Nissan Forum banner

1 - 20 of 23 Posts

·
Registered
Joined
·
60 Posts
Discussion Starter #1
I dont know what its does simple as that
 

·
ex-Super *********
Joined
·
1,410 Posts
It phases the cams to create a varible overlap situation. Do you know what cam overlap is? If not Ill go on
 

·
ex-Super *********
Joined
·
1,410 Posts
Niss200SXGTR said:
think of it as a cheap ass supercharger..
Well, not really. If you wanna have a way to think of it, think of it like having a one cam for gas mileage while cruiseing, and one cam for power mid-range and up. We have DOHC, and we can phase them relative to each other so we dont have to rip the motor apart to put in our "agressive" cam. The VTC does it for us. Its pretty complicate for the uninitated, but I can help. :)
 
N

·
Guest
Joined
·
0 Posts
Okay I'm interested. Please go on. How does it know to kick into aggressive mode? Is it at a set rpm? Is that rpm set by the ecu?
 

·
ex-Super *********
Joined
·
1,410 Posts

·
Registered
Joined
·
393 Posts
VTC only varies cam timing. its like the "i" in "i-VTEC" it allows the intake and exhaust cam to stay open variable amounts of time, relative to eachother: for better efficiency(overlap, like the previous post stated). there are 3 VTC phases. (these are off the top of my head) 3400, 5000, and 6700. at 3400, VTC retards timing, b/c @ lower RPM, you dont need highly-advanced timing. at 5000, VTC advances timing, b/c @ higher RPM, the engine is moving so fast, that advancing ignition helps in getting a complete burn. @ 6700, VTC retards again, so that it degrades power slightly (ga16 doesnt even make great power anyway) and encourages an upshift, just before redline. JWT can alter these VTC shift points or get rid of the last one, b/c there is no good in it being there.
BTW VTEC stands for variable valve timing w/ electronic lift control. this is how you get a "big cam and a little cam on one camshaft" it has 2 lobes: one for low-rpm and one for high-rpm. the low-rpm lobes have lower valve lift, and they stay open for a shorter amount of time... (lower demand for fuel) the high-rpm lobes allow for longer valve lift and they stay open slightly longer, due to higher fuel demand. but VTEC is like a step, not progressive... which is why you get that "VTEC kick." i think most of the german variable valve timing systems and the newer-generation ones like VVT-I (toyota) and i-VTEC (honda) are more progressive, (almost infinately so) so you dont get a nice kick anymore.
VTC does not have the ability to vary valve timing and lift. i believe the new Q-series nissan motors do (qr25, qg35) or in japan, i think the NEO VVL motors do this.
 

·
No Nissan Yet
Joined
·
139 Posts
themonster4door said:
I dont know what its does simple as that
hey monster. read ALL of this site!!! very great info i have for you and others as well!!

technical crap

you will learn alot. it is one of the best site i came across so far.......

James
 

·
ex-Super *********
Joined
·
1,410 Posts
V i V i D 200sx said:
VTC only varies cam timing. its like the "i" in "i-VTEC" it allows the intake and exhaust cam to stay open variable amounts of time, relative to eachother: for better efficiency(overlap, like the previous post stated). there are 3 VTC phases. (these are off the top of my head) 3400, 5000, and 6700. at 3400, VTC retards timing, b/c @ lower RPM, you dont need highly-advanced timing. at 5000, VTC advances timing, b/c @ higher RPM, the engine is moving so fast, that advancing ignition helps in getting a complete burn. @ 6700, VTC retards again, so that it degrades power slightly (ga16 doesnt even make great power anyway) and encourages an upshift, just before redline. JWT can alter these VTC shift points or get rid of the last one, b/c there is no good in it being there.
BTW VTEC stands for variable valve timing w/ electronic lift control. this is how you get a "big cam and a little cam on one camshaft" it has 2 lobes: one for low-rpm and one for high-rpm. the low-rpm lobes have lower valve lift, and they stay open for a shorter amount of time... (lower demand for fuel) the high-rpm lobes allow for longer valve lift and they stay open slightly longer, due to higher fuel demand. but VTEC is like a step, not progressive... which is why you get that "VTEC kick." i think most of the german variable valve timing systems and the newer-generation ones like VVT-I (toyota) and i-VTEC (honda) are more progressive, (almost infinately so) so you dont get a nice kick anymore.
VTC does not have the ability to vary valve timing and lift. i believe the new Q-series nissan motors do (qr25, qg35) or in japan, i think the NEO VVL motors do this.
The VTC has nothing to do with ignition timming. Only cam phasing. Like I said before its all about cam overlap. Lets define the term cam overlap in simple terms.

Cam overlap:
The amount of time that the intake and exhaust valves are open together.

Why bother with it?
At lower rpms less overlap helps idle quality and fuel efficancy. At higher rpms more overlap rpms it helps make power.

What does this mean and what does it do in a GA with VTC?
At low rpms(under 1500 it has been stated somewhere) the GA is in a low overlap mode. After that it goes into high overlap to help make power. Then at about 5500 rpm it goes back into low over lap to "make" you shift.

How does it do it?
IIRC the VTC acts only on the intake cam. It advance and retards its timming relative to the exh cam. At the switch over point(1500prm) it retards the intake cam giving you greater over lap, then at 5500rpm it advances the intake cam causing the over lap to become smaller, thus losing power and "making" you shift.

As far as ignition timming the VTC has nothing to do with it. The only thing that controls the ign timming is the ECU, there are no preset stages, the ECU can put the ign timming anywhere it wants(to a point) at any time.
 

·
Nissan Fetish
Joined
·
150 Posts
i was just think about it

Just out of curiousity, i was thinking if you could hook up a vtec controller to the vtc? or is that just honda. And i dont think that vtc is electonic either so i dont think a vtec controller would work anyway.

It was just a thought. I know a vtec controller is just for vtec.
 

·
ex-Super *********
Joined
·
1,410 Posts
The VTC is electronic. It is a simple soleniod. Vtec is a totally different system, i doubt it would work. You could possibly mess witht he VTC system with exterior controllers, but I dont think it would be very usefull.
 

·
ex-Super *********
Joined
·
1,410 Posts
The info I had heard about VTC points seems to be incorrect(I always thought it was).
Cam retard(high over lap stage) happens at 5300rpm
Cam advance happens(low over lap stage) at 6600rpm
 

·
Registered
Joined
·
393 Posts
ok. lemme open by saying sorry i typed "timing," rather than "cam timing," which is what i meant. cam phasing is pretty much cam timing. otherwise, i think i gave a pretty good explaination. the points, like i said were off the top of my head. i think youre right about the advance, retard, advance thing tho. its kinda backwards w/ cam timing, rather than ignition timing. thats why i thought that. (you want advanced ignition timing @ high RPM and lower ignition timing @ low RPM versus retarded cam timing @ high RPM and advanced cam timing @ low RPM) i just checked @ kojimas garage (sentra.net) "retards @ 5300; advances @ 6600" i would assume its on "advanced cam timing" from idle up to 5300. so we were all wrong! o... and VTEC is a hydraulic system; there are 2 pairs of cam lobes, and the camshafts physically move from one lobe to the other. and about using a VTEC controller.... dude, thats honda only
 

·
ex-Super *********
Joined
·
1,410 Posts
I wasnt wrong. I said it retards at 5300 and advances at 6600. Retarding the intake cam(again relative to the exh cam) causes increased overlap. Advancing the intake cam causes decreased overlap. Low overlap= good low rpm performace, high overlap= good high rpm performance.
From idle to 5300rpm the system is in low overlap mode. Once 5300rpm is crossed the intake cam retards putting the system into high overlap mode up until 6600rpm. Once 6600rpm is crossed the intake cam advances and puts the system back into low overlap mode "telling" you to shift.

Cam timming or phasing has nothing to do with the amount of time the vavles are open, only the amount of time BOTH the exh and int valves are open TOGETHER.

You shouldnt compare it to ign timming, it only confuses the situation.

VTC and Vtec are both hydraulic and electric. An electronic solenoid opens or closes the oil flow that allows the change points.

Im not trying to shoot you down vivid, only trying to give proper info. I come off harsh sometimes because I am well educated in the automive field and do this stuff everyday. Sometimes I forget that not everyone has had the schooling I have.
 

·
Registered
Joined
·
60 Posts
Discussion Starter #17
THank u all now i understand how that thing work but now i have another question if u cant use a APEXi VAFC then what type of vtc or even vvl controller can us nissan people use to make it kick in earlier
 
1 - 20 of 23 Posts
Top