So I recently had my Z tuned to around 398whp in 10lb springs.

i ended up roasting the stock clutch so I replaced it with a JW light weight stage 2 clutch and flywheel package.

I was previously running the stock exhaust and have switched to a new single exit 3” exhaust. Took it to the dyno with this new set up because it was hitting lean around 2k rpm.

Well last night the tuner called me and said congrats you made 438whp with a clean tune. He said I made some where around 12lbs of boost when I asked how I gained 30hp...

i have brand new SS lines coming from my waste Gates, no boost controller and am only running on 10lb gate springs.

he said the tune is clean but why am I over boosting past spring pressure to 12lbs?

i know if I had hose leaks I would overboost but as far as I know I don’t have any. I’m hoping some of you guys can maybe shed light to why I’m over boosting to 12lbs all of a sudden from something else. Springs and Gates are about 2 years old. If springs can sag some and lose spring pressure over time some to allow slight over boost to happen I guess that’s fine.

i just don’t want 12 to turn into 15... then 20 and kaboom.... Or this be a sign of a bigger problem I need to fix.

So what else would cause over boosting off spring pressure besides line leaks or a bad controller

 

What boost controller/EMS and wastegate are you running?

 

you reduced exhaust restriction.
turbos can over boost when the wastegate doesnt bypass enough exhaust
and it spools the turbo any ways.

you can always put the stock exhaust back on.
or remove the turbos and open/port the waste gate holes for a bit more flow.

very common.

 

No controller.... yet.

I’m running twin Tial Gates with the boosted performance DE kit. Forgot the exact size off the top of my head

 

How are your SS lines hooked up? and what size inside diameter are they?

also what V35guy said - how are you tuning? Can you splice in a boost control solenoid?

 

First your tune should have over-boost protection. My car will cut ignition at 8psi with my utec.
I am running stock exhaust with no cat, 60-1 ebay turbo
I have a .34 bar(5psi) wastegate spring on a 38mm emusa (ebay) brand wastegate and I think I see about 6.5psi boost in 3rd gear/higher.

So, if it was me I'd run a 8psi spring /shrug

 

I think the OP is raw-*******-it and just has his vac lines attached to the manifold

 

It's gotta be from the exhaust swap. If you're ok with the new power then leave as-is. Otherwise reduce timing, boost or swap exhaust back(I personally like a quiet car and a loud BOV)

 

^I would do the same but add boost control.

 

Running a turbo set up with out a boost controller sounds like a very bad idea.

It sounds like the waste gates are not big enough to keep up with the new flow the exhaust is allowing.

 

They are the same diameter as the lines that came with the kit. Only difference is they have the SS outer body.

they were only replaced because the hi temp rubber hoses that came with it kept cracking from heat by the headers.

Its being tuned with Uprev. And that would be up to the tuner. I think I have 2 38mm gates.

my last tune I was under boosted to 9.5psi, this go around I’m hititng high 🤷🏻*♂️

thats how the boosted kit was set up. So that’s how I installed it. Didn’t have a problem before that.

Im fine with the power, but don’t want it to increase and damage my set up. I want to make sure the Gates are doing their job.

 

I'm being crass - has no reflection on you or your build!

Ive since swapped over to aluminum hard lines because the negative effects of heat & exposure within my engine bay.

Remind me - are you running twins? and describe how the lines run - do they meet at a Tee and then a single line to the manifold? do they run to the side or top port of the waste gate?

Can uprev take a boost control solenoid?

 

No you’re good bro, I’m just answering questions as they come in to hopefully help me figure out the cause.

No it’s the single 6266 scroll kit he offers(d), both gates connect with a T hose connector then run to a single line to the intake manifold just before the TB.

they run off the top and then go up the firewall inside the engine bay but do cross one header. Only way I could rout it really due to the location of the intake manifold nipple being just above the driver side headers.

but again I never had a issue with over boosting with the standard silicone hoses with this set up.

 

Posts 3+4+8+9=your answer.

 

There is an issue with the vacuum lines to the gates, and they were clearly changed. The hoses that come with the kit are 6mm (1/4"), and are silicione, with very high heat tolerance. You would have to have one sitting on the manifold for it to be an issue. Check your lines, it has to be an issue there. With two MV-S gates, you can run 4psi spring and it will not overboost because of restrictions...I have tried it on my own car.

 

Yea the line from the gate to the charge pipe literally has to pass right by the driver manifold because of where the nipple is located. Which is right above.

The tuner tuned for it at 12lbs which it apparently holds pretty steadily. So hopefully it won’t become an issue in the future. Still loving our kit Sash!

Just sucks every time I take it out some random crap goes out or starts acting up. Mostly random electronic gremlins.

 

For the record... A boost controller wouldn't help. It can only increase boost, not reduce it. The spring opens the gate, the boost controller holds it closed against the spring. If you're worried about it, try 8 Lbs. springs.

 

Yea that was my understanding as well. It just restricts flow to/from the gates and increases boost by closing the gates for higher pressures. Can only increase boost not decrease it.

 

I am guessing by now the issue has been sorted, However:
With Tial wastegates they say the spring rate is calculated with 1:1 back-pressure ratio. Likely the stock restrictive exhaust was what kept your boost pressures down previously. The larger exhaust freed it up. See this often with the stock twins on a 2JZ once you put on a large downpipe/exhaust. Instant overboost.
Generally when setting up the MV-S's at lower boost it seems to hit boost goals better by using one step lower/softer than they suggest. A test you can run is if you have shop air and a regulator, connect to your wastegate source line and increase pressure at idle to the point you can hear the audible change once the wastegates open. A 10lb spring running up to 12lbs sounds within expectations to me. I just set up some MV-s wastegates for an RB26 the other day and when setting to 1 bar (14.5psi) the cracking pressure (piston lifts from fire ring) is in the range of 18-19psi when no exhaust back pressure is involved(bench test with pressure regulator).