Help- 300rwkw Aiflow Problem

[sky30]

My current RB30det setup is making 312rwkw on 20psi, problem is power peaks at 5800rpm, then drops off fast. I tried adding a set of Tomei 260deg cams, this did nothing to the peak power figgure and it still drops off at 5800rpm.

Specs are:-

RB30det with GT35/40, 600x300x57mm IC, 3" exhaust, 260deg cams,stock plenum, stock exhaust manifold, big feul pump+ injectors, microtech.

I can only suspect there is a major airflow restriction, which i think could be

1.intercooler not thick enough (using 57mm thick core)

2. Stock exhaust manifold

3. stock plenum

If any one has had a similar problem and found the cure, advice would be great.

Cheers

[lordsnipe]

i remember reading from someone to do a run with your cat dropped? if the run has significant gains, could be your exhaust?

[paulr33]

yeah i had similar issues with stock setup, i was told to do a dyno run with turbo basically venting straight out and see if the power drops off still, if so then as lordsnipe has said its a restriction in your exhaust / cat setup. youd want a 4" exhaust for that big sucker

[Cubes]

How many people are making this sort of power with the stock exhaust manifold?

Any issues with detonation?

Another question.. Who's doing the tuning?

Edited September 23, 2005 by Cubes

[sky30]

The exhaust is straight through, no cat, doesnt make more power when i dropped it off on the dyno.

There is no detonation.

[sky30]

anyone know when 57mm thick intercooler cores become real restrictive?

[Busky2k]

Do a pressure drop test. Tap a boost gauge between the outlet of the cooler and TB, and also the outlet of the turbo and intercooler input. Do a couple of dyno runs and compare the readings. Shouldnt be too hard to do. If its more than a couple of PSI, theres your problem.

Also you might need some headwork to get some more top end power..

Edited September 23, 2005 by Busky2k

[StockyMcStock]

i would point straight at the cam timing here. on a 30DET it's never OEM cam timing so you could really be anywhere and not know it. lathe up some adjustable gears and tweak em, i bet you pull that top end power figure up a fair bit.

if you've already done this and it doesn't work, next thing would be that exhaust manifold. i'm amazed you got that much out of it actually, they're ugly little buggers.

[sky30]

Stocky-

Have played with cam gears, made some midrange difference but didnt effect top end much at all, still dropping power at 58000rpm. What settings did you find work best??

[Cubes]

I've always suspected nasty unequal reversion due to the stock exh. manifold.

Which is why I asked about detonation, similiar to mine with the stock turbo.

As you near peak power and over it the motor can generally take more ignition timing. Not the case with mine, it goes backwards due to backpressure.

[discopotato03]

I am curious to know what form of GT3540R you are using and what style of waste gate . Others here have got more but exhaust restriction was delt with ie better manifold such as the cast HKS .

If by chance you're using the XR6T style GT3540R the T04E family compressor cover it may have reached its flow limit . In this case you need the T04S comp cover and adapter ring/backplate that the generic GT3540R comes with .

Its a good idea to compare exhaust manifold pressure to inlet manifold pressure at full boost . Don't be surprised if the exhaust manifold pressure is significantly higher indicating a restriction to flow . Testing at the exhaust manifold will show any ills in the entire exhaust system .

I'm sure many would like to know AFR and timing under full load as well .

Best of luck , cheers A .

[sky30]

Turbo is GT35/40 with the .7 comp, .82 exhaust.

[retrotec]

Turbo is GT35/40 with the .7 comp, .82 exhaust.

<{POST_SNAPBACK}>

A 30det with that turbo should be dropping off somewhere around the 6800 rpm mark.

[Cubes]

A 30det with that turbo should be dropping off somewhere around the 6800 rpm mark.

<{POST_SNAPBACK}>

I've been thinking about this for a little while now.

You really need the exhaust side of things flowing easily to aid top end VE. i.e nice manifold and large turbine housing.

A 3ltr pushes the same air at 5800rpm as 2.5ltr does at ~7000rpm.

If the 3ltr was making power until 6800rpm, bolt a 2.5ltr under the head setup and that would make power until ~8000rpm.

Stock or near stock cams don't do this.

My thinking is.. You want a 3ltr to make power to 7000rpm then drop off, build it as if you were building an rb25 that makes power to 8200rpm then drops off.

[mumbles] 272dur, 1.06 turbine, exh. manifold [/mumbles]

Another option to help with the gearing and acceleration of the car, Diff ratio.

EDIT: Another thought, have you had valve seat tension checked?

Edited September 24, 2005 by Cubes

[R31Nismoid]

with a 3ltr id have a 1.06 rear personally.

especially with a det head as opposed to the sohc

Cams you have should be fine. my stock cam'd RB25 made 270rwkw with a gt30... 17psi ... there was only a 15kw drop @ 8000rpm where the limit was.

Even when we put fuel in and 25psi the stock cams again only dropped in the top end 20kw from the peak and it was only after 7500 the drop occured

[Bl4cK32]

but stock rb25de cams are different to det ones...power noses over at 5500 rpm ish.

[Cubes]

Remember sky30 is running 260duration cams and noticed no improvement in top end (~5800rpm peak for both aftermarket and stock).

This to me is an indication you need to work on getting the exhaust out and back pressure down, or as I said prior, have you had seat tension checked with the new valve springs in? You may still be getting a little float.

Bl4ck32's head would have most definitely had valve float no matter what springs he used. One reason it was shimmed.

Mine on the other hand was fine, upon inspection my valve seats sit slightly higher where as bl4ck32's were sunken in the head slightly more.

Not all heads are equal.

There is very little difference between the DE and DET cams, only a couple points duration and lift.

So..... Get that hotside flowing better to raise VE.

I know you don't really want to start playing with exhaust manifolds etc.

Maybe look at a cast HKS item. Bl4ck32's looks quite good and could be hidden under a modified stock heat shield with a little work.

Edited September 25, 2005 by Cubes

[R31Nismoid]

but stock rb25de cams are different to det ones...power noses over at 5500 rpm ish.

but he didnt say what head he used exaccary

but yeah, ot wont matter as he has the cams @ cubes said

manifolds from GCG look very nice. seen a few on cars here and 12months later they have not cracked.

$1100 i think.. maybe a tad more

[Cubes]

I believe sky30's turbo also runs a big diesel .82 internal gate housing.

Edited September 25, 2005 by Cubes

[discopotato03]

I reckon its worth trying the 1.06 housing , gotta get more out than you put in .

A .