Gtr Front Facing Plenum On Rb25 Neo Intake

[godzilla_753]

Hi,

Im new to the forum, I figured id ask you guys since over here in the states this topic might not get any attention. Please excuse any gaps in knowledge as ive just began the installation of a r-34 Neo engine into my s13.

Ive read up on many GTR to RB25 intake threads but no ones seemed to have tried this so far (as far as i can tell)

Now i dont have the GTR manifold in front of me, but from what I've read, the main problem seems that the stud pattern is completely different. Adapter plates are available but rare. One guy on here i believe redid his whole head (welded, cut, etc) to fit the GTR plenum.

people that have tried to cut the runners on the RB25 plenum and weld them to the 26 intake have said that the runners curve too much, which makes it hard to line up the runners on both manifolds

Now I know this may sound a little obvious, but after looking at some greddy inlet manifold for the RB25 it seems they solved the problem of the curving inlets, the 6 inlets on the aftermarket manifold seem to come out straight into the plenum. This made me think that if they did it, why cant it be done to the OEM 25 plenum?

My idea is to cut the runners just as they leave the the head so there is no curves, and weld on short straight portions of aluminum runner to basically extend the straight portions of the intake.

This should allow the RB26 manifold to be used. This solves the issue of hitting the VTC at the front, and it doesnt move the injectors any farther away from the intake ports. Im not sure about the rest, like the balancer shaft? (not familiar with it) and the vacuum/cooling ports. In addition i dont know how the electronics would work out ( including the IACV). Mechanically my theory looks doable to me though, which is the hard part.

Is this a valid theory? To me this seems stupidly obvious, so maybe im missing something here. It seems like the ports are paired up together (groups of 2) on both the 25 and 26 plenums. And they look to be of similiar shape.

If someone can confirm what im thinking, ( they have a 26 intake infront of them) I will go ahead and purchase the 26 intake and begin the process.

this seems like a stupidly cheap option, as the aluminum needed for this project would be minimal. in addition all of the rb25 injector/rail stuff could be reused. If someone could also chime in on how the rest of the sensors and cooling passages work that would be great. (ill keep researching)

any helpful input would be greatly appreciated.

thanks

[lachlanw]

are you using the gtr throttle bodies or walding a big single one o the front?

[Rowdy]

http://www.skylinesaustralia.com/forums/Rb...Va-t328810.html

i was thinking about using adaptor plates etc. etc. but this way seems the easiest.

this is what im doing. but instead of directly welding the cut runners to the gtr manifold, im making a flange plate to weld to the cut runners, that will bolt to the gtr manifold. this way i can get in there with a die grinder and clean up any faults resulting from mismatched runners.

i think your talking about doing the same thing, but adding in a longer straight section? so an extra spacer between the cut runners and the gtr plenum?

im not going to use the itb's, i'll just get a plate welded on the front of the gtr manifold and run my stock tb.

[boostn32]

i have done this on my rb20, its a lot of work and the heat you put into the manfold welding on the new plate for the gtr plenum/throttle

bodies makes it go like a banana, you then need to heat and press straight then mill both surfaces, i spent around 20hrs with the die

grinder. you weld then grind, weld then gring and on it goes to build up the bits that dont line up, then use a small flapper wheel

in the runners to smooth out and then it becomes the right shape.

[godzilla_753]

ahh thanks for the link, thats almost exactly what im talking about doing. except id like to keep the ITB's

I like your idea too, welding a flange to the cut runners makes the plenum easily removable if need be and the ports can be matched up better. I dont know if i will go that route simply because i dont have the facilities or knowledge to try and make a flange like that.

But like your idea, Instead of a flange, ill be welding in some runners connecting the rb25 oem flange to the gtr itb's and plenum. I wont be able to smooth out any bumps like your idea but, depending on how deep they are i might be able to get in there with a dremel from either the ITB side or the flange side.

In either case, i think the plan would work. so far...

Can anyone chime in on how to make the AAC valve to work?

Im also going to be running Air con on the car, so is there some kind of sensor on the tb that controls the idle for that?

[Adriano]

If you want to run the itb's then you have to make a flange, can be done easily with a jigsaw if need be. The problem compared to the link above is that the rb25 runners curve a lot more and earlier than the rb20 ones. IMO an adapter plate is easier. If you are going to weld, simply mount the head flange to a head or a piece of plate steel to reduce the warping, thouhg you will still have to get it surface ground.

[godzilla_753]

If you want to run the itb's then you have to make a flange, can be done easily with a jigsaw if need be. The problem compared to the link above is that the rb25 runners curve a lot more and earlier than the rb20 ones. IMO an adapter plate is easier. If you are going to weld, simply mount the head flange to a head or a piece of plate steel to reduce the warping, thouhg you will still have to get it surface ground.

thanks, I will most likely get the flange decked to ensure its flat.

there is a guy selling me a plenum including the throttle bodies and tps, what else is needed to run the plenum on the 25? do i need the AAC as well?

[Mr GTS4]

ok attached is what i have now..

i am doing this to my neo stagea so i need to run the neo tps because of it bring auto.. now the neo runs a aac/iac(cold start valve) in one where as the gtr ran them seperatly. this is as far as i have got, i have the airbox underneath that the std gtr aac vavle is connected to. i just hope the ecu can run the gtr one.

depending on how the gtr iac vavle works/runs it will have to be connected seperatly somewhere else. other than that because you are still using the front runners to the rb25 like mine you'll have no drama with hitting vct or water inlet and you'll be able to use the std injectors too

if you have questions or want to share some more info pm me