Rb26 Plenum And Itb On Rb20

[boostn32]

Im looking at modifying my manifold so i can use the itb's and plenum of the RB26, is there power to be gained, what is the max power a RB26 can make with this setup.

I want to do this as its different, im not fussed on low down torque want power 5000 - 9000rpm and engine has been built for this. power should be around 450rwhp.

i have read another thread on it but there were no results. is there performance to be gained with 6 tb's instead of 1?

[Cjmartz2k]

If you are doing it for the "gee whiz" factor because you want to do it different, that's your choice. If you think it's a cost effective mod or the best way to do it, skip it.

[paulr33]

i would expect 0rwkw increase, there would be an increase in throttle response and transition time from closed to half open etc

the throttle body doesnt make power, air and fuel in the system does, so increase air and youll make more power

[boostn32]

cost is not a problem, its more a fact of is this a good up grade. will i gain anything out of it, there is no wow factor about my car.

the wow that i want is to do this and gain something and not loose power/response.

[Cjmartz2k]

You'll gain throttle response and loose low end power compared to the factory RB20 intake. IMHO it's better to spend your money else where, and this is coming from a guy with RB26 ITB's on his RB25.

[boostn32]

You'll gain throttle response and loose low end power compared to the factory RB20 intake. IMHO it's better to spend your money else where, and this is coming from a guy with RB26 ITB's on his RB25.

so, where should i spend my money?

[R31Nismoid]

3ltr bottom end...

Seriously though, head work. RB20 head's need big coinage spent just to equal stock 25 head flow rates.

And given you've really told us nothing about your setup it is very hard to say where you should spend money.

ITB's will overall, give you little benefit

[Cjmartz2k]

3ltr bottom end...

Seriously though, head work. RB20 head's need big coinage spent just to equal stock 25 head flow rates.

And given you've really told us nothing about your setup it is very hard to say where you should spend money.

ITB's will overall, give you little benefit

[boostn32]

3ltr bottom end...

Seriously though, head work. RB20 head's need big coinage spent just to equal stock 25 head flow rates.

And given you've really told us nothing about your setup it is very hard to say where you should spend money.

ITB's will overall, give you little benefit

ok guess i should of given specs;

ported head, cc'd chambers 264 HKS cams, cam gears, 40thou os forged pistons, shot peened, balanced resized rods, balanced and grub screwed crank with extended

oil pump drive collar. grooved main oil galleries, ACL race big end and main bearings, ARP rod bolts, main and head studs, steel head gasket, R33 RB26 oil + water pump

Garret GT3040R 48mm pro gate. 750cc injectors.

[bubba]

3ltr bottom end...

+11ty

[paulr33]

do you want more rwkw or more acceleration? they are different things

[boostn32]

I just dont want to loose power, if i can a bit of response that would be good. i have decided to do it as its going to cost me around $400 all up. so no harm in testing,

and yes i should of built a 3ltr but ive had this engine for a while and havent run it yet so thought i would have a play.

[seamonsta]

Zoom Magazine did this years ago with a HKS 2535 turdbo on RB20, in the end they went back to the standard RB20 plenum. I would spend my money elsewhere.

[Sydneykid]

ok guess i should of given specs;

ported head, cc'd chambers 264 HKS cams, cam gears, 40thou os forged pistons, shot peened, balanced resized rods, balanced and grub screwed crank with extended

oil pump drive collar. grooved main oil galleries, ACL race big end and main bearings, ARP rod bolts, main and head studs, steel head gasket, R33 RB26 oil + water pump

Garret GT3040R 48mm pro gate. 750cc injectors.

That's a fairly serious RB20, far more upgraded than the Zoom test RB20, which if I remember rightly was pretty much standard with a turbo only. You've done pretty much everything else and I guess it's down to a choice between a standard RB26 setup and say an aftermarket inlet like a GReddy etc. Since the cost is low I'd be tempeted to give it a try. I assume the engine is out, in which case I would suggest careully matching up the ports to the inlet manifold.

Cheers

Gary

[boostn32]

Thanks Gary can always depend on you for a positive response, the engine is in the car. im thinking this will make it easire to check for fitment with length of runners.

then once i have the maximum lengh that will fit i will take the lower manifold off and cut from there and match port it all up.

[Space Goat]

hey,

i had the idea to do the same thing only on a 25... being a fitter machinist and having access to full machine shop facilities i was able to fabricate a inlet manifold...

as you can see instead of making the adapter flange one piece i made it 6 separate parts, bolted them onto each tb and then welded the pieces onto my modified inlet manifold...

the main problem that i came across was matching the ports up correctly... you need to machine the manifold down enough that each hole almost lines up with its respected port on the rb26 plenum easy you say... perhaps not because the rb25 plenum collects together to line up with the standard plenum then opens up to line up with the ports on the head... derr you might say but take a closer look at the rb26 plenum and throttle body setup the ports arent equally spaced out see my intricate diagram below

rb25 manifold 1 2 3 4 5 6

up the top- O O O O O O

down the bottom - O O O O O O

the rb26 manifold

O O O O O O

this spacing is needed for the mechanisms that operate the itbs to work properly

i have since decided not to fit them as the standard plenum/ throttle body that is on the car at the moment will be able to handle the power that my engine/tune will be putting out

looking at your sig it seems that you have all the required machinery to get the job done so i'd say go for it, what have you got to lose

p.s. sorry if i told you information you already might have known but they were the problems i came across when i did my modifications

Edited August 11, 2009 by Space Goat

[bubba]

The alignment of the ports is even worse on an RB20 manifold as the last two runners are stepped where it joins the top half.

I had a GTR plenum welded to my stock runners and my welder had to heat/bend the first and last runners and then find the happiest medium he could.

[GTRNUR]

I'd be interested in knowing what the power output of the engine is as it is right now. If your reving to 9k and are pumping 30lb boost into it, it would have to be pretty close to 475rwhp as it is. Provided you have a decent intercooler and exhaust on it and im sure you do considering the rest of the package.

[boostn32]

I'd be interested in knowing what the power output of the engine is as it is right now. If your reving to 9k and are pumping 30lb boost into it, it would have to be pretty close to 475rwhp as it is. Provided you have a decent intercooler and exhaust on it and im sure you do considering the rest of the package.

i would like to see the difference between standard and the rb26 plenum but in stuck for time as i need this finished for jamboree. i have it booked in on the 27th to be run in and dynoed.

here is a rb20 manifold that has been made to fit the 6 throttles.

[GTRNUR]

Just a opinion...

but the whole point of multi throttles it to improve instant throttle response. They do this becase the plenum is full of air that is at atmospheric pressure and the moment you crack the throttles there isnt a lag to getting that air into the engine. Where as with a standard manifold the entire manifold is in a vacuum to the single throttle. There is a delay between when the throttle is opened and when the vacuum is equalised. The length of that delay is determined by the size of your intake piping, intercooler and air filter.

Multi throttles will have no affect at all on improving boost response.

Two other considerations. You have a small displacement per cylinder engine there with some fairly reasonable camshafts. Factor in the porting and its safe to say that the idle vacuum isnt going to be all that strong. It will get a lot worse with the multi throttle setup. To give you an idea, I had a 2.4lt engine using multi-throttles and 260 cams and it would pull -10inHG at idle, not -20 like a stock RB20.

Now this has 2 effects. One is that your brake booster isnt as effective when your driving in traffic as it doesnt get a good vacuum unless your downshifting to slow down and the RPM gets up to something decent. The other side affect is that if your tuning with a MAP based ECU, you will find the off boost load points a lot harder to get right. This isnt an issue if its using a MAF air sensor though.

Single throttle setup is a lot easier to make "streetable". If that doesnt matter and its an all out race car then go with the multi-throttle setup.

Edited August 11, 2009 by GTRNUR