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Rb26 + Vct

sh@un

By sh@un,
in Engines & Forced Induction

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Swiper the Fox Grand Master

Swiper the Fox

Posted
Posted
Thinking about adding variable cam timing to my next GT-R. I know HKS had the V-cam setup, but does anyone know if VCT from an RB25 Neo can be adapted to the RB26 head?

Anyone done it? What's involved?

yes it has been done...ive seen it and been in a car with it...amazing results.

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TriniGT Experienced

TriniGT

Posted
Posted

Okay so what about using an RB25 Neo head, on an RB26 block and adapting the individual throttles on the Neo head and a big single or even adapting the twin manifolds to the Neo head? I actually have everything to try this, really has me thinking now. I have a damaged RB26 engine and an extra RB25 Neo head. Just a couple of questions but I will still check it out, will I have to bore the bolt holes in the head to allow for the 26 headstuds? Anything else will I have to mod or it should be fine?

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The Dan Grand Master

The Dan

Posted
Posted

The only difference is the manifold bolt up pattern but guys like ShaneF can make the adaptor plate for you and has done so with the 26 plenum on 25 head.

You will also have to externally feed oil into the vct like the RB30 guys do. But yeah, that would be the most practical way to do it. Both 25NEO and 26 heads have the same flow potential but the camshafts specs are different.

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TriniGT Experienced

TriniGT

Posted
Posted

I am almost done with the indivdual throttle setup on the Neo head, did like GTS4WD and changed the bolt holes and retapped, just need to alter the water neck on the throttle setup to accommodate the VCT solenoid. We'll see how it goes. Yeah may be a little wild but what the heck.

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R34GTFOUR Mentor

R34GTFOUR

Posted
Posted

before you go too far, the combustion chamber in the neo head is smaller than the rb26 head, so that would bump up your CR. I would get the neo head cc'ed first to see how much it will jump up, otherwise sell the neo head and get the normal r33 rb25 head and use that since it has the same cc's as the 26

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Adriano Grand Master

Adriano

Posted
Posted

I believe it could be done quite cheaply, using external solenoids and 2 rb25 intake camgears using either head, however it isnt VCT by any stretch of the imaginiation, and tuning two switch on/off points could be time consuming. You may then have to go away and modify the vct mechanism for different angle throw. IMO if you are going to go to all this effort it would be worth investigating a different mechanism say off an evo or mx5, and get true vct, as dirt said the results would be very worthwhile

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TriniGT Experienced

TriniGT

Posted
Posted
before you go too far, the combustion chamber in the neo head is smaller than the rb26 head, so that would bump up your CR. I would get the neo head cc'ed first to see how much it will jump up, otherwise sell the neo head and get the normal r33 rb25 head and use that since it has the same cc's as the 26

Maybe I can run a thicker headgasket to compensate for the higher CR? Ideally would be to get it CC'ed.

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RB26SX Rookie

RB26SX

Posted
Posted
Okay so what about using an RB25 Neo head, on an RB26 block and adapting the individual throttles on the Neo head and a big single or even adapting the twin manifolds to the Neo head? I actually have everything to try this, really has me thinking now. I have a damaged RB26 engine and an extra RB25 Neo head. Just a couple of questions but I will still check it out, will I have to bore the bolt holes in the head to allow for the 26 headstuds? Anything else will I have to mod or it should be fine?

You would need to run a external oil feed to the head for vct, as the RB26 / RB30 block do not have the oil feed in the block to supply the vct.

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Count Grantleyish Grand Master

Count Grantleyish

Posted
Posted

I found this a workshop in Japan that does NVCS Conversion in RB26 while trawling around on gtr.co.uk forums.

http://www.rising-web.jp/03works/03works_frame.html

Look like it was taken off RB25 to me. And from what I've read above comments, it's more than what it is.

What does it need to have one implanted to a 26, looks to be interesting way to gain power and torque.

Would your average Power FC be able to 'control' the NVCS seeing RB26 doesn't have one?

Is it possible to copy the data on NVCS from RB25 and program it into 26 PFC?

Or better get other ecu that already has the software to support variable timing?

Is it worth going all the trouble for?

Cheers

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GTRNUR Grand Master

GTRNUR

Posted
Posted

I came across this conversion too a while back and it showed some of the machining, head modifications to the oil galleries to hook up an external oil feed etc. They used an inline solenoid to supply oil from the oil pressure sender line to valve, and then used a RB25DET intake cam and gear.

I cant find the pics, but they used a -4 oil fitting screwed into the front of the head and then had drilled galleries to supply the cam gear.

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rob82 Mentor

rob82

Posted
Posted

Delphi make a cam phasor for belt driven camshafts - as used on the EVO9. You could probably adapt the solenoid from the EVo9 as well. Remember that full cam control is a bitch for most speed density sytems and that total "bump and check" cam phasing is alot of work for not much gain. Your better off with just an on and off cam advance solenoid

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