What engine could produce more hp?? sohc or dohc?

jorge · Post by **jorge** » Sun Dec 16, 2007 10:40 pm

I am rebuilding my engine it is a 1.6 dohc. I am plannig to to a hybrid engine a 1.6 sohc. This engine can produce more power???

Pir0 · Post by **Pir0** » Sun Dec 16, 2007 10:54 pm

I dont know much about those actual engines but common sense tells me the DOHC can. From my experiences DOHC tend to me more delicate than a SOHC though... but that's what i've found with Vauxhall engines, not Daewoo.

daewoomofo · Post by **daewoomofo** » Sun Dec 16, 2007 11:27 pm

daewoo's run vaux engines, so they are the same

Pir0 · Post by **Pir0** » Sun Dec 16, 2007 11:30 pm

I know they're all GM and have a lot of the same dimensions etc, but they are different

Post by **PrecisionBoost** » Mon Dec 17, 2007 12:04 am

A SOHC engine will produce more torque at lower RPM but less top end power

A DOHC engine will produce less torque in the mid range but it will have more top end power

So a SOHC will feel quicker than a DOHC for daily driving because it is better in the mid range RPM levels

But a SOHC will start to feel like nothing is there when you get up around 4500 RPM

The DOHC will feel gutless in mid RPM but pick up quickly as you pass 4000 RPM

In a race it's most likely the DOHC would win because you would run it up near redline then shift (bringing it down to 4500 RPM ) then run it up near redline and shift.

So the SOHC would pull ahead in 1st gear due to it's supperior low end torque it would have less power at high RPM (4500 RPM ) so the DOHC would quickly catch it as you moved into 2nd and 3rd gear.

So it's a trade off..... better torque in mid RPM levels with the SOHC where you are on daily driving versus the power of a DOHC at high RPM.

The difference between the two engines is not so much the cams ( two versus one ) as it is the valves.

The SOHC will have two valves and the DOHC will have four valves.

At lower RPM the SOHC will have a better efficency than the DOHC but as the RPM rises the DOHC will become more efficent than the SOHC.

The best engines (like my Mazdaspeed 2.3L DISI turbo ) have a shutter valve to make maximum power.

Basicly at lower RPM the engine shuts a valve and completely closes off one of the ports in the DOHC head so that it's more efficent and makes more power

Then at higher RPM the valve opens and the engine intakes air through both ports which again makes it more efficent and makes more power.

So... a DOHC that blocks one valve path at low RPM will be the most efficent and therefore fastest engine.

Hope that helps.

Chris

jorge · Post by **jorge** » Mon Dec 17, 2007 1:00 am

Ok good info... I am planning this because I have a 1.5 sohc and a 1.6 dohc. And I feel the 1.5 better than the 1.6.
Ok the 1.5 sohc have, nubira ported throtel, cold air intake (custom made whit the factory intake hose), no cats, no resonator and dynomax exhaust muffler (2 1/4). And the 1.6 dohc have only a air intake (3''), header 4-2-1, and race pipe. But 0-60mph the 1.5 run better than the 1.6. Considering the final drive the 1.5 have a 3.944:1 and the 1.6 have a 4.176. So the 1.6 its supposed to react better than the 1.5 and other thing have more "hp". This thing turn to confuse me a little bit whit this test. Other thing with stock engine 1.5 sohc have 83.5 hp / 5600rpm, and 96 lb-ft./ 3400rpm. And the 1.6 dohc have 105.3 hp/5800rpm, and 107.2lb-ft/3400rpm.

MMamdouh · Post by **MMamdouh** » Mon Dec 17, 2007 7:31 am

great info Chris... i got a question though

why does the SOHC be the moe effecent at low RPMs whereas it has the less flow intake setup? i can't comprehend that fact, is it related to the vacuum in the intake and so?

MMamdouh

mr_g · Post by **mr_g** » Mon Dec 17, 2007 10:41 am

DOHC is superior in any way to SOHC. SOHC is only better in that way, it is stronger if you put forced induction...
In all other cases, DOHC will eat SOHC for launch...

I had 1.6 16V and I was killing every lanos 1.5, even I had more weight (200lbs more) due to A/C, ABS, LPG kit...
A16DM got big potential, but it has to be released... The best way is to make it turbo forced induction... If not, lower the head, port and polish, put bigger throttle body because stock one is silly little thing... And it would put out at least 130HP...

Anyways, that thing about mid range and high end is nonsense... A16DM has VGIS (variable geometry inlet system), and if you get beaten by 1.5, means your 1.6 16V is broken or VGIS doesn't work...

Remove EGR and check VGIS... VGIS will give you strong mid range and on 4500rpm it opens and give you high end...

Also remove catalytic converter... It powers down much A16DM...

Alto my lanos was around 2400-2500lbs (1150kg), I had 9.5-10s 0-60mph time... On good 195/50-R15 tiers... Find me a 1.5 8V Lanos with that time... Even 1.5 8v has about 2200lbs (1000kg)...

jorge · Post by **jorge** » Mon Dec 17, 2007 11:54 pm

I cannot say you what times do my lanos because I never go to the track on it. But I can say. In my lanos 1.5 I win 4 cars of distance betwen my lanos and my friend lanos a 1.6 dohc... That is the test who I do in my lanos. In my lanos 1.5 I win more times than my 1.6 lanos is more slow... Just my two cents...

mr_g · Post by **mr_g** » Tue Dec 18, 2007 9:03 am

There is something wrong with that 1.6 16V (A16DM)...

Take a 2.0 engines for example...

2.0 8V (C20NE) produce 115HP and 150Nm...
2.0 16V (C20XE) produce 150HP and 200Nm...

They are almost the same except pistons, and head... Alto the second one is limited to 150HP... It goes over 160HP easy...
So, I was racing this Lanos with C20SE (2.0 8V 120HP) plus Wizard of NOS 50HP shot, and I beat it good with C20XE (2.0 16V) then it had only 160HP... And the other lanos was less weight than mine... Then I bought NOS from the same guy as he was furious about that race...

2.0 8v with forced induction can go up to 200HP... 2.0 16V with forced induction goes on 300HP with no problems...

Let's go the other way... ITB (individual throtle bodies).... 2.0 16V goes up to 280HP N/A.... 2.0 8V 150HP? It's the head flow problem, so anyway, DOHC heads ARE SUPERIOR...
And if you have some variable timings on valves, or vtec, or vvti, or anything like that, than, SOHC can kiss ass of DOHC as DOHC is like God to them!

:P

Do you want another examples?
My friend drives vectra-A with C20NE (8V) and NX 50shot... Best time about 15.8s...
I drive lanos with c20xe (16V) and wizard of NOS 70shot... Best time about 13.9s...
The weight is almost the same...

mr_g · Post by **mr_g** » Tue Dec 18, 2007 9:23 am

BTW, If you want to open 1.6 engine, that do this... Lower the head (1mm), port and polish the head... Then, put some bigger throttle body. Port and polish intake manifold also. Remove catalityc converter... Put 50mm pipes from exhaust manifold to the end... Put 2 full flow exhaust racing mufflers... Also if you put some aftermarket electronic, or remap stock ECU, you must see at least 130HP! VGIS is very important... So keep the stock inlet manifold...

A16DM has pretty low CR about 9.5:1... You can go up to 11:1 with CR... So lower the head at least 1mm...

http://www.cardomain.com/ride/705337/4

jidasas · Post by **jidasas** » Tue Dec 18, 2007 2:26 pm

Jorge-is your car a 5 speed and his an auto? I know my auto lanos with the 1.6 only does a high 18in the 1/4 mile. the manual does a low 17 though. so maybe that's where the difference lies.

Jimmy

jorge · Post by **jorge** » Tue Dec 18, 2007 10:07 pm

Yes my two lanos are manuals, the lanos 1.6 who I race are automatic, but is 1.6vs1.5. Mr g I understand you but I only say my personal expierence. In my lanos I win to 2.0 lancers, Hyunday Accents 98 and 2005. Mitsubishi mirage 1.5 and 1.8, Toyota echo, Volkswagen golf 95, so I dont know if my car is a aborted one but runs good with a simple 1.5 sohc engine.
And other thing who I see, the 1.6 engine is more $$$ to mantain and repair it, are two tensioners, 16 valves and more, the 1.5 are one tensioner and 8 valves. But if you say a dohc engine produce more fine thats the only thing who I want to know. Thanks...

Post by **PrecisionBoost** » Wed Dec 19, 2007 2:46 am

mr_g wrote:DOHC is superior in any way to SOHC. SOHC is only better in that way
Anyways, that thing about mid range and high end is nonsense... A16DM has VGIS (variable geometry inlet system), and if you get beaten by 1.5, means your 1.6 16V is broken or VGIS doesn't work...

Sorry man, I don't like the fact that your misleading people with the thing "nonsense" comment

I have to say that you don't know anything about volumetric efficency and cylinder filling if you think that a DOHC is superior to a SOHC in low/mid range.

The VGIS system has nothing to do with the valvetrain layout.... the VGIS improves efficency by tuning the runners for particular RPM.

So..... on to the technical stuff.

Obviously the whole goal is to get as much air into the cylinder as possible during each stroke.

The port size is a big factor in how well the cylinder fills, and the port size is directly related to the number of valves.

At low RPM most DOHC engines are less efficent because they have too low of a port velocity to fill the cylinder and burn efficently.

Basicly the square area of the port is the determining factor for velocity

A DOHC has two ports, and overall the ports are usually significantly larger than the SOHC engines.

I will equate it to something simple so people can understand....

Imagine blowing air through a small straw, then switching to a larger straw.

The air coming out of the small straw is very fast, the air coming out of the larger straw is slow

The resistance in the small straw is fine when your not blowing hard but as soon as you really try to blow it starts to give resistance.

The resistance in the big straw is next to zero when your not blowing hard and as you blow harder the resistance only increases slightly.

So a SOHC engine will have a smaller port area and therefore it will offer more resistance to airflow at high RPM

But at lower RPM the air entering the cylinder will be coming in very fast which helps the air/fuel mix better and burn better (producing more torque/power at low/mid RPM )

A DOHC on the other hand has a low port velocity at lower RPM levels and therefore the air/fuel mix doesn't burn as well ( resulting in less torque/power at low/mid RPM )

At higher RPM the port velocity starts to rise quickly and the engine becomes more efficent.

At higher RPM the larger port area allows for less air resitance and therefore more air getting into the cylinder.

In short the DOHC is the best engine for racing but the SOHC is better for every day driving.

When your racing you keep the DOHC up into it's peak power range which makes the car faster.

However.... if you race a DOHC against a SOHC and shift at 3000 RPM the SOHC will kick the ass of the DOHC

That is also the reason why a SOHC will get better fuel efficency if your driving like a granny shifting at relatively low RPM.

The fuel efficency is directly related to the percentage of fuel/air that burns during each cycle.

Higher port velocities will result in a better burn (larger percentage of air/fuel burnt ) during each cycle.

This again is the reason why some companies run their engines like my Mazdaspeed3 MZR 2.3L DISI turbo as a Single overhead valve at low/mid RPM and then open up the other port to be a Dual overhead valve at high RPM.

Hopefully I've made sense of the SOHC vs DOHC issues.... and please don't consider it nonsense as mr_g would suggest.

If it wasn't true then companies like Mazda wouldn't be going through the hassle of adding a restrictor on one of the valve paths.

Keep in mind my Mazda makes nearly 300lbft of torque and still manages to get 25 MPG when I drive the crap out of it on a daily basis.

Post by **PrecisionBoost** » Wed Dec 19, 2007 2:51 am

mr_g wrote: I had 1.6 16V and I was killing every lanos 1.5, even I had more weight (200lbs more) due to A/C, ABS, LPG kit...

Your comparing apples versus oranges... the 1.5L has a different displacement and compression ratio.

The 1.5L was designed with economy in mind, and the 1.6L was designed to have more power (and lower fuel efficency)

I allready stated that during "racing" where your keeping the car at high RPM the DOHC will win, but most people aren't reving up to redline every second of every day.

Both engines have advantages and disadvantages.... but again... you have to understand thermodynamics to know why the differences occur naturally.