Confused with 2.5 bar tune on 2005 C6

[wewing]

I have started looking at changing my tune to a 2.5 bar tune. I received my 2 bar map sensor, there doesn't seem to be such a thing as a 2.5 bar sensor for an LS2, and since I have APS twin turbos, I set my fuel settings to what I was using with my 1bar tune, and I set my spark settings to match the tune that came from APS which is only 1bar.

Here is my question. The demo is for a 2bar tune, not 2.5, so it is only but so helpful, and since I have a 2bar sensor, if the sensor is seeing maximum boost which is supposed to be 210kpa, will this be using the 210kpa, or 255kpa cells on my boost VE table. In hptuners, I see in another setting where the map sensor is set to indicate 200kpa at 5 volts, and this only confuses me more. That seems to indicate that it would read only 200kpa when the map sensor is really sensing 210kpa.

The reason for the question is that I would like to know whether I should set my 255kpa cells to 1.25 times the 105kpa number for my interpolation, or should I set my 210kpa to 1.25 times the 105kpa number like the demo suggests in the 2bar tune. Its confusing since the table is 2.5bar and the sensor is 2bar.

I wonder if anyone really knows the answer? I hope my explanation and question are clear.

[12secSS]

If you got the Cobalt SS 2-BAR BAP sensor (not to be confused with the Cobalt SS 1-BAR MAP sensor, yes there is a difference from what I found out), it will read 255 kpa. I just recently tuned a 2005 Magnacharged Corvette with this BAP sensor and HPT's 2-BAR setup. It came out great (490rwhp thru an A4, factory stock otherwise).

[Chris@HPTuners]

the 2.5 bar program can be used with a 2bar or 3bar sensor (with the 3bar you can only read boost up to 255kpa obviously). Be careful with the cobalt sensor cos it has an integrated IAT sensor as well, although it is a true 2.5bar sensor.

The boost VE table uses the value of whatever is being shown in the scanner for the MAP PID.

The MAP Sensor calibration (Linear and Offset) are used to calibrate the MAP sensors pressure/voltage characteristic. Typically the 5V output pressure is the Linear + Offset. so if you have Linear at 200kpa, offset at 10kpa then at 5V the PCM will assume 210kpa. Depending on the sensor type the default values are usually ok. some sensors have a 185/5 or 190/8 etc. but usually 200/10 is good enough for most 2bar sensors. To get is exact you need the manufacturers datasheet for the MAP sensor where it gives you the linear curve for the pressure/voltage characteristic.

Load up one of the Boost VE histograms to see where you are on the Boost VE table at any time. if your kit is making around 10-12psi you will be around the 170-185kpa mark.

[wewing]

Thanks Chris, that mostly explains it, and I do only plan on running 8 or 9psi boost, so I'll just have to look at my scans and see where they put me, but it still doesn't answer my real question. Since the 2bar demo sets the 210kpa cells in the VE to 1.25 times the values for the 105 kpa does that mean that with the 2.5 bar OS I should set my 255kpa cells to 1.25 times the 105kpa cell numbers and interpolate, or should I set them higher like say 1.35 times the 105kpa cell numbers.

I realize this is just an initial setting for safety sake and my real numbers will come from my scans and my wideband O2, but since it is for safety sake, I want to be safe, and didn't want to assume anything from the demo which clearly doesn't cover the 2.5bar OS.

All this bearing in mind that I really won't be going above about about 150kpa or 160kpa anyway. Thanks.

[EC_Tune]

That should get you pretty close.

[wewing]

Sounds good EC_TUNE, Chris mentioned that the Cobalt sensor I have GM#12580698 is a 2.5bar sensor. Do you change the sensor map sensor calibration value in Hptuners from 200kpa to 255kpa when you use this sensor in your tunes, or do you just leave the Hptuners default of 200kpa for this?
I know he said defaults are usually ok, I was just wondering if you use the default for this sensor.

I don't know where to get the datasheet.

[Chris@HPTuners]

there are a few cobalt sensors, the most commonly used one is not actually the manifold sensor but the barometric pressure sensor (i think) and it is a 2bar sensor.

The other one, the MAP sensor on the boost side, incorporates an IAT sensor as well and has more wires (5 i think) and is a 2.5 bar sensor.

An easy way to check is to run your car with the stock OS and the stock MAP sensor and not down the barometric pressure PID at key on but engine not running, then start the engine and note down what your idle MAP is approximately.

Then load up the 2bar OS and install the 2bar sensor and check that the baro and idle MAP are close to what you had with the 1bar sensor. Tehn when you are dyno testing you can make a 3rd test with a calibrated boost sensor on the dyno with the values you are seeing at full boost in the scanner.

Chris...

[wewing]

That sounds right Chris, I have only three wires on my Cobalt sensor, 5V, Gnd, and output, so it is probably the 2bar sensor. So it sounds like the Hptuners calibration is setup right for it. I'll try the tests you gave and see if its right, but it sounds like it will be good with the defaults. Thanks again.

[12secSS]

there are a few cobalt sensors, the most commonly used one is not actually the manifold sensor but the barometric pressure sensor (i think) and it is a 2bar sensor.

Chris...

No thinking about it Chris, you have it correct! As I have personally experienced the MAP vs BAP a couple of times. BAP is the one you need, as the Cobalt SS has both a MAP and BAP.

[nmp27]

Just chiming in here.... I just bought a part #12614973, it's a cobalt SS map sensor, is this the 2.5 bar sensor?

Thanks!
Nick