Wastegate Mod/Boost Creep Help!!

dierr · Oct 21, 2008, 10:39 PM

ok so i got my perrin mbc installed and everything is fine. set it so it hits 1.6 bar and it tapered down to 1.2ish. read about the wastegate mod and so today i tried it.

trial 1. turned it all the way and left everything the same, hits max boost at 1.5 bar then a second later, it crept to 1.8 not even redline yet. and this is in 3rd gear

trial 2. only difference is i turned the perrin mbc down 3 clicks. hit 1.4 bar. stayed there and then crept to 1.8ish. in 3rd gear

trial 3. turned the wastegate back down 1 turn and kept the boost same as trial 2 and hit 1.4 and crept to 1.6 and back and forth as i went to redline. so its a little better. still in 3rd

trial 4. turned up the boost to trial 1 again. and hit 1.6ish bar and stayed around there. so i'm very happy at this point.

UNTIL:

i tried this setup in 4th gear and got boost creep! hit 1.6 and crept to 1.8 and tapered back down. tried it again and this time crept even more and somehow i feel like i had boost cut or something. the car just stopped violently for a second and i let off the throttle.

pulled over and lowered boost 4 clicks. and it hits 1.5 and tapers to 1.4 and stays so now i'm happy again.

UNTIL:

i tried this in 5th gear and what the heck, creeps up to 18 again! by this time i figured i should just ask all of you what i'm doing wrong! thanks in advance as i'm stumped. should i turn back the wastegate 1 more full turn?

STi2EvoX · Oct 21, 2008, 11:45 PM

The wastegate mod is tricky. The problem is that is limits the flapper angle of the wastegate and this causes insufficient venting of the wastegate which in turn causes boost creep. If you have an MBC or a reflash with ecu boost tuning done then it really isn't necessary and tends to cause more problems than it solves. A better route to go is with the forge uprated actuator. Noteworthy is the fact that no matter what you do to the wastegate, it's still going to taper to like 19 psi at redline because that's the most that this turbo can really push while still being efficient.

Forcing it closed to help improve taper will only cause worse boost creep on spool up, especially in higher gears when the engine is under higher load, and it will overspin the turbo causing it to go beyond it's efficiency range and heak soak your intercooler. If you wanted to go this route then you would have to do ecu tuning and pull some timing to prevent knock, but even then why bother?

You won't make any more power and you'll be a lot more prone to detonation so the best way to go is to just get the car reflashed, max out the wastegate duty cycles at high rpms to get the best taper possible while still staying within the efficiency range of the turbo, and then just run more timing as the boost tapers in the high rpms. This will net maximum power and it'll be a lot safer and more efficient.

So to sum up, I would set the wastegate back to normal and just let your mbc take care of the boost until you get it reflashed, at which point I would ditch the mbc and let the ecu take care of the boost. You'll achieve the same taper and have better control, as well as be able to utilize the boost correction features in the ecu to prevent spiking and have more consistency and safety. Hope this helps.

dierr · Oct 22, 2008, 12:05 AM

thanks. yea makes sense. i thought maybe if i messed around with the wastegate and mbc i could make it so that it would taper. anyhow i will do that tomorrow. any other people's thoughts and input would be helpful as well.

tonyboy · Oct 22, 2008, 07:55 AM

i think this link would help for holding the boost better..IMHO..

How to: Stock WGA spring mod

the pictures aren't there anymore but the idea is in it

dierr · Oct 22, 2008, 04:12 PM

i read that over. all they did was change the spring and turned the clevis like i did rite? would getting a stronger spring be just like turning the clevis? correct me if i'mi wrong. i'm a noob

dierr · Oct 23, 2008, 08:11 PM

bump for some more answers!

NateDaJew · Oct 23, 2008, 08:32 PM

Quote:

Originally Posted by STi2EvoX

The wastegate mod is tricky. The problem is that is limits the flapper angle of the wastegate and this causes insufficient venting of the wastegate which in turn causes boost creep. If you have an MBC or a reflash with ecu boost tuning done then it really isn't necessary and tends to cause more problems than it solves. A better route to go is with the forge uprated actuator. Noteworthy is the fact that no matter what you do to the wastegate, it's still going to taper to like 19 psi at redline because that's the most that this turbo can really push while still being efficient.

Forcing it closed to help improve taper will only cause worse boost creep on spool up, especially in higher gears when the engine is under higher load, and it will overspin the turbo causing it to go beyond it's efficiency range and heak soak your intercooler. If you wanted to go this route then you would have to do ecu tuning and pull some timing to prevent knock, but even then why bother?

You won't make any more power and you'll be a lot more prone to detonation so the best way to go is to just get the car reflashed, max out the wastegate duty cycles at high rpms to get the best taper possible while still staying within the efficiency range of the turbo, and then just run more timing as the boost tapers in the high rpms. This will net maximum power and it'll be a lot safer and more efficient.

So to sum up, I would set the wastegate back to normal and just let your mbc take care of the boost until you get it reflashed, at which point I would ditch the mbc and let the ecu take care of the boost. You'll achieve the same taper and have better control, as well as be able to utilize the boost correction features in the ecu to prevent spiking and have more consistency and safety. Hope this helps.

Best explanation ever! Should be made into a sticky.

triso · Jan 22, 2009, 10:28 AM

Does an MBC actually increase power?