Rb20Det Upgrade Rb25 Turbo Questions

[Leeroy94]

I've read 1000 topics on this and haven't got a clear answer.

I have an rb25 turbo with hardly any shaft play. It is stamped 45v4 on the compressor housing and 21U on the exhaust housing.

It's going on a track car but will not be limiter bashed (6000-6500 max). Running a JJR bell mouth dump pipe to no exhaust.

Is 13psi okay to run? Also, I have a manual boost controller. Can i run the boost controller off the stock 7psi actuator or will should I just get a spring for 13psi?

Edit: I was told the rb20 puts less strain on the turbo than the rb25 and therefore can run more boost. Is this true?

Edited February 1, 2014 by Leeroy94

[GeorgesR34]

LoL the turbo is probably older then you are so what do you think? Run it 13psi till it blows up then get it high flowed.

[GTSBoy]

If you've read 1000 threads then you have already seen the true situation. Which is this.....

1) Ceramic turbos die when they get to a shaft speed that upsets them.

2) The exact shaft speed that this will happen at will vary with,

a) the turbo itself - some will simply be stronger than others as manufactured,

b) the age of the turbo and it's usage history,

c) dumb luck.

3) An RB25 turbo is slightly bigger in the compressor than an RB20 turbo, hence when a 25 turbo is used on a 20, you will achieve the same boost level at slightly lower shaft speeds. So, yes, they are a bit less stressed on a 20.

3) A 25 turbo is generally younger than a 20 turbo, so that could mean it will be in a bit better condition - but there's no guarantee here.

4) An RB20 ECU will allow you to run >14 psi on the original turbo without too much shenanigans. A 25 ECU will not allow you to run much more than 11 psi without shenanigans. So there is a chance that a 25 turbo has had an easier life. But again there's no guarantees here either.

5) 13 psi from a 25 turbo on an RB20 is probably broadly equivalent to about 15 psi from the 20 turbo, which is about the limit of most parts of the 20 system (AFM, injectors, original turbo). So you are probably limited to not much more than about 13 psi from a 25 turbo. Might be less. Might be a bit more if you have upgraded the rest of the stuff on the car.

So, the advice given by George above is valid. Run it. Hope it doesn't blow. It might or it might not. Don't boost it up unless you know the injectors and AFM can take it. And it is definitely worth tuning it to get the most out of it anyway.

And put the RB20 10 psi actuator on the 25 turbo, and a boost controller will work very well to get it up from 10 to about 13 no problems.

[Leeroy94]

Thank you GTSBoy.

Mods are:

- FMIC

- JJR bell mouth dump

- walbro 255 fuel pump

Soon to be rb25 turbo

My compression is low but the motor refuses to die.

Cylinder 1 - 135psi

Cylinder 2 - 120psi

Cylinder 3 - 120psi

Cylinder 4 - 124psi

Cylinder 5 - 126psi

Cylinder 6 - 135psi

I'm going to run it till it blows and then upgrade to an rb25det.

Is it worth getting a tune on the stock ECU if I can't afford a nistune?

[GTSBoy]

You can't tune the stock ECU without Nistune. Well, you can, but no-one in their right mind uses tuned ROMs any more.

With the mods you have, you should be fine torun a 25 turbo at ~13 psi, but you would be well advised to sit it on the dyno to make sure it's all good.

FWIW, on my RB20 I ran the stock turbo at ~15 psi with no tuning for years. Then when I Nistuned it I had to back the boost down to ~13.5 psi because I was maxing out the AFM and injectors above that. Made more power from fixing the mixtures and timing up which flowed more air making the AFM go a bit higher than it had been before. If I'd gone on to putting a 25 turbo on it I would have had to do something with the injectors and AFM in order to gain any benefit.

Anyway, the point of that is that my car was fine, but others' cars have suffered from the same treatment because of old, dirty injectors, rotten coils, whatever else can go wrong.

[Leeroy94]

Okay thanks for your help GTSBoy!

[niZmO_Man]

Put the RB20 actuator on the RB25 turbo. I had a NEO turbo on my RB20 with stock everything else, no issues.

Yes it'll run at 10psi, but 2-3 psi isn't going to make much difference.

[Leeroy94]

Yeah I've fitted the turbo with the rb25 actuator (came with a 10psi spring attached). I'm going to weld a brass nipple onto the intercooler piping and run a MTBC off it. I've been informed that the boost controller should run 13psi fine on the rb25 actuator with a less than 2psi boost spike. Does that sound about right?

My mates turbo just blew on his rb20 so I'm going to give him my old one as it is in really good condition.. Hence why I didn't swap the actuators.

[niZmO_Man]

RB25 actuator has 5psi spring. Does your mate have a stocker RB20 turbo? He can use whatever actuator he's running.

Reason I say to use the RB20 actuator, you don't have to worry about a manual bleed valve failing/leaking and spiking. You're going to run the standard ECU so no point pumping more air into the engine if it isn't tuned for it.

Plus running it at 10psi will keep it in tact i.e. a bit more reliable.

[Leeroy94]

Nah he had an aftermarket turbo.. It's his daily and he has no money so I'm just going to help him out.

The rb25 turbo I have doesn't have the stock 5psi spring, it has an aftermarket 10psi spring.

Yeah I went and talked to a turbo rebuilder and he said 14psi on the rb25 turbo through an rb20 engine is fine as long as I don't limiter bash all the time. I usually keep it third gear around 5-6k rpm so should be fine. Plus my rb20 is super tired..

As for the spikes ill have to look out for it. I might run it 12psi for a track day to see how much it spikes.