Only Rarely Makes Full Boost?

[mattis96]

Excuse the long story, so i'll try and keep it quick and to the point, i have tried googling first but to hard to pinpoint.

My boost is set to 18psi for high boost, 13psi low boost, although when driving it only hits 15psi most of the time. I went for a drive down a private road and it was making 18psi again ( which it hardly ever does this even though it is suppose to). Went driving around that road again later and still constantly maxing out at 15psi, with exactly the same driving style. Nothing was touched or changed between drives. The car doesnt feel like its struggling or choking, no flat spot with high boost, it just will hold at 15 psi through all gears.

What should i look for as I'd like to get back the 50+hp i am not making, and this was all setup at a workshop if that changes anything.

setup is RB25, Tial 44mm external gate with 1 bar spring, greddy profecb 2, gt3040, wolf v500.

[benelli]

Set your boost controller on high mode (18psi).

Your wastegate spring is set for 1 bar (~14.5psi-15psi) which means there is no way you will be able to hit 13psi.

15psi/1Bar is the lowest pressure you'll be able to run in your setup.

[GTSBoy]

Ever heard of a restriction in the pipework?

[mattis96]

Why would it be a restriction in the pipe work for if sometimes it does reach full boost?

Pipe work is all stainless anyway, 3 inch from turbo to inter cooler all 1 piece, inter cooler to throttle body is 3 inch all 1 piece, 4 inch intake piping, 3.5 inch turbo back exhaust.

[GTSBoy]

Hmmm.....simple things like rubber elbows that are under mechanical load and crimp off when hot. Or variations on the theme. Use your imagination.

Let's face it. If a turbo cannot reach even wastegate pressure then there can only be one a rather short list of things wrong. That would be;

Restriction in the turbo's inlet or outlet pipework.

Wastegate stuck open.

Massive boost leak.

/spoon

[mattis96]

I don't know if it matters they are silicone joiners. I don't think it's a boost leak cause rarely it does make 18psi which is what it's set to, and I don't have a vacuum leak if its the same as boost leak?

I might not have worded my problem properly.

Lo boost is 13 psi and it stays on that no problem

Waste gate spring is 1 bar (14.7 psi if I remember correctly)

Hi boost is 18 psi but only reaches 15 (might be 14.7, to close on gauge to tell) but rarely does go to 18

I don't want to go replacing parts cause knowing my luck the last thing I change it will be

So could it be waste gate stuck open? If it was I assume lo boost would be stuck on 1 bar (but it isn't)

Solenoid? But it does hold lo boost fine.

Anything else? Does the wolf v500 have a safety boost cut as it could be the map sensor?

I don't know...

[Hanaldo]

I'd be looking for boost leaks mate. Boost leaks aren't the same as vacuum leaks, if you have a split in a hose somewhere that seals itself under vacuum but leaks air at 15psi then that explains your problem.

[GTSBoy]

Faulty boost controller is another option. If your wastegate is 14.7 psi and that's what it runs to when set on high boost, then the boost controller may be failing to do what it has to do (basically bleed enough air or otherwise limit the signal to the wastegate) so that you can go higher. If it does it sometimes and not others then you are looking for an intermittent problem, which is the sort designed to send you insane.

But, as has been said by benelli above, it should not be possible for you to only get 13 psi out of the thing at low boost setting. This is because 13psi is less than your wastegate actuator, and it is not normally possible to achieve that. The wastegate is the physical device with the spring in it. You can fool it to give you more boost by losing some boost on the way to it, but you cannot fool it into giving you less boost, because there is no way to do it.

On that basis, you are back to looking for changeable restrictions or your boost gauge being crap. If the boost gauge is telling you lies, then that is easy to understand. Put a known good boost gauge on it and check. If you have a restriction in your plumbing, then it would be possible for you to get 13 psi against a 14.7 psi actuator, because the turbo could be working to a 14.7 psi output pressure but then you waste some of that boost on the way to the plenum, where the gauge sees boost. That would explain both the 13 psi vs 14.7 wastegate spring and the 15 psi vs the 18 psi high boost setpoint.

[mattis96]

Yeah it is driving me crazy. But I definitely get 13psi at lo boost, gauge tells me and dyno printout with map pressure from wolf tell me.

I might try turn boost controller off and see what happens then, don't know why I didn't try this yet.

Bought new silicone hose for vacuum and boost lines so I'll replace all that.

[Jayden.K]

Do actually notice the 15 to 18 psi difference because what If its going to 18 psi but your believing your faulty displays? And when it hits 18 is it a cold time of the day and when it doesn't its hot??. Your boost controller may have a faulty control solenoid