actual boost more than wastegate spring

 
Old 02-20-2017, 04:09 PM
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Default actual boost more than wastegate spring

whelp, ive been toying with the car during this warm spell. I swapped out my 60mm tb for a 66mm one. I reused the old map sensor and i recalibrated the tps in the neptune to read 0-100%.
I also replaced my 7 psi wastegate (tial 44mm) spring with an 11.6psi spring. yeah, well right off the gate with the mac solenoid disconnected (vacuum line to the top of the wg open atmosphere and line to the manifold plugged) and disabled in the ecu boost plateaus out in the mid 13's and then creeps to 15 psi (this setup has always had 1-2 psi creep likely due to manifold, wg placement etc)


Shouldnt the setup at least start out around the wg spring pressure? The car is still pretty streetable on 11-12 psi which is why i got the spring but now at about 15psi it roasts the tires bad and Its kinda pointless. Would adding a larger throttle body cause this or is it relatively normal to boost over the wg spring with no boost control. my setup has been about the same for sooo long i wanted a second opinion on this.
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Old 02-20-2017, 04:17 PM
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Default Re: actual boost more than wastegate spring

Manifold design, wastegate placement relative to that manifold design, and boost reference points are all what are causing the issue. the throttle body has nothing to do with it.
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Old 02-20-2017, 10:24 PM
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Default Re: actual boost more than wastegate spring

Originally Posted by TheShodan View Post
Manifold design, wastegate placement relative to that manifold design, and boost reference points are all what are causing the issue. the throttle body has nothing to do with it.
^^^ This. Your wastegate placement in relation to exhaust flow is most likely not optimal, thus the boost creep.
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Old 02-21-2017, 03:13 AM
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Default Re: actual boost more than wastegate spring

Point taken. I guess what i was trying to get at is why does the boost at 13 something psi (2 psi) above the wastegate spring before it starts to creep.
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Old 02-22-2017, 11:41 AM
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Default Re: actual boost more than wastegate spring

Originally Posted by blackeg View Post
(vacuum line to the top of the wg open atmosphere and line to the manifold plugged)
can you clarify this statement? are you sure the wg is connected properly? Sounds like you a purely overboosting, not creeping.
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Old 02-22-2017, 04:36 PM
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Default Re: actual boost more than wastegate spring

the wastegate side port is hooked directly to the manifold.

i cant readily get to the top of the wastegate so instead of taking the fitting off the top i left the fitting and vacuum line on the wastegate but disconnected it from the electronic boost solenoid so the line itself is open to the atmosphere. the rest of that line from the boost solenoid to the intake manifold was also plugged so it would not leak air. after that the pwm was disabled in the neptune.

that setup should run the wastegate off just the spring, right? thanks for the help, i havent really messed around with the setup in a few years the car kinda has just been collecting dust in the garage
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Old 02-23-2017, 07:19 AM
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Default Re: actual boost more than wastegate spring

got it. sounds like you are good. as long as the only boost reference is on the side port you should be good.

what manifold are you using? 2psi above wg pressure is quite a bit. are you sure the 11psi spring is in? do you remember the color (large green)?
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Old 02-23-2017, 06:29 PM
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Default Re: actual boost more than wastegate spring

Yes it was large green. My other spring is small blue like 7.5 psi. Manifold is a peakboost equal length ramhorn not the old version1 ramhorn. It has the wg off the front of the collector and im using a tial 44mm. I checked the boost plot on the datalog with the 11 psi spring im at 12 psi by 4200 rpm in 4th gear and its at 15 psi around 7800rpm. This spring spools the turbo up better than the softer spring hitting more psi at a bit less rpm.

Even with the old softer spring it makes like 2 psi more after the tb swap than it used to at the same duty cycle.

Anyway i put the 7 psi spring back in and am going to use the boost by rpm feature to taper off the duty cycle to try and keep boost psi consistant
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Old 02-26-2017, 08:11 AM
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Default Re: actual boost more than wastegate spring

all the above is pretty accurate to what I was going to reply with as well. I can add this though:
the port you use on the intake manifold may be contributing to the creep as well. Most setups are run best by connecting the wg to the compressor housing on the turbo instead of the intake manifold, or the source for the solenoid connected to the compressor housing. Reasons being: 1) when connected to the intake manifold the wg/solenoid will also see vacuum, which usually isn't a problem, but sometimes can be in rare instances. 2) longer hose can slow down the response time of the wg in relation to actual manifold pressure. 3) if intake air is travelling at high velocity past the port on the intake mani being used, it can cause a vacuum effect which can mildly reduce the actual pressure in the hose going to the wg, thus increasing boost. higher rpm = higher velocity = higher vacuum effect = more boost creep.
Case in point, I actually connected my wg hose to the intake manifold recently on purpose because i was expecting the above results. I raised my boost and made some engine changes that made a considerable increase in higher rpm power, and my overall airflow is a little beyond the ideal flow rating of my fmic. With this new setup, when I still had the wg connected to the compressor housing I was getting some boost drop as rpms climbed because the fmic was starting to be a restriction. So I moved it to the intake manifold, which cured the boost drop, and gave me a tiny hair of boost creep, which I like for my car because my torque curve drops off at higher rpms early than I'd like and I don't yet have the funds to get bigger cams.

edit: I previously was getting about a 1psi drop through the rev range. after connecting it to the intake mani I get about 0.5psi boost creep. I have a 14.5psi spring in mine currently, it was dropping from 14.5 to 13.5. now I run 15.0 psi consistently to around 6k, then it creeps to about 15.6psi at 7200.
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Old 02-26-2017, 06:12 PM
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Default Re: actual boost more than wastegate spring

mvr and mvs wastgates usually make more boost then make more boost then what the chart says.
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