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Location:
Pine Rivers QLD
Registered:
April 2005
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inaccurate boost gauges????
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Tue, 29 November 2005 06:17
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Hey all i had my car at the dyno the other day and they said they measure the boost at the turbo's and they read 8PSI, my boost gauge which comes off the intake platinum (or however it is spelt) reads 10.5PSI, so assuming there is loss in the IC and stuff (which i heard there usually is, i have the stock IC on an early gen 1G-GTE) then i am looking at about 3 - 4 PSI inaccuracy. Is this normal, even though i only paid 90 odd bucks for the gauge i would have still thought it would have been semi accurate.
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Location:
Pine Rivers QLD
Registered:
April 2005
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Re: inaccurate boost gauges????
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Tue, 29 November 2005 08:26
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anyone??? moreover who should i believe? my gauge or the dyno guys, as it seems that this dyno always seems to mysteriously give higher power values 
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Location:
Sydney
Registered:
February 2003
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Location:
Pine Rivers QLD
Registered:
April 2005
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Re: inaccurate boost gauges????
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Tue, 29 November 2005 10:56
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my boost is done buy a $90 boost gauge run off a single outlet (no T pieces) on the plenum  . I guess i could run if off the turbo and i feel it would make sense if the pressures were the opposite (eg, more power seen at the turbo then at the intake) but this other way seems as if the gauge is badly out. Does this sort of thing happen often?
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Location:
Brisbane
Registered:
May 2002
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Re: inaccurate boost gauges????
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Tue, 29 November 2005 11:22
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The other day I saw a brand new Speco gauge read 20 mmHg vacuum when it wasn't attached to anything. Either we were floating in space at the time or inaccurate gauges are more common than you think.
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Location:
Sydney
Registered:
February 2003
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Re: inaccurate boost gauges????
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Tue, 29 November 2005 17:07
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no i meant, what where you doing when you read the boost off the gauge?
high gear up a hill?
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Location:
Sydney
Registered:
June 2004
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Re: inaccurate boost gauges????
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Tue, 29 November 2005 18:49
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a friend of mine runs his boost guage off the plenum and the readings change with every degree in temop change... i always thought that having the guage off the plenum would read air pressure within the plenum and not actual boost pressure
but then again i thought that the boost guage is run off the waste gate hose to give absolute pressure...
i could be wrong but that has been my understanding
cheers
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I supported Toymods
Location:
Perth
Registered:
May 2002
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Re: inaccurate boost gauges????
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Tue, 29 November 2005 23:09
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I've heard of people complaining of inaccurate boost gauges. Generally, they have been American brands like Autometer or cheapies.
My APEX'i gauge appears to be deadly accurate, reading pretty much spot on what my Gizzmo does, as well as what the dyno printout did.
What did they mean by reading boost at the turbos?? There is no way you'd be pulling the line off the turbo, as a) it's a PITA and b) you'd have no boost control.
You'd be right in your assumption with the loss across the IC and piping, but that shouldn't explain why you have a different reading.
Personally, I'd be believing the dyno guys for the boost pressure. While some dodgy operators can fiddle with values (although they are severely limited in what they can modify with something like Shootout) the boost pressure is just a readout and shouldn't be part of the power calculation. What does the dyno sheet look like, can you print it out?
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Location:
sunny coast, qld
Registered:
October 2002
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Re: inaccurate boost gauges????
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Tue, 29 November 2005 23:17
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I agree with JCMF. Can you borrow somebody elses guage and see if it reads the same?
I have a $30 guage in my car and it seems to be pretty accurate to what the wolf MAP sensor reads.
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Registered:
November 2005
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Re: inaccurate boost gauges????
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Wed, 30 November 2005 01:15
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hey man.....i would be putting it down to conditions on the day....i meen boosting along on a cold day you would be looking at arise in psi but on a dyno you arnt getting as much air to the cooler.....when i had my cords it ran 12 psi on hard boosting on the road...and the dyno only read 9.....
BUT then again it is highly possible to have a defective gauge... as really all it takes is a bit of air leak in the system to put it way out...and as anyone would know air can escape fairly easy...especially under presure...
try a mates guage!!
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Location:
Pine Rivers QLD
Registered:
April 2005
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Re: inaccurate boost gauges????
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Wed, 30 November 2005 09:25
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yeah i know someone with a gauge so i will go steal his,
STR8 2.8
my gauge seems to read 11PSI every time so i don't think its a hill problem,
JCMF
I have a controller (valve thing) so i guess they T piece it and check that.
I only got a printout of the AFR because last time i got boost, i was cut that it didn't have AFR, and what was my AFR reading???? 14 at idle and 10 at peak power  they say my injectors need cleaning...
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I supported Toymods
Location:
Perth
Registered:
May 2002
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Re: inaccurate boost gauges????
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Wed, 30 November 2005 23:26
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| ndgcpr wrote on Wed, 30 November 2005 17:25 |
JCMF
I have a controller (valve thing) so i guess they T piece it and check that.
I only got a printout of the AFR because last time i got boost, i was cut that it didn't have AFR, and what was my AFR reading???? 14 at idle and 10 at peak power they say my injectors need cleaning...
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Still seems like a silly way to measure boost.
Should've asked them to print two graphs for you like I did, my first one had boost, and my second one had AFR's. How did they determine your injectors need cleaning, are they psychic?
If they're saying it's because the AFR's are slightly erratic, mine are all cleaned here:
http://users.bigpond.net.au/justcallmefrank/dynosh eets/2.jpg
Got a copy of your sheet you can show us?
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Location:
Pine Rivers QLD
Registered:
April 2005
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Re: inaccurate boost gauges????
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Thu, 01 December 2005 05:36
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yeah sorry, i was gonna post it up last night but it meant i had to get the camera out, then take a pic, and i am just lazy, but here you go (sorry i left the flash on)
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Location:
sunny coast, qld
Registered:
October 2002
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Location:
Pine Rivers QLD
Registered:
April 2005
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Re: inaccurate boost gauges????
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Thu, 01 December 2005 07:14
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too rich and too lean... I am pretty sure they said they pulled one of the injectors out and it dripped instead of spray or whatever it does. Yeah the prospect of an SAFC is interesting, as i am trying to keep mine as a "sleeper" so i don't want anything special and the first SAFC's are cheap now
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I supported Toymods
Location:
Perth
Registered:
May 2002
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Re: inaccurate boost gauges????
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Thu, 01 December 2005 09:16
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Given you have some electronics skills, I wholeheartedly recommend a Jaycar Digital Fuel Adjuster instead of an SAFC. A shitload more resolution, and very cheap.
Why were they pulling the injectors out, that's a lot of effort to go to!
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Location:
Carlingford, Sydney
Registered:
May 2002
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Re: inaccurate boost gauges????
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Thu, 01 December 2005 12:59
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i got a speco gauge and i think its way off, but it also reads to low anyway for the aplication so its not much use, i just use the boost cut set at the limit of the map sensor then back it off a click or 2 once it hits that
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Location:
Pine Rivers QLD
Registered:
April 2005
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Re: inaccurate boost gauges????
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Thu, 01 December 2005 23:55
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| justcallmefrank wrote on Thu, 01 December 2005 19:16 |
Given you have some electronics skills, I wholeheartedly recommend a Jaycar Digital Fuel Adjuster instead of an SAFC. A shitload more resolution, and very cheap.
Why were they pulling the injectors out, that's a lot of effort to go to!
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Yeah i dunno man i am REALLY not a fan of the place, they have stuffed me around once to many times. So you reckon my Injectors are ok? And i will still need a DYNO to tune whatever i get (fuel adjuster/SAFC) anyway so i doubt i will be doing anything for a while, i need to find another dyno...
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I supported Toymods
Location:
Perth
Registered:
May 2002
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Re: inaccurate boost gauges????
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Fri, 02 December 2005 00:18
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Just take it to another dyno later on and get the DFA tuned. Sure it's a possibility it's leaking, I just can't see them taking the injectors out to check, it's not exactly a 5 min job with everything in place on a 1G.
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Location:
Brisbane
Registered:
July 2005
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Re: inaccurate boost gauges????
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Fri, 02 December 2005 01:51
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Gav,
I cant beleive that this thread got so far without someone asking you why you made a gain through your IC - assuming both gauges are correct.
Its physically impossible to to have a pressure increase after both; a)plumbing which always suffers some static loss. b)cooling which increases density, therefore reducing pressure.
This is the fundamental reason why you control and measure boost AFTER any cooling device if you wana know/control whats really making it to your engine.
Statistically, knowing the pre-cooler figures (boost, & temp) is always handy in assessing / tuning / further modding. Furthermore this is how you measure the efficiency of your (inter)cooling system. Greater temp drop for less pressure drop equals more efficiency. I laff daily at dickheads with truck cores who have no comprehension of this.
Getting off topic tho... I say bigtime gauge error. Probably both gauges to some degree. Looking at figures... hard to say, but i think its possible they plumbed up bad and it was bleeding during the test. I would think that you would have to have rock bottom minimum 8.5psi with a FMIC on a dyno, and erratic AFR's, to be able to get 145. Do these guys use a fan?
This is my only other explanation. No fan to actually cool the front. Instead you have an "interheater" as the heatsoaked core actually raises intake temps and boost value. And fucks up your AFR's as temps sensors go nuts...
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Location:
Brisbane
Registered:
July 2005
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Re: inaccurate boost gauges????
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Fri, 02 December 2005 01:54
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| Quote: |
This is my only other explanation. No fan to actually cool the front. Instead you have an "interheater" as the heatsoaked core actually raises intake temps and boost value. And fucks up your AFR's as temps sensors go nuts...
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Infact the more i think about it the more convinced i am of this theory.
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