Help- 300rwkw Aiflow Problem

[sky30]

Ok, as i said adding bigger cams made No difference to peak power.

I suspect the stock exhaust manifold to be robbing some power.

Anyone had before and after results of going from a thin to a thicker intercooler core??

[archie01]

In your first post you said "suspect there is a major airflow restriction"

Have you considered the size of the air filter being a restriction at high rpm?

Have you tried taking off the air filter and seeing if this helps?

Saying this b/c a friend of mine in his rb30det changed to a newer (smaller) air filter compared to the original one he had on and with only this change lost approx 35rwkw.

[sky30]

Yeah, tried removing the airfilter, gained only 3rwkw.

Archie- How much power is your mates RB30det making, and what size differences were there between the 2 air filters he tried?

Edited September 26, 2005 by sky30

[StockyMcStock]

valve float is a possibility too, didn't think of that. the exhaust manifold is reaching its limits pretty hard up around those sorts of airflows though, it seems to be the likely culprit if you've tried adjusting the cam timing with no significant effect.

[sky30]

Valve springs have been upgraded, so there in no valve float.

[Cubes]

Upgrading valve springs alone will not resolve valve float if there isn't enough seat pressure to begin with. It will only resolve the issue if the valve springs are too soft to handle the inlet and exhaust pressures when making some decent power.

I.e comparing my head to Bl4ck32's. Mine was nice and tight, bl4ck32's was loose and required shimming, upgrading springs in bl4ck32's head would have made a small difference but not completely resolved the float he would have experienced.

Yours may be fine, but it is something to look in to. Much cheaper than replacing the exhaust manifold.

Bl4ck32 is currently running 16psi on stock n/a springs with zero signs of valve float.

Its something you can do yourself.

Edited September 26, 2005 by Cubes

[matlowth]

G'day Sky - I'm the guy who changed pod filters and saw the power drop...

I went from 350ish rwkw to 312 (or there abouts)....

My skyline made good power from about 3500rpm right through till about 7000rpm, and power dropped off gradually after that (7500rpm limit).

I went from the old style apexi pod filter (the round/cylindrical model) to the current cone-style model - and saw this power restriction.

To be honest, if you've already checked that, I'd (As previously mentioned) get a couple of gauges and measure the pressure drop through the intercooler... My car had a 4" IC core, so it's very possible that your I/C is your restriction...

Your intake plenum is fine - I retained the factory plenum and never had any real flow restrictions.

Cheers,

matt

Yeah, tried removing the airfilter, gained only 3rwkw.

Archie- How much power is your mates RB30det making, and what size differences were there between the 2 air filters he tried?

<{POST_SNAPBACK}>

[Cubes]

matlowth,

How was the hotside setup? turbine a/r size and exhaust manifold?

I'm a firm believer this is what needs to be done to the 3ltr in order for it to rev.

[sky30]

Joel-

Upgrading the valvesprings does give more seat pressure, it totally fixed my valve float problems. If Darren is only running 16psi, it may not be enough pressure to cause float, mine only occured when running over 18-19psi.

[Cubes]

Sky30, I think you don't understand what I mean.

If your valve seats are pulled up in the head the stiffer valve springs will make some difference but not completely resolve it.

Lifter jacking to the point where it causes the car to miss is the extreme end of valve float, that is being extremely close to smashing valves on the pistons.

It may not be the case but its something I would look in to especially after bl4ck32s head being so loose from factory. Its easy to check.

I still think its the stock exh. manifold and nothing to do with the above, but its worth a shot.

Here's a little tech write up on seat pressure.

http://www.cranecams.com/?show=faq&id=5

Edited September 27, 2005 by Cubes

[R31Nismoid]

FUNBOY POSTS

all hail

[sky30]

Joel- I understand you mean some heads have their valve seats recessed further into the head, But by using a longer spring it will do the same job( if not better) than using shims under the stock springs.

[PurpleR32]

FUNBOY POSTS

all hail

<{POST_SNAPBACK}>

well he is the pioneer of air restriction

[Cubes]

Joel- I understand you mean some heads have their valve seats recessed further into the head, But by using a longer spring it will do the same job( if not better) than using shims under the stock springs.

<{POST_SNAPBACK}>

Its only a suggestion, if you are 100% confident the valve springs have good seat pressure and are not floating under high back pressures then I wouldn't worry about it.

The inlet mani is fine, the exhaust is fine and the valve springs are fine.

That leaves the fmic and exhaust manifold.

I would probably look at trouble shooting in the following order

Drill/tap pressure guage in to exh mani or turbo housing.

Then consider if the exh. manifold needs replacing if there are extreme back pressures that may also be causeing a little float and reversion.

Replace FMIC

As I said quite some time ago.

The bloke I bought that machined GT35R turbine housing off had it on his stock exh. manifold, he was running 18-19psi with 256duration cams and made 306rwkw. That was the limit.

He changed exh. manifolds to a ext. gate setup and on the same boost picked up 20rwkw.

How much of the 20rwkw was due to the exhaust manifold is to be debated.

[sky30]

joel- 20rwkw is a nice gain.