Whats a safe boost level? - Subaru WRX Forum
 
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#1 Old 10-28-2002, 12:18 AM
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Whats a safe boost level?

Hey hope you guys don't mind if I "invade" the site as I am a DSMer. I have a friend who just got a 01 WRX and he knows nothing about cars. I have plenty of experience with the pile o crap I call transportation (Eclipse GSX...) but do not know the specs and limitations on these engines.
First things first, he has the filter, BOV, and rear strut tower bar. Aside from spending the $600 for the exhaust system, a MBC would be the next best choice on my car. I assume the same goes for the WRX. How high are you guys setting your boost levels with stock pistons, fuel systems, turbo, etc.? Any good websites would be helpful too for a proven upgrade path and advice. Thanks guys
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#2 Old 10-28-2002, 01:52 AM
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im on stock boost...but most of the people i talk to w/ manual bc's leave it at about 16 unless in extreme occasions....

my moms blitz bc's "HI BOOST is set at like 18 psi or around there but thats hi boost....

it will never get weird saying "my mom's"....

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#3 Old 10-28-2002, 09:02 PM
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General consensus from other forums is that 15.5 psi tends to be the safest without any engine management, and 16.5 psi with engine management. Above that, the turbo isn't going to be putting out any more power.

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#4 Old 10-28-2002, 11:04 PM
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why doesnt it put out any more power?

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#5 Old 10-29-2002, 10:05 AM
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Simply because the turbo is too small. Stock fuel cut-off is at about 17-17.2 psi since that's already out of the effective usable range of the turbo. If you boost more than that, you're not generating more power, just blowing out hot air

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#6 Old 11-12-2002, 11:00 AM
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Plus putting your turbo in extreme, probably unsafe territory.
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#7 Old 11-13-2002, 02:47 PM
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The turbo is small butt thats not the problem if u go higher than 15.5 your fuel injectors are at like 98% duty You can risk injector failure and thats not a good thing.
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#8 Old 11-13-2002, 02:56 PM
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Quote:
Originally posted by noobracer
The turbo is small butt thats not the problem if u go higher than 15.5 your fuel injectors are at like 98% duty You can risk injector failure and thats not a good thing.
98% duty above 15.5 psi on the stock turbo? Where'd you hear that? I can see the fuel system being in trouble with that amount of boost on a larger turbo, but not on the stocker...

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#9 Old 11-14-2002, 11:56 AM
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Quote:
Originally posted by Verdugo


98% duty above 15.5 psi on the stock turbo? Where'd you hear that? I can see the fuel system being in trouble with that amount of boost on a larger turbo, but not on the stocker...
Your right on a stock turbo its higher than 15.5 i keep on forgeting i have the stock turbo butt its been modified by FP i keep on forgettn cause it was like that when i bought my rex but my stock turbo modified taps out at 15.5.
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#10 Old 11-14-2002, 06:31 PM
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I don't know how Subees are different from my Eclipse but with my car, the injectors do not have a problem being run at 100% of stock regardless of the fact that you would only be running at that percentage for about 1 second in each gear as you top out the rpms and thus the capacity of the injectors/fuel pump. The only problem with running higher boost levels is because you get a higher knock count as more fuel spontaneously combusts inside the chamber because the fuel acts as a coolant...thus water injection on rally cars which acts the same way. It is true that a turbo's efficiency differs as the boost created increases but seeing how the T25 (stock 2g Eclipse) is visibly smaller than the model on your Rex's, I cannot see how you can be out of that efficient range at only 15.5 psi. I know that the intercooler has a strong role in efficiency but again, the Rex's have a larger top mount i/c than my puny stock smic. I believe I read somewhere that the compression on stock Rex's pistons is 8.0:1 which also allows for more boost than the stock Eclipse which runs the 8.5:1.
Bigger turbo + bigger i/c + lower compression pistons = Higher potential boost levels.
Of course as we were discussing, the fuel system has to be able to keep up with the rest of it all and I haven't looked up the injector size of fuel pump capacity. Nor have I looked up what the fuel pressure regulates the pressure in your fuel line to which is the only thing I could see that would create injector failure. I am not an expert on how the fuel system works so I could very well be wrong there...
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#11 Old 11-20-2002, 05:24 PM
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Ive been playin around with my mbc and anything over 15.5 I actually loss power.......on the stock turbo / inj........
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#12 Old 12-02-2002, 03:28 AM
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I think I would have to disagree with the power loss opinion. I run 1.2 Bar...(Roughly 17.64 PSi) Fuel cut isn't until about 18 PSi. And yes- this is on a stock turbo.

I DO agree that it maxes out your duty cycle, and isn't exactly the best thing for keepin the turbo healthy... BUT- a 2 PSi drop is a noticable difference. Even when you have a bigger intercooler (say a front mount, like a Blitz) you will need to increase the boost due to a pressure drop through that huge intercooler.

Make sense?
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