Single Turbo Setup Can't Reach Wastegate Pressure

Arrtus

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Apr 24, 2021
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Hey guys,

I originally had posted this in the N54Tech forum but got little to no help. I'm really stuck on and can't understand what is causing this problem.

This is a brand new DR700 setup and ever since making the swap, I am unable to reach more than ~9 psi (14 psi spring). The car is obviously way underboosting and I have no idea why. All the vacuum lines have been checked and are brand new. I have pressure tested from the turbo output all the way to the charge pipe and have found no issues. I also tested the compressor housing side of the turbo (and intake) and it did not leak whatsoever. I went through all the V-band connections and everything is on correctly and tightened to the max.

Symptoms: The car sounds different. I don't know if it's because of the single turbo but when going on WOT it doesn't sound like it's spooling. It's also very loud, like it just changes sound as soon as it starts building pressure.

With other maps, the wastegate (I think?) starts pulsing and sounding like it's hitting a rev limiter or 2-step while it's on WOT. It's most likely because of the mac that it's switching the air into the wastegate but it's not able to hold pressure or something. With maps aiming at higher PSI, it reaches ~12 PSI. What would cause the wastegate to do this? Can it be defective? It's a turbosmart gen V 45mm. I also checked the wastegate by putting some pressure on it and I can hear it open and closing. The MAC solenoid is also working just fine (which doesn't matter since it's not in use in map 0 and the problem is still there).

Log of a map 0 pull attached. Any advice or suggestions would be really appreciated!
 

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shushikiary

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Jun 4, 2018
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Stainless tends to be harder, and therefore more brittle (more likely to crack) than "normal" steel or the like.

During welding if too much heat is applied to the weld it will often make the weld its self very brittle, or the HAZ (heat affected zone). Another thing that can cause cracks like this is called hydrogen embrittlement, this is when hydrogen gets into the metal while it is cooling or during the welding. The protection for this is proper shielding gas. On a stick welding setup where the burning of the flux of the rod makes the gas the shielding gas is under high pressure and works well even outdoors (and a low hydrogen stick is used (any stick ending in 18). When doing tig or mig however if there is even a puff of wind the shielding gas can be blown away causing issues, flux core is NOT advised when welding stainless.

Because stainless is already so hard, when welding thin metal it is important to cover the back side of the weld with shielding gas due to the embrittlement problems. This is called a "back purge". It's likely that during the welding process they either did not use a back purge, got too hot, or had a fan or something in the shop (or the shop door open) which then blew away the shielding gas.

Tisk tisk on the welder who did that work if any of that is true.


In any case, do you know who makes an awesome bottom mount kit that doesn't have these problems, is twin scroll and has shown awesome numbers and offers the same turbo you're already using? Speedtech.... I'd suggest you give them a try if you're done with the doc race kit.
 
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martymil

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Sep 6, 2017
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Down Under @ madautodevelopments
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We back purge all our welded exhaust manifolds where extreme heat will be a factor and it cost a lot of money that's the difference between cheap kits
and ones that have been done properly.

People don't understand how much money and r&d goes into something like this, all they do is bitch about the final price.

If all you want is cheap expect the manufacturer to try and cost cut in one way or another.
 
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fmorelli

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Yes ... and back purging with argon is run of the mill knowledge to anyone that knows what they are doing - that should be a given on that manifold. My twin turbo outlets are custom made from stainless ... and of course are back purged.

Wondering if these guys had a bad batch...

I'm sure you are frustrated. Stick with it - you are almost out of the woods it seems.
 
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Arrtus

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Apr 24, 2021
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I would not be surprised if a bad first batch went out. The kits were delayed multiple times and could have been rushed to get them out.

I know DocRace is more than capable of making quality products. I didn't mean to make it sound like their company isn't up to par with other kits by any means.

By the way, @Steve135i, I also noticed I have the same thin crack as well at the center location you posted a picture of. If your manifold is not installed yet, I would highly recommend you get the other welds maybe re-done/reinforced or something. There's no guarantee that the rest of the welds are going to hold up. But If you already installed everything, I hope your manifold doesn't succumb to the same failure points as mine did.
 

Steve135i

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Nov 16, 2020
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I would not be surprised if a bad first batch went out. The kits were delayed multiple times and could have been rushed to get them out.

I know DocRace is more than capable of making quality products. I didn't mean to make it sound like their company isn't up to par with other kits by any means.

By the way, @Steve135i, I also noticed I have the same thin crack as well at the center location you posted a picture of. If your manifold is not installed yet, I would highly recommend you get the other welds maybe re-done/reinforced or something. There's no guarantee that the rest of the welds are going to hold up. But If you already installed everything, I hope your manifold doesn't succumb to the same failure points as mine did.
Well i also bought this kit with the thought that doc race was the company you want to get a n54 ST from. Saving money had nothing to do with it. By the time i added the gen2 turbo and open dump option and ceramic coating i spent as much as any other kit i could have bought. Except ces lol. I was like #3 on kit preorders. The guy in front of me and the guy behind me also had cracked manifolds. Im guessing a bad batch. Which im sure was not the way he wanted these kits to hit the market. I did see when putting it together there was some pieces that were not up to par. I bought my own oil feed line, i dbl wrapped the oil drain and the waterpipe to radiator hose. Changed all the worm clamps to tbolt spring clamps. Changed the oil drain -an on the turbo to a better one. I see they were trying to make a price point, and wasnt worried about it. Its a good kit. And i will move forward with it. As far as welding the manifold, i have a really good welder down the block from me. He told me they didnt purge the welds like mentioned above. I asked if we could grind out all of them and re-weld but he said "if it aint broke dont fix it" so i only did the one that was cracked. Doc race will stand behind their products and as i said and has a better welded version already that doesnt have the center seam that i could have got in place of this one. And a cast version in design. But at the time i couldnt wait for shipping. Im moving soon and needed to get the engine back in the car.
I put this kit in first time with subframe in, was pretty quick and easy, second time with subframe out because i spun a waterpipe bolt and had a small drip that bugged me, I needed the extra room to tap the hole. Now i put it on a 3rd time with motor out. I will keep an eye on it and see if any more cracks start. Im hoping it lasts until im done building the motor im working on. But if not its a pretty easy removal. Just take dp off. Drop turbo off vband, let it sit on waterpipe. Take off wastegate and dump pipe and every bolt is accessible. I will update if i have any further cracks.
Good luck to you. Its a new product and has some bugs to work out. But i think once the manifold is corrected we got a good kit at a good price. Stick with it and give it a shot.
 
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