Flow Restriction :*(

[Wogan]

Got my car on the dyno finally.. Made 227hp at 6000rpm.. but the problem is that after 6000 my power drops off quite steeply.. and by just over 7000rpm i'm only making 180hp.

Apparently i have a hefty flow restriction.. But my set up should be quite free flowing.. apexi pod, fmic, JJR split dump, Xforce cat, greddy cat-back ..

i think it might be my turbo itself.. bought a rb25 turbo off ebay and it's always been quite whirry.. Do you guys agree that this could be the issue?

Anyone selling a good condition, low km's rb25 turbo? (preferably a neo if possible) ... would this fix the issue?

[Luciano]

coilpacks

from what you've explained about the loss after 6k rpm, it sounds like coilpacks. Doubt it would be restrictive flow. Does it feel like a sort of miss firing?

[bubba]

I'll put money on it being that Xforce cat.. the 3" "hiflow" xforce cat I got is sh~t.

I still have a similar flow restriction but that's because the turbo is too small for the motor.. goes from 245rwhp @ 5800rpm to 90rwhp by the time it hits the 6800rpm limiter

[Luciano]

i thought the X-Force cats were pretty good & free flowing! I hadn't heard any bad feedback about them until now.

From Wogans setup description, it is very similar to what i have (induction & flow wise).

[bubba]

They're sh~t.

Wogan, what happens to the boost over 6000rpm?

[Pattygtst]

I had my xforce cat removed a couple of weeks ago

Dont think it really made any difference, hard to say.

How much boost you running, stock ecu?

Maybe fuel pump

[Luciano]

i shall take your word for it bubba.

i always questioned the cheap price tag on em

[bubba]

Yeah well basically I got a sticker, grabbed one of those cats to go over the pits. It made a huge difference to response and topend that I took it out before the car went to the tuners.

Might not be an issue on stock motors at stock boost but on my 30, no good

Edited September 23, 2008 by bubba

[R32 Driver]

is it tuned?

[Wogan]

yeah car is tuned.. was a dyno tune yesterday..

it's not missing or anything.. definitely not coilpacks .. (why does that answer come up for every skyline related problem? haha)

only running 13.5 psi at the moment, but it's not losing any boost at the high end.. it's dead flat on 13.5 from 4000 to 7500

[Wogan]

also the fuel / air mix is flat on 12 for the whole dyno sheet so it's not starved for fuel.. i've put a gtr pump in and have a regulator on standby if i feel fuel will become an issue.

[Baz]

It doesn't sound like an intake or exhaust restriction to me. To me it sounds like something electronic related. Could be some sort of igntion issue, airflow meter (running outside of its resolution), faulty injector(s), faulty fuel pump or an ecu. I've got my money on it being a fuel pump, pretty common, replaced a few fuel pumps in my time. If the turbo is holding boost, then i doubt its a turbo problem.

[bubba]

Are you sure it's a 25 turbo? almost sounds like a 20 turbo running out of puff..

[Wogan]

definately a 25 turbo. replaced it myself.

well it's definately not a rb20 turbo .. could possibly by one from an rb30 or something i suppose... never throught about it that much.. but it's not really out of puff.. like i said it's maintaining boost all the way..

From what the guy at Hyperdrive was telling me, it's not so much the lack of boost, but it's the restriction on the exhaust flow. .. but i do agree that it's hard to understand how it could have restricted flow and also maintain boost.

I might try taking the zorst off and putting it back on the dyno before going out and buying a new turbo.

[bubba]

I have a restriction, 245rwhp down to 90rwhp over a 1000rpm span (5.8k to 6.8k) and boost climbs from 12psi to 14psi (in the higher gears) so I wouldn't exactly call yours a massive restriction

I was insinuating that it could be the turbo out of it's efficiency range, yes it's holding boost but airflow and temperature of air probably isn't optimal..

Edited September 23, 2008 by bubba

[RRob]

Cam timing?

[Wogan]

I have a restriction, 245rwhp down to 90rwhp over a 1000rpm span (5.8k to 6.8k) and boost climbs from 12psi to 14psi (in the higher gears) so I wouldn't exactly call yours a massive restriction

I was insinuating that it could be the turbo out of it's efficiency range, yes it's holding boost but airflow and temperature of air probably isn't optimal..

wow.. yeah i guess mine isn't too bad. It definitely is possible that the turbo simply can't hack 14psi at 7000rpm.

[Wogan]

Cam timing?

Timing was set during the tune yesterday. I'm pretty happy to investigate the Cat and if that doesn't prove to be the issue then i'll replace the turbo and air filter and hope for the best.

[autoworx]

turbo

25 stockers generally run out of puff right at the top

drop your exhaust if you think thats the restriction but i think you will find it will be roughly the same

[-Dukes-]

Updates?

I'm looking for highflow cat. but not sure about the xforce ones. How did your investigation go?