Power Fc Vs Nistune

[Torques]

I found the attached dyno, it's different boost levels with VTC on or completely off.

VTC is switched at around 4700

I have no dyno with VTC switched on all the time, sorry!

The graphs shows torque only.

Edited March 20, 2012 by Torques

[Torques]

AFAIK the inlet cam is advanced by around 18 degrees.

This gives the charge more time to fill the cylinder, especially at lower boost this might be helpful.

However this measure also increases valve overlap which leads to charge reversion.

Turbo engines usually have very tame camshafts anything 'wild' or overlap is no good since the back-pressure in the cylinder is reversing through the inlet.

(Of course there are many different turbo engines ...)

I think some people don't understand what VCT is actually doing..

Edited March 20, 2012 by Torques

[bubba]

AFAIK the inlet cam is advanced by around 18 degrees.

This gives the charge more time to fill the cylinder, especially at lower boost this might be helpful.

However this measure also increases valve overlap which leads to charge reversion.

Turbo engines usually have very tame camshafts anything 'wild' or overlap is no good since the back-pressure in the cylinder is reversing through the inlet.

(Of course there are many different turbo engines ...)

But I believe it advances it an even 20deg.

My comment wasn't directed at anyone in particular but more so at the generic comments of "leave it on all the time".

I know when it is enabled at idle in my car the idle is far from smooth but could probably be tuned smooth. If left on in the high rpm range my set of the pants dyno tells me it has lost power.

It also makes a huge difference in the midrange, particularly with a bigger turbo and helping it get on boost (even more particularly because my car is auto with the standard stall speed).

Jez, if you get your setup working with the VCT on all the time below 'X' rpm, will that affect overrun running? i.e. trying to get my head around how the engine will respond on decel with the intake cam advanced 20deg

[KiwiRS4T]

I had vct permanently on for a few days while my ecu was being modified ( chipped R32 ecu piggy backed on to my Stagea ecu) . Idle was not so flash and I knew that I was losing a bit of power at the top end (over 5000 roughly) - so its driveable but not recommended .

[Torques]

Yes, the overlap of the camshafts is no good for low rpm / idle.

The exhaust gases revert into the inlet ..

That's why the Z32 ECU only switches to 'on' at

higer rpm > 2000

a minmum speed

car in gear

I had vct permanently on for a few days while my ecu was being modified ( chipped R32 ecu piggy backed on to my Stagea ecu) . Idle was not so flash and I knew that I was losing a bit of power at the top end (over 5000 roughly) - so its driveable but not recommended .

[Rolls]

It advances the intake cam, this decreases overlap increasing the intake velocity at low rpm removing reversion but causes a restriction in the top end, surely this would make the idle better not worse, eg it is the opposite of putting a big cam in?

[zebra]

It advances the intake cam, this decreases overlap increasing the intake velocity at low rpm removing reversion but causes a restriction in the top end, surely this would make the idle better not worse, eg it is the opposite of putting a big cam in?

[JonnoHR31]

It advances the intake cam, this decreases overlap

increases overlap

[Don Dada]

Found it.......

Green(tq) / black(hp) = stock ecu 10psi nvcs off (huge dip due to R&R)

Dark blue(tq) / Red(hp) = Tuned ecu 10 psi nvcs on from 1500rpm right up ( notice how it shits itself after 5000rpm)

Orange(tq) / Light Blue(hp) = Tuned ecu 10 psi nvcs off

..so for reference from the graph at 3000rpm it makes about 10hp and 17 ft-lbs more when nvcs is activated

Edited March 21, 2012 by Don Dada

[Torques]

It advances the intake cam, this decreases overlap increasing the intake velocity at low rpm removing reversion but causes a restriction in the top end, surely this would make the idle better not worse, eg it is the opposite of putting a big cam in?

Overlap = Time Inlet and Exh\aust Valves are open at the same time, so when you open the inlet earlier overlap is increased.

Larger ovelap is in general not helpful to idle.

At low rpm overlap also causes the intake charge to be sucked out of the exhaust due to the relatively long time the exhaust side is open with regards to rpm.

[Torques]

Very nice,

Would you have this a bit larger please (it's stamp size)

Found it.......

Green(tq) / black(hp) = stock ecu 10psi nvcs off (huge dip due to R&R)

Dark blue(tq) / Red(hp) = Tuned ecu 10 psi nvcs on from 1500rpm right up ( notice how it shits itself after 5000rpm)

Orange(tq) / Light Blue(hp) = Tuned ecu 10 psi nvcs off

..so for reference from the graph at 3000rpm it makes about 10hp and 17 ft-lbs more when nvcs is activated

[Rolls]

increases overlap

ah yes, confusing it with exhaust cam.

[Don Dada]

Very nice,

Would you have this a bit larger please (it's stamp size)

^^ fixed

[zebra]

increases overlap

But the cam is advanced. Opens sooner closes sooner

So there is less overlap with the exhaust valves

[Rolls]

Opens later, not sooner.

Advancing intake cam means it overlaps more, retarding exhaust cam means it overlaps more. Think of advancing as turning clockwise and visualising the cam profiles.

edit:

good explanation here

http://www.dsmtuners.com/forums/articles-engine-fuel/221200-cam-basics.html

Edited March 22, 2012 by Rolls

[zebra]

You guys need to re- Read what advancing a cam does

Increasing overlap increases cylinder filling at high rpm

So why would you want that when trying to increase bottom end mid range torque

Advancing the intake cam means that it closes earlier than when set at zero.

Hence decreasing the amount of time both intake and exhaust valves are open I.e overlap

Advancing the exhaust cam increases overlap as does retarding the inlet cam

[Rolls]

You guys need to re- Read what advancing a cam does

Increasing overlap increases cylinder filling at high rpm

It isn't that simple, you can change the amount of overlap, but also the where in the filling cycle the overlap occurs.

Advancing the exhaust cam increases overlap as does retarding the inlet cam

it is the opposite to that.

[zebra]

I've always been told different to that....

Eg advancing the cam is turning it the same direction as the crank rotation

Eg http://www.compcams.com/technical/FAQ/LSAproperties.asp

In the case uou are describing the 25s VCt must retard the cam as having huge overlap on a small motor is a sure fire way to lose all bottom end grunt

As you say Not that simple but a good rule of thumb

[GTSBoy]

It is very very simple.  Stop thinking about everything else and start fresh.

1) Overlap is the time when the exhaust valve is closing and the inlet valve is opening.  Inlet valve closure has nothing to do with it.  Only opening.

2) Advancing the inlet cam will of course make it open earlier.  This will increase overlap.

VTC is active between 1500-4700 (or thereabouts, depending on what ebgine we're talking about).  Make your own conclusions about whether it is advanced or retarded by the actuator.

Edited March 22, 2012 by GTSBoy

[D_Stirls]

Zebra, think about the order of the strokes,

Your thinking that the exhaust stroke happens after the intake stroke (which it does, eventually) so if your advance the intake cam timing your moving it away from the exhaust stroke, but the exhaust stroke is immediately before the intake stroke so advancing the intake timing moves it further into the ending exhaust stroke. The intake stroke has compression and power before you get back to exhaust.

Edited March 22, 2012 by D_Stirls