Ford Forums banner

1 - 20 of 23 Posts

·
Mr Photoshop
Joined
·
1,155 Posts
Discussion Starter #1
Is VCT similar or the same as Honda's version which gives a more agressive cam profile at a certain rev range? Would this allow for a fairly aggresive cam that would not usually be considered for street use to used and able to have decent low range power?
 

·
BOFH
Joined
·
7,560 Posts
the VCT (from my limited understanding) simply changes the timing of the cam at the 3700rpm range (in the AU at least).

Stolen from another thread:
VCT - Variable Cam Timing. IIRC the Falcon Six's VCT setup retards the cam timing by 10 degrees after the engine revs exceed 4000rpm(is actually 3700rpm). From my understanding of it, what happens is that when the engine revs exceed 4000rpm, the engine retards the camshaft timing 10 degrees in relation to the crankshaft position, which allows a better higher RPM cylinder fill. Unfortunately, it also retards the exhaust timing, being the Falcon's head is still an SOHC design. This feature should be better when the Falcon comes out with a DOHC head.

I'm not sure about the actual retardation, I thought it was 13 degrees however the concept is correct.

So can you use a more agressive cam? Thats a good quetion which I would love to find out myself.
 

·
If Only I Had Lexus Power
Joined
·
827 Posts
The cam changes all the time aparently in the ba. if you have an auto and roll the car forward slowly in drive apparently you can notice the timing change even at just above idle
 

·
Blue Blood
Joined
·
1,375 Posts
redGhia said:
The cam changes all the time aparently in the ba. if you have an auto and roll the car forward slowly in drive apparently you can notice the timing change even at just above idle
I can notice it in my BA XR6 manual :)
 

·
Blue Blood
Joined
·
1,375 Posts
CSV_LS1 said:
Is VCT similar or the same as Honda's version which gives a more agressive cam profile at a certain rev range? Would this allow for a fairly aggresive cam that would not usually be considered for street use to used and able to have decent low range power?
I'm not sure about Honda's VTEC, however it is similar to Toyota's VVT-i used in the 1.3, 1.5, 1.8 Echo/Corolla's. That is the cams vary with throttle position/load/requirements. However it does not effect the cam lift which is what Toyota have in the VVTL-i (variable valve timing and lift) which is the 1.8L 4 cylinder in the Corolla Sportivo and the Celica (142kW out of 1.8L ain't bad)

VTEC my guess is something to similar to VVTL-i which is the best of both worlds, allowing timing of the cams/valves to adjust to performance/economy requirements and lift to ensure maximum engine breathing (all the benefits of a lumpy cam without the idle problems).
 

·
Birth, Drift, Death...
Joined
·
3,039 Posts
on the AU XR6VCT the cam is retarded a little at idle (the actual number escapes me, though i was reading about it just the other nite) then is advanced slightly from just off idle to about 3700, when it is retarded again.

im pretty sure its not load dependant, only revs.
 

·
Registered
Joined
·
1,447 Posts
Does the VCT engine pull hard when it hits 3700 like a Honda VTEC engine does? The VTEC system feels almost like a turbo at really low boost...
 

·
Blue Blood
Joined
·
1,375 Posts
MustangNicko said:
Does the VCT engine pull hard when it hits 3700 like a Honda VTEC engine does? The VTEC system feels almost like a turbo at really low boost...
Nah its not like that, its just really progressive power and the smoothness makes the 6000rpm limiter makes it feel like it could go another 500 at least.
 

·
BOFH
Joined
·
7,560 Posts
same with the AU VCT, you dont feel it happen, it just keeps pulling all the way to the limiter. And it does not get that harsh sound to it at all.
 

·
RIP Sox.....
Joined
·
2,580 Posts
VCT has pretty much been summed up by others here already, in that the cam(s) are always in there optimum position relative to the crank, based on RPM.
That is, advanced at low revs, and retarded at high revs.

Ideally and if done properly there should be no step in power, such as a 'powerband' felt because this is exactly what VCT is attempting to rid.
VCT encourages a smooth and wide powerband from idle onwards, and is keeping engine efficiency high at all revs.

If Ford implement dual VCT on the current BOSS 290, it will be a formidable engine indeed.

Rick.
 

·
Birth, Drift, Death...
Joined
·
3,039 Posts
yeah what Soxx said.

with the VCT on the barra engine and the SOHC 5.4 it only alters the cam timing, not the lift.

currently the intake and exhaust cams on the twin cam I6 car moved in unison ie they both are advanced 20degrees or retarded 20 degrees or whatever.

i think they can move though 40 degrees in total (20 retard to 20 advance) but it could be twice that i cant remember. the range of movement inside that is infinite though, its much better than the AU VCT.

currently they have the ability to move the cams independantly which would give even more power and economy, but it would require something like 24 million more programming operations or something - give them a few years im sure it will be an upgrade.

in answer to your original question "Would this allow for a fairly aggresive cam that would not usually be considered for street use to used and able to have decent low range power?"

then in theory, yes. you can use much bigger cams, and then advance them at idle to try and compensate to get a bit better cylinder filling at idle, to give more power off the mark compared to a non-VCT car.
 

·
BOFH
Joined
·
7,560 Posts
Just for those who are curious, I wrote to Crowcams about getting a new, more agressive, cam for my AU VCT and this was the response:

Hi

We could do a cam for this engine but you would need to fit a piggy back computer and have it tuned we can supply cam only the cost is $440 inc Tax

Yours Ray
So yes, there are other cam choices but with the cost of the cam, the fitting AND the new piggy back chip it would become a fairly expensive excercise I think.
 

·
Can't wait for Winton...
Joined
·
2,759 Posts
Casper said:
This feature should be better when the Falcon comes out with a DOHC head.
Yep should be, and will when they separate the cam phasing for intake and exhaust.

VTEC uses a third cam lobe and a separate rocker that comes into action above the set rpm point.
 

·
100MPH Hunter
Joined
·
1,045 Posts
I also heard from a Ford enigineering report that all the people who pour premium petrol into there VCT equiped cars where actually not benefiting at all from the petrol, and I think they were doing more damage. It was to do with the movements of the cam in relation to revs.
 

·
RIP Sox.....
Joined
·
2,580 Posts
They may or may not be benefiting from the use of premium fuels as that would be determined by C/R, however they certainly would not be doing any damage.

Rick.
 

·
100MPH Hunter
Joined
·
1,045 Posts
This is just what I got told, so I thought I would put it up here. This gentleman had to replace several series 1 and 2 vct components due to something to do with the use of premium fuel.
 
1 - 20 of 23 Posts
Top