Underpowered Rb25det

[Bullet32]

Hi all,

Im stumped, and so is my mechanic / tuner... I need some good advice please.

Here's the story:

I have an R32 Gtst which I put an R33 S1 RB25DET into a while ago and I have been building it up for about 12 months to try and get some serious power, I have put all of the goodies on it that I know I will need to make the power but after spending over 4 hours tuning on the dyno we have only managed to get 233rwkw and 550nm from it, its running a consistent 11.7 - 1 AFR and pretty solid boost = 17 - 18psi at the manifold.

Im not happy because I know that there is so much more power waiting to be unlocked, it should make around 260 - 270rwkw but it just wont...

Im not a mechanic and I dont know how to tune a car either but I am fairly good with a spanner and I know enough to get me by, but my local tuner said to me that he couldnt get anymore power from my car even running 21psi!

The modifications include:

*Power FC

*Splitfire DI ignition coils (NGK iridium plugs, gapped to 0.8mm)

*SARD 550cc injectors

*Bosch 040 fuel pump

*3 inch mandrel dump pipe - full 3 inch mandrel Tannabe exhaust system with 3.5 inch high flow "metal cat"

*Large front mount intercooler (300x600x75mm), Turbosmart supersonic BOV

*GCG Garret GT30/71R ball bearing turbo

*Turbotech manual boost controller

I have checked to see if the cat is blocked and it isnt and the O2 sensor seems to be working fine, however I dont know if one or both mufflers are partially blocked in the exhaust.

What could possibly be keeping my engine from making peak power?

Can anyone help?

Edited September 5, 2007 by Bullet32

[CEF11E]

heya bullet32

if you are making no more power at 21psi than 18 psi you are suffering from Valve float.

not really that much of a drama, you will need to pull off the cam covers, cam gears, cams, lifters, retainers, collets and then replace the springs. A good set will cost you $300 form performance springs.

the drama will be the labor bill for the work. most workshops would charge 8 hours to do it and its not really something you can do yourself.

I had to make a special tool to replace the springs in my head and it is still a pain in the ass. and this is with the head is off my car.

[Bullet32]

Thanks Nic,

I'll look into that, Do you think I should look into cam gears aswell Ive been told that if I get adjustable cam gears it might help.

[swanny180]

It definitely does sound as though there *could* be a restriction somewhere in the exhaust...

Id simply try swapping over to a complete different exhaust temporarily if possible, just for one or two dyno runs, to check if it alleviates the problem.

Also perhaps check simple things like if your air filter is blocked?

[CEF11E]

If it is valve float and it is borderline then cam gears can also help by reducing overlap but it sounds like the more boost = no more power at all. was this done at Autotech?

if so get Pete to print out one of your runs at 17psi and one at 21psi and post em up so we can have a look at what is happening.

Cheers!

[Bullet32]

Yeah it was at Autotech.

Ed did the tuning not Pete, and he said that he thought that it was a blocked cat but like I said, I checked it and its fine so I think you might be right that it could be the valves...

Could a blocked exhaust restrict the power that much?

Oh and there seems to be heaps of inlet reversion now even though Ive backed the BOV right off.

Edited September 5, 2007 by Bullet32

[The Mafia]

can you give exact specs of that turbo? My old GT3076 struggled at making 220rwkw at 18psi.

Rememeber, a GT3071 is smaller..

[Bullet32]

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).

[1400r]

errr its a 33 35 det right so why you thinking it valve float

not like its a r32 de 25

Edited September 5, 2007 by 1400r

[Bullet32]

35 DET?

Its a Series one R33 RB25DET, only about 100,000 - 120,000km old, its been driven hard for all those km's though.

Edited September 5, 2007 by Bullet32

[paulr33]

whats the ign map look like?

can you post it?

have you checked base timing ?

[thrtytwo]

i'd be very surprised if an exhaust could make that much idfference, and i dont know what would, not engine savvy but i rekon it sounds like someone who is has given you a good answer

[1400r]

sorry r33 25det

[Bullet32]

I have a couple of dyno sheets, I'll take a pic of them and post them up by tomorrow.

They only have peak power and AFR's on them though.

[CEF11E]

it's not not unusual for an rb25 to valve float at around that boost level. it's not common but not unusual.

also not much else will cause a "no power increase" with more boost added.

I am speculating without seeing the car but my money would be on valve float

[race_snooze]

Mick, I know of another rb25 that had the same issue, they just couldnt get any more HP out of it, Then they did the head and perfect all was good.

[BAMR33]

Is it just a ceramic cat? Usually these are a fair bit of a restiction...

What knock figures were getting?

[Bullet32]

Did the head?

Did what to the head?

[Bullet32]

No its a 3.5inch Metal cat apparently flows over 850cfm and its pretty clean, not clogged.

Knocks were under 20, so basically nothing.

[BAMR33]

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

Edited September 5, 2007 by BAMR33