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Old 04-13-2020, 06:35 PM   #1
Nickagriffin
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Default Boost drop at high rpm

Hey all,

In my 244 +T I'm having an issue where the boost will drop from about 11 or 12 psi down to 7psi at redline. It seems like as soon as it hits 11 psi it will start to drop back down. I'm running a 13c, which many people have told me gets choked up at high rpms, but is a 4-5 psi drop normal? I've seen a few other threads with this same issue but haven't seen a definitive answer.

Any input is appreciated

Additional specs if needed
Stock M cam
850T injectors (redtops I think)
NPR intercooler
Manual boost controller (spring and ball type)
Full 3 inch turboback exhaust, side exit, single glasspack, no cat

Nick
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1989 Volvo 245

Last edited by Nickagriffin; 04-13-2020 at 06:53 PM..
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Old 04-13-2020, 06:46 PM   #2
MikeSr.
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Back pressure will do that.
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Old 04-13-2020, 06:50 PM   #3
iamrolling
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While researching my turbo problem, I found a thread from another forum where someone mentions losing 5 psi from the wastegate shaft popping up. I'm sure the wastegate is one of the first things you checked, but I thought it might be worth mentioning because the amount of power lost is similar.
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Old 04-13-2020, 06:58 PM   #4
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I checked the wastegate action but I didnt check the shaft, so I'll take a look at that. Another thing I should mention is I'm running a homemade wastegate mounting bracket that the guy who sold me the turbo sent. It's pretty thin metal and is easy to bend backwards (closing the flap) but it doesn't really move forwards at all, which would cause the flap to open and the pressure to drop. I originally thought this could be the problem but it seems like it would be hard for the exhaust gases to force that flap open since I can barely move the wastegate with my hand. There seems to be pretty good tension holding the wastegate closed in the neutral position, so no exhaust gas should be leaking out below the pressure I have the MBC set to.
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Old 04-13-2020, 08:42 PM   #5
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I'd look at the muffler/convertor/undersized exhaust.

Make sure you are not jamming 200hp thru a 100hp pipe.
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Old 04-13-2020, 08:49 PM   #6
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It's got a 3" turboback exhaust with only a single glasspack and it's a side exit, so I don't think the exhaust system is the problem
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Old 04-13-2020, 09:22 PM   #7
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Quote:
Originally Posted by Nickagriffin View Post
Full 3 inch turboback exhaust, side exit, single glasspack, no cat
Please install a cat. Great high flow options out there that will keep your car fast, and not kill the planet.
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Old 04-13-2020, 09:45 PM   #8
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Quote:
Originally Posted by Kestrel View Post
Please install a cat. Great high flow options out there that will keep your car fast, and not kill the planet.
https://www.nytimes.com/1998/05/29/u...l-warming.html

Worth a read. I'm not in a super dense area so smog is not a big concern, but greenhouse gas emissions are a big a problem here as anywhere. The choice between cat or no cat is more of a "lesser evil" decision, not a right answer and a wrong one. This article along with a bunch of studies show that cats reduce overall system efficiency which increases the greenhouse gas emissions.

PS - Have an electric 240 build planned for sometime in the future when funds allow.
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Old 04-13-2020, 10:39 PM   #9
Wesdunns70t5m
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When I first installed a 19t I had a flimsy wastegate bracket. When the rod would "push" the puck open, it would bend the bracket towards fhe front of the car, causing my boost to oscillate. Might just need a beefier bracket
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Old 04-13-2020, 11:19 PM   #10
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What's that thing sound like with a glasspack and no cat? I have to imagine at least a little meaner than the happy putter of the stock motor.
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Old 04-14-2020, 02:46 AM   #11
Nickagriffin
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Quote:
Originally Posted by Wesdunns70t5m View Post
When I first installed a 19t I had a flimsy wastegate bracket. When the rod would "push" the puck open, it would bend the bracket towards fhe front of the car, causing my boost to oscillate. Might just need a beefier bracket
Alright I'll fab up a new stiffer bracket and report back. Thanks for the input
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Old 04-14-2020, 02:49 AM   #12
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Quote:
Originally Posted by iamrolling View Post
What's that thing sound like with a glasspack and no cat? I have to imagine at least a little meaner than the happy putter of the stock motor.
Shes pretty loud, but I think it sounds a lot more refined than a straight pipe. When this car was NA I had a 2 inch side exit straight pipe with a cat, and it was loud and super rapsy. The turbo and big glasspack seemed to quiet it down enough for me even with it being 3 inch and I really like the tone it has now too. It has a cool rumble kinda like a subaru boxer engine had a baby with a tractor

Oh yeah, and it has lots of pops
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Old 04-14-2020, 05:54 PM   #13
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Quote:
Originally Posted by Nickagriffin View Post
Alright I'll fab up a new stiffer bracket and report back. Thanks for the input
So I got the new bracket installed today and that was definitely the problem. It's holding 11lbs all the way to redline now with no major peaks

I still need to adjust the tension some since it's making about 10lbs on gate, but that should be as easy as modifying my bracket a little bit.

Thanks everyone for the help

Nick
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