INFO: 3 bar MAPs on Stock LNF base file

[Iam Broke]

I've gotten about 10 pm's in the last month with peeps asking the purpose of the 3 Bar MAP sensors on the LNF if you use a stock base file for the tune.

The short answer is "Because!" This is an FYI so feel free to add your input as you see fit.

First of all the stock sensors are 2.5 bar. 2.5 bar absolute is ~36.26 psi, now subtract 14.7 psi for 1 atmosphere and you are left with the ability to read and control boost up to ~21.56 psi.

3 Bar MAPs following the same example would be ~43.51 psi, subtract 1 ATM and you can measure and control to 28.81 psi boost.

I understand the ECU limitation for logging the manifold pressure is 255 kPa, or 2.55 Bar, this appears to be the same for the 2.5 or 3 bar sensors. We are left with this limitation in logging the mani boost.

The Lower Charge Pipe MAP is another story however. It is listed in the PID's as Boost Sensor LoRes (PID.2338.PSI) and appears to be capable of 512 kPa from what I have read. This gives us the ability to log and control boost pressure up to the limit of the sensor or ~28.81 psi boost.

While you can certainly boost over the 21.56 psi fooling the ECU with the stock sensors, it runs out of the control area, in other words, you are just telling it to shoot for the moon with no means of really controlling it.

The benefit of using the 3 Bar MAPs is expanding the control range.

The purpose of pasting the data into the stock base file for the 3 Bar MAPs is that there seems to be less turbo overspeed control in the stock file than the GMS1 base file. I have no formal proof, but I can tell you the same tune holds more boost and much longer with the stock file than the GMS1 file. Remember there are many, many ECU tables we have no access to.

The 3 Bar sensor data that needs to be pasted into the stock file is shown below once more. You have to expand the precision of the fields out as far as you can to make it accurate.

Right click on the field Title box, select Precision and expand it to all the digits.


Here's the 3 Bar data...



At WOT the mani pressure is essentially equal to the lower boost pressure minus the TB pressure differential so we have the ability to log boost up to ~28.81 psi using the Boost Sensor LoRes PID.

The formula I use is =[PID.2338.PSI]-[PID.51.PSI] in the scanner table and chart. PID.51 is the Barometric Pressure (SAE) PID. Subtracting the atmospheric pressure from the Lower CP pressure lets you see the level of boost above atm. You will see 2-3 psi pressure in the lower CP during cruise speeds as the turbo is building some boost even though the manifold is in vacuum with the throttle plate only partially open.

I hope this helps explain why the 3 Bar MAPs are preferred. It is always better to tune a system within the control range rather than to let it run 'Out of Control'.

Now that CED offers pigtail adapters for the 3 Bar MAPs, they can be installed plug & play.

[Dayhoff35]

awsome info, thanks tom!

[Leafy]

What do the two sensors look like? Is one a tmap and the other like the normal GM late model sensor like the lsj scip sensor? If so I have a significantly cheaper option for those whole like to cut and paste wires.

[Iam Broke]

The 3 bar sensors are Bosch and are both TMAPs, but only the one for the lower charge pipe uses the temperature connection.

[BackyardTurbo_FTW]

Ive actually been running the stock sensors on the GMS1 file. Seems to run better for w/e reason. Still haven't gone for the GMS sensors tho.

[Kelu]

First of all the stock sensors are 2.5 bar. 2.5 bar absolute is ~36.26 psi, now subtract 14.7 psi for 1 atmosphere and you are left with the ability to read and control boost up to ~21.56 psi.

As far as I know stock sensors are 2.75 bar, for Kappas after 2007 you can see 1.75 bar (or 25 psi) of boost on the DIC.

[kennysabarese]

Tell me if I'm understanding this correctly:

With the stock sensors I can limit boost up to 21psi. But if I wanted to boost up to 24psi, it wouldn't work since it's out of the stock sensors range of control. So the turbo would then just "shoot for the moon" and push as much as it can (approx 27psi+)

But if I use the 3bar sensors. I could limit it to 24psi.

Is this what you mean by control?

[BackyardTurbo_FTW]

You can boost 30 psi on the stock sensors just fine, it just wont read that amount accurately.

[kennysabarese]

You can boost 30 psi on the stock sensors just fine, it just wont read that amount accurately.

I am totally aware of that. But what I'm after here is an example of what IAB means when he talks about the 3bar sensors giving you the ability to control, which you don't have with the stock sensors.

[BackyardTurbo_FTW]

IMO, it really makes no difference to get them. Which is why I still haven't.

[kennysabarese]

That's what I'm trying to figure out here

[Leafy]

The 3 bar sensors are Bosch and are both TMAPs, but only the one for the lower charge pipe uses the temperature connection.

So they look like this?
http://www.bmotorsports.com/shop/pro...oducts_id/1721

[kennysabarese]

This will save you a few bucks

http://www.crateenginedepot.com/stor...7-P2533C0.aspx

And these will keep you from having to cut.

http://www.crateenginedepot.com/stor...P9409C413.aspx

[Iam Broke]

You can boost over the range of the sensors however and how far you want to pushing the DAL's, WG DC ect. but if you understand control loops for instrumentation or whatever, you would understand what out of control is. You never have the ability to go closed loop.

No accurate feedback given to the controller (ECU in our case) to help the system react.

Not a debate point, just offering my opinion since I've been doing industrial control for 35+ years.

I never said you cannot run out of control to achieve the boost level you desire.

It's your engine and tune. Enjoy.

[kennysabarese]

I don't understand, that's why I'm asking if there is an example for us normal folks

So I'll assume that the answer to my question above is no. So now I'm even more confused

[Iam Broke]

I only explained my view on why I prefer the 3 bars.

Consider the 02 sensors. Would you rather run open loop counting on the tune tables setting your fueling as air, humidity fuel ect. as conditions change or run closed loop letting the ECU control the Lambda?

Better to run close to setpoint and let the ECU fine tune for changing conditions IMO.

Set your boost to run 24 psi open loop at 90*f and see how high it boosts at 40* f in the midrange on the stock sensors. Closed loop in control it will adjust, open loop out of the sensor range, it cannot.

[jboogie67]

so, your saying it will adjust things such as fuel more accurately when the computer knows exactly whats going on, right?

[gmtech16450yz]

What Tom is saying is totally correct. Of course you can boost higher than 21 or 25 or even 30psi on stock sensors. What he's saying is any tables that reference boost will not know what's going on past the level of the stock sensors. That means all it can do is interpolate up from the last known point, which could be as much as a 7psi difference from actual pressures. A lot can happen in those 7psi, but the computer isn't gonna know it, it's just gonna think the boost is still at 21 or so.

Tom knows his chit, and what he's saying about a closed loop system is totally correct. As far as real life for "normal folks", here's an analogy...
Say you have an oil pressure gauge that only reads to 60psi. Say normal driving everything is fine because it's usually between 0-60 psi. Now say the pressure relief valve sticks and you're pumping 150psi worth of oil pressure. The gauge itself has no control over the actual pressure, it's still gonna go to 150 whether you have a gauge or not. Obviously the problem is you (the computer) are gonna think everything is fine since it's been normal for you to see 60psi before. So you (the computer) just go driving along like everything is wonderful, until your lifters pump up and make the valves hit the pistons. If you (again, the computer) had been able to "see" that 150psi with a gauge that read that high, you'd have "control" over the situation and could turn off the motor.

Make sense? In respect to cars we learned about this in the '80's when computer controlled carbs first came out. When you rebuilt a carb, you had to set up the "mixture control solenoid" so it had the proper amount of range to control mixture. If you had it too far one direction, it wouldn't have the control range to keep the mixture correct. If you set it up right in the center of it's range, it would then have full control over mixtures whether they went lean or rich. The carb itself can do whatever it wants, but the computer has to have it's sensors and control devices working within a range that it can "see" and "control".

[Iam Broke]

^^^^Thanks for the analogy, John.

so, your saying it will adjust things such as fuel more accurately when the computer knows exactly whats going on, right?

Not only fuel, but boost. Yes, once boost is outside the range of the sensors, it can only adjust for the max it can 'see'. Anything over this range is considered out of control. It can mean boost, fuel, temperature, pressure or whatever depending on the sensor value you exceed. When you exceed the range of any sensor it will be out of the control range of the ECU.

[Kelu]

which could be as much as a 7psi difference from actual pressures. A lot can happen in those 7psi, but the computer isn't gonna know it, it's just gonna think the boost is still at 21 or so.

IS 3,5 psi, not 7 psi, ECU sees 25psi with stock sensors, only HP Scanner is pegged, not our ECU.