Stcok boost pressure?

ilikebigbutts

ilikebigbutts

workin' my dream
Jun 10, 2007
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ok i'm only getting 5psi and i cant figure out why... i searched and i came up with 3 different answers, 5 psi, 8 psi and 10 psi...so what is the stock wg sprung to?I just got the car running i bought with a blown turbo that i replaced and like 3 boost leaks that i fixed so i doubt i got any other leaks.this sunday i'm making a leak tester but if it was a leak wouldnt boost fall off at higher rpm?could my wg cause lower boost?
 
starscream5000

starscream5000

Senior VIP Member
Aug 23, 2006
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The wastegates don't matter, the auto is a fluid coupling, or "slushbox" they do not put as much load on the engine, hence the turbo doesn't work as hard as if the engine was turning a manual tranny.
 
Nick M

Nick M

Black Rifles Matter
Sep 9, 2005
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The car makes about 230 horsepower at 6.8 psi. The speed tolerance, due to mass production and engine load, is 5.5-7.5 psi. The automatic tolerance is 4.8-6.0 psi.

This is factory stock.
 
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cjsupra90

previously chris90na-t
Jun 11, 2005
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Lakeland, FL
The stock wastegate is actually closer to about 9 or 10psi, but due to system restrictions like exhaust and intake tracks, the intake only sees about 6 to 7psi of manual trans cars and about 5psi for auto's.

With an unshimmed wastegate, stock turbo, stock IC, 2.5" IC hard piping, and full 3" exhaust (turbo to tip) and no cat, I'd get just over 8psi all day long and in 5th gear on a long sustained boost run on the highway it will slowly creep to abour 9.5psi and then stay there.

Side note about autos, an auto only produces less boost because the trans always has a small about of slipage and therefore less load on the engine and being that a turbo is 100% load dependent then this means less boost due to less load seen by the motor.
 
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cjsupra90

previously chris90na-t
Jun 11, 2005
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Nick M said:
The car makes about 230 horsepower at 6.8 psi. The speed tolerance, due to mass production and engine load, is 5.5-7.5 psi. The automatic tolerance is 4.8-6.0 psi.

This is factory stock.
Click to expand...

Not to mention, altitude will also effect it.
 
ilikebigbutts

ilikebigbutts

workin' my dream
Jun 10, 2007
347
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Pittsburgh
so...i'm still running lower boost than i should...the car has a 3" cat so it aint stock...i due have a really big exhaust leak right after teh cat though would that affect boost that much?
 
tlo86

tlo86

Ninja Editor 'Since 05'
Jul 24, 2005
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it does have to do where you live, in texas (with an auto) i would boost 8psi and in colorado 4psi.

downpipe or intake didnt raise psi in texas but it did help quicken the spool (of course) and in colorado i took off apexi intake and put stocker back on it put on spearco replica and got 6~7psi (8psi with an intake at higher loads but with stock intake it didnt want to go past 7)

and an exhaust leak wouldnt affect anything... might even help if anything hehe depending on how bad it is as long as it isnt before your o2 or turbo
 
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cjsupra90

previously chris90na-t
Jun 11, 2005
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Nick M said:
You need to hang out here more often, and quit playing with the UZ swap.
Click to expand...

Yeah I know, I have actually been lurking around for a while and just dont bother to posting that much being that most of the time its to late and I dont like to repeat what others have already posted unless they are correct and others want to argue that they are wrong or if info is left out.

The sad part is that I haven't even been messing with the UZ that much cause I have so much other crap going on. (dame I need to get back on that project.)

Anyways, back to the topic at hand. If you are getting lower then usuall boost then there is probably a problem somewhere and you just need to do a series of tests to determine where or what the problem is.
 
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cjsupra90

previously chris90na-t
Jun 11, 2005
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Lakeland, FL
Oh, something else to add to the topic besides altitude effecting boost pressure is the barometric pressure, temperature and the realitive density of the air.

On extremely hot days with a low pressure front coming through (very typical down here in FL when in hurricane season), i have noticed loses of boost pressure and significant power looses.

Any lose in atmospheric pressure will equal the same lose in boost pressure and now add in the hot temperature and you end up with a lower realitve density and there is the significant lose in power being that the absolute density entering the motor along with the fuel is where the power comes from.

Humidity plays into it also, but only on the power aspect, not the boost pressure itself.

All in all though, besides all that, if the boost was fine one day and then all of a sudden has droped, there is either a boost leak, a problem with the turbo, and problem with the motor, problem with the trans (if auto) or possibly a slipping clutch if it is a manual trans.
 
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cjsupra90

previously chris90na-t
Jun 11, 2005
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Lakeland, FL
tlo86 said:
and an exhaust leak wouldnt affect anything... might even help if anything hehe depending on how bad it is as long as it isnt before your o2 or turbo
Click to expand...

Unless the exhaust leak is before the turbo (i.e. somewhere between the head and the turbo), then that will affect the boost. Think of a wastegate, it is nothing more then a device that gives a controlled exhaust leak pre-turbo.

Other then that, yes, any leak after the turbo will have either no affect or will actually cause a rise in boost if the exhaust is restrictive enough and the leak is large enough (i.e. stock exhaust with a large leak very close to the turbo will probably show a small rise in boost).
 
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