Stumped: Low Boost
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Tuned
Joined: Jan 2014
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I left my red line capped until I could exceed 35 PSI boost - then I hooked it back up to protect the intake valves. We wouldn't want those opening precipitously, now would we.
I have seen 20 PSI boost on a stock truck, red line capped, and an AIS with no other mods. Same truck, bumped the exhaust to 4" and I topped off at 22 PSI boost - at which point the truck would defuel. 22 PSI is max without a chip or a boost fooler - the type that regulates the pressure to the MAP line.
The adjustment for the wastegate is a turnbuckle on top. The hardest part of the whole job is to not lose the C-clip keeper. I parked a Mythbusters uber-magnet on top of the turbo while adjusting the wastegate, in case I dropped the keeper.
I have seen 20 PSI boost on a stock truck, red line capped, and an AIS with no other mods. Same truck, bumped the exhaust to 4" and I topped off at 22 PSI boost - at which point the truck would defuel. 22 PSI is max without a chip or a boost fooler - the type that regulates the pressure to the MAP line.
The adjustment for the wastegate is a turnbuckle on top. The hardest part of the whole job is to not lose the C-clip keeper. I parked a Mythbusters uber-magnet on top of the turbo while adjusting the wastegate, in case I dropped the keeper.
Hotshot
Joined: Jan 2011
Posts: 18,849
Likes: 179
From: Puget Sound
Yeah... those instructions were how I did it with the turbo in the truck. It would have been easier to do this while the turbo was out - just like the instructions said to do (which I read after the install and I had low boost). 
Logistics Pro
Joined: Dec 2010
Posts: 4,738
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From: Temperance, MI
Tie a piece of dental floss/fishing line around the C- clip and the other end to something that is not going anywhere like a bolt. This way when it does go flying around all you have to do is pull it back up from its hiding spot.
Hotshot
Joined: Jan 2011
Posts: 18,849
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From: Puget Sound
About 17 is the norm on a Superduty. Without saying you are mistaken, I have seen people swear on a stack of bibles that they have no leaks, then finally find one or more. It's always possible something else is at play, like a loss in turbo efficiency or wastegate control needs some attention.
Go Bills !
Joined: Jan 2008
Posts: 2,778
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From: Buffalo, NY
True. And to add the gauge itself,barometric pressure, sea level , humidity. The moon is aligned. We have gauges at work that fail calibration. It is frustrating that we buy new gauges to only return them because they fail . being 15 psi in an un chipped truck . I would call it good and remember that is the norm for trouble shooting purposes and the reading on that particular gauge . Everyone said I should get 17. I chased after it for two freakin years. New plenums . Boots . Clamps. Gaskets. A couple of different gauges. The turbo on the garage table a couple times. I gave up. Even put in two different sets of blades . Over 2 psi. Ha. I figured what the hell, that is beer money I am spending and wouldn't notice the difference towing anyways. Grew tired of messing with it . Tossed in a dp tuner and it is a different now ! Hal la!
Just saying I hope the op is not spending the money I did tracking down 2 or 3 psi as I did to only loose out. For what reason I asked my self. More important to only know what it is and it stays there .
Just saying I hope the op is not spending the money I did tracking down 2 or 3 psi as I did to only loose out. For what reason I asked my self. More important to only know what it is and it stays there .
Hotshot
Joined: Jan 2011
Posts: 18,849
Likes: 179
From: Puget Sound
With the other low boost (13-14 PSI) thread that's active now, everything being done is testing - not spending. Now that we have some test results, there are indications that spending can make an improvement with boost. In this thread, we're talking a GTP38R giving low boost - which is a clear and obvious problem. While the GTP38 is a nice turbo, I always see a big efficiency loss (growing gap between EBP and MAP) when the boost numbers climb beyond stock boost. The 38R gives me very close to 1:1 all the way up the dial (I limit mine to 35 PSI), but I have "balanced" my entire air in/out system.
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Tuned
Joined: Jan 2014
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With the other low boost (13-14 PSI) thread that's active now, everything being done is testing - not spending. Now that we have some test results, there are indications that spending can make an improvement with boost. In this thread, we're talking a GTP38R giving low boost - which is a clear and obvious problem. While the GTP38 is a nice turbo, I always see a big efficiency loss (growing gap between EBP and MAP) when the boost numbers climb beyond stock boost. The 38R gives me very close to 1:1 all the way up the dial (I limit mine to 35 PSI), but I have "balanced" my entire air in/out system.
Hotshot
Joined: Jan 2011
Posts: 18,849
Likes: 179
From: Puget Sound
Yes, a compression test would preclude more money going into an engine.
As mentioned, my 38R is about 1:1, the MAP should closely parallel the EBP. A failed wastegate adjustment will kill the EBP (and subsequently the MAP/boost), and no amount of tuning will undo that. At the time I had my 38R faux pas, I had Stage II injectors with all the air mods and tuning - but couldn't build EBP or boost above 18 PSI. Total and utter fail. Tighten the wastegate arm and up comes 35 PSI boost with 36 PSI EBP.
As mentioned, my 38R is about 1:1, the MAP should closely parallel the EBP. A failed wastegate adjustment will kill the EBP (and subsequently the MAP/boost), and no amount of tuning will undo that. At the time I had my 38R faux pas, I had Stage II injectors with all the air mods and tuning - but couldn't build EBP or boost above 18 PSI. Total and utter fail. Tighten the wastegate arm and up comes 35 PSI boost with 36 PSI EBP.
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