn through the opening....

So for a low RPM engine a low opening valve will keep intake velocities high and help keep the fuel atomized and distributed more evenly inside the combustion chamber, thus equaling more powerfor less usage of fuel...

So are you saying that the higher the velocity, the better atomized the fuel is?

Vtec kicks in at higher rpms because you need to feed the engine more fuel in that higher range. If it kicked in at 1000, your engine would be choking with gas and oxygen making it not very efficient and not running very well.

Why would the engine be choking at 1000 RPMS when the valves are wide open?

[rubix777]

spark ignition engines are designed to run rich during idle, lean during cruising, and rich during WOT.

[83-944]

i dont think SOHC can have 4 valves per cylinder.

Examples proving otherwise
99 Chevy Metro 1.3 SOHC 16 valves
95 Chevy Lumina 3.1 SOHC 24 valves
87 Porsche 944S 2.5 SOHC 16 valves
95 Dodge Neon 2.0 SOHC 16 valves
94 Mercury Sable 3.0 SOHC 24 valves

DOHC heads are more efficient cause they don't use long rocker arms to control the other set of valves. Less rotating mass = more HP. Most DOHC engines hydraulic lifters that directly engage the valve. IIRC

[83-944]

The last paragraph is IMO

[-Jayson-]

yeah after i posted that i remember by buddy who had a dodge neone that was SOHC with 16 valves. . .