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PostPosted: Thu Mar 22, 2012 3:19 pm 
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Just curious if anyone else thinks that their guage isn't that accurate? I have a custom Piasini Tune and my boost psi is set to 18 psi and tapper down to 16.5 but yet today at WOT I was hitting boost numbers of 22.7psi. So is there something in the guage that I need to change ( a parameter of some sort ) or take it back to my tuner and put it back on the dyno for some new numbers?


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PostPosted: Thu Mar 22, 2012 3:47 pm 
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OK, so after searching your website and finding some more literature I found this:

9. BOOST – Intake vacuum/boost displayed in inHg/PSI. Corrected by altitude entry or barometer**

I will give it a try tonight.


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PostPosted: Mon Mar 26, 2012 5:13 pm 
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nufan78 wrote:
Just curious if anyone else thinks that their guage isn't that accurate? I have a custom Piasini Tune and my boost psi is set to 18 psi and tapper down to 16.5 but yet today at WOT I was hitting boost numbers of 22.7psi. So is there something in the guage that I need to change ( a parameter of some sort ) or take it back to my tuner and put it back on the dyno for some new numbers?


Sorry for the delay, still working out bugs with the newly updated forums.

The boost parameter is obtained from the stock Mazda MAP sensor, which we then convert from psia to psig (using the barometer reading from the car) to make read as a boost gauge would. If your reading is not what you think it should be, I highly doubt it's the reading on the gauge. What altitude are you at? If you're at some extreme altitude, like 5000' in Lake Tahoe, you may want to enter that value in the "Altitude" menu option. Otherwise, don't enter anything there and use barometer. The stock MAP is pretty accurate, to about .1 psi, and barometer is accurate to about the same, so even with a .2 psi error it's still better than just about any boost gauge you could buy.

Todd

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PostPosted: Tue Mar 27, 2012 8:49 pm 
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Todd,

No worries about the late reply, thank you for replying. I currently live in Killeen Texas, altitude is 895 feet. I noticed today at 85 degrees outside that at WOT I was still boosting 22 plus and at one time boosted 24, which both numbers are cause for concern as I am custom tuned to 18. So I need to use the barometer reading and level the values blank in the altitude reading correct? So then now I need to find out barometer and see what happens. Back to google for barometer information. I'll keep you posted.

edit: Just thought of something, doesnt baromter pressure change daily? So how would you go about putting this into the guage? Is it something you would have to check and change daily?


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PostPosted: Tue Mar 27, 2012 9:11 pm 
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Todd wrote:
nufan78 wrote:
Just curious if anyone else thinks that their guage isn't that accurate? I have a custom Piasini Tune and my boost psi is set to 18 psi and tapper down to 16.5 but yet today at WOT I was hitting boost numbers of 22.7psi. So is there something in the guage that I need to change ( a parameter of some sort ) or take it back to my tuner and put it back on the dyno for some new numbers?


Sorry for the delay, still working out bugs with the newly updated forums.

The boost parameter is obtained from the stock Mazda MAP sensor, which we then convert from psia to psig (using the barometer reading from the car) to make read as a boost gauge would. If your reading is not what you think it should be, I highly doubt it's the reading on the gauge. What altitude are you at? If you're at some extreme altitude, like 5000' in Lake Tahoe, you may want to enter that value in the "Altitude" menu option. Otherwise, don't enter anything there and use barometer. The stock MAP is pretty accurate, to about .1 psi, and barometer is accurate to about the same, so even with a .2 psi error it's still better than just about any boost gauge you could buy.

Todd


Since I am not running the stock map on my car will this reading ever be correct? I was reading on barometer or barometric pressure and its not a constant number if I understand it correctly, so what should I use. Also can you read the thread about knock retard as I posted a question in there also.


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PostPosted: Tue Mar 27, 2012 9:22 pm 
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Here is a table that gives the atmospheric pressure at various altitudes. The altitude is given in feet and the pressure is in inches of mercury.

Altitude Pressure Altitude Pressure

0,000 29.92 20,000 13.75
1,000 28.86 25,000 11.10
2,000 27.82 30,000 8.886

3,000 26.82 35.000 7.041
4,000 25.84 40,000 5.538
5,000 24.89 45,000 4.355

10,000 20.58 50,000 3.425
15,000 16.88 60,000 2.118
18,000 * 14.94 100,000 0.329

* This is almost exactly one-half the sea-level value.
To convert in/Hg to psi, multiply by 0.491.

So to do a check on learning, this table shows that altitude of 0 ft up to 999 ft is around 29.92 for barometric pressure, which is close to todays reading of 31.00. Is it safe to say that this could be used as a constant pressure? But how would this be if there is a low and high pressure from start of the day until the end of the day.

Sorry if I seem to be really reading into this.


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PostPosted: Wed Mar 28, 2012 7:15 pm 
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So my guage doesnt have barometer.


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PostPosted: Thu Mar 29, 2012 10:58 pm 
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If you're only at 895' you have nothing to worry about. I mentioned high altitudes like Denver or Lake Tahoe, 5000+ feet. Even at these altitudes, your car does a quick check of the MAP when it is started, before vacuum is drawn, to determine barometer. You should be able to read this value BTW.

If you keep the "altitude adjustment" at 1000', the default value, the gauge will continue to use the vehicle barometer to correct the MAP reading to psig. If you enter 895 this will have virtually no effect on the boost reading as 125' makes virtually no difference. I have no worries that your boost reading is not accurate. Basically, I'm saying don't do anything to adjust this, the gauge is reading properly.

Todd

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PostPosted: Thu Mar 29, 2012 11:00 pm 
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nufan78 wrote:


Since I am not running the stock map on my car will this reading ever be correct? I was reading on barometer or barometric pressure and its not a constant number if I understand it correctly, so what should I use. Also can you read the thread about knock retard as I posted a question in there also.


Just noticed this. What MAP do you have? Did the tune adjust the OBD2 MAP readings? If not, then no, you can't use the OBD2 MAP or Boost reading because we only display what the vehicle sends.

Todd

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PostPosted: Fri Mar 30, 2012 7:13 am 
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The tune didnt change the map readings from what my tuner has told me or he miss understood me. At idel my gauge reads -24psi, and with the ap i was reading -10ish psi. So from the sounds of it the boost portion isnt gonna work for gauge .


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PostPosted: Fri Mar 30, 2012 8:28 pm 
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nufan78 wrote:
The tune didnt change the map readings from what my tuner has told me or he miss understood me. At idel my gauge reads -24psi, and with the ap i was reading -10ish psi. So from the sounds of it the boost portion isnt gonna work for gauge .


AP won't be accurate either. It's reading the same thing as we are. Your gauge is not reading -24psi, it's reading inHg in vacuum. We take the extra step to convert the vacuum reading to inHg as you'd see using a standard boost gauge. The AP does not do this thus why it reads -10. Most people are using to seeing -20 inHg at idle to the AP reading confuses them.

What is your new MAP sensor range, and what was it before? Is this a common thing to replace? If enough people have this issue we could add a second boost parameter for this sensor and correct the data from the PCM. There'd have to be a lot of people wanting this though.

Todd

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