Background
---------------
As you know, the P rows in the PFC can be remapped using a Datalogit to represent different values for pressure in the manifold.

My standard configuration started at 1,000, went up to 16,000 in increments of 1,000. From there, it goes in steps of 2,000 until it reaches 24,000.

The "problem" (if it really IS a problem) is that up near the higher end of the boost range, the steps are bigger and therefore might be more sloppy on the tune-ability. That's the theory anyhow.

So I had my car all tuned the way I like it for the standard P rows already and then I decided to re-do my setup to use equally spaced P rows.

How I did it
------------------------
I wrote a spreadsheet in Excel where I set up my old p row definitions 1,000 to 24,000 as described above... and I defined my "new and improved" p rows which I made from 1,500 to 24,015 in equally spaced steps of 1,185. I drop in my current fuel map and ignition map and it calculates the new value on the new system. Paste that back into FC Edit, type in all the new p rows and I was done.

Results
-------------------------
I've only been driving for about 2 hours on the new setup and so far I've detected NO difference in how the car drives. More testing to come, but so far, I can say I've not noticed any change.

Just because I haven't felt some huge difference doesn't mean I don't think this is a good idea. I'm going to continue to use my new p row setup because I think that's the "right" way to do it.

I'll post more if my opinion of this changes or I get some interesting new data.

Brian

 

Now is the time to tune at various boost levels to solidify your fuel maps.

Good time to study fuel map to ensure it ramps up toward the torque peak along each p-row then down as rpms climb. Then as p-rows go up so should fuel. Amazing what you find when only one or two boost levels have been tuned and especially when not tuned well. I have seen maps where fuel is all over the place. Not an issue if you tune way rich or if you always run same boost and roll into WOT at the same rpm, but, if you roll into WOT at different starting rpms or run part throttle up the rpm band etc etc it can be an issue.

 

When you redo your P rows, you should first calibrate real boost to real PIM volts and PIM ABS pressure.

The PIM absolute values in the PFC are not true. The PFC has calculation errors in converting the MAP sensor voltage to PIM and then to boost. The stock sensor also maxed out around 18 PSI.

1) Get and set up the map sensor you want. I am using the stock sensor.

2) Hook a controllable pressure source to your map sensor and to your most accurate boost gauge/s. I use a hand air pump going to my stock map sensor to Blitz boost gauge in the boost controller and to my AUTOMETER boost gauge. Also hook up your DATALOGIT.

3) Using my video camera to record the boost gauges and commander PIM voltage, I pressurize between 10 to 20 PSI.

4) Playing back the video to my TV, I write down the values to create my boost pressure to PIM voltage table.

5) Using the DATALOGIT log, I then cross referece the PIM voltage to PIM absolute values.

6) Using the new CORRECT PIM values, modify your PIM rows values for the boost you want for each.

Mine are for the stock map sensor and stock twins:
P17 12 psi, 18000
P18 14 psi, 19369
P19 16 psi, 20745 and
P20 which will never be used but at 18 psi is 21850.

Thus I am using 2 PSI boost steps instead of the 2.8 stock values(if they were correct). When boost reaches within .5psi of the next higher row, it will start using it.
Thus if boost is 12 to 13 it is only using P17. If boost is 14 to 15 it is only using P18, etc!

Now my PFC and datalogit are accurate and in sync.

 

I have been tuning my FD at 5900 feet above sea level and notice the following results when relating PIM as measured by the PFC to PSI measured on analog gauges (auto meter boost and 30psi tire gauge).

I get the following results:
Mine are for the stock map sensor and stock twins:
18000 PIM = 14.5 psi
19369 PIM = 16.6 psi
20745 PIM = 18.6 psi

My plot of data measured using Chuck's methoud is attached.

These readings are all about 2.5 psi higher when read on an analog gauge at 5900 feet above sea level.

I believe this happens because the PIM reading from the PFC is an “absolute pressure” value, vs. analog gauges which are “relative pressure” (read 0 psi when resting at 5900 ft).

This fact confirms my conclusion: Air pressure decreases with an increase of altitude — about one millibar (0.03 inches of mercury) per 27 feet (8.23 m) near sea level. Let me know if you want this equation in excel.

So, dose this mean that I can boost at levels 2.5 psi higher than people can at sea level, with the same octane fuel and AF ratios, with the same safety margin?

 

I don't know about FD's, but on a stock FC there is an atmospheric pressure sensor that makes adjustments to the fuel map based on barometer/altitude. I find it interesting that the PFC relies on calibration of the map sensor for this function.

 

The PFC does not have an atmospheric pressure sensor so it must be calibrated for local pressure. From the formulae I listed in another thread, the PFC's displayed boost (which is equivalent to gauge pressure) is calculated from the PIMV voltage using the following formula:

Gauge pressure (in kg/m2) = scale * PIMV + offset - 10332

The PFC displays boost on the Commander in kg/cm2, so this number must be divided by 10000 (not 1000 as I mistyped in the original post).

10332kg/m2 is standard atmospheric pressure and since the PFC has no way of knowing what local pressure is, the offset number needs to be adjusted to compensate. The scale number basically describes how the sensor voltage reacts to pressure change (measured in kg/m2/V) and is not altitude dependent.

If the offset is not adjusted downwards as altitude increases to compensate for the lower atmospheric pressure, the PFC's displayed gauge pressure will be lower than actual gauge pressure.

 

Wargasm (or anyone else who knows),

what is the formula I should put into excel when I remap my P rows? I want to get everything calculated properly so I don't blow my engine up. I need to get PIM up to at least 25000 on the GM 3 bar, because I plan to run ~20psi or whatever I can get out of the turbo on my setup (using race gas).

Honestly if you still have that excel spreadsheet you used it would be very helpful, because I have a T04S.

 

I've been holding off on doing this due to the risk of a miscalculation. When you change your P rows, I assume you're interpolating new map values based on a weighted average? And this would have to be done on both the fuel and the ignition maps correct?

 

yes I would very much appreciate an explanation from anybody of how to remap P rows accurately, assuming your MAP sensor is calibrated properly in terms of both scale and offset.

 

Since you have my tuning notes package, you should be able to apply examples.
Look at how I did the AIT sensor and remapped the P rows.

 

alright i'll check it out thanks