Rb25det Gt3582r My Predicament,

[Ryanrb25]

ok guys,

I've recently fitted a brand new Garret GT3582r with a .63 rear housing with the internal wastegate machined and a much larger wastegate flat added. Fabricated my own Bellmouth dump pipe, which is all mounted on a DMAX exhaust manifold.

My problem lies with the wastegate, Had it on the Dyno yesterday and found even the much larger internal gate was wide open with an 8psi actuator but boost was climbing well above 19-20psi and still climbing. I kind of expected a higher boost level than the 8psi actuator but wasn't expecting this much. Being an Unopened rb25det i am trying to keep it sensible. Yes i have checked to see if the dump pipe i made is fouling the wastegate flap and its not. hehe

My options are:

Either pull the turbo off and fit a .82 rear with an internal gate hoping this will help with the issue but i sacrifice any response i was trying to keep with the .63.

Fit an external gate (38-45mm?) to either the DMAX manifold or to the .63 exhaust housing and hope it gives me alot lower minimum boost level.

Who has encountered a problem like this and what's the best, cost efficient way of getting around this.

[Dale FZ1]

Check with BHDave, or search his threads. He had boost control issues with a GT30 0.63 combination. I suspect you'd be dealing with similar issues.

With that spec turbo you'd have to be chasing some pretty big power output, and an 8psi actuator seems seriously underdone. Go to a 0.82 A/R housing and fit a 14psi actuator at minimum - choose an actuator that is close to your intended boost and fine tune it with your controller from there.

If chasing high output from your RB25 then I hope your plans and budget extends to engine hardware upgrades - it will only stand being leaned on for just so long before something gives out.

Keep on it, and keep us posted. Very keen to hear how this combination works especially if you have a manual transmission. Hopefully your turbo supplier is willing to work with you on this one.

[Ryanrb25]

It may seem like a stupid turbo choice i know, but i really like the fact i can flat throttle it off the line in first and second and it's just fast enough not to break traction. A 3 litre bottom end will replace this motor once something let's go, Just eager to see how reliable this sort of thing will be. I really wanted to keep the .63 rear housing as i want as much response as i can get my hands on. I've had responsive turbo's now keep for some higher numbers with more aggressive power curves.

Any more info on external gate setups will be greatly appreciated.

[bubba]

.63 is going to be tremendously small on a 3L.. maybe go .82 for now, it might help solve your problems and be more appropriate when you drop a 3L in there..

[Ryanrb25]

yea i assumed the 3L would need a .82...Im not too concerned about that just yet as that's a fair while away. I want to get this layout fairly good first.

Anyone's thoughts on External gates welded onto Exhaust housing of turbo? My manifold doesn't have a large collection area where i can plumb into it.

[dangerman4]

hi

have you got a link amd or piks of the manifold, and the waste gate mods?

im running the .82 on a 25 with 0 issues

[Ryanrb25]

what front housing is infront of this .82?

[Ryanrb25]

Manifold

[Ryanrb25]

i should have gone the GT3082r way instead. Much more useable.

[R31Nismoid]

Your custom dump isnt blocking the wastegate flapper is it?

EDIT: Its one of 'those' manifolds... ugh i really dont like that design at all...

It may seem like a stupid turbo choice i know, but i really like the fact i can flat throttle it off the line in first and second and it's just fast enough not to break traction. A 3 litre bottom end will replace this motor once something let's go, Just eager to see how reliable this sort of thing will be. I really wanted to keep the .63 rear housing as i want as much response as i can get my hands on.

Why didnt you go the other way? Choking the turbo is the wrong way to do it IMO.

Correctly sized rear housing (.82) and then a GT30 compressor wheel (500hp) would be the way to do it... or if you REALLY want proper response, .63 with the GT30 (GT3071/3076 style) - not the GT35!!!!

Then sell the turbo, and get a GT35 when you get a 3ltr.

They hold value near enough, and with a GT30 - 270-280rwkw... the RB25 you might find will probably last you a fair few years...

So you would be waiting a fair while i reckon for that 3ltr and in turn can go all out with a big GT35 on a full build, 1.06 housing, 400rwkw etc.

Remember the GT35 wheel is a 700hp wheel or there abouts. Putting a .63 on there means your basically hurting turbo output for no real reason (response doesnt count as a reason if you get the correctly sized compressor wheel).

All of that restricting will bring the flow down to a stab of around 550-600hp worth of top end air. Not good at all as you then bring heat, backpressure and other nasties into the equation.

Just my thoughts on it

[Ryanrb25]

your thoughts are good R31nismoid.

what a waste of 2+g's lol

[Ryanrb25]

Would changing the front housing and wheel back to a gt30 spec front resolve any of this overboost problems..

If anyone has a GT30 with a .63 rear housing on an rb25 please elaborate

[RB30-POWER]

not sure why it is overboosting, have a good look at the gate and actuator.

there is a jpc vl with 0.63 housing on gt35 running 9's (370+rwkw), so it can be done, just not the obvious choice. (or logical, but who can argue with the results)

the turbo you want would be a gt3076, good front to rear ratio with regards to gas flows, no point of the gt35 82mm front with a gt30 rear wheel. aka gt3082 bad match

Edited November 11, 2008 by RB30-POWER

[Ryanrb25]

Yea but im sure that rb30 was build to handle 30+Psi lol

Can front wheels and covers be swapped over like rear ones?

[donut_kng]

Have experiences with an rb25 with an 3582 .63

external gate 38mm, holds beautifully, which just a dual stage bleed valve (no ebc as yet)

Logic would tell you me that if your having boost control issues its from your wastegate or bc.

size of the rear end will just cause lag etc as explained above.

3582 may seem big for a stock 25 but comparing to say a GT30, the 35 may come on a bit later but when it comes its well worth the wait, just an effortless tyre fryer.

[Ryanrb25]

what sort of boost levels were you using donutkng?

[donut_kng]

16psi all day every day

[R31Nismoid]

there is a jpc vl with 0.63 housing on gt35 running 9's (370+rwkw), so it can be done, just not the obvious choice. (or logical, but who can argue with the results)

So its 100% that the housings and/or turbo aren't modified?

Was it done on PULP?

Cause i mean, if people have modded housings and non-standard fuel, it totally changes the dynamics

[Adriano]

And is it definately internal gate?

[RB30-POWER]

So its 100% that the housings and/or turbo aren't modified?

Was it done on PULP?

Cause i mean, if people have modded housings and non-standard fuel, it totally changes the dynamics

race fuel, modified + 50mm external gate