How many revs for DOHC switchover?

[ssharple2001]

Hi guys,

   I've got a 2012 metal edition mk7 Fez and was wondering at what revs the cam switches over? Anybody know?

TIA

Steven

[Luke4efc]

It's not VTEC lol.

DOHC just means you have 2 camshafts (one controlling intake valves and the other controlling exhaust valves). Having 2 cams means you can have 4 valves per cylinder (2 intake, 2 exhaust). In simple terms, you increase the amount of air you can get in the cylinder so more power and easier/ more flexible tuning at the factory.

[Kental]

I thought the normally aspirated 1.1 and the old 1.25 were VCT engines, not sure about the 1.0 Ecoboost. Are they not like a VTEC or a Toyota VVT?

[ssharple2001]

It's a 1.6 ti vct

I thought it was like a Vtec but Ford called it Zetec instead - doh!!

So, after a very quick google (i'm at work), it looks like it constantly adjusts the valve lift - not just at a specific rpm?

[Comares2001]

It's just a standard twin cam 16 valve engine.Ford have used the name Zetec for at least 25 years.

[pragmatix]

24 minutes ago, Comares2001 said:

It's just a standard twin cam 16 valve engine.Ford have used the name Zetec for at least 25 years.

Not exactly a standard twin cam as VCT stand for variable cam timing

[Luke4efc]

4 hours ago, Kental said:

I thought the normally aspirated 1.1 and the old 1.25 were VCT engines, not sure about the 1.0 Ecoboost. Are they not like a VTEC or a Toyota VVT?

I don't think the 1.25 was VCT, the 1.6 was though.

Basic explanation lol so don't have a go.

It works pretty much the same as Toyota VVT in the fact that the camshaft isn't keyed to the pulley and can the independent rotation can be controlled to a few degrees. 
However VTEC is different in the fact it it has a second set of cam profiles on the cam shaft which keep the valves open for longer. These profiles are only used when the engine hits a certain RPM.

 

[Kental]

1 hour ago, Luke4efc said:

I don't think the 1.25 was VCT, the 1.6 was though.

Basic explanation lol so don't have a go.

It works pretty much the same as Toyota VVT in the fact that the camshaft isn't keyed to the pulley and can the independent rotation can be controlled to a few degrees. 
However VTEC is different in the fact it it has a second set of cam profiles on the cam shaft which keep the valves open for longer. These profiles are only used when the engine hits a certain RPM.

 

Once the engine was in the Ka+ (2016-18) the 1.2 Engine in either 70 or 85ps was VCT.  I assumed this was the same engine as the Fiesta 1.25 engine.

Being thick, what advantage does 2nd profile give over independent rotation? I assumed variable timing would be more advanced as it has many  options rather than just 2.

[Kental]

Sorry the Ford engines are Ti-VCT apparently Twin Independent Variable Cam Timing 

[Luke4efc]

22 minutes ago, Kental said:

Once the engine was in the Ka+ (2016-18) the 1.2 Engine in either 70 or 85ps was VCT.  I assumed this was the same engine as the Fiesta 1.25 engine.

Being thick, what advantage does 2nd profile give over independent rotation? I assumed variable timing would be more advanced as it has many  options rather than just 2.

If the intake valves open more (higher profile cam) then you can force more volume of air into the cylinder on each rotation. More air means you can put more fuel in and therefore get more power.

If you rotate the valve timing so that the exhaust valve shuts slightly earlier than before, you leave some of those exhaust gasses in the engine. This means on the next stroke, less air has to fill the remaining space (effectively making your engine capacity smaller. So going from a 1.6L to a 1.4L for example.). This happens at low speeds where you don't need as much power so can use less fuel.

In most circumstances, the intake valve opens slightly earlier at low RPM's and later at high RPM's to get the best performance from the engine (I'd suggest looking up a video animation if you want to understand this better).

[Eng_Ahmad1986]

^{On ti-vct ( Time independent Variable Cam Timing ) equipped engines the camshafts are connected at their ends with a hydraulic cam phasor and an electronic solenoid valve, the engine control unit according to many inputs actuates the oil pressure within those cam phasors by the means of the solenoid valve to increase/decrease oil pressure inside the phasor unit to shift the cam profile in either direction to decrease emisions, save fuel, induce the so called " scavenging " process that improves engine efficiency and reduce the turbo lag as much as possible in turbocharged engines 🙂} 

[Kental]

On 2/27/2020 at 8:34 PM, Eng_Ahmad1986 said:

^{On ti-vct ( Time independent Variable Cam Timing ) equipped engines the camshafts are connected at their ends with a hydraulic cam phasor and an electronic solenoid valve, the engine control unit according to many inputs actuates the oil pressure within those cam phasors by the means of the solenoid valve to increase/decrease oil pressure inside the phasor unit to shift the cam profile in either direction to decrease emisions, save fuel, induce the so called " scavenging " process that improves engine efficiency and reduce the turbo lag as much as possible in turbocharged engines 🙂} 

Interestingly the only Fiesta engines that quote Ti VCT are non turbo ones.

[TomsFocus]

30 minutes ago, Kental said:

Interestingly the only Fiesta engines that quote Ti VCT are non turbo ones.

The EcoBoosts also use VCT, they just don't need to advertise it as the 'EcoBoost' branding is enough.

[Eng_Ahmad1986]

2 hours ago, TomsFocus said:

The EcoBoosts also use VCT, they just don't need to advertise it as the 'EcoBoost' branding is enough.

actually Ford defines the Ecoboost as a technology which includes turbocharging, direct injection, and Ti-VCT 🙂 

[Kental]

On 2/27/2020 at 7:16 PM, Luke4efc said:

If the intake valves open more (higher profile cam) then you can force more volume of air into the cylinder on each rotation. More air means you can put more fuel in and therefore get more power.

If you rotate the valve timing so that the exhaust valve shuts slightly earlier than before, you leave some of those exhaust gasses in the engine. This means on the next stroke, less air has to fill the remaining space (effectively making your engine capacity smaller. So going from a 1.6L to a 1.4L for example.). This happens at low speeds where you don't need as much power so can use less fuel.

In most circumstances, the intake valve opens slightly earlier at low RPM's and later at high RPM's to get the best performance from the engine (I'd suggest looking up a video animation if you want to understand this better).

This week’s Wheeler Dealers Ant describes VANOS. Is that VCT?

[eddie eastwood]

https://en.wikipedia.org/wiki/VANOS

https://www.eeuroparts.com/blog/bmw-vanos-explained/