Want To Change Rb20Det Plenum

[luvboost]

hey guys i want to change my stock plenum to a forward facing one but dont no what to get. ive read that people have put rb26 plenums on, does this work? or has anyone used anything different?

cheers

[Roy]

Whatever you decide, do us all a favour and do an accurate back to back comparison. ie have it tuned and run on the same dyno before installing the plenum and give it another tune by the same tuner and run on the same dyno post install

I am real curious to see how the RB26 plenum will go

[TTT]

tell him about your war story.. lol

[TiTAN]

he wont ever do it if troy does that.

[Dobz]

I've read an old zoom mag before where they did a back to back test of both manifolds on an rb20 using an hks 25/30 turbo. The rb26 manifold was using the six throttle setup.

It showed that the rb26 manifold made more power up at the top end but lost a lot of mid range compared to the stock rb20 manifold. My opinion is the long inlet runners of the stock rb20 manifold create good pulse which helps fill the cylinders more efficiently off boost hence creating more power down low. On the other end the short runner rb26 manifold has weak pulse down low losing mid range but can flow more air at higher rpm creating a gain in top end power.

The rb26 manifold would make the setup a lot neater but being an rb20 it needs all the help it can get in the bottom end power side of things and unless you like driving a car that's a slug until it hits boost i would't do it.

[DR 32R]

ISL33P on this forum fabricates them, see the fabrication forum. Hypertune make them, seem to be doing more non RB26 lately. Plazamann on the standard runners seem pretty good to me. My choice was Hypertune.

[kila32]

I used the plasmaman one using the stock runners and it worked great... Droped the lag a bit down low and the runs heaps better loved it best thing I did for my car

[Sarumatix]

Dyno before and after or it's nothing more concrete than hearsay .

[Roy]

I used the plasmaman one using the stock runners and it worked great... Droped the lag a bit down low and the runs heaps better loved it best thing I did for my car

On an RB20? More details such as turbo setup, what ecu and whether you have cam gears etc. Was the car tuned by the same person before and after? Real curious to know why i have had the opposite experience and have had to chase other things and lean on the tune harder to try and get the response i lost. There is perhaps some merit to how it hangs in at the top end, but ...still trying to get the car sorted with my Plazmaman plenum

[Kris..]

theres a guy on NS that has fabricated an adaptor kit for rb26 plenum onto rb20, this is the info i got from him

hi kriss.

well ive been meaning to do a full write up on it but i wanted to wait untill it was in and running and at least dynoed. i didnt want to start an ideas thread i just wanted to show a go to wo and i only got the car running last week due to my work load and buying a renivators delight of a house.

the one i have just finished has been a real challenge beacuse it was such a learning curve. i am about to start on a rb20det one as mine was on a rb25de on out of a r32. they are the same design in the head and block as an rb20det not to be mistaken with an r33 rb25de or det.

So step one the GTR plenum has 3 parts to the sandwich. part 1 the plenum camber that every one knows so well. part 2 the throttle bodies. part 3 the inner bit that makes it all work.

part 3 then brakes down into 3 parts, part A being the main runners that also houses the studs for connecting part 1 and 2 together and also has all the holes for mounting. part B being the water balance bar under neath. this plays a very crucial role of circulating the coolant around block and head. and part C being the Vacume chamber side of things, it acts as an air balance bar between all 6 runners and is where the idel valves ect connect to.

Part B is the most modified pice as we found out the hard way, for some reason during all my test fitting of the plenum and adapter plate ect to the head i never had this bolted up. the problem we struck was due to the lower block height of the rb25de and rb20det than the rb26 the water bar wont fit due to the thermostat housing. we have cut and shut this part and added water outlets and used heater hose to bypass this are and then redirected the coolant into the top radiator hose where it was ment to go anyway. basicly we had to restrict the volume of water at its highest volume point and bypass the restriction. its hard to explain but its one of thoes things that we cut and shut as we needed but now we know that we are doing the next one will be easier.

to help clear part B we also had to grind a fair bit of excess off the thermostat housing and a little bit off the block.

Above is the only major part to the job.

Testing so far shows no hot spots in the block. ( we have been using a lazer pirometer) which i was afraid of.

the adapter plate was made using an rb20det intake gasket being layed over a rb26 intake gasket. all bar 4 bolt holes line up. for 2 across the top we put in counter sunk bolts to connect the adapter plate to the head and for the other 2 on the top we tapped a thread so that the GTR inlet bolted to the adapter. the bottom 2 were only out marginally so a bit of cutting and they will fit up. (some of this can be picked up by the pic of the adapter plate in the thread)

the adapter plate itself plays 2 main roles in the job. creating connection points between the plenum and head where they dont fully align and the other is to taper the runners in. the rb26 runners are around 4mm bigger all around than the rb20 ones and they are quite different in the actual shape. the adapter plate tapers these in and changes the shape of the runners all in one go.

My rb25 has bigger ports than a rb20 so we didnt worry about copying it but the rb20 one we are about to make we are looking at getting copied in cad and getting plates CNC machined as we need at least another 2 all ready. the plates and also be ported out with the head to accept the rb26 runners better. out built rb20 will have the head and adapter plate matched to the shape and design of the rb26 runner.

other points are.

the air (cold start and idle) can be custom made or you can use the big air bot that normaly bolts on under the plenum on a GTR. i just re-plumbed mine (ive got pics waiting for a build thread)

you need a gtr fuel rail. rb20 wont fit. the fuel lines end up in a differnt spot so they need extending. some wiring needs extending. throttle and idle wiring. you need the rb20 tps to suit the stock gtst wiring loom.

i run a gtr cooler on my car so i got all the stock gtr bits that connect from the cooler to the plenum including bov's. then i found that a gtst has all the holes for this stuff to be put in punched into the body but not drilled out. so using all the gtr stuff made it a pice of cake and cheap but after marked would be just as good. i also had a nice HKS hard pipe ready to go in the engine bay but because of the block height and adapter plate fitment it was miles from fitting.

as far as cost.

i got plenum and every thing for around $150-200

gaskets for all the intake $100 trade price

throttle links $10 each, mine were worn in the rose joints

GTR intake pipes $40

alloy for adapter plate $20 Got a good deal

nuts and bolts (needed for the extra length) $40

hoses and fittings for all the air plumbing and water plumbing $150

alloy welding and fittings $100

and all my time and bits i had laying around. all works tools ect.

The only way i would do them is a drive in drive out job because there is to many things that the average joe couldnt do.

If we get this next one CAD copied than i would sell the plates to people that wanted to have a go but i think that it would be better as a package with most of then nuts and bolts and we could get the water galleries modified to our specs for the customer. this is how ever a long way off and as you can see from the price i have listed it soon adds up and its not really a cheap option.

Research: i started to try a few different options like welding flanges onto rb20 runners ect but they were to costly and to hard in the end so i went with this.

a bloke in america made one that was around 40mm thick and talked about making it into a kit but he wanted around $1000 for the kit.

have a think about it. if you want to give it a go we can make a plate for you and thats a start. we have also been sourcing the last few plenums out of japan as its heaps cheaper than in AUS

hope that helps

damo