Boost creepin' like a mofo
 

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 (one on Begi's website)- 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 (ARTech). 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 from ARTech as well.

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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.

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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???

Just want to add, seems like I'm the only one who got it ported and still having issues... saw that thread Doppelgänger made, where he got a new CHRA, boost crept, then the issue went away when he got a new turbine housing and got it ported. As far as I know this one never got a new CHRA or anything?

What kind of boost controller are you using? Perhaps the bleed hole is too large, if any. Or a leak in the vac line.

Forgot to mention that. This is on straight wastegate pressure (7psi-ish says the product page)-- I did two different boost sources, with new vac line, all ends zip tied off etc.

My setup seems similar to yours. 2560 with short tubular manifold and 3" exhaust, so I'm interested to see if mine creeps like yours.

There's no reason an internal wastegate shouldn't be able to handle what you need, so I wouldn't go EWG with your setup. If your wastegate is a 7psi wastegate, it should fully actuate with 7psi of pressure. I would probably try to loosten the wastegate by backing off the adjustable arm (to the point that the flapper is loose), and then see what happens with boost. Another option is to just disconnect your wastegate and see if you still make boost while driving. If you start making pressure when your wastegate is completely open, then there's something wrong either with the downpipe design or the turbo itself. Your wastegate actuator could just be screwed as well. It might be worth while putting it on a dyno and watching the engine while a run is done, so you can see where it is actually opening up.

So let me get this straight . . .

Your turbine gets a luxuriously sized 3" exhaust.

Your wastegate gets a smaller exhaust (you didn't mention size, but visibly smaller). You've taken pains to make sure your wastegate can't share that luxurious 3" exhaust.

As you increase RPM, you increase flow through the engine. The flow follows the path of least resistance, whether that be through the turbine or through the wastegate. Boost creep means that the exhaust is choosing the turbine when you don't want it to.

So, your path through the wastegate is restricted. You've already addressed the obvious by porting and ensuring the wastegate can fully open. I wonder if you're outsmarting yourself with the separate exhaust pipes. Most that I've seen will rejoin the main exhaust. This allows the flow on the turbine side to "venturi" additional flow from the separated wastegate side. You don't have that setup -- might be worth a look -- although I don't know of a way to prove it without tearing up your downpipe.

Actually that's a good point, by having the internal wastegate not joining up, you won't be creating any turbulance that could slow down spool of the turbo.

There's one flaw to your logic though. When the wastage opens there is NO restriction for the air to hit, there is a restriction through the turbine the wheel is a restriction. If this was always a problem with open dump tubes, nobody would use them. I think the problem is in the wastegate actuator. I'd take the above advice, and run with the wastegate stuck open and see if you make boost. When I did this i would make 1-2 psi at 6000-6500 wot in 5th gear.

+1 to unhook the WG can and do a pull.

Wastegate is brand new and actuates fine when pressure is applied thru a pump..but I agree, definitely worth unhooking it and seeing what happens. Ill try this weekend or tomorrow and report back!

This. :)

Of course there's a restriction. The wastegate only opens so far. That's a restriction. Flow forced through a tube is a restriction -- the narrower and longer the tube and the higher the pressure at the end of the tube, the more the restriction. As you noted, being forced through a turbine is a restriction.

The trick is to balance the restrictions to achieve the turbine work extraction you're after. Turbos are designed with a balance between the path through the turbine and the path through the wastegate. If you have the exact setup used in the lab, then you'll get nearly perfect design boost control. Anything off-design changes that balance. We can change the balance with things like EBC, separated gasses downpipes, porting, etc.

It is helpful sometimes to take a step back and think of the underlying physics involved.

As bad as this creep is, I would have guessed wastegate as well. However, the OP seems to have already checked this out. I wonder if there is any binding going on when components come up to temperature.

pics of the porting?

Okay I'm just trying to learn here and explain my point of view from a physics perspective. I understand that the flapper is a restriction, because it is a small internal wastegate design. But i don't understand how you claim that forcing a 1.5 inch tube full of air back into a 3 inch tube full of air is going to be less restrictive than having them both go to atmosphere.

I'm thinking along the same lines as why a larger downpipe is beneficial, pressure differential. Are you saying it better because the exhaust is "pulling" out wastegate gasses? In the catch can thread, it has been researched that the exhaust pulls only 1-2 psi at wot on the track cars. Also, some guys have had power losses from switching from dump to recirculated, don't know which thread that was off the top of my head.

All in all, I dont think the dump tube is the cause

The problem is more that the increase of flow is so great through the main exhaust tube, it's hard to get the exhaust gasses to divert and turn 90° out the wastegate. That's why BEGi adds the "tunnel" into the housing to help divert gasses and point them in the right direciton and this typically works well.

When the dump tube is connected into the main tube, it creates turbulence and slows the gasses coming from the turbine, creating some backpressure. This effectively helps, using pressure differentials, to allow the gasses to bypass into the wastegate tube.

When you removed the wastegate tube from the main, you removed that from the formula. While there is zero pressure behind the dump tube, there's also nothing really helping scavenge or force the exhaust to change directions. Both tubes have little restricition, and it's simple too easy for the exhaust gasses to keep moving forward instead of dumping off before the turbine.

I still need to do the wired open flapper test, just to rule out the possibility of the wastegate being bad..but yeah its hard to know if open dump or recirculated would help promote boost creep more. Open dump allows better, smoother flow for each tube separately, but if the turbine flow is too efficient...that's not good I guess either when working with a small IWG. I went this route for better efficiency...anyways here's a pic of the porting, its just like how they show on their site.

Also to note is, dsm and evo guys have done IWG dump for quite awhile, and I've never heard of it being a big issue. Bottom line I don't think open dump alone is going to make it creep as bad as it is....probably more like the sum of a few things....but this all assumes my wastegate checks out. I'm running one from begi's site, don't know if its legit garrett or what...what is everyone else using?

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they went more agressive with mine:

http://www.boostedmiata.com/gallery2...2/DSC_0007.JPG

but that's also a different housing (t3)

Yeah I thought they could have maybe done a bit more---but it was free so I can't really complain. They did steal my turbo studs though, lol.

Put a potato in the tailpipe and see if there's an improvement ;)

hahah, yeah, when I called in the first time to get the WG ported, Stephanie wasn't in so I got transferred to corky and be basically said with my setup, I might have to put something in the primary exhaust just to purposely restrict flow. I went ahead and ordered a high flow cat to have handy just incase I go that route...but that's going to be last resort for me. Random side note, summit racing is awesome, ordered this thing yesterday afternoon, and it's supposed to get here today..free shipping option too.

also, messiahx is going to let me try his WG from his 2554 I think, might help narrow it down even more.

I couldn't agree more with the "disconnect actuator/wire flapper open" comments. I can also see where running the dump pipe back into the exhaust makes sense. Though it's been done on other cars, they are running different turbos and different exhausts and different manifold designs...all things that can make a difference. If it were possible, I'd try to get something like the FM elbow/downpipe (borrow?) and see if you get the same results....though that would be a PITA.

do those two dirlled holes between the two ports go anywhere? like are they drilled through the flange?

I was wondering about those as well. Sort of strange. It looks like the flange I had on my old turbo setup. It had those holes and there was a metal block off plate bolted down to divide the chambers. I don't think the holes went all the way through though.

On mine they went all the way through the flange. I had to plug them until I got a bolt in WG seperator.

The fact that Corky had a gut-feeling you would have this issue seems like a Red Flag to me. Lots of experience behind those gut-feelings.

Anyway, what we're basically talking about here is the balance between the restrictions through the turbine vs. through the wastegate. If you don't want to restrict the turbine side, then you have to figure out how to unrestrict the wastegate side. It was noted before that some race catchcans can generate 1-2psi by artfully connecting to the main exhaust in such a way that a venturi is created. That's not insignificant and much better than dumping to atmosphere. The problem is that you are in serious trial and error mode to find the right balance/angles/etc. going down this path. And doing it with a beautifully welded piece.

If the WG checks out and you have to get into a balancing act, my recommendation would be to put a cutout valve into your main exhaust. The catch is that you seal off the "cutout" port so that it dead-ends. Now you have a way to infinitely vary your main exhaust back-pressure. The way I see it, restrict a bit for street driving where you want 7psi, and then open it up and let it run wild at the track where you have better gas. Just a thought.

Do you have any Aero friends that can do some Computational Fluid Dynamics on your setup?

Yeah cause they go directly into the wastegate section of the housing.


https://www.miataturbo.net/attachmen...1&d=1302893714



before you do anything, wire the wastegate fully open and go take a WOT log to redline.

Still at work, but yep step 1 is fully open flapper test.

The holes are welded shut on the back side..I asked Abe about it before. Basically, most setups he runs a divider plate there, so he bought a bunch of flanges set up for that, but I obviously didn't need one since mines welded into turbine housing. No gasses leak past the divider, id definitely be able to hear it being open dump on the wg side.

Hornet, you're exactly right and I agree...if it comes down to a pressure difference problem, I'm gonna hate going into a guess and check way of things and hack up this awesomely made downpipe. If it comes down to it...I could still just go ewg, although that seems pretty ridiculous for a 2560

Hit the basics and keep us advised.

Those holes that are welded shut can be thought of as bleed valves or fixed "wastegates." By allowing flow through those passages, you decrease flow through the turbine. There are lots of reversible things like that (including removing the divider on the turbine housing) that you can try which don't involve cutting up that beautiful pipe.

that would result in the loudest car ever.

lol

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.

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Ewg.

Already PMed ARTech about it and contacted streetunt about the actual wastegate... to me it sounds like the only real fix to the issue at hand, VS some sort of bandaid fix, but I wanted to hear your guys' opinions on it too.

First GT2560R miata to need EWG?? fml

Need? Pretty sure your car is telling you to run 17psi.

yeah...it felt pretty good, not gonna lie

that's what she said?

When are you getting a real turbo tony?

EWG is a sure fix that preserves the performance built into your exhaust. Anything else could become a long and frustrating road of hacking and experimenting.

I think the proper conclusion is that your turbine flows far too well in comparison to your wastegate. So, let's give the wastegate the flow it deserves. EWG.

As soon as my brakes, chassis, and suspension can keep up with the one I have... or when you give me a good deal on the little demon you have now. :makeout:

yep... i agree 100 percent. I'll have a good setup ready to go also if I ever go built motor/bigger turbo as well. Thanks for all the help here

My FMII GT2560 creeps pretty bad too. I upgraded to the newer style FM actuator/bracket, but haven't done the porting yet. At this point I'm living with it, and will probably do the porting when I install my '99 head. I really hope I don't have to go EWG, because I've got the FM cast o2 housing and downpipe, and it'll be allot more involved than what you have to do.

C

that creep is insane and doesn't make sense. It's obviously bypassing the turbine almost completely, then WHAMO.

Honestly I would try to merge your pipe in. It could create enough turbulence to fix the problem.

it could very well fix it or it could not...and what I don't like is the possibility that it doesn't...then I try something else....still doesn't fix it....then im back to square one, but now with a recirculated wg flow, high flow cat and who knows else (all stuff i originally didnt want), and still creeping and still have to go EWG. I think going EWG now will just be less headaches overall, and a sure way to fix the issue? Overkill? I would have definitely thought so prior to seeing my own creep on this turbo, but meh, at least with EWG I can swap springs and stuff too.

You can still get creep on an external waste gate, and seeing as how your making 12psi with an open internal wastegate, you should definitely consider modifying that downpipe.

well, still, EWG gonna do a lot more than recirculating the bypass gasses. While Abe is doing my EWG stuff, I may have him make the new dump tube recirc into it though- im not sure, i have a few days to think about it. open dump is cool, but the sound is losing its.....cool factor already- i'll sleep on it.

I'm just saying. Garret designed that turbo with an internal wastegate, so it's not the turbo's fault or the wastegate, it's the things around it. The downpipe is the number one culprit - it's just far too efficient for that turbo. Like if you put a gt30 or something on there it would probably work great, so personally I would either a) change turbo, or b) change downpipe. It's not like you won't be able to find a buyer for either of them.

I still don't see how it can prevent the car from making any reasonable amount of boost at WOT all the way until ~4500, then it simply can't?

The exhaust was obviously bypassing through the wastegate, then it was like, fuck this time to spool this shit.

Recirculating the WG gasses didn't do shit. I didn't get any hard datalogs of it- I feel like maybe it's creeping a little less slowly... it's also a cooler night tonight, so perhaps it's helping, but only marginally. Still hit my 16psi overboost pretty easily. Here's a pic... looks funny cuz the guy sprayed it with some of that high temp paint stuff (since its aluminzed and not stainless...whatever it's not like you can see it anyways). Also, open dump got old really fast, this is much better anyways :).

Apparently one of my turbo water lines decided to develop a small hole too. So tomorrow, gonna replace the water lines, then go to get this Magnaflow cat welded in (Metallic spun). In my previous experiences.... high flow cat made a huge difference in boost creeping, I just hope it helps enough to allow me to continue tuning from here.

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Thought you were going EWG?

I've got the same setup on a chinabob2870.... I hits around 16psi even with the wastegate locked wideopen.

I had a chinabob3071 with fm's cast downpipe before and got "zero" boost creep.

I'm treating it as the car is telling me to run that boost setting.

After watching your video, I think your flapper has a certain number of degrees where it isn't opening completely into the dp channel for the gate. Instead of opening 90 degrees at full open into the WG tube on the dp, it is opening say 80 degrees which in essence diverts the WG gas into the wall of the wg tube and also actually closes that tube up a fair amount. That coupled with the 90 bend for the WG tube once it approaches the fire wall gives you a bigger restriction on the WG tube than you think. That would also cause creep with the WG disconnected. While a bellmouth designed DP does introduce some turbulence, it also allows the WG to dump into a larger chamber.

I would mark the distance of full open with the DP on and with the DP off and see if there is a difference in the movement of the flapper arm. See if it opens less with the DP on.

It also appears that when your actuator is attached, you are limiting the travel of the flapper even more. That would explain the lower creep with it detached vs attached.

I believe this statement is the truth.
There is less room for the wastegate flapper to open into and therefore less room for the air to travel with the seperated gasses DP.

Hell...just look at the size of the flapper, and the size of the hole that it is in. The flapper takes up a huge chunk of the opening.

looked at the video one more time, it really does look like the flapper is covering most of the outlet once it's open. It opens into the dump tube, and since it's a small round tube and not the size of that entire cavity, there's a huge restriciton.

I bet if you could bellmouth the tube like show below you could solve the issue.

Can't argue with your guys' points... those would definitely help.

Regarding flapper movement, yes eventually it hits the downpipe, but the wastegate actually restricts its movement slightly more (pretty close though)...so basically, the wastegate actuator fully actuated, it wont ever open far enough anyways to hit the downpipe. With that in mind, I think something like what Brain posted would probably help the most... just giving the gasses larger path to flow around and out thru the flapper.

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.

edit: the only other thing that bugs me is that there's plenty of others, running ARTech stuff....both catless and catted I'm sure, that aren't boost creeping (that I know of)...What about all the other guys running similar or the same turbo, with same downpipe flange design- why aren't they getting this? So I don't know, maybe there is something we are overlooking.

I had this dp below with a 2560 and it did not creep at all. Maybe Abe's manifolds are just that much better!

https://www.miataturbo.net/miata-parts-sale-trade-5/fs-stainless-turbo-manifold-fm-downpipe-exhaust-gt2560-t25-54735/

Oh hey, my old stuff happens to be for sale too.

Well if anything you could put some spacers between the wasteagete actuator bracket and compressor housing and move the wastegate actuator closer to the firewall a few mm. That should allow it to open further with the wastgate attached. This way you can at least see the minimum boost level you hit when you wired the wastegate open (13psi).

The rod length is adjustable, I could make it longer, but then the flapper will be slightly open at idle/cruise....before it was open dump so I stayed away from this....I could do it now, exhaust might be a little louder, but any reason why I shouldn't do this?

that's why i suggested moving the the physical location of the wastegate. so even if you need to shorten the rod to keep it tight, the amount it can extend doesn't change...so moving it closer to the wastegate flapper should allow the flapper to open that much further.

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.

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Don't see any creep whatsoever in that plot. ?? If EBC gives you that much control, it means your wastegate is pretty effective. Is the complaint that you can't achieve that control at a lower boost setting?

yep exactly- I just can't really run anything less than 16 consistent. I could target 14 ish, but it would creep a little then from 6000-7000. In the above logs, my boost duty starts around 62 percent, then slowly walks up to around 90 by redline, and boost 16 to 16.8-9 at redline. I have exactly 16.0 psi set in the boost target table- I'm pretty happy with it but i may tweak it some from here.