OBD Boost Gauge?

[Jason11213]

I’d like to add this to avoid dragging my laptop and Ross tech cable out but are the OBD gauges reliable? I’m assuming they just take the same data I’m getting when doing logging?

[Grouch]

It's not going to be as accurate as a proper boost gauge. But for shits and giggles I compared the numbers to my Podi and Torque Pro, it was almost he same for the most part. Except when I gunned it then it was all over the place.

[Jason11213]

It's not going to be as accurate as a proper boost gauge. But for shits and giggles I compared the numbers to my Podi and Torque Pro, it was almost he same for the most part. Except when I gunned it then it was all over the place.

Do you know if they adjust for atmospheric pressure every time I turn on the car? I figure if they do that then at least it’s as accurate as when I export the log data to excel then adjust it on my own?

[lorduvtherings]

I have p3 gauge guys right into my air vent has multiple options Fully Reversible Installation: Simply plug into your OBD-II port and you're functional. No splicing or rewiring required.

Precise Color Match and OEM Integration: Seamless integration with interior lighting including auto or manual dimming to match dash brightness.

Advanced Custom Programming: Designed and programmed specifically for each car and engine, so you can be sure all features will function as expected.

Live Performance and Sensor Data: Real time “as it happens” data display of multiple parameters with virtually no lag or delay.

Built In Acceleration Performance Timer: Automatic start and stop 0-60mph (0-100kph) timer for evaluating your car’s performance and driving skill.

Diagnostic Data Interpretation & Reset: Read and clear diagnostic trouble codes (DTC) to reduce trips to the dealership.

3x Analog Inputs for High Precision Sensors: Universal 0-5v inputs for adding additional sensors or switching boost to an analog vacuum tap.

Easiest Installation Possible: Put it in, plug it in, installation for even the most novice do-it-yourselfer. Optionally pre-installed in an OEM vent for further ease of installation.

I love it fits in perfect with my set upScreenshot_20201111-160516_Samsung%20Internet.jpg

[Grouch]

Do you know if they adjust for atmospheric pressure every time I turn on the car? I figure if they do that then at least it’s as accurate as when I export the log data to excel then adjust it on my own?

The atmospheric pressure is what you set it as in your vehicle profile in the app. I never compared my Torque Pro numbers to VCDS as I'm lazy so I couldn't say for sure how they compare.

[Smac770]

I'm confused what you guys are going on about. Anything reading data via the OBD is working with the one single pressure value which the car measures, the MAP value before the throttle body. And of course it's accurate, unless you're sensor is shot. The value from the ECM PID is absolute pressure, so it's up to the gauge to grab an ambient value to subtract from the absolute value to give you a gauge value. When is MAP reading ambient? Anytime the engine is idling.

So as to the recomputation of the data to various forms, that's a question for the processing performed by the tool. As to the accuracy of the data, of course it's accurate. "oh, but I wanted an in-manifold pressure reading, post throttle body". Then put a boost tap on the PCV connection to the IM and read that. Will that be the same as the MAP reading? Of course not, you're reading two different things.

[Grouch]

So as to the recomputation of the data to various forms, that's a question for the processing performed by the tool. As to the accuracy of the data, of course it's accurate. "oh, but I wanted an in-manifold pressure reading, post throttle body". Then put a boost tap on the PCV connection to the IM and read that. Will that be the same as the MAP reading? Of course not, you're reading two different things.

Just curious, what's the difference between the MAP reading vs PCV connection to the IM?

[Jason11213]

I'm confused what you guys are going on about. Anything reading data via the OBD is working with the one single pressure value which the car measures, the MAP value before the throttle body. And of course it's accurate, unless you're sensor is shot. The value from the ECM PID is absolute pressure, so it's up to the gauge to grab an ambient value to subtract from the absolute value to give you a gauge value. When is MAP reading ambient? Anytime the engine is idling.

So as to the recomputation of the data to various forms, that's a question for the processing performed by the tool. As to the accuracy of the data, of course it's accurate. "oh, but I wanted an in-manifold pressure reading, post throttle body". Then put a boost tap on the PCV connection to the IM and read that. Will that be the same as the MAP reading? Of course not, you're reading two different things.

Okay thank you for clarifying. It sounds like there’s no doubting the accuracy of the readings. Do you know if you can graph your boost curve with this tool or do I still need to bring my laptop and Ross Tech cable?

[Smac770]

Just curious, what's the difference between the MAP reading vs PCV connection to the IM?

The MAP sits at the top of that hard pipe on the left end of the engine bay, before the throttle body. So it's going to read no less than ambient pressure. The intake manifold, on the "inside" of the throttle body, is going to be anywhere from 20 inHg vacuum at idle (rather than the ambient pressure present outside the throttle body) to boosted. But how different is the boost at the MAP vs the boost in the IM? No idea; while I can hook a gauge up to a boost tap at the PCV line connection, I don't have a digital pressure sender whose output I can log alongside the logging of the MAP readings. I would imagine they should be similar at WOT though, the throttle body should be open a lot and so they would essentially be the same airspace. Which would be more important in engine tuning? Don't know; I'm not an engine tuner. But suffice to say, Audi cared more about knowing the pressure outside the throttle body than confirming the pressure inside the throttle body.

[Smac770]

Okay thank you for clarifying. It sounds like there’s no doubting the accuracy of the readings. Do you know if you can graph your boost curve with this tool or do I still need to bring my laptop and Ross Tech cable?

What specific product are you asking about?

[Jason11213]

What specific product are you asking about?

I use VCDS to graph boost curves, intake temps, etc... I’m just wondering if this OBD gauge gives a reading of the boost real time or if it also has the capability to export historical data to something like Excel so I can view boost at different engine speeds. For example, if I did a 3rd gear pull and want to read at what engine speed do I hit max boost and does it hold till redline.

Bottom line it sounds like this tool does a lot more than I thought which is great for monitoring the car. My K04 is easily hitting 22psi but it also has a spike every now and then where it jumps up to 26 psi when I do a third gear log. I’ve been using the Ross Tech cable to monitor this but want something easier. Thank you for everyone’s input!

[Smac770]

"this OBD gauge"

what OBD gauge? I don't see where you ever referred to an actual product.

[Jason11213]

https://www.uspmotorsports.com/P3-Ve...keep_https=yes

This is the one I was considering but there may be others out there. I saw Unitronic offers one too on the B9 S4s

[Smac770]

Well, you can make no assumption about a product from one company based on another product from another company. But in general, no, these devices are live display, not data logging.

Looking at the actual P3 company site for information on the Audi B8 P3 V3, https://www.p3cars.com/audi/p3-v3-ob...uge-2008-2016/ , it makes reference to an installation page: http://www.p3gauges.com/v3-install/

We see no means for interfacing to the tool with an external device like a PC. So how would you get the data out of the device to manipulate it in a graphing tool? Maybe they'll add a microSD card in the future for logging data capture; would be a worthwhile feature. Even more so because it does have those two 5v analog inputs that could be logged alongside the OBD data. I do wonder what the OBD data sample rate is. Is it fast enough for logging and graphing purposes.

You would probably be better off with a phone based tool like OBD11 if you want to do data capture without having to lug a laptop around. If you have a HEX-NET, you could use VCDS Mobile on the phone, but I've not tried anything like logging. If I need that, I have a laptop for that.