This means that it's accurate at 20psi, not that it's accurate at all boost levels up to 33psi.

Matt, I'm glad you're finding more comfort in your logs via ZDL, but this doesn't explain why the GM 3 BAR sensor also read like your ZT sensor (much lower in high boost scenarios than the JDM MAP). How do we explain this? It was with this same sensor (GM 3 BAR) that I was noticing the exact same phenomena.

I just can't get over the fact that this JDM MAP says that I'm running 29psi on Cali 91 with no knock (and without having to run negative timing).

 

That is why I used the qualifier of "on my car..." mrfred has reported that the JDM MAP sensor is accurate on his car and IIRC his car boosts to 24-25 psi. I do not intend to boost higher than 21 psi on 91 octane so the JDM MAP sensor serves MY purpose well.

 

But it does explain it if the GM sensor is logged via the same logging device and its input filter. So the same filtering applies no matter what sensor you hook up.
If the JDM sensor is mounted directly in the manifold, and the GM or whatever sensor is hooked via a hose, the same applies as well. The connection hose damps down peak spikes. If a MAP sensor is mounted in the manifold, you will often see pressure peaks from the pressure waves in the intake manifold. The peaks will be RPM dependant as the pressure wave peak location in the manifold changes with RPM. As the Evo ECU makes its decisions MAF based, I am pretty sure it does not do fancy engine cycle dependent oversampling or crank angle based sampling of the sensor. It just gets the momentary value when it samples, no matter what it is. Most of the MAP sensor ICs I have seen (which are used by the various MAP sensor manuf.), can resolve pressure frequencies up to about 1 kHz. That's faster than needed for most engines. Also, when their linear range is exceeded, they tend to show LESS pressure than actual, not more. A pressure spike in the manifold, as explained, depending on the dynamics of the gas flow, can actually be a few more PSI at the sensor location than the engine sees as end pressure when the intake valve closes. Which is what really matters.

- Klaus

 

It does explain why the GM MAP is reading the same as the ZT-2. I'm using the ZT-2 user1 input to log the GM sensor voltage, thats why its matching the ZT-2's own MAP sensor. The spike from the JDM sensor is very short, less than a second. Its very well that manifold pressure spikes that high initially, but the ZT-2 doesn't show it due to its own smoothing algorithm. I'm going to log the output of the JDM MAP sensor through the ZT-2 tomorrow. I can almost gaurantee that it will match the other 2 sensors almost exactly.

 

Thank you, Klaus, for your informed and technical contribution to this thread. This is making much more sense now.

So I guess the million dollar question that remains is: Which sensor location is best for monitoring the actual pressure when the intake valve closes? If it's not at the top of the manifold, is just outside (near the FPR, etc) a more realistic sampling spot?

 

Hi,

The FPR pickup location is actually a very good spot as it is carefully selected by the OEM to reflect the true manifold pressure during the injection process. Otherwise the fuel pressure would fluctuate a lot as well. Just make sure that the T-off connection to the sensor is as short as possible. You don't want resonances in there that would affect the actual fuel pressure. Best would be to T off as close to the manifold connection as possible.

- Klaus

 

So, one can conclude the following:

1.) All indications suggest that the JDM MAP sensor itself properly samples and reports pressure accurately up to 33psi (physical limit of the sensor).

2.) Installing the JDM MAP sensor will allow for accurate logging of boost pressures (as seen by the intake valve) up to approximately 20psi.

3.) Running above this amount, say 23psi, may result in exaggerated boost readings from the JDM MAP due to the pressure spikes in the manifold that don't actually reach the intake valve (engine).

Correct?

 

Hi,

3) can be verified to be true only if the same sensor, with the same logger (the ECU, as it does not filter) shows significant less pressure at a different location in the manifold. It could very well be that the peak pressure peaks as high as posted without knock. Knock is a function of the temperature of the gas in the cylinder before the flame front consumes it. It is only indirectly related to manifold pressure. If you could keep that temperature down you could boost to ANY pressure without knock (even on Cali 87 ).

- Klaus

 

Keep in mind that JDM Evo 9s use the MAP sensor to provide feedback for control boost, so the factory mounting location for the Mitsubishi MAP sensor is apparently acceptable to Mitsubishi.

 

I would agree with 1) and 2), but definitely not 3). I am boosting regularly to 23-24 psi, and the JDM MAP sensor is in excellent agreement with my factory boost gauge that I have bench tested for accuracy. Other people who are boosting to 23-27 psi (AaronBradley, Ralph) have reported excellent agreement between the JDM MAP sensor and their previous boost measurement equipment. If you are looking for an answer to your high boost levels, I think it goes back to what I've been saying to you for over a month: You probably are boosting to 29 psi. klatinn explains it well in his last post.

 

Agreed. I understand how all that (basically) works. My comment was based upon the "common knowledge" that pressures above 23psi (or so) on a stock-ish turbo will result in too much heat which causes knock on low octane fuel such as Cali 91. Now it's becoming apparent that the sampling location of this "common knowledge" figure is very important. Since the most common place to sample boost is from the FPR manifold port, it's quite possible that 23psi seen there equals 29psi at the top of the manifold (where the JDM MAP sniffs).

If this is indeed the case, it would be ideal to have a calculation routine which adjusted for the manifold spikes that occur at the higher pressure levels so that we could tune on more realistic boost numbers.

 

Yes, and I am also sure that the control loop that controls the waste-gate solenoid(s) has adequate filtering so it does not overreact to spikes. That's by its nature (turbo inertia) a relatively slow reacting control loop anyway. Two different applications: accurate measuring or adequate control. These applications don't neccessarily overlap.

- Klaus

 

I wish I had my GM 3 Bar sensor handy so I can go out and log boost with it. When I get my hands on it I am going to conduct a test that logs the GM 3 Bar and the JDM MAP sensor via the LM-1 and at the same time log the JDM MAP sensor via the ECU port. I will place the GM 3 bar as close as possible to the JDM MAP sensor. I will basically zip it to the STB and run a very short hose an T it to the FPR hose.

I suspect that the reading from the JDM MAP and GM 3 Bar via the LM1 will be very close to each other while the results of the JDM MAP from the ECU will lag a bit behind.

I agree with you mrfred that he is probably boosting that high and because of the ZT-2 sensor placement and the filtering mechanism of the ZT-2 he is getting lower results.

 

Let's be very clear about this. I now believe that my car is producing 29psi at the top of my intake manifold. So yes, the sensor is likely reading/reporting pressure accurately. The question, however, is what amount of pressure is actually seen by the intake valve when it closes. From what's been said today, it seems reasonable that sampling boost at the FPR port can provide a more accurate value of actual intake valve pressure than sampling at the top of the intake manifold.

 

I will test the FPR placement of the GM 3 Bar sensor vs. the JDM MAP intake manifold placement soon. I will log them both with the LM-1/LMA-3 and will get a reading from the ECU on the JDM MAP as well. I do not have my GM 3 Bar at the moment, so this will have to wait. I really doubt that the JDM MAP and 3 Bar MAP are that far off from each other. IMO, it is 1-2 psi at the most and part of it is due to the noise generated by the JDM MAP plugged into the manifold. A 0.25 second smoothing will take care of that.