Restricted Flow

[Wogan]

Hey all,

I have a restriction on my air flow in my R32 gts-t .. I'm currently in the process of troubleshooting to work out which part of my intake / exhaust is causing the problem, and i was wondering if anyone could offer some good knowledge to see if i'm on the right track.

Here is my car's setup.

rb20det

apexi pod filter

greddy spec-m fmic

rb25 turbo

just jap split dump

x-force hi-flow cat (since been made even more higher flowing )

greddy pe2 cat-back

gtr fuel pump

nistune ecu

manual boost controller

Here are my assumptions .. please correct me if i'm wrong:

- The dyno sheet shows a quite steep decline in horsepower once revs reach over 6000rpm. This indicates i have a restriction?

- The sheet also shows that boost is maintained flat on 14psi all the way to the end of my revs. This means the restriction is not on the intake side?

- The Greddy cat-back wouldn't be restrictive would it?

- Could the turbo itself be the restriction?

- Is it possible the wastegate pipe on the split dump is too small?

any advice / suggestions are highly appreciated. Unfortunately my budget is quite small, so i want to minimise trips to the dyno.

Thanks!

[bubba]

Post the dyno sheet, preferably with afr's..

I will address a couple of your points: it won't have anything to do with the wastegate hole in the dump being too small, if it was too small you would see massive overboosting.

I also fail to see how an RB25 turbo could choke an RB20.

It possibly could be the catback..

It could possibly be on the intake side as boost pressure is really just a measurement of restriction (i.e. you could have a restriction which results in the pressure you're seeing but flow would be limited).

[Wogan]

Post the dyno sheet, preferably with afr's..

I will address a couple of your points: it won't have anything to do with the wastegate hole in the dump being too small, if it was too small you would see massive overboosting.

I also fail to see how an RB25 turbo could choke an RB20.

It possibly could be the catback..

It could possibly be on the intake side as boost pressure is really just a measurement of restriction (i.e. you could have a restriction which results in the pressure you're seeing but flow would be limited).

I'll post sheets tonight once i get home from work.

I didn't think it'd be the turbo, but it is quite noisy.

My theory on the intake is that if the flow was restricted, then not enough air would be able to get into the system to maintain the boost.. but point taken. i will investigate that side of the system also. Perhaps a larger filter is in order.

I hope it's not the cat-back.. sounds really nice and cost a pretty penny.

Thanks for feedback

[bubba]

Flow and boost pressure are two completely different things. Pressure is a function of flow (velocity/force) by area. Yes turbos will flow more air at higher pressures (to a point), but what you're measuring on the engine is the turbos ability to create pressure against something (closed valves etc). If there was no restriction, you wouldn't be able to make above atmospheric pressure as the air would just flow straight through.

This is also why by removing intake restrictions (bigger pipes, better flowing head etc) people can make the same power on less boost.. there's obviously always tradeoffs though

[lachlanw]

has your fuel filter been replaced lately /at all . has very similar symptoms although had no dyno sheet as proof but you could just tell by driving . pulled old one off and struggled to blow through it at all . put a new one on and it went 8 million times faster . maybe not 8 million . but atleast 6 million times faster . yeah seeing your A/F ratios would help a lot

[Wogan]

got it dyno'd twice (once an initial tune with the new ecu and again when i "hi-flowed" my cat and upped the boost a little) .. Both showed the same symptom of the restriction.

On the first initial tune the A/F ratio was bang on 12:1 for the whole rev range..

the second (which i will post tonight) is less consistent, but still in a good range.

i believe the filter was replaced with my 100,000k service (which was only 8000k's ago)

Edited November 10, 2008 by Wogan

[342Four]

but for $20 (which is what they cost i think) its easy to replace and you'll know that its DEF NOT the fuel filter

[Tezzah]

just jap split dump FTL

is the power dropping? or is the torque dropping?

if its just the torque, then you could be maxxing out the rb25 turbo's efficiency.

dyno sheetz please =D

[Wogan]

kk fuel filter will be replaced then.

Dyno sheets coming tonight.. i'd love to drive home and get them, but i do kinda need my job. Power is dropping.

[Cartman]

standard intake pipe sucking shut by the sounds of it.

[Wogan]

that's a possibility i hadn't considered... one of those silicone intake pipes much better? .. or need something more rigid?

[Cartman]

go to your local exhaust shop or shop of some sort who has thin walled pipe.. ask them for 10cm's of 3inch pipe.. than go buy 2 3inch hose clamps.. go home and chop your standard intake pipe in half and fit the pipe in and clamp it back up in position.. have a search there is a thread on here somewhere.. i think its called $5 intake pipe mod

Edited November 10, 2008 by Cartman

[jay1]

check fuel intake/ filter

[Wogan]

Dyno Sheets:

22nd Sept 08:

24th Oct 08:

[KiwiRS4T]

Dyno Sheets:

22nd Sept 08:

24th Oct 08:

I don't really see that you have a problem (other than running a stock turbo at 14psi). 240hp looks pretty good for your setup. Can't quite see the point in trying to wind it up past 7000 rev/min.

[rev210]

Just Jap dump pipe is probably the culprit. Peice of crap.

[rob82]

The boost takes a bit to come on, you havn't got a boost leak have you?

[Wogan]

Series 1 rb25 turbo .. fair bit laggier than standard.. and should be able to maintain power at the top end.

full boost at 4000 isn't too bad

[Wogan]

The boost takes a bit to come on, you havn't got a boost leak have you?

don't think so.. but i'll double check. Thanks

[bubba]

Just Jap dump pipe is probably the culprit. Peice of crap.

Why? we have already discussed this. Would be nice to substantiate what you are saying.

The boost takes a bit to come on, you havn't got a boost leak have you?

Boost seems to be hitting about 500rpm later than my RB20 setup was and that wasn't even tuned.. 240rwhp is about on the money though. I would suggest that maybe 14psi isn't really doing anything other than pushing hot air.. here's my RB20 sheet:

Red line was where we we tried to run 14psi but it pinged so dropped it back to 12 (as I wasn't tuning it at that point in time).