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Q"s about VVT RB25DET??? WHAT IS WHAT??

85URK

By 85URK,
in Engines & Forced Induction

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Col-GTSX Grand Master

Col-GTSX

Posted
Posted

Sydney kid is correct... I will confirm

All R33's i have seen and to my knowledge are al VVT

As for the coil packs the only difference inbetween the S1 and S2 is the ignighter pack.

My personal understanding is that the R33 25 motor has a signal from the cam mag to the reciever pictured above which switches the ECU to VVT stage. But i dont believe it cuts out at any rev range... It works from 3200 rpm right threw to red line.

The Neo R34 can adjust due to load... any where inbetween 0 and 17 degres (if i remember corectlly). I covered this module at Tafe and we used the skyline neo as a test engine. But that was 5 years ago....

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Maxx Veteran

Maxx

Posted
Posted
Sydneykid, i'm not calling you a liar, but i'm pretty sure the R33 NVCS is OFF from 0 - 1050rpm, then ON until 4500rpm, then OFF again until redline. This is how it is setup on my RB30DET and I've noticed a distinct lack in power up to 4500rpm when the NVCS plug falls off the solenoid! (due to lost metal retaining clip).

i heard similar as well, the other "sydneykid"(someone else who knows a lot)

told me it was from 1050rpm - 5200rpm

MonstaS4 Collaborator

MonstaS4

Posted
Posted
....My personal understanding is that the R33 25 motor has a signal from the cam mag to the reciever pictured above which switches the ECU to VVT stage. But i dont believe it cuts out at any rev range... It works from 3200 rpm right threw to red line.......

Wrong!!! The ECU uses the CAS signal (RPM) and load to determine when the NVCS solenoid switches ON. If the engine is at light load, irrespective of RPM, the solenoid stays OFF, improving economy and emissions. If the engine is under load (dunno what the trigger point is) AND it is between 1050 and 4500 rpm, solenoid switches ON, advances the inlet cam 20 degs, giving more overlap and stronger midrange performance.

That is a solenoid, not a reciever, circled above. It controls the flow of oil to the cam advance mechanism.

Sydneykid Grand Master

Sydneykid

Posted
Posted

Let's kill 2 birds with stone stone here. I have the Datalogit plugged into an R33 RB25DET and on screen "Settings 1" it has the VCT set at 4,700 rpm. I have not changed it on this engine, so that is the default RPM as selected by Apexi. It doesn't have different "on" or "off", or "in between" or "load" or any other selection. Just RPM and just ONE RPM, so it turns on at 4,700 rpm on the way up and off at 4,700 rpm on the way down. That's it, no more complicated than that.

So tango, yes the PFC does have VCT control and it is adjustable, ie; pick an RPM.

How do I pick an RPM?

Well I do a power run with the VCT off until 8,000 rpm (ie; past the rev limit, so it never turns on). I graph that.

Then I do a power run with the VCT on at 800 rpm (ie; at idle, so it is on all the time). I graph that.

Then I overlay the 2 graphs, where the power curves cross is the best VCT change over point. Nissan's 4,700 rpm is pretty close every time, regardless of the engine mods. So it appears to me to be rpm dependant ie, the speed of combustion cycle. Load, throttle opening, power etc all seem to be irrelevant in a simple "on" or "off" scenario.

BTW, the power curves only ever cross at one point, so it makes no sense to have multiple "on's" and "off's"

In an R34GTT, with its more sophisticated VCT control via the more powerful and faster ECU, there are obviously other parameters taken into account. Logically to allow appropriate selection of the amount of inlet camshaft timing changes and the circumstances as to when they are required.

Hope that clarifies:cheers:

MonstaS4 Collaborator

MonstaS4

Posted
Posted

Guess i'll agree to disagree! Here are a few links....

http://www.tomei-p.co.jp/_2003web-catalogu...haft-specs.html

http://www.max-boost.co.uk/max-boost/cylhead/cams.htm - read "under construction" section at the bottom of the page.

http://www.v6performance.net/forums/showth...?t=15976&page=1 - not an RB25 but operation is identical, just different switch points.

Col-GTSX Grand Master

Col-GTSX

Posted
Posted

As i said MonstaS4 it was "my understanding" i was not sure....

This system is very different to Toyotas system... Although i didnt remember the topic from Tafe. I did work with the RB25 motor, but that was long ago. Ill try and retrieve my notes from Tafe and get you an exact answer. As we compaired Nissan with Toyota.

Sydneykid Grand Master

Sydneykid

Posted
Posted
Guess i'll agree to disagree! Here are a few links....

http://www.tomei-p.co.jp/_2003web-catalogu...haft-specs.html

http://www.max-boost.co.uk/max-boost/cylhead/cams.htm - read "under construction" section at the bottom of the page.

http://www.v6performance.net/forums/showth...?t=15976&page=1 - not an RB25 but operation is identical, just different switch points.

Let's start with the Tomei spes, what Tomei are recommending to me is to set the VCT switch point at 4,500 rpm on the ECR33 RB25DET using their camshafts. There is always a no switching point at low rpm as zero overlap is best for emmissions. That's is usually just above idle, but it isn't adjustable, well not on any PFC or chipped std computer I have seen. There is also the question of sufficicent oil pressure at idle (to rotate the camshaft), so switching is best left till above the fastest idle rpm. So Tomei say 1050 which should be above the a/c or other load compensation (fast) idle point.

OK max boost, they confirm two timing positons 0 and 20 degrees only. They say 1500 rpm for the lower limit, it may be a typo (1050 rpm). Or they are simply wrong. Either way a 1500 rpm lower limit wouild have it switching on/off/on/off at strange times for no good reason. They indicate 4,200 rpm as the switching point.

Lastly V6 performance, they indicate (on the graph) a single switch over point at ~4,900 rpm on the VE30DE from the 92-94 Maxima SE. But the words directly below say 6,100 rpm, so I assume that must be for the VG30DETT. Bit confusing. Note that the graph starts at 1200 rpm, just enough above fast idle with the VCT already switched.

Bottom line, I don't think we dissagree at all. The only issue I can see is the use of the words "on" and "off". Most people say "4500 rpm switch "on" vct". Whereas the more corrrect terminology would in fact be "4,500 rpm switch "off" vct".

:cheers:

PHaT MR30 Grand Master

PHaT MR30

Posted
Posted

hmm confusing none the less.. but interesting discussion all the same.

so what your saying now sydneykid in basic terms is at the 4700rpm point, the ecu is allowing it to complete the circuit and switch the solinoid 'On' and 'advance the camshaft timing'???

MonstaS4 Collaborator

MonstaS4

Posted
Posted
Bottom line, I don't think we dissagree at all.  The only issue I can see is the use of the words "on" and "off".   Most people say "4500 rpm switch "on" vct".  Whereas the more corrrect terminology would in fact be "4,500 rpm switch "off" vct".

Spot on. That's what i was trying to say earlier. The solenoid switches on at 1500 or thereabouts (advancing the inlet cam 20deg), and off at 4500.

I've tried switching VCT on at idle via the Haltech and it is faily lumpy. There is a distict change in idle quality, so it does appear there is enough oil pressure to rotate the cam mechanism.

PHaT MR30 Grand Master

PHaT MR30

Posted
Posted

hmm still confused but i think i have got it now after studying what sydneykid said and MonstaS4's reply.

Sydneykid when you said you overlayed the two graphs with the vct off on one and on at idle on the other and marked the cross over point i am guessing this point is where it is turned off? my tuner is getting interested in it all and is pushing me along to get the engine running so he can play with it.

  • 3 years later...
frozenwaffles Mentor

frozenwaffles

Posted
Posted

so was there a final answer to this???

1. the advance is off at idle and turns on at 1050 rpm and then turns off at 4700 rpm (or whatever setting you have in datalogit)

2. the advance is off all the way up to 4700 rpm and then on from 4700 all the way up

to me option 2 makes more sense...but yeah whats the go?

SK have you tried any further experiments with changing this value from 4700???

maximajim Community Regular

maximajim

Posted
Posted
original question: From what i know - R32 RB25 = No VCT/VVL (or whatever)

- R33 onwards RB25 = VCT/VVL

No VVL in a RB engine, just NVCS (VCT,VVT,VTC whatever)

so was there a final answer to this???

1. the advance is off at idle and turns on at 1050 rpm and then turns off at 4700 rpm (or whatever setting you have in datalogit)

2. the advance is off all the way up to 4700 rpm and then on from 4700 all the way up

to me option 2 makes more sense...but yeah whats the go?

SK have you tried any further experiments with changing this value from 4700???

NVCS is designed to increase mid range torque. There's really no sense in changing it...

89CAL Grand Master

89CAL

Posted
Posted
No VVL in a RB engine, just NVCS (VCT,VVT,VTC whatever)

lol yeh theres to many names thrown around for it thats why i added the whatever in brackets

Ive been calling it VCT for a while now, In the power FC sensor chec it has a VTC dot that comes on, but VCT makes more sense so i just use that.

I didnt relise that in the R33's it just advanced everything 20 degrees from x to y in the rev range so this thread has taught me something interesting

  • 9 months later...
85URK Grand Master

85URK

Posted
  • Author
Posted

Whoa, i started this thread so long ago, i have since gained alot more knowledge about the ol skylines. lol but it seems i opned up a can of worms ha ha. hope this thread helped somebody out along the way.

P.S. (i now know about the coilpacks differences between series 1,2 etc. also timing belts, just for those of you who were wondering.)

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