swan

I've got a Subaru boost gauge fitted on a MY01 WRX with Prodrive ECU. The gauge shows me running a sustained boost of 1.2-1.25bar (17.4-18.1psi). If I look at the DD logs for the same runs it shows 1.02-1.06bar (14.9-15.2psi). On questioning this discrepency with Ecutek I initially got the following response:
<quote>
the numbers you are seeing from DeltaDash will be the more accurate. This is what the ECU is seeing from the MAP sensor which is much more accurate than the gauges. If they are the genuine STi/Defi gauges we know they read high!!
</quote>

On raising the issue of the Prodrive ECU:
<quote>
The Prodrive ECU alters the input signal to the ECU from the MAP sensor. You will have to contact Prodrive for further information on this.
</quote>

Can anyone tell me what the true boost is likely to be? Is the gauge then accurate? What correction factor should be used with the DD software?

dnb

I'm not too familiar with Deltadash, as I have a MY96. I do have my own diagnostic software though (it does a similar thing to Deltadash...)

Is the deltadash reading relative pressure or absolute manifold pressure minus an offset that may or may not be true atmospheric pressure (also read by the MAP sensor)? Remember atmospheric pressure changes slightly, and this can change readings a little.

I've not seen a boost gauge that's a precision measuring instrument - I take it there is no calibration certificate. Then again there's no certificate with the MAP sensor is there?

I believe the only way to be totally sure is to use a properly calibrated gauge that reads absolute pressure (zero in a total vacuum). (Read expensive - unless you can borrow it.) Use it to read atmospheric pressure and then total boost pressure and subtract them to get true boost.

Delta dash may do this with the MAP sensor to give you the readings you get - so it could be reading boost more precicely.

Sorry for the rambling post - hope some of it's useful.

swan

I'm referring to relative pressure. AFAIK it can also capture absolute but there's no correction factor as per your post.

Fair enough that the atmospheric pressure may change but I'm looking at figures from two sources (gauge and DD) on the same run.

Thanks for the response, I'm now trying to figure out which is more accurate than the other without having access to the expensive tools you mention. Or determining the "fudge factor" to use with DD.

HHxx

PPP on the MY01's used a boost clamp. DD will be wrong and your gauge will be correct.

swan

I assume this is a mechanical device? If only the ECU is fitted then what?

dowser

The PPP on your car, as mentioned above, included altering the MAP signal to the ECU making it think it's running less boost that it actually is. This means your boost gauge is more accurate than DeltaDash for boost readings

Richard

swan

Are any of the other signals modified i.e. what other figures recorded by DD will be inaccurate?