Underpowered Rb25det

[race_snooze]

new springs lol... and a little re seat, and match port thats about all i can remember them doing to it.

ok and thicker head gasket.

Edited September 5, 2007 by race_snooze

[Bullet32]

Id like to get that done but that means a lot more cash...

Thanks though Shawn.

[Bullet32]

More ignition timing maybe? knock level of 20 is fairly conservative. Maybe an ex cam gear like you said earlier.

We were running out of ignition timing towards th end, it was starting to ping the more he advanced it, so he brought it back.

Ive been told that an exhaust cam gear is a good idea but surely thats not the answer, Ive seen RB25DET's with less mods make more power than mine.

[Dale FZ1]

If you have them please post up

- the dyno sheet with boost curve overlaid

- the ignition map

- the CHRA number and housing A/R from the turbo you're running

It can be hard to search for something if you're blindfolded or running with partial information only.

cheers

[R31Nismoid]

Easy test for the exhaust

Drop it from the cat... and just run off the dump.

If there is going to be a change, you'll see it easy enough on the dyno and either confirm or eliminate the exhaust.

Takes less than 5mins to do so its a cheap/easy check if your unsure

[The Mafia]

Ive e-mailed GCG and asked for exact specs but as far as I know its a 450hp rated turbo and its peak efficiency is between 18 - 24 psi, so that should be plenty for the power I want (260 - 270 rwkw).

yeah I have been told crap figures like that too, and they aren't worth shit.

I've got a better idea - Get me the Number on the little plate on the core. should be 700177-xxxxxx

I'll tell you exactly what it will do. As many other people will be able to.

Dale_FZ1 knows his shit, he'll give you a excellent idea on this too.

So go get us that number

[Bullet32]

Ok I'll have a look for the number on the turbo if it helps...

Here are the dyno sheets that I got:

The first one was a comparison between the first an second runs, the second is the final run when we got the most torque and the best curve but the peak power is less.

I dont have the ignition map though unfortunately.

[The Mafia]

have you got the CHRA number yet? It will tell us the whole story!

[Bullet32]

I couldnt really make out the numbers but I got some pics of the plate on the turbo.

Can anyone make sense of these?

[swanny180]

Looks like it says its a GT2835?

Is that smaller than a GT3071R?

Edited September 6, 2007 by swanny180

[R31Nismoid]

Ye, 2835... and its a old Garrett tag, im pretty sure there is a different Garrett tag with much better stamping/etching, and this was 18months ago too.

[The Mafia]

the Garrett 2835 is the same as the GT3071.

The Garret 3037 is the same as the GT3076

Now this explains all.

I just want to see what kind of rear housing you have - If you have a ground out RB25 rear housing, then your power is spot on.

I had a GT3076 with a RB25 rear, and it only made 230rwkw.

[Bullet32]

I think you might be right... I bought it as a straight bolt on for RB25 from GCG.

Perhaps I had expectations that were to big for that turbo?

[The Mafia]

you just need a bigger rear end, or one like mine.

Don't expect anymore power out of the RB25 rear housing.

I got 240rwkw with Water Methanol injection. That was it. Its simply too small.

[R31Nismoid]

Considering everyone else with the normal GCG hi-flow can get 250rwkw with the RB housing machined.

I dont see why you cant, even with a larger comp wheel, it will just be possibly a bit surgie/laggy compared, but shouldnt "not" make the power.

[Dale FZ1]

Specs sheet says the assembly # 700382-003 should equate to

71mm GT35 compressor family, 56T. 0.50A/R comp housing

56.5mm turbine, 84T. 0.63A/R GT25 turbine housing.

Yes, it is a GT3071R, or its same product/different name alter-ego GT2835R.

Obviously it is running a different turbine housing with T3 flange, since it's a bolt-up. Mafia's probably correct that it's an OE style housing, machined (or remanufactured, or high flowed - take your preference of term) to accept the Garrett assembly.

While the GCG style high flows claim a capacity up to 250-260kW, their impeller specs are hugely different to this Garrett. A visual inspection and measure of the 4 impellers is very telling. GCG have got it pretty well sorted with their spec - and they have trialed at least a couple of versions to get things right.

I believe Mafia is on the money with this one. Experiences with his own earlier hybrid, and from a Central Queensland SAU member who ran a GT3071/RB hybrid suggest that particular turbine combination might get another 10kW but bugger all more. And so we hit on the issue of "happy" dynos yet again.

Your AFR shows fairly conservative figures around 11.5 - 11.7:1, and narrative on ignition timing signifies that it has been given as much as it will safely take. Realistically, not anything holding it back there.

A boost curve overlay may help identify other potential problems - eg. either poor wastegate control or a system restriction. Definitely drop the exhaust off pre-cat and just see with a quick squirt on the dyno. That will take very little effort and avoid paying for something you may not need ie. another cat. A genuine HKS turbine housing - which is not easy to come by economically - might make it a very different proposition.

The question to ask is: what does it go like on the street? And have you lined up against any other modded Skyline with similar goodies to see what's what? Take it to the sprints, drags or whatever gets you going, and go nuts. Then tell us. I will be most interested.

cheers

I couldnt really make out the numbers but I got some pics of the plate on the turbo.

Can anyone make sense of these?

[race_snooze]

I am glade its not valve float Mick!!!

[Dale FZ1]

Well nothing is a certainty - it could still be valve float.

But there is an order of convention that he should run through to identify what the "problem" is. Otherwise there is a risk of just throwing money at it for no net return.

What I can say is there is a total of 4 different cars nominated in this thread that are/were running a similar turbine configuration with Garrett/OE hybrids. They basically all found a limit somewhere around 230-240rwkW. I'm unaware of complaints about their rate of spool, but the common factor seems to be a ceiling on their mass flow capability - ie what maximum power they are able to support. It may be that the RB25 housing / 56.5mm turbine combination just hits a brick wall in terms of mass flow. Perhaps the GCG unit can extend that ceiling a bit further (but not much in the scheme of things).

If there was an issue with mass-flow capability, the demon rising exhaust manifold pressure (aka back pressure, turbine efficiency) would be evident if you were able to fit a pressure gauge to that manifold.

A genuine HKS housing may be just the ticket if he is chasing a particular max power level, but there is a cost factor involved.

Dropping off the exhaust from the cat will merely prove/disprove whether exhaust restriction is a major factor and allow him to decide whether to pursue it further.

Edited September 7, 2007 by Dale FZ1

[Bullet32]

Well I must say a HUGE thanks guys.

You have all helped settle my confusion, Im not unhappy with the way the car drives at all, I was just haoping for a higher peak power figure.

Dale FZ1 - Thanks for the helpful info and advice, I can say that the car is pretty quick, has heaps of pull anywhere in the rev range, its very smooth, not laggy at all and lots of fun to drive so Im definately not unhappy with its performance, everyone who has been in it has said that it is pretty impressive.

the_mafia - Thanks very much for your knowledge and info also, I think Im now leaning very much towards the fact that Ive got the maximum from the turbo Ive got rather than something "wrong" with the engine.

I will check the back half of the exhaust by dropping it off and doing another dyno run though.

Cheers heaps everyone, I hope most of you will be coming to Texikhana on the 16th so I can say hi and shout you all a beer if we go out.

P.S. I hope its not valve float Shawn... I dont have that kind of cash to fix it

Edited September 7, 2007 by Bullet32

[The Mafia]

keep us updated!

I love hearing back results, and to see if we know what we are talking about haha.