RB25DET Intake Plenum change

[Guest wegs]

I'm puzzling over the best way to configure my RB25DET with a FMIC. I have assumed the best solution for airflow/lag reasons would be to position the throttle body at the front of the intake plenum to keep the return pipe length short and need some advice before i waste my time and money.

1. If i don't put the throttle body at the front of the plenum i will have to run the return intercooler pipe back along the length of the FMIC, up along the side of the engine and over the top to the standard throttle body position - this will introduce lag/air pressure restrictions won't it?

2. Cut/Shut existing plenum to position throttle body at the front. I was quoted $650.

3. Upgrade to custom plenum but then worry about added costs for fuel rails and injectors. Provides a good opportunity to upgrade injectors. Plenum $650-1000??, injectors and rail $1000+??

4. Will an RB26DETT plenum bolt up to the rb25? This would solve all my problems but i'm guessing no because I've never seen it done?

Anyone with comments please post up or suggest other options or contacts/workshops i could speak to about this.

Thanks,

Wegs

[meggala]

unless your power goal is over 500 hp jsut keep the stock intake with the return there are people onhere makig well over 300 rwkw with the standard intake.

you money would be better spent else where

my cooler has is built with a return pipe under neath which is much better

meggala

[meggala]

[Guest wegs]

Thanks meggala - I assume if i got hold of a rb26 plenum it wouldn't be a straight fit.

Extra power wasn't the driving force behind this idea - i want a responsive 250rwkw when i'm finished. Because i'll need to upgrade injectors at a later stage i wanted to consider all my options. I agree i'd rather save money for other areas which will show results provided i don't suffer from long piping. How did you find your turbo response after your FMIC upgrade?

Do you know anyone local (Melb) to supply the intercooler with pipe modification like yours? I won't accept dodgy tanks or core.

[GTS-t VSPEC]

I have a Greddy plenum, cost $1500, and a mate of mine had his throttle body moved to the front of the plenum. Both of these options work perfectly well, but unless your after big power, like we are, then money is better spent elsewhere. These different plenum designs certainly reduced the amount of pipework and bends, reduce intake air heating etc, but it will all depend on what your end goal is to determine whether it is money well spent.

See'ya:burnout:

[meggala]

yeah mine is a race radiators one the tanks are flowed they are a great cooler my car only has an r33 turbo and cooler )its a r32 It has run a 14 flat with more in there so the cooler works very well I'm happy full boost by 3200 rpm its a good set up my site has other pics of my cooler int~~~

[GTS-t VSPEC]

With most custom plenum setups you will still be able to keep the existing side feed rail and injectors. It will however give you the ability to also run a top-feed rail and injectors at a later date if you want.

See'ya:burnout:

[rev210]

If you need to get an aftermarket intercooler then make the pipes as short as you can. If that means a plenum change, then if you have the cash go do it. Provided the throttle body size is kept stockish it should provide good throttle response and a nice fat power band.

The RB26 plenum won't fit straight up. It requires extensive machining. On top of that the multiple throttle body design is a son of a bitch to get right again if the linkages are moved and have not been marked.

[GTS-t VSPEC]

Yeah rev210's right, the RB26 plenum would not be worth all the hassles, but I much perfer the RB26 style plenums, simplifies the pipework and looks much better.

See'ya:burnout:

[Mick]

this might sound stupid but couldnt you just take the rb25det plenum to somewhere that does alloy welding and get them to cut and relocate the throt body to the front and weld a plate where the throt body used to be ... it wouldnt cost 1/4 of the price ....

or is there more to it than that .. ie plenum internals ...

[SLY33]

someone hasnt read the thread thoroughly

[Doctor]

What are your thoughts on No 1 cylinder starving of air in that design.

[Steve]

Thing to remeber is that you could pick up a set of 550cc top feed high impedence injectors, to go with the new plenum for $400-$500. The fuel rail might cost up to (tops) $200.

Side feed injectors generally are alot more expensive, expect to pay another $500+ for a set.

Sub Zero manufacture a plenum used on their 9sec GTST, it flows well and costs about $1400 and comes with a fuel rail and (I think) a throttle body. Add the cost of buying some injectors, then subtract the cost of selling your old injectors and plenum (if anyone wants to buy the plenum), and the cost of upgrading comes down to a few hundred dollars difference - in theory.

Some food for though

Steve

[GTS-t VSPEC]

Doctor,

I know some people that used that design and they haven't had any issues as of yet. It was thought that with the internal baffles that the turbulance might cause some issues, but so far no problems. Sub-zero have used this design to good effect, so if your after a cheaper way out of redisigning your plenum then I think it is a good approach.

See'ya:burnout:

[Guest wegs]

Ok, some very good feedback thanks people...it looks like the cheapest solution is to cut/shut the existing plenum.

Now to throw a spanner in the works....

I intend on changing my dump pipe and injectors down the track. The following thought comes to mind.

What if i use the full top end from an RB26dett?

1. Does it fit?

2. Assuming i can source a top end or blown bottom end complete engine, how much would i have to allow $$$ before labour?

3. Upgrades plenum, injectors, addition of twin turbo.

4. Need to modify dump pipe (easy)

5. Need new head gasket(how much $$?)

6. Could i bolt the head straight on or would it need to be reconditioned?

7. Any show stoppers that i've left out?

[GTS-t VSPEC]

You can add the RB26 head to the RB25 bottom end, with only some minor changes necessary, but in my opinion I wouldn't bother unless you do a whole RB26 transplant. If your after big power then choose and RB26 engine or do an RB30 with RB25 head. The amount of money to do this could make the RB25 go very hard, so I'd suggest saving your money for that.

See'ya:burnout:

[Guest wegs]

hmmm you're right, time for my reality check i think...easy to get carried away with ideas.

If i invested those kind of dollars into other areas i'm sure i'll be better off.

[GTS-t VSPEC]

Hey, don't worry, we all get carried away with ideas, but do your RB25 up first, then if your keen buy another car to build as a race car.

See'ya:burnout:

[kik-ass]

I've seen a plenum from nizpro on a modded R33 in Zoom a while back, they didn't give an exact price but they said it was 'very affordable' or something like like that. Looked to use the std throttle body on the front of the plenum.

[GTS-t VSPEC]

There are alot of local manufacturers starting to make inlet plenums at the moment, I know of 5 different people here in Perth, one is even making it out of carbon fibre. I'm not sure if any research into airflow goes into these designs, but even the cut&shut standard plenum gave a substantial increase in power to my mates car.

See'ya:burnout: