Originally posted by kpt4321
However, in a turbo car, it's much better to use manifold pressure for this load reference, which is why I always set the SAFC up with a 3-bar map sensor instead of a throttle input. Start a new thread if you want to discuss that, it's a MUCH better method than using throttle.

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I'd like to hear what you have to say about this.

I have an emanage, with support tool and ignition harness. There is an optional pressure sensor for the emanage. With my set up, for my fuel map I get a 16x16 map, throttle vs. rpm. On my timming map I also get a 16x16 map airflow in Hz vs. rpm. With the pressure sensor I could optionally use pressure sensor instaed of throttle on the fuel map. Also I could use the pressure sensor instead of the airflow sensor on the timming map, I'm not sure which is better here if it even matters.

Are you sure that the timing map is based on airflow in Hz? That would be a bit...stupid...considering that the Hz signal can change without the mass airflow changing, or that the mass airflow can change without the karman Hz changing.

The maps in the stock ECU are based on mass airflow per rev.

I would highly suggest that you use the optional MAP sensor, and here is why:

Obviously, in a turbo car such as a DSM, you have a varying amount of timing, and a changing A/F ratio. There are several reasons for this, but one important one, which is the most relevant to this discussion: engine load. Engine load, which is in essence directly related to cylinder pressure (pre-combustion), determines how much timing advance is necessary for the combustion to take place when you want it to, and it also helps to determine how much extra fuel is necessary to keep the combustion under control.

When you set up an engine management system, you base the maps off of engine load (and rpm, but that's something you don't have a choice about so we won't worry about it.) The thing is, different companies and different systems have different methods for estimating the load on a motor.

TPS: By using the throttle position, you get a general idea of how much the motor is working. On non-turbo cars, the throttle position is a fairly good indicator of load. Since the intake air is a constant pressure and a fairly constant temperature, if you open the throttle more, more air goes in, and cylinder pressure/load increases.

However, on a turbo car, TPS doesn't work so nicely anymore. Next time you're out driving, pay attention to throttle position and boost/vacuum. At a constant throttle position, the manifold pressure can vary quite a bit. Depending on if you're going downhill in a low gear (very easy load) or uphill at a higher speed, the boost pressure can vary quite a bit. This is because when you have more load, the motor needs to make more power, and more load means more airflow which will spool the turbo. Very different load, same throttle.

MAP: The manifold pressure is a very god step above TPS in terms of load measurement, especially in a turbo car. In the example above, while the throttle position would have been the same in both cases, the manifold pressure would NOT. TPS makes the fuel and timing mapping much more linear, especially in the transitions between high boost and vacuum.

Airflow/rev: This is what the stock ECU uses to figure load. Out of all the methods I am familiar with, I feel that this is the best. If you think about it, the compression in the cylinder is dependant upon how much stuff is getting stuffed into the cylinder. MAP and TPS both are somewhat of an indication of this, but they aren't perfect. For example, you get the most stuff in the cylinder at the VE peak (also the torque peak, for obvious reasons), and as VE starts to drop off the cylinder pressure falls off too. Measuring airflow/rev will allow you to see this happen, but MAP would be constant the whole time.

Hope this helps!

...Kyle T.

Good right-up Kyle.



Rogue

It would be really cool if it was a good write-up, but I guess a right up isn't bad.

Hehe.

Originally posted by kpt4321
Are you sure that the timing map is based on airflow in Hz? That would be a bit...stupid...considering that the Hz signal can change without the mass airflow changing, or that the mass airflow can change without the karman Hz changing.

The maps in the stock ECU are based on mass airflow per rev.

Click to expand...

Yeah they are, could you elaberate on how or why the signal could change with out the mass airflow changing? If its becuase of temp and/or barometer, does it matter that I have the MAFT and those values are locked?

I'm going to reread it and ask you some more question's when I have a little more time. Thanks for the write up.

Heres a pic of what the timming map looks like, Hz Vs RPM.
<IMG SRC="http://s92256161.onlinehome.us/hz.JPG">

Can you please trim that picture down a little bit? It's absolutely huge.

Here's the short explanation. If you want more info, ask me, and I will post it up later.

The stock MAF is there to calculate mass airflow, but it can't do that directly. What it does measure is temp, pressure (baro) and air velocity (karman Hz).

If you guys remember the ideal gas law (PV=nRT), then you will remember that the mass of a gas is dependant on a lot of things: how much space it takes up, as well as its temperature and pressure.

The velocity of the intake air can stay the same (constant Hz), but if the temp or pressure change, then you will have a different total mass airflow.

With the MAFT you'll be fine, as Hz correlates directly to mass airflow.

If you want to discuss it, let me know. I have to run.

I was playing around with some maps for my car along with maps for some other cars. It seems that the pressure sensor cant be used in the airflow adjustment map. It can be used in the additional injector map, sub injector map, and the timming map. Of these maps that can utilize the pressure sensor the only one I use is the timming map. Do you think it is worth buying the sensor for a $100 to use it for timming? I don't really think so, but you are alot more knowledgeble about this stuff than I am and could possibly convince me that it is.