Boost creepin' like a mofo

[aaronc7]

Scroll down to last line for short version of this thread... sorry for the long drawn out post.

Boost creeping pretty bad on my miata... hoping to get some ideas/advice to fix the issue. First let me lay down exactly what my setup is, what it is doing, and what I have done so far to troubleshoot.

Setup:

Garrett GT2560R, internal wastegate- adjustable preload, anywhere from 6-11 psi advertised. I am running no preload, just enough to keep the flapper shut at rest. As far as the turbine/downpipe design... it's a split downpipe. Main pipe is 3", no cats, exhaust is 3" as well, single magnaflow straight thru muffler. The wastegate gasses run in a separate pipe and dump to atmosphere. There is a "divider plate" of sorts welded into the turbine housing to keep the flows separate and not allow leaking either way (see pics later). Manifold is a short tubular manifold.











What I am seeing:

Boost creep entire rpm range. Once I put my foot down, boost always steadily increases. I've done all my pulls in 2nd gear (lower load...but I do have pretty long gearing, I can go around 65mph in 2nd). I saw 15psi around 5500 and 17psi by 7000 (redline).

What I've done:

First thing I did was send my turbo off to Begi to get the wastegate ported. When they got it, they said it had already been ported a little, but they would do all they could, in addition to adding in a 'tunnel' (see pics). Well, that didn't help one bit. Of the two datalogs below.. first one is Pre porting, and 2nd is post-porting- they are basically identical.

I tried two different boost sources: compressor outlet and 'out' side of the intercooler end-tank...same results.

I have checked the wastegate flapper and actuator movement, to make sure the flapper is not hitting something and it's range of motion being affected, as well as making sure nothing is binding when pressure is applied to the wastegate with the flapped connected (video below). Everything seems fine... it cracks open around 7 psi, it takes something like 20-30psi to get full actuation, but of course this isn't a 'realistic' test by any means, as in this state there's no exhaust gas pressure on the flapper as well. My ears tell me the wastegate starts opening around 2-3 psi.

YouTube - Wastegate Test

YouTube - Wastegate Test

So basically as I see it, my options are now:

a.) EWG
b.) High flow cat in downpipe
c.) New/different turbo (good excuse to upgrade to something bigger?)

Option B is the quickest and easiest and may very well fix it, but there's no real way to know until I do it...also it's really more of a bandaid than fixing the issue. Option A seems pretty logical too, but at this point I'd have to send the manifold, downpipe and at least the turbine housing off most likely to get it all modded and done.... some extra money, that's not a huge deal but who knows how long... I want to get this car running right now!!! Option C... well I know there's really no point going bigger for my power goals etc, but it's still always tempting haha.

Anyways, just looking for some ideas/thoughts/advic...anything I might have overlooked or if something you see in here doesn't look right.

Sorry for the long drawn out post lol!

Short Version

Car is boost creeping even after wastegate ported....what now???

[Tomas]

Have you tried disconneting the wastegate actuator completly? Just let the flapper flap around and see if it still creeps.
I would do that first and see if it still creept.

As far as the test you did that's not accurate to determine cracking and full open pressure. You need a valve, air source, and pressure gauge like this

[rodrigo]

u texted me and i answered ...why are u making a thread ??? is there anything more to know than what i say???

punk bastard lol

[aaronc7]

Wiring the wastegate open crossed my mind, but I haven't done it yet, it's going to be so ridiculously loud, even at idle with the open dump lol.

Yeah I didn't really do the pressure test to see what the cracking pressure is- because like I said, it's not realistic because there's no exhaust gas pressure on the flapper in a test like that- it's going to open before it does with the car off and air pressure only. I just wanted to make sure it was going thru the range of motion normally.

I supposed I should wire it open and see what happens, but at this point I'm 99 percent sure it will still creep, and my issues is simply that there is just not enough backpressure in the main exhaust to encourage enough gas to flow out thru the wastegate.

[Tomas]

Originally Posted by aaronc7 I supposed I should wire it open and see what happens, but at this point I'm 99 percent sure it will still creep, and my issues is simply that there is just not enough backpressure in the main exhaust to encourage enough gas to flow out thru the wastegate.

It doesn't work like that.

The compressor will generally not make boost unless there is pressure on the turbine. To make 15 of boost with only 5 psi exh manifold back pressure you'd need a super efficient turbine which does not exist. With the displacement and A/R you have I can guarantee you will have higher exhaust manifold pressure than boost pressure at 4K rpm+. That means the gas flow will follow the path of least resistance. I.e the wastegate port.

It's really a simple test. Deeew it.

[rodrigo]

part out niggah, get something gayer ........oh wait u cant

[aaronc7]

dammit, tried to ban you from thread lenny...wouldnt let me, lol.

[rodrigo]

niggah.......we aint kneegrows...u cant have silver on silver crime

[MS3-a(sore)ASS-rex]

Do you have an exhaust leak between the exhaust wheel and the IWG flapper? All inside the downpipe bellmouth I mean.
I think recirculating the wastegate back into the downpipe may fix your issue.
But I may also be an idiot lol

[rodrigo]

Originally Posted by MS3-a(sore)ASS-rex But I may also be am idiot lol

+1

an****

[aaronc7]

Originally Posted by MS3-a(sore)ASS-rex Do you have an exhaust leak between the exhaust wheel and the IWG flapper? All inside the downpipe bellmouth I mean. I think recirculating the wastegate back into the downpipe may fix your issue. But I may also be an idiot lol

My first thought would be that the dump tube would flow better, therefore work better dumped to ATM vs being recir'd, but maybe there's something I'm not factoring in....you have any reason to believe that, or it just sounded like the right thing to say? lol

[MS3-a(sore)ASS-rex]

Originally Posted by aaronc7 My first thought would be that the dump tube would flow better, therefore work better dumped to ATM vs being recir'd, but maybe there's something I'm not factoring in....you have any reason to believe that, or it just sounded like the right thing to say? lol

No first hand experience but I've never seen an IWG run VTA. I'm thinking the IWG would need the back pressure from the rest of the exhaust to hold the flapper shut until which time it's supposed to open from actual exhaust gases.
My thinking would be the less back pressure the easier time the spring would have of opening, idk if that makes any sense to you. I'm trying to explain what I'm thinking in my head and it doesn't seem to be working lol

[Tomas]

I don't know your set up but exhaust back pressure is prob 1 max 2 psi.
Not a big influence as far as resistance against the flapper.
I bet the spring is just too stiff.
Do the test. Disconnect the wastegate and drive it. Fuck your neighbors.

[aaronc7]

also forgot to mention this is all on WG pressure...no boost controller or anything. Just straight vacuum line from compressor outlet to WG or IC endtank to WG. I used new vac lines...all zip tied off, they not leaking.

[aaronc7]

I will try it this weekend. i still dont have headlights on the car, so too late right now, hahah

[Tomas]

go commando. And I don't mean without underwear.
head lights are for pussies.
ha ha.

[Tomas]

The more back pressure you have after turbo the more pressure you will need on the wastegate actuator to open a certain degree (edit: when dumping into the exhaust pipe). So if the wastegate rod moves 3mm at 10 psi boost pressure and you have 2 psi back pressure it will be as if you are only pressing with 8 psi on the wastegate = less than 3mm by whatever amount. Or put another way, you will need 10 psi of boost to move the rod 3mm.
Usually back pressure after turbo without catalytic converters is not more than 2 psi. It's negligible as far as boost creep is concerned.

Two things can cause boost creep.

1. Waste gate port too small.
2. Too much wastegate spring pressure

First you test with no wastegate actuator at all. If there is still boost creep you know it needs porting. If there is no boost creep when the flapper is loose you can either get actuator with smaller spring pressure or keep the same spring and port bigger depending on time / cost. Both options have benefits and drawbacks.

[messiahx]

Your WG has to be fucked. After you wire it open you can borrow mine and see that everything works.

Edit: Only if you promise not to break it...lol...like you've done with two now apparently.

In all seriousness, you must get this car running. How else you gonna get down on Friday?

[Lex]

Given your actuator works fine, you have two options:

1. Add a cat
2. Get an external gate.

Internal gates usually don't deal so well with catless exhausts. That being an open air car, it's probably best for everyone to throw a high flow cat in there.

[aaronc7]

Originally Posted by messiahx Your WG has to be fucked. After you wire it open you can borrow mine and see that everything works. Edit: Only if you promise not to break it...lol...like you've done with two now apparently. In all seriousness, you must get this car running. How else you gonna get down on Friday?

Originally Posted by Lex Given your actuator works fine, you have two options: 1. Add a cat 2. Get an external gate. Internal gates usually don't deal so well with catless exhausts. That being an open air car, it's probably best for everyone to throw a high flow cat in there.

Yeah- going to the wired open flapper today and see what happens.

I don't think the WG is broken, again it is brand new, and actuates fine when I pressurize it with a compressor, but perhaps just not working right for some reason in this application. There are several different wastegates that I've seen people use on these turbos- it's probably worth me trying some others out there, assuming I don't still boost out of control with the WG wired open. That would be sweet if I could borrow yours this weekend steve, might need the bracket on yours too, depending on how it's mounted etc. Got a pic?

Even with a cat in the exhaust, open dump still gonna make the car stinky, but whatever. I actually already ordered the cat to have it on hand, but I don't want to install it unless I feel I has no other choice.

Anyways I'll report back after I run the WG wide open. Thanks for the help guys.

[Tomas]

If you don't boost creep with the actuator disconnected, or wired open, get an actuator where you can change the spring. They aren't cheap but I would say it's the best option. At least the way I see it.

[aaronc7]

Well, looks like the turbine just flows way too well... disconnected the flapper...took forever to spool up but in the upper rpm I got up to 12.9psi... lol. Hey it sounded cool/loud at least...right?

With WG connected I got about 17psi at redline... 4-5 psi difference- so I guess we can weigh out the WG being bad.

At this point I could: recirc the wg tube, add high flow cat...but I would be guessing and checking. I might just send the stuff back to Abe and have him modify it for EWG- I will be out of town for about 2 weeks here soon so it actually would work out pretty well.

What do you all think? Thanks for all the help thus far.

[cpolly69]

Put a cat in the dp leave the dumptube open and deal with it for a little while - sell me the mani/turbo/dp in a few months and get ewg mani and turbo set up for it


Sent from my iPhone using Tapatalk

[aaronc7]

I bought all this stuff new, as much as i'd wanna give you a good deal, i would take a big hit buying all new stuff again, lol.

I already PMed the guy about modding my stuff for EWG, i think that is my best option.

But if you are really serious about it cpolly...hit me up, we'll talk.

[Tomas]

yeah 12.9 is pretty high with the actuator disconnected. Not sure how much lower you can get that with porting.

My experience is that adding a restriction in the exhaust pas the turbo doesn't pay a lot of dividends but if there are so many people here that recommend that then may be I am missing something.

How much boost are you targeting at red line?

[aaronc7]

I just got back from getting a high flow spun cat welded in... it helps, but does not solve the issue. In 3rd gear (I have pretty long gearing, 5 speed, 3.9 rear end), I can stay below 16psi.... perhaps it's just a sign I need to run moar boost . I think I would be alright with that, I was planning to push the limits a little anyways.

Right now I'm not motivated at all to remove the downpipe again start trying more stuff, or just going EWG...but I will be out of town for awhile, maybe when I get back, I might, we'll see. Downpipe slightly annoying to remove....turbo and manifold have to come out first.

Anyways I'll keep this thread updated on what I do next. At least I need to now hook up the EBCS and get some low end torque...supercharger/creep mode ftl.

[aaronc7]

Well, looks like I'm just going to live with 16psi for now .

Feels great, pretty aggressive, but I dont drive/beat on the car daily... will just continue to keep an eye on things the best I can. Got the boost curve/response decent today with the help of EBC and @messiahx. Nice to finally have some low end torque back...and not running the turbo is supercharger/creep mode.

I know when the weather gets colder the creep will get worse, I'll just have to see by how much...and figure it out when the time comes.

[Darksun280]

Why is the OP scared of boost? Thread starter is a homosexual

[aaronc7]

stock motor, yo.

Hey Darksun, let's talk about that "93 Black 240SX HB" in your profile.....

[Darksun280]

Originally Posted by aaronc7 stock motor, yo. Hey Darksun, let's talk about that "93 Black 240SX HB" in your profile.....

It was stolen out my drive way.

Nice avatar I thought the picture of me by your bedside would be enough......

[Neverlift]

Hey Aaron, it should be getting warmer, not colder from this moment on.

[aaronc7]

Yeah, this summer will be fine- I'm thinking further ahead when winter rolls back around. It's been in the high 70s and low 80s lately..but it gets down to 30s here in the winter. I prob wont be driving the miata much at those temps though anyways

[messiahx]

EBC shsould disrefard t4emps. I win. I am so goddamn drunk right now. Did you hit overboost at all after yout dropped me off?

[aaronc7]

Nope, not once at all. If I went from low throttle/cruise, quickly into wot (not going part throttle boost initially), it would undershoot slightly at first, but that's fine, seems like right now it's been able to handle every situation so far without overboost.

[messiahx]

I just got home. Finally.

That's good that it didn't overboost. You could drop the P term a couple and up D by one to maybe get it to peak quicker.