boost question

[iahtnoob]

when checking for max boost of a stage 2 map, should the boost be at a steady number across the log? and is it fine that the boost decreases at a slow pace?

[rao]

That is normal - the stock turbo (and several larger turbos) cannot maintain max boost pressure at higher RPMs - they can't move enough air.

[iahtnoob]

so when datalogging, the max boost is just that, the highest manifold relative pressure number and not some average.

[rao]

Max boost is the upper limit that the ECU is targeting for a given load, rpm, etc.

 

When you log you are seeing the actual relative pressure at that given point in time.

[qikslvr]

Try logging "target boost" as well. This will give you an idea what boost level the ECU is aiming for. The "Max Boost"(boost limit) you speak of is (like RAO said) the maximum allowable boost you can hit at a given barametric pressure before the "overboost" protection kicks in. It's pretty hard to hit the boost limit on the stock turbo, injectors and Boost control solenoid.

You may also hear us speak about "peak boost" which refers to the highest boost reading given during a WOT logging run. Depending upon the tune and the turbo; you should/could/might hit "peak boost" between 2800 and 3800RPMs and then it should gradually fall off to around 11psi near redline. It will generally drop more quickly above 5000RPMs.

[Infamous1]

Target boost is only useful if you are at sea level.

[qikslvr]

Target boost is only useful if you are at sea level.

I was just giving him a tool to see what his actual boost targets are if he doesn't already know;).

I agree that it's basically useless since it's just what the name implies; a target, a relative one at that, and not necessarily the actual boost level that is going to be acheived. Much like how Cobb states that their Stg2 map has a target boost of 16.5psi, but in reality it can produce results that vary from 14.5psi to 17.5+psi depending upon location, hardware and temperature.

[Infamous1]

I was just giving him a tool to see what his actual boost targets are if he doesn't already know;).

I agree that it's basically useless since it's just what the name implies; a target, a relative one at that, and not necessarily the actual boost level that is going to be acheived. Much like how Cobb states that their Stg2 map has a target boost of 16.5psi, but in reality it can produce results that vary from 14.5psi to 17.5+psi depending upon location, hardware and temperature.

No, thats not what I meant. It is a calculated parameter in the logger which unless you are at sealevel (atm 14.7). It is not an accurate representation of what the ECU is in fact targeting boost at.

[qikslvr]

I think were basically saying the same thing but differently. That's the relative(calculated, based upon a number of conditions such as location i.e. elevation, hardware i.e. pressure drop across a given TMIC, and ambient air temp) part I was talking about. But I was just trying to simplify it so a NOOB could get his head around the concept not the details.

Whatever... I don't even care anymore. You guys have fun. I'm out.

[Legend]

Target boost is only useful if you are at sea level.

 

It's still useful at altitude if you apply the ECU calculation to the target boost - that's what I do. I can't find where Mickey posted it... know I have it at home.

[Infamous1]

It's still useful at altitude if you apply the ECU calculation to the target boost - that's what I do. I can't find where Mickey posted it... know I have it at home.

The Boost comp Atmoshere Multplier=0.05208, too much work

[merchgod]

No, you do not apply any boost compensation to the logged "target boost" value as it already has the compensations applied. The ECU deals with absolute pressure for boost control.

[Legend]

I still don't recall the equation Mickey provided, but I noted in my spreadsheet that the multiplier for my altitude (12.1) is 0.876. But as for application of the correction for altitude, this is what I use in my spreadsheet:

 

http://beeez.com/lgt/altboost.jpg

 

- The '95' column is my 95% throttle boost target (in Romraider).

- The 'Sea Target' column is that target summed with sea level pressure (14.7) (really what the ecu is targeting if I was at sea level).

- The 3rd column applies my specific multiplier to my ecu-adjusted target.

- The 4th bolded column subtracts my atm pressure (12.1) and is what my MRP boost target is.

 

The utility comes from plotting the corrected MRP target to actual log data, which allows adjustment to WGDC to accomodate the exact target boost.

[merchgod]

If you live and drive primarily at altitude, I would modify the boost atmospheric compensation so that at your average local atmos. pressure, the multiplier would be 1 (i.e. no compensation). With the LGT ECU, you can accomplish this by change the offset portion. This will still keep the same compensation if you go higher (that is, target boost will still drop at the same rate if atmos. pressure is lower than your avg. local pressure). That way, you don't have to worry about factoring in that particular compensation.

 

You can also modify the ECU defs to display the correct relative pressure based on your avg. atmos. pressure. Looking at the scaling for target boost map in RomRaider:

<scaling units="Boost Target (psi relative sea level)" expression="(x-760)*.01933677" to_byte="(x/.01933677)+760" format="#0.00" fineincrement=".01" coarseincrement=".5" />

 

The ECU deals in absolute pressure in mmHg. Figure out your local atmospheric pressure in mmHg (ap/0.01933677). You can see that the defs just assume sea level pressure (14.7 psi = 760 mmHg). So, under expression AND to_byte attributes, change the 760 to your local atmos. pressure in mmHg (it is cruicial you change both attributes). Make sure you are matching up the correct tables that are relevant to your defs (some have a space(s) at the end to differentiate tables that may be seemingly the same).

 

If you don't feel comfortable messing with the defs, you can always get an idea of the relative pressure that will be targeted as follows:

 

boost map target + (14.7 psi - local atmos. pressure psi)

[Legend]

That's pretty cool, merchgod. I just might try that. The only other ecu def change I made was to have the fuel table display lambda (for E85). I love that.

 

I've never logged target boost, actually. Instead I plot the corrected target boost on the same plot as the MRP corrected from data logs and compare. I think I'll make that change and give it a shot. Thanks!