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Rb25det Vct Info

Fastrotor

By Fastrotor,
in Engines & Forced Induction

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Fastrotor Proficient

Fastrotor

Posted
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Hey guys,

Just though i'd put some info in a post for anyone down the track looking, as when i searched, there was no info on exactly how much advance the VCT adds.

I was degree'ing my std cams, looking for a bad lag problem, and i pulled the VCT cover and put a socket onto the cam nut and advanced the cam manually and then re- degree'd it all

The Advance the VCT adds is 20 Degrees.

The readings i got for the std rb25det S1 cams are. (NOTE :- Don't take these as gospel please, was just a quick check over. There was some weird stuff, as both intake and exhaust seems to close 30 degrees later than the factory specs indicated..... but it was only a tiny amount over quite a few degrees, so i just put the factory number working it out of 240 degree cams as per the manual)

All TDC references on the intake cam reference the compression stroke TDC

Intake Opens at TDC (vct off)

Intake Opens at 20deg ATDC (vct on)

Max lift at 120 ATDC (vct off)

Max lift at 140 ATDC (vct on)

Intake closes 240 ATDC (vct off) see note (270 actual to totally closed)

Intake closes 260 ATDC (vct on) see note (290 actual to totally closed)

All exhaust TDC references to the Exhaust stroke TDC

Exhaust opens at 240 BTDC

50 thou lift opening at 215 BTDC

Max lift at 117 BTDC

50 thou lift closing at 25 BTDC

Exhaust closes at TDC see note (30 ATDC actual to fully closed)

Let me know if anyone disagrees.

Gary

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Fastrotor Proficient

Fastrotor

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Just note, the anomalities were only on closing, and as mentioned, only over the very last 15 thou odd of lift, so i wrote it off as a bad setup on my part possibly...... opening and max lift were very well defined.

Gary

**RB2530** Proficient

**RB2530**

Posted
Posted

I've got something VCT related to add. Not sure if this has been posted elsewhere before but if you are running a VCT head in an application where it is the VCT can't be used you should always look at locking up the cam pulley.

I had situation where my RB30DET with VCT head had issue with inconsistent performance and crap idle. As soon as I plumbed up the oil feed to the VCT gallery the engine became much smoother and the idle became very consistent. The build was ok at first but over time these issues crept in..

My theory is that the VCT cam pulley mechanism without oil dries up and can move and stick at different advances. The thinkers out there will say this cant happen because the friction in the cam shaft will always act to retard the cam pulley preventing it from advancing. Thats what I thought too..But when you think about it when you stop the engine if the cam shaft is on a lagging edge of a cam lobe it may have a tendancy to advance the cam. If the mechanism is sticky then once it does advance it may stay there for while. Not positive about this...it is just a theory..

But what I do know for sure is the engine became a lot more consistent in power delivery and idle after the VCT was reconnected. BTW it took a fair amount of playing around with the VCT mechanism to free it up even after the oil feed was returned to it...

Fastrotor Proficient

Fastrotor

Posted
  • Author
Posted

Thanks for the info mate.

Hey, if anyone has tried, please comment.... I noticed when rotating the cam and advancing it, it was VERY stictiony (ie got stiff in multiple locations while advancing) ... letting it come back (retard), was alot smoother.....

Is this common , or has anyone been able to smoothly advance it ?? I did check another parts engine, and it was abit more sticky than mine on advance, but i figure if someone with a working car had same probs, then its as its meant to be.

I am just chasing a bad lag problem, taking till 4700 to make 10psi (to3 stage 3 turbine and .63 a/r rear) Turbo guy says it shoud be on at mid 3's and results on this site from guys with similar indicate same..... so i thought maybe vct is taking its time to engage...

Anyone offer any help / experience with this ?

Gary

  • 2 weeks later...
Fastrotor Proficient

Fastrotor

Posted
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Posted (edited)

Just to add some pics to this VCT repository, as its one thing to hear a description, but when i was looking for info i never saw one pic of the VCT stuff. Enjoy !

Front VCT actuator with the plate and big cam bolt removed

IMG_1545.jpg

Back of the VCT pulley.... note the slots in the bolts holding inner to the gears....this is the adjustment possible people mention.

IMG_1547.jpg

Inside showing where it slides onto the cam. Small inner slot is for the alignment pin. 4 larger slots are for oiling the cam as the outer part rotates on the cam when the actuator advances. Mine was scratched on the cam, possible causing my sticking problem...

IMG_1550.jpg

Looking at cams without the pulleys

IMG_1564.jpg

VCT oil holes. These provide the oil to the actuator and lube the cam journal. When on oil comes from one hole and turns actuator on, when off oil drains back thru other hole. (switched by the VCT solenoid) I have to assume then, when off the cam journal doesn't get an active oil feed ??

IMG_1570.jpg

Those oil holes feed into the cam ....see the hole in the middle of the journal ....

IMG_1582.jpg

And then up thru the cam bolt into the front cover (hence the o-ring used)

IMG_1580.jpg

IMG_1576.jpg

Edited by Fastrotor

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