Removed Boost Restrictor - Peaking Over 15psi

[semislickR32]

Hi,

Although I am usually cautious, the other day I experimented with removing the boost restrictor on my R32 GTR to see what would happen. Car is mostly stock engine-wise, with only apexi pods and a 3.5" full exhaust (and perhaps what sounds suspiciously like an after-market fuel pump).

Some observations:

• With the restrictor in, boost was peaking at 12.5psi
  
• With the restrictor out, boost came on much quicker () but peaked at just over 15psi ()
  

Some questions:

• 12.5psi with the restrictor in seems pretty high compared to what I thought stock was (ie around 10?). Presume that this is just due to the free-er flowing exhaust?
  
• I know people tend to be conservative with advising people against overboosting 15-year-old-ceramic-wheeled gtr turbos, but does anyone have insight as to what the safe limit is and whether peaking over 15psi is just stupid?
  
• Rather than smash the old turbs, I am considering doing a full upgrade, but reckon that once I factor in turbos (~3k 2nd hand), a PFC (~$1k), injectors (~$0.7k) and a decent oil cooler (~$0.7k) I'm looking at around $6k plus $1k of labour. Is that the ballpark?
  

Cheers

[Penfold]

Some questions:

• 12.5psi with the restrictor in seems pretty high compared to what I thought stock was (ie around 10?). Presume that this is just due to the free-er flowing exhaust?
  
• I know people tend to be conservative with advising people against overboosting 15-year-old-ceramic-wheeled gtr turbos, but does anyone have insight as to what the safe limit is and whether peaking over 15psi is just stupid?
  
• Rather than smash the old turbs, I am considering doing a full upgrade, but reckon that once I factor in turbos (~3k 2nd hand), a PFC (~$1k), injectors (~$0.7k) and a decent oil cooler (~$0.7k) I'm looking at around $6k plus $1k of labour. Is that the ballpark?
  

Cheers

An R32 GTR is 20 years old - if you don't have $10,000 for a rebuild run it at the 12.5psi (exhaust raises stock boost).

For the upgrade - factor in $1000 for tune as well but you might get injectors & cooler cheaper & turbo price would depend.

[semislickR32]

point taken. I do have $10k but would rather spend it on a build rather than a rebuild

Another question: Can anyone explain the theoretical function of the boost restrictor to me? I've been studying the vacuum diagram, and it looks like the restrictor is in the line that goes to the wastegate actuators. To me it seems counter-intuitive that removing the restrictor works the way it does,

my brain says:

• restrictor in => actuator sees pressure lower/later => wastegate opens later => more/earlier boost
  
• restrictor out => actuator sees pressure higher/earlier => wastegate opens earlier => less/later boost
  

but the car says

• restrictor in => ...? => less/later boost
  
• restrictor out => ...? => more/earlier boost
  

Edited December 6, 2009 by semislickR32

[heller44]

What are you using to measure the boost pressure? Just wondering if it is a gauge issue as I have had one do the same.

[semislickR32]

What are you using to measure the boost pressure? Just wondering if it is a gauge issue as I have had one do the same.

i'm using a turbosmart eBoost2 controller gauge, which should be relatively accurate I guess.

And just in case you're wondering "why don't you just use the eBoost2 to control the boost instead of removing the restrictor?", it's because I haven't figured out how to hook it up yet - it was much easier on my old S15 with one turbo, non-cram-packed engine bay and an easy-to-understand vacuum diagram.

The R32GTR diagram in the manual is difficult to interpret to figure out where to get the boost signal from and how to get the solenoid control signal to the actuators... and previous forum searches and questions haven't been answered - poor me

[Moodles2]

With the EBC, you can use the existing wastegate actuator hose that goes to the stock boost controller, but you can't use the manifold pressure source the factory hose uses as it's from an already bled location at the rear near the clutch, need a new hose ran from the intake manifold to the EBC (and the bled source one blanked off). It's how Boostworx did the piping to my Gizzmo MS-IBC's actuator.

[semislickR32]

With the EBC, you can use the existing wastegate actuator hose that goes to the stock boost controller, but you can't use the manifold pressure source the factory hose uses as it's from an already bled location at the rear near the clutch, need a new hose ran from the intake manifold to the EBC (and the bled source one blanked off). It's how Boostworx did the piping to my Gizzmo MS-IBC's actuator.

thanks for the tip, that makes sense from looking at the diagram which shows that bleed. Do you happen to know whether the take-off from the intake manifold was from the fuel pressure reg signal line, or is there a better safer place to T in?

Thanks again...

[MrStabby]

FWIW my 120,000km old turbos let go at 13.5 psi on a very conservative tune. Factory turbo replacement interval is 100,000km and that's standard setup. Get the turbos changed now, the other stuff can wait until whenever you like.

New garrets will cost around $2600 for the pair - no need to go second hand. I'd guess installation would be at least $500, maybe a bit more. Do o2s at the same time, and if you're ever going to do the dumps do it at the same time.

[Moodles2]

thanks for the tip, that makes sense from looking at the diagram which shows that bleed. Do you happen to know whether the take-off from the intake manifold was from the fuel pressure reg signal line, or is there a better safer place to T in?

Thanks again...

You know that black box in the enginebay on the firewall on the drivers side, thats the MAP sensor that feeds the triple gauge boost reading, I tee'd in there as the pressure source for the PSI reading. You can tee off at the FPR directly, it will technically be less laggy than tee'ing into what I used. The stock MAP sensor gets pressure reading from the FPR anyway, it just enters the balance tube first, and a hose comes out the other end to it, then connects to that black box.

With the engine pressure source (stock one is the bled source), I can't remember if mine is before or after the throttle bodies.

[semislickR32]

You know that black box in the enginebay on the firewall on the drivers side, thats the MAP sensor that feeds the triple gauge boost reading, I tee'd in there as the pressure source for the PSI reading. You can tee off at the FPR directly, it will technically be less laggy than tee'ing into what I used. The stock MAP sensor gets pressure reading from the FPR anyway, it just enters the balance tube first, and a hose comes out the other end to it, then connects to that black box.

yep that's where I've got the PSI reading too.

With the engine pressure source (stock one is the bled source), I can't remember if mine is before or after the throttle bodies.

so I take it you didn't use the MAP sensor lines or the FPR lines for the solenoid pressure source... but in theory could you? I guess the only post-throttle-body source would be off the balance tube anyway,

My understanding is that the best place for getting the signal for the solenoid is pre-throttle and pre-intercooler if possible, but I assume that would require drilling into the hotpipe - not my preference by a long shot.

[heller44]

That is where my solenoid feed is connected, a small barb threaded into the 'twin turbo' pipe just before the large hose going to the intercooler.. Signal is coming from the same point as the map sensor.

[SiR_RB]

i recently took out my boost restrictor after i fitted my front pipe and high flow cat, and my boost didnt increase after the restrictor was removed !

im still only getting around 11ish psi !

what can be the problem??