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TD04L-13T - What Amount of Boost Creep is Typical?
I am looking for a bit of insight. I recently completed a build using a TD04L-13T ('05 WRX) for my VVT miata, and I am getting some unwanted spool at high RPM. Even with the wastegate wired open, it will easily spool to 12psi by 7k. This wouldn't be a problem, except once spooled, it takes a significant reduction in throttle (down to 65% ish) to reduce the boost, making for poor drivability.
I know there are some folks here who are quite knowledgeable on the WRX turbos - do you have any suggestions?
1) What level of boost creep should be expected?
2) Did you make modifications to mitigate it? If so, what?
-When prepping the turbo, I did do some light internal porting of the wastegate passage, mostly just to break some of the sharp edges.
-I chose to use the stock FLAT subaru downpipe flange, which has the unfortunate effect of limiting the travel of the wastegate (flapper hits the DP flange). I suspect that this lack of wastegate valve opening angle is the cause of my boost creep, but I wanted to see if some of the more knowledgeable folks on here could offer some insight, before I go wild fabricating a new downpipe setup. Thanks!
On my 1.6 with kraken manifold/downpipe, I had zero issue holding wastegate pressure (about 7psi) all the way out to 7400rpm. I think I had 2 maybe 3psi at redline with the wastegate wired open? But it has been a long time since I did that.
Had a machine shop do some minor port work for me to solve creep, and it didn't solve anything. Sent to BEGi and once returned I never had the creep issue again; It seems that "light porting" may be insufficient to solve any issues, but that well done porting makes a hell of a difference.
I don't think the wastegate flap is able to adequately open with that downpipe you have. It's gotta be hitting the flange.
I had a 1.6 with this turbo no porting and super short piping from turbo to intake. It boost crept up to 10psi. (at almost 8k mind you)
That was with a 2.5 exhaust all the way back. Wastegate flap could fully open. No porting was ever done on the turbo. Once I had an intercooler and full range of 2.5 IC piping, it was 7psi all day every day.
I've never seen creep like that on a TD04 even with flat downpipe flanges like that. Some people suggest that a more typical bell mouth a the turbine outlet causes creep as it tends to promote flow away from the wategate flapper.
You need to redesign your dump pipe. The reason your getting boost creep is that the exhaust flow is finding it easier to go through the turbine than the waste gate hole. That flat plate over the waste gate exit is restricting your waste gate flow.
This is my dump pipe. Notice the extra triangle shaped section which has the waste gate flow
You need to redesign your dump pipe. The reason your getting boost creep is that the exhaust flow is finding it easier to go through the turbine than the waste gate hole. That flat plate over the waste gate exit is restricting your waste gate flow.
This is my dump pipe. Notice the extra triangle shaped section which has the waste gate flow
I agree. Thanks for the input and photo. I have been considering fabricating a similar triangle shaped section. An alternate option may be to remove some material from the inside of the flange where the valve contacts it. This would allow around ~25% more valve flow area.
The boost creep issue is less prevalent now that ambient temps have warmed up, so I probably won't make the change for a bit yet. I have coilovers to install first. I will report back on the boost creep issue once I make the downpipe modifications.
Do you have better photos of the actuator and arm ?
Yep. A little background is needed though. This is a very custom actuator setup I made. The intent is to provide maximum EBC modulation of boost, down to a minimum of just a couple psi at WOT, up to as high as I want to calibrate it. So I settled on a 4-port setup of course. However, I wasn't happy with the high shaft leakage on a couple of the commercial actuators I considered using. Thus, I sourced a pneumatic actuator like those commonly used in the automation and other industries. Some math helped me determine the required piston diameter, and also a spring. I disassembled the actuator and installed the spring to force the piston and wastegate closed. Since the actuator has far more stroke than needed for the wastegate arm, I can adjust the spring preload by shortening the length of the arm (screw adjustment on the left side). It only has a pound or two of spring force.
Pics make more sense. Here is the actuator setup
As mentioned, the goal is to be able to control to a very low level of boost, even at WOT. Here is a WOT pull with a 0psi boost target. It will maintain 1.5 to 1.9 PSI boost up until 5000rpm, at which point the boost creep I am talking about comes in, and it spools to 170 kpa at 6600 in this pull.
Here is an example of the control when I calibrate target boost up to 12psi:
Anyway, I was just looking for some feedback about what level of min-boost (aka basically wastegate wired open) one might expect from the TD04L-13T turbos on a 1.8 miata. It sounds like I'll probably need to modify my downpipe to allow the valve to open farther. Thanks everyone for your input.
With that custom of a setup, the quickest test to figure out where the problem is is tie the waste gate flapper as open as you can get it with it disconected from the actuator and see what boost you make.
With that custom of a setup, the quickest test to figure out where the problem is is tie the waste gate flapper as open as you can get it with it disconected from the actuator and see what boost you make.
Yep, the first post shows the data with the wastegate tied 100% open. Interestingly, wastegate wired open and wastegate hooked up give the same boost creep results for this setup. Since the wastegate spring is only a pound or two, at high RPM where the boost has crept up, there is plenty of pressure for the actuator and exhaust pressure to fully open the wastegate. I haven't put a camera on it to confirm, but I'm pretty sure it is fully 100% open with 0% duty even when it's not wired open.
Last edited by speedengineer; 05-28-2020 at 08:20 PM.
I also had huge boost creep with my TD04L-13T and a kraken setup (2.5" exhaust). I would hit boost cut by about 4500 rpm in second gear. I ported the insides of the turbo, creating a channel for the exhaust gas to more easily go into the wastegate. That helped quite a bit, but I'm not fully there yet. Still about 10-15 kpa boost creep with the wastegate actuator disconnected. Next up is increasing the wastegate diameter.
I also had huge boost creep with my TD04L-13T and a kraken setup (2.5" exhaust). I would hit boost cut by about 4500 rpm in second gear. I ported the insides of the turbo, creating a channel for the exhaust gas to more easily go into the wastegate. That helped quite a bit, but I'm not fully there yet. Still about 10-15 kpa boost creep with the wastegate actuator disconnected. Next up is increasing the wastegate diameter.
Wow, what pressure was your boost cut set to?
For your wastegate actuator disconnected test, that's 10-15 kpa creep throughout the rev range, above some kpa of base boost level? I would be interested to see screenshot or log, if you have one handy. I would be completely happy with 10-15 kpa creep by redline above my base boost of 10 kPa.
For your wastegate actuator disconnected test, that's 10-15 kpa creep throughout the rev range, above some kpa of base boost level? I would be interested to see screenshot or log, if you have one handy. I would be completely happy with 10-15 kpa creep by redline above my base boost of 10 kPa.
My boost cut was set at 0.8 bar boost with a ~0.5 bar spring.
I misspoke for the wastegate actuator disconnect - it was actually not disconnected but connected without EBC. Attached a log and below a printscreen. Please don't mind the horrible EBC tuning in this log, but for the relevant bit it doesn't really matter. This in third gear - because I can't really go to 7000 rpm on public roads in fourth here. I'd imagine it's worse in 4/5, although you might only use them on a track.
You can see that it can hold about 150 kpa until 5300 rpm, but then it increases even though the boost duty is at 0%. It peaked at 165 kpa.
One other downside of limited wastegate flow is that the EBC had a hard time controlling it, because even just slightly closing the wastegate leads to significant boost increases - effectively giving the EBC a very small range.
For porting I used a tungsten carbide dremel kit from aliexpress (link). I removed a good amount of material that was the closest to the shortest path from the exhaust manifold to the wastegate. That was pretty straightforward - removing and fitting the turbo again was by far the most effort. I'll soon also open up the wastegate hole by about 10-15% in diameter, hopefully that will get rid of the boost creep.
My boost cut was set at 0.8 bar boost with a ~0.5 bar spring.
I misspoke for the wastegate actuator disconnect - it was actually not disconnected but connected without EBC. Attached a log and below a printscreen. Please don't mind the horrible EBC tuning in this log, but for the relevant bit it doesn't really matter. This in third gear - because I can't really go to 7000 rpm on public roads in fourth here. I'd imagine it's worse in 4/5, although you might only use them on a track.
You can see that it can hold about 150 kpa until 5300 rpm, but then it increases even though the boost duty is at 0%. It peaked at 165 kpa.
One other downside of limited wastegate flow is that the EBC had a hard time controlling it, because even just slightly closing the wastegate leads to significant boost increases - effectively giving the EBC a very small range.
For porting I used a tungsten carbide dremel kit from aliexpress (link). I removed a good amount of material that was the closest to the shortest path from the exhaust manifold to the wastegate. That was pretty straightforward - removing and fitting the turbo again was by far the most effort. I'll soon also open up the wastegate hole by about 10-15% in diameter, hopefully that will get rid of the boost creep.
Thank you for sharing. What boost pressure do you achieve when running wastegate pressure (locked to 0% EBC duty) at the lower rpms, 3000-4000 rpm? It would be interesting to see a 3k-7k wot pull with wastegate arm disconnected, to observe what boost you build, and at what rpm. It's more difficult to compare setups with the actuators attached, since we have different wastegate spring forces.
05-15-2020, 02:02 PM
TD04L-13T - What Amount of Boost Creep is Typical?
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