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Rb25Det Variable Cam Timing And Adjustable Cam Gears

DatsunMotorSports
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DatsunMotorSports Explorer

DatsunMotorSports

Posted
Posted (edited)

1994 Skyline GTs-t RB25det S2 engine.

So I came across a set of adjustable cam gears for the RB. They are new in the boxes, and less than half the cost of any store out there with them. This particular set is made by Fidanza part # 95048 9. Fidanza lists these gears for RB20, RB25, and RB26.

So what Im looking at is an identical set of gears.

Ive been poking around on the net searching for how this is done.

I have seen references to the stock intake gear being slotted already, but I have never taken it apart to discover this. BTW there was only 1 reference to this and I never found anything else on it.

There were a ton of guys just eliminating the variable cam timing components. Thats pretty common. Id like to keep the variable cam timing esp considering I have control over it with the APEXi PFC.

I found another reference here stating that very few manufactures design these gears to work with the stock variable cam timing components. I believe they were Greddy, Tomei, and a few others, but after searching for pictures of these gear sets I found none that looked much different to mine.

I would have a much clearer view of things if I disassembled the timing components, but Im just not there yet.

Id like to be able to adjust both intake and exhaust. Im curious what I will actually end up seeing on the dyno though. With the variable cam timing Im not sure how adjustable the intake cam will be before I see a drop in power, but I suspect I can play with a couple of degrees and make a small gain on the intake. I think the biggest gain will be in the exhaust. Its hard to tell with stock cams and the VCT, but Id like to try and see what happens. There isnt much out there on people doing this with real world performance results.

I suspect these gears will not work for the intake side, but the price was good, so Im just looking for a discussion on adjusting the intake side cam gear with VCT in place. I dont have specifics on exactly what the VCT is doing. I suspect it retards the cam at idle and then actually turns off and lets oil pressure advance the cam at a determined RPM range. (My PFC lets me determine that RPM range at this point). I dont know if this is correct or how many degrees the cam is allowed to move. If someone knows please fill me in. Im starting to get into the design aspect of this thing so I can re-engineer it if I determine it would suite my purpose. I need to understand the operation first though.

Thanks for any light you guys can shed on the situation.

for reference I have read these:

http://www.skylinesa..._1#entry5690602

Adjustable cam gear on inlet side has been tried and found to be a waste of time. You can put one on the exhaust side .. It is not hard to enable vct and more than worth the effort.

http://www.skylinesa..._1#entry5570467

http://www.skylinesa..._1#entry5487613

http://www.skylinesaustralia.com/forums/topic/316272-greddy-rb25-vct-adjustable-cam-gear/page__p__5187272__hl__adjustable+cam+gear__fromsearch__1#entry5187272

http://www.skylinesaustralia.com/forums/topic/300784-has-anyone-seen-these-before/page__p__4995997__hl__adjustable+cam+gear__fromsearch__1#entry4995997

So if the stock gear is adjustable and the best setting for the intake cam is straight up then Im good to go. The key is to make sure with the stock cams that it is STRAIGHT UP! That is the purpose behind having any adjustable cam anyway is to dial it in to exactly where you want it. Just in case anyone is wondering about my thoughts behind all this.

Edited by DatsunMotorSports
DatsunMotorSports Explorer

DatsunMotorSports

Posted
  • Author
Posted

Variable Cam Timing Operation

Just found this.

Took me a few hours. Google searches suck. Im going to stick with the forum search next time.

20* advanced when VVT on.

Thats a lot of advance for a cam!

Dose Pipe Sutututu Grand Master

Dose Pipe Sutututu

Posted
Posted

I believe it's +10 degrees on the intake. +20 degrees is not possible, there's going to be a massive overlap.

I personally wouldn't bother at all with the intake cam gear, even if it's made for VCT. There's no real benefit really, just make sure you set the cut off point around MBT so it doesn't choke the motor up top. By default it's set at 4700 rpm, many have done 2x dyno runs with it set high up and low down, and overlaid the two to find the optimum point.

I would only get the exhaust cam gear.

DatsunMotorSports Explorer

DatsunMotorSports

Posted
  • Author
Posted

To be honest even 10* sounds like a lot! But that is coming from NA engine building where most power is dialed in withing 3 degrees of spec most of the time. Ive seen some aftermarket cams with a little more, but never 10 degrees much less 20 degrees. More over lap at top end sounds good to me. Clear the chamber and fill longer is usually beneficial. cant wait to check it all out on the dyno.

KiwiRS4T Grand Master

KiwiRS4T

Posted
Posted

Forget about the inlet cam. There are adapters available to make it adjustable but everyone who has done it says don't bother. Your exhaust seting will be around 4deg retarded but dyno will tell. It should give you more midrange not top end.

bubba Grand Master

bubba

Posted
Posted

+1 for the 20deg, pretty sure I found it in a workshop manual when I was trying to figure out why mine wasn't working (turned out to be wrong water temp sensor so it wasn't getting up to temp enough to engage).

rob82 Mentor

rob82

Posted
Posted

To be honest even 10* sounds like a lot! But that is coming from NA engine building where most power is dialed in withing 3 degrees of spec most of the time. Ive seen some aftermarket cams with a little more, but never 10 degrees much less 20 degrees. More over lap at top end sounds good to me. Clear the chamber and fill longer is usually beneficial. cant wait to check it all out on the dyno.

Both EVO's and Subaru's can go up to 50degrees advance on the inlet! They really dont respond with more than about 30degrees advance though.

RRob Community Regular

RRob

Posted
Posted

The inlet gear on RB25DET's is slotted and therefor adjustable. Can dial in both cam's correctly with an adjustable exhaust cam gear and degree wheel, dial guage etc.

20 Degrees sounds right VCT on/off.

  • 6 years later...
Dobz Experienced

Dobz

Posted
Posted

Digging up an old thread to set the record straight about the amount of advance on rb25 vct. I have an rb25 neo vct cam and pulley that i'm planning on retro fitting on my rb26 head.

After mounting the cam in a vice with the pulley I turned it to full advance and marked the points.  Each tooth is 7.5° so two teeth are 15° advance on the cam making it 30° on the crank.

I was thinking it seems like too much but the step 1 hks v-cam has a 30° maximum advance so I guess there are advantages.

I'm not sure if r33 rb25 vct has the same amount of advance but it would be good to find out.

Hope this helps anyone else wondering.

IMG_2065.JPG

IMG_2066.JPG

  • Like 5
  • 3 years later...
silencium Apprentice

silencium

Posted
Posted
On 4/24/2017 at 1:54 PM, Dobz said:

Digging up an old thread...

I'm digging up an old thread that has been dug up already... so it doesn't make me the ghoul 🤪😁.

@Dobz Can it be, that this 30° VCT gear was from a NA RB25DE? I am searching the internet for clues about the RB VCS gears, and it looks like it could be the case that NA RB25's use a 30° gear and turbo RB25's a 20° gear.

  • 3 weeks later...
silencium Apprentice

silencium

Posted
Posted

I'm gonna answer this myself as it might helps someone later on.

I've bought the NEO NA RB25 VCT gear, and it is in fact the 30° version as suspected.

13025-5L701 is the part no.

Great upgrade for someone that wants more out of the VCT. New tune etc. is surely needed though.

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