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RB26 Plenum -->RB25?

R31Nismoid

By R31Nismoid,
in Engines & Forced Induction

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R31Nismoid Grand Master

R31Nismoid

Posted
Posted

Does the RB26 plenum go onto the RB25 easily?

And the GTR fuel rails and stuff like that too ?

Or is it not viable...

Reason i ask is i can get a 26 plenum/GTR fuel rail etc cheap...

and my current injectors are virtually maxed out... I've got 190rwkw on 10psi of boost and just not getting enough fuel right at the top end.

So rather than just use the two extra injectors i have in my intake via a microfueler or something...

I'm thinking of just doing all 6 via GTR stuff...

ALSO i can half the amount of cooler piping to :)

thoughts/comments?

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Ronin 09 Grand Master

Ronin 09

Posted
Posted

but aren't RB26 injectors low impedance and RB25 injectors high impedance? This will confuse the ECU won't it? Again i'm just speculating, best check with Sam or Gerald or Sydneykid - someone who knows! ;)... disclaimer in signature

Otherwise go to a Greddy front facing plenum, get a custom fuel rail made and get top feed injectors - they're cheaper than the side feeds RB25s need

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Ronin 09 Grand Master

Ronin 09

Posted
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so that basically replaces the 'over-the-cam-cover' intake part and replaces it with the front facing RB26 intake, much like the Greddy unit? where is your throttle body then? as i'm aware there is no facility to bolt it onto the front of the RB26 intake, unless you have a plate welded on and adapted to take the RB25 throttle body? cheers JNR24

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predator Grand Master

predator

Posted
Posted

Just grab the GTR injectors.. u need a resistor pack to get the impedence right.. get a customised fuel rail made up to run them top feed (people say around $200-$300), and/or run a rising rate fuel pressure regulator. Its probably going to cost you close to $1k all up.

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T0nyGTSt Grand Master

T0nyGTSt

Posted
Posted

It was my impression that the RB26 plenum did not bolt on with a lot of work and money.

Let me get this straight...

Can you use the RB26 plenum, standard 440cc injectors and say a PowerFC?

Can you use the 6 butterfly throttle body? I have the z32.

The cost is almost the same as a Greddy plenum almost which defeats the point.

T.

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JNR24 Proficient

JNR24

Posted
Posted
Originally posted by Ronin 09

so that basically replaces the 'over-the-cam-cover' intake part and replaces it with the front facing RB26 intake, much like the Greddy unit? where is your throttle body then? as i'm aware there is no facility to bolt it onto the front of the RB26 intake, unless you have a plate welded on and adapted to take the RB25 throttle body? cheers JNR24

Thats it!

Its fairly straight forward.

I am running a XF throttle (65MM) on mine and i am running it on the front of plenum with a adapter plate made for it.

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STUGTS Apprentice

STUGTS

Posted
Posted

I personally wouldnt bother...

Using an rb26 plenum would have an impact the a/f ratios of the rear cylinders due to uneven airflow causing them to run richer. Also the larger plenum can increase turbo lag, plus you dont need a huge plenum, your turbo should spool fast enough to not need a huge plenum. There are skylines out there making more power using the standard inlet manifold. I'd save my money for a mod that would give a greater benefit.

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Sydneykid Grand Master

Sydneykid

Posted
Posted

Hi guys, this has been discussed at least 100 times. The inlet system on an RB26 is plenum>throttle bodies>inlet manifold>head. The stud pattern, water inlet and port layout on the RB25 head and the RB26 head are entirely different. So an RB26 inlet manifold will not bolt up to an RB25 head.

What you could do (and what has been done on the HPI RB20DET) is to cut the standard RB25 inlet manifold off close to the head and past the injectors (like the RB26 inlet manifold) and weld a flange plate on it to take the RB26 throttle bodies. Then the plenum will bolt up to the throttle bodies. This means you can use the RB25 inlectors and fuel rail.

As some one posted, HPI (or was it Zoom) found that the car had more power everywhere with the standard RB20 inlet manifold than it did with the RB26 multiple throttle bodies and plenum.

I have never found a standard RB25DET inlet manifold to be a restriction to power output and we have had them up to 450 bhp. The standard internals (pistons and rods) are more of a problem at that sort of power than the inlet manifold. As for extra intercooler pipe length, having a 120 degree bend in the pipework at the throttle body eliminates most of the extra length.

Hope that helps

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JNR24 Proficient

JNR24

Posted
Posted

Sydney kid,

This is what i am doing at the moment.

I have taken the throttles & intake manifold off on the RB26Plenum and i have cut the runners off on the RB25 about one inch or so in.

now i will just get it all sitting at the right length and then i will weld it up (alloy welded of corse) & get it polished.

take a look below:

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