OPEL's 1.6 DOHC vs. 1.6 SOHC

[MMamdouh]

while looking at the spec. sheet of both the OPEL Corsa and OPEL Astra that we have here i found out a really strange thing... both cars got a 1.6 engine but the Corsa got SOHC with 8 valves engine while the Astra got a DOHC 16 valves engin, both engines pump out 101 HP

logically i assumed that the 16v DOHC will have more power than the 8v SOHC but i was shocked to know that both are the same... i went further through the spec. chart and fout that:

- both engines got the same bore x stroak (79mm x 81.5mm)
- both engines pump out 101HP @ 6200RPM.
- the SOHC's torque is 140nm @ 3000RPM whereas the DOHC is 145nm @ 4000RPM.

the way i see it the SOHC is much better than the DOHC as its max. torque is at lower RPM as the extra 5nm of torque is just 3.5% more at 16.6% more RPM so i have to rev the engine more to make so little gain.

my question is how can a SOHC engine produce as much power as a DOHC?... the DOHC breathes better so with all things being even it should have the upper hand... right?

also why the SOHC almost produce the same torque but at much less RPM, why is that? what are the factors that decide the RPM at which max. torque is produced??

MMamdouh

[PrecisionBoost]

From what I remember about engine dynamics SOHC engines allways make more torque than DOHC engines at the lower RPM levels.

The SOHC are more efficent at low RPM.

It has to do with port velocity.... DOHC setups have a larger cross sectional port area.... which result in slower intake port velocity.
( think of blowing air out of a small straw vs no straw.... the air from the straw moves very fast and is concentrated.... this is what a SOHC valve is like compared to a DOHC)

So although a DOHC with lots of lift is great at higher RPM it sucks at lower RPM.

Some of the new engine designs use an electrically closeable plate to cover one set of valves so that the engine runs on 2 valves per cylinder at lower RPM and switches to 4 valves per cylinder at higher RPM.

The result is great torque at lower RPM with the top end of a less restrictive DOHC setup.

Also keep in mind that the 1.6L DOHC was capable of nearly 150hp when tested by Lotus but they chose to bring the power levels back down to make it more driveable, more fuel efficent and have less emissions.

So I'm not at all surprized that the DOHC makes similar power to that of the SOHC.

When modifying..... I'm sure the DOHC would make way more power than the SOHC.

[MMamdouh]

thanks for the reply man... you are really great, i got one more question though:

- does this mean that if i removed the intake resonator i will inhance my high RPM HP and hurt my low RPM torque??

- does this apply to the CAT and exhaust resonator removal too?? (effect on low and high RPM torque and HP).

MMamdouh

[abdulr76]

Dear All,

Please help me. Could you guys please confirm that, Opel Kadett E SOHC / VAUXHALL Astra/Belmont SOHC 1.6 CAM SHAFT can be fitted in Daewoo Racer 1.5 TBi SOHC Engine (G15SF).
My Daewoo Racer CAM SHAFT is not working properly, needs to be replaced.
I feel both engines are same.

Regads,

[Efratech]

it should fit.

[PrecisionBoost]

thanks for the reply man... you are really great, i got one more question though:

- does this mean that if i removed the intake resonator i will inhance my high RPM HP and hurt my low RPM torque??

- does this apply to the CAT and exhaust resonator removal too?? (effect on low and high RPM torque and HP).

MMamdouh

This is an old one.... but it appears that I missed answering it.

No.... the intake resonator is for sound deadening purpose only.... it's a restriction.... so removing an intake resonator will give you hp gains all the way accross the RPM band.... but it will be more noticeable at higher RPM levels.

There are lots of different answers about removing restrictions in the exhaust system.... I'm a firm beliver that less restriction equals more power but it seems that each engine will react to a "straight through" system differently.

There is something called reversion where the exhaust from one cylinder will go up a pipe from the other cylinders.

Sometimes this causes a great deal of restriction since the exhaust pulse from cylinder 1 might push against the pulse from cylinder 3.

There are very complex dynamics at play in the exhaust system.... you can get all kinds of nasty things like resonance and reversion.

So.... sometimes when you take out this stuff you will find that there are spots on the RPM band which actually decrease in power.

Most good exhaust manufacturers will fool around with different header lengths and designs ( eg 4-2-1 or 4-1 ) until they get the best horsepower curve.

So..... in answer to your question about exhaust.... I have no idea

The only way to find out is to dyno your car, remove the parts and dyno it again.

I removed my resonator but left my factory catalytic converter and I made some significant power gains without any noticeable loss in power throughout the RPM band.

[Stefan]

My question is how can a SOHC engine produce as much power as a DOHC?... the DOHC breathes better so with all things being even it should have the upper hand... right?

The DOHC is horribly restricted from the factory. The reason? Far as I know internal politics and marketing...

Stef

[nefary]

Also keep in mind that the 1.6L DOHC was capable of nearly 150hp when tested by Lotus but they chose to bring the power levels back down to make it more driveable, more fuel efficent and have less emissions.

.

did you have a confirmation about that " website , video, or an article"

& if so what is parts in our cars restrict that power?

[Stefan]

what is parts in our cars restrict that power?

First 1.6 DOHC's used by opel had better intakes. The cylinder head had larger ports too. Early management was different also. There may be other things but I can't remember them off the top of my head :P

Stef