VH45DE VTC Operation

[SSDwellah]

Can somebody please verify that this is the correct operation of the VTC on VH45DE's?

http://www.nissanv8.com/viewtopic.php?t=57

If these diagrams are correct it looks ***-backwards. Look in the power graph how the torque peak is higher in RPM when the VTC is on (but is on less than 4600 RPM) and the torque peak is lower when VTC is off (but its off when less than 4600 RPM).

This can't be right because this looks soooo backwards. Was this done for low RPM emissions or something? If the diagrams and output graphs are correct... then we should get significant gains by doing the following:

1. turn VTC off below 4600 RPM, which moves the torque peak lower (which is where you are in the rev range),

2. turn VTC on at and above 4600, which moves the torque peak higher again (which is where you are in rev range)

This will result in a sort of double torque peak (or a wide torque band if you smooth it out). I'd be interested to see dynos from someone with torque/hp curves for:

VTC always off - easiest way is unlug it, assuming that it doesn't piss the ECU offVTC always on - connect 12V or 5V (not sure what is sent but I'm pretty sure its just DC and not some kind of PWM since its always on after a certain RPM point)

That way we should see what kind of operation gives the best performance. Also I would be really interested in seeing people with custom cams try this. I know it requires two dyno runs which costs money, bu I think you may be pleased at how you may be able to regain some of the lost low end that typically comes with hot cams.

Discuss

[maxnix]

You're thinking maybe Nissan didn't do their research?

[Stinky]

Check this out.

zerothread?id=194978

[Raxephon]

FYI: The ecu controls the VTC solenoids via ground, not positive.

So if you want to manually control VTC solenoid actuation you simply have to control the grounds.
Modified by anlasak at 7:04 PM 4/20/2007

[SSDwellah]

Ok, thanks for the great follow up. So this is consistent with what was done for the VG30DE. Then I would still say in terms of the effects, the excerpt from the link I referred to look like a misprint. If this in their factory service manual (or wherever the person got this info), it clearly shows VTC off curve as having a earlier torque peak and the VTC on curve as having a later torque peak. This is counter intuitive and I think someone screwed up the drawings (not the engine).

Also, as you can see with the VTC off we have 8 deg overlap, with it on we have 28 degrees. This makes sense and goes along with theory: at higher RPM, overlap will help the VE by filling the cylinders more fully (VTC ON), whereas at low RPM this is not needed (VTC OFF). Also, in the table, with VTC on they say overlap is Sooooo... all things considered I think those drawings/tables are mixed up! Thanks for sending the link to the dyno graph... that definitely cleared up what's REALLY going on: bad documentation.

[Raxephon]

.....If this in their factory service manual (or wherever the person got this info).....

I'm the person that posted the vtc diagrams on nissanv8, and they came directly from my factory service manual.

[SSDwellah]

Oh Ok then can you see what I mean about it looking backwards from the actual operation? If not and you want to talk offline from this thread, the feel free to send me a PM.

[mtcookson]

Looks like the numbers themselves are just backwards... though, I'm a little on the tired side to be looking at that kind of stuff.

[SSDwellah]

Unfortunately its not just the numbers. For example in the table, it says valve overlap is INCREASED with VTC on when actually its decreased... with VTC off it goes back to its intrinsic overlap which is HIGHER (28 degrees VTC off vs 8 degrees VTC on). Basically there are inconsistencies there that confused me at first, but now that I know the real behavior is similar to the VG30DE and saw the dyno graph Stinky linked to, I see right through the factual errors. I am tempted to modify the graphics and repost them here corrected.

[Q45tech]

VVT off at idle = smooth idle from low overlapVVT on until 4600 = increases air flow when velocity is slow to increase peak torque.

VVT off after 4600 as over lap is no longer need as velocity is high to fill cylinders.

Remember the runners are tuned to increase torque at 4,000 rpm and the 4th helmholtz resonation occurs at 5500 and the 5th at 6,000 rpm.Runner diameter is set at plenum for 6,000 and taper at head is 5500.

On an engine dyno you see peaks at 4,000, 4500-4600, 5500 dip at 5750, final peak at 6,000 depending on air temperature.

This is a high pro engine adapted to work with AT and pull a 4300+ pound lux automobile.

Serious design [tuning] compromises to function down to 1500 rpm* in 4th lugging with AC on.

* Total intake out to air horn designed to bump up torque by 3-5% at 1500-1700...............45-51 mph with 0.694 x 3.538 = 2.455 total gearing in 4th with 215/65/15 tires.

The 4.0 lexus of the same era had lower rpm torque/hp peaks and thus more torque at same low rpm without intake tricks and VVT........which was added in 1998.

Don't confuse peak torque with sucky low rpm torque...............what happens when you use BIG 2 x 1.5" [1.3" exhaust] intakes on such a small engine.........todays 4.5 has much smaller intake valves 1.42" and 1.23" exhaust ~~~11% larger valve area on early 4.5.

If you take the old engine and tune runners for peak HP vs modern engine you will see how very very good the old girl was.

[PopPop]

Plus all VVT Sensors were not created equal or not the same on the 90-94 models. If I remember correctly had different effects on your timing advances kicking in and out.

[Q45tech]

There are no VVT sensors just an oil pressure cut valve driven by a solenoid [both wired in parallel] so there might be a fraction difference in time to move valve depending on oil pressure at valve.

[SSDwellah]

Q45Tech - Yes you are right! I made a typo, the VTC is off at high RPM causing DECREASED overlap! Damn I can't believe I screwed that up. Here is a link to an article on the VG30DE/TT which includes a section on the NVCS. It confirms what you are saying and has dyno graphs consistent with the operation of the contemporary VH45DE.

http://autospeed.drive.com.au/....html

[Q45tech]

I'm almost always right [about Q] because I spend a few moments [hours, days, weeks] researching even things I know to be true before engaging typing fingers.

Plus after 9 years of moderating on web you better be right or stand by for extreme abuse.

I have a dedicated raid sever that copies everything I've typed and transmitted over emails and the web since 2000.............teaches you to be careful what you say. I even copy all work communications to my home server.

Luckily most sites allow editing after the fact.

[Mettler]

Summarised as follows:

Idle \ VTC off \ Cam retarded \ 8deg overlap

<4600rpm \ VTC on \ Cam advanced \ 28deg overlap

>4600rpm \ VTC off \ Cam retarded \ 8deg overlap


Modified by Mettler at 1:47 AM 4/28/2007