[OpenFlash]

A quick How-To. By no means is this a recommended mod. But if you are going to do it, might as well do it for free (or something close to it).

Background:
Boost pressure is regulated by the pressure sensor that is located in the intercooler pipe, just before the throttle body. There is also another pressure sensor located in the manifold but that's another story. To raise boost by X%, one needs to make the former pressure sensor (in the IC pipe) to read lower than it otherwise would. One way to do that is to use a computer that inputs the original signal voltage and outputs a modified signal based upon other inputs (throttle angle, MAP, RPM, intake temp, etc,.) Another way is to use something known as a voltage divider.

More info on voltage dividers: http://en.wikipedia.org/wiki/Voltage_divider

To make a voltage divider-based boost controller, you will need the following:

1k ohm 1/4 watt resistor
100 ohm 1/4 watt resistor

This will cost you about $0.50 total. Next you will need to intercept the pressure sensor/MAP signal that goes the ECU. This is pin 10 on the large black subconnector on the large ECU connector. You can either cut this wire (eww) or just get the necessary terminated wires from your local BMW dealership.

With the MAP wire effectively cut, you have two ends. The end that leads to the ECU is called MAPout. And the end that leads to the sensor is called MAPin.

Next, let's get back to the resistors. Join them together in series. Join MAPin to the end of the 100ohm resistor. Join the other end of the 1kohm resistor to a ground (either chassis ground or Pin 9 on that same subconnector). Next, you will need to join MAPout to the point at which the 1k and 100ohm resistor are joined together.

What you have now is a simple circuit that is fed a voltage, X, and spits out a voltage Y that is precisely 90% of the original voltage (1000/100+1000=0.9). This will induce roughly 10% more manifold pressure. So if stock peak manifold pressure is 22.7psi (8psi + 14.7 atmospheric), the new pressure will be roughly 25psi or 10-11psi.

The upwards boost adjustment can be lowered or increased by changing the resistor value of the first resistor (100ohm in this example) upwards or downwards. If lower, the less boost raise. If higher, the bigger boost raise. Or if you want to get tricky, you can use a variable potentiometer in place of the 100ohm resistor and dial in the boost that you feel is desirable.

Downsides:
-This mod is not invisible to the ECU logs/snapshots. Remember that second MAP sensor that is located in the intake manifold? Well, now its readings wont jibe with the readings of the other map sensor that we are adjusting. This is because it is always ON, even at ignition ON, when those two sensors should read the same pressure. Luckily, this does not induce a code. But it does induce implausible sensor readings if someone knows what to look for, when to look for it.
-You will need to do some variation of a solenoid bypass if you want to raise boost much above 12psi. If not, you will get a "boost too low" code/limp. This is caused when the ECU can't achieve the desired boost within the solenoid duty cycle range it believes it should operate in. Unfortunately, a solenoid bypass does reduce the operating efficiency of the boost control system, making it more subject to spikes and oscillations.
-Without any form of fuel and ignition adjustments, you will need to run a race gas mixture if you want to run much more than 10-11psi of boost. And even that may be pushing it in warm conditions and on 91oct. But if you chose to use a variable potentiometer in place of the first resistor, you can adjust it downwards when conditions take a turn for the worse.

Upsides:
- It costs less than a dollar and is worth a quick and dirty 40whp. More if you run race gas.

So thats basically it. A DIY boost controller for less than $1. And I believe that it has been recently confirmed to work on the v81 ECU. Don't quote me on that though. And please not that I haven't actually installed this device on any customer car. Just my own.

Cheers
shiv

PS:

[sdwilly]

Originally Posted by stillclaimndp

That or it is a contribution to the n54 community, i see only information.

It seems like good information to me, not like I'm going to do it anytime soon but I'm sure there are some were looking for this kind of information.

[OpenFlash]

Originally Posted by rwalker

I realize your post may be rhetorical (i.e. used for persuasive effect), but I'd like to pursue some questions I have about your design:

Would a 1.1kOhm path to ground hurt our T-MAP? How much current does it normally supply? How much is it capable of supplying?

When calculating values for the divider, you have to account for the path to ground through the ECU itself, right? Otherwise, you may have built an 11% divider or a 90% divider... In other words: is impedance to ground through the ECU effectively infinite?

Thanks,
Rob (an EE among other things, as if that matters)

Nope, a 1.1kohm path will not hurt the MAP sensor. I've run quite a bit less than that with no issues. You can always scale up the resistor values to 2k and 200ohms if this is a concern. The last one I built has a 2.2k ohm resistor and a 1kohm potentiometer, FWIW.

Not quite following your second point. Keep in mind that EE, to me, is the sound of someone screaming.

Shiv

[rwalker]

Originally Posted by shiv@vishnu

Nope, a 1.1kohm path will not hurt the MAP sensor. I've run quite a bit less than that with no issues. You can always scale up the resistor values to 2k and 200ohms if this is a concern. The last one I built has a 2.2k ohm resistor and a 1kohm potentiometer, FWIW.

Not quite following your second point. Keep in mind that EE, to me, is the sound of someone screaming.

Shiv

Sorry about the scream.

My 2nd point: There's a virtual resistor, a path to ground, that you omit in your schematic, through the ECU itself. It's tedious, hard (impossible?) to measure voltage (as the ECU obviously does) without pulling at least a little current.

This load must be added in parallel to the 1kOhm resistor in the bottom of your divider. The formula to calculate the resistance of 2 resistors connected in parallel (call 'em R1 and R2) is:

R = 1/((1/R1)+(1/R2))

If we set R1 to your bottom resistor, then R2 (ECU to ground) needs to be much bigger than 1kOhm to make your math come out right.

-Rob

[Jason]

To fanboys of ANY tuning product. Keep this thread on technical discussions of the DIY and keep the tuner vs. tuner crap out of this (or ANY other thread).

Failure to do so will result in double infraction points, or immediate ban if you already have a history of igniting or fueling those types of discussions.

Take this warning seriously. Or, try it.

** I encourage all members to report posts violating this (by using the exclamation icon below the offending poster's profile).

[phantom330]

so I'm assuming this is basically the JB1 more or less?

[De90man]

OP: The 'high road' is often smoother than a paved one.

[Wiredless]

Maybe a "noobie" question but isn't this how the SSTT works?

Thanks Shiv

[calimba]

how long do the log files stay on the computer?
Has anyone tried this?

[Malek@MRF]

Originally Posted by phantom330

so I'm assuming this is basically the JB1 more or less?

This is the exact same thing as a JB1.

BMW pins from the dealer with 12 inches of wire already pre-crimped is 0.97 each.

[calimba]

just picked up my pins, (paid $4 each btw) and instantly got a warranty lecture. the guys knew right away what I was up to.

[marconi118]

Is it possible to rhise the HPFP pressure with the same sistem?
This would allow to avoid ECU to see that the injection timings are greater (more air needs more fuel) and not to throw a limb code