Using a MAP sensor to control timing

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C5Performance

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I have been toying with MAP sensors lately and wanted to share it here.

As many of you know, we can change timing maps on the C5 ignition while riding.
Most people use toggle switches, a small rotary selector switch, or a VOES (vacuum operated) switch to accomplish timing changes.

While those methods work great, the VOES can only change timing maps once. It is a grounding switch held closed by vacuum. Under a load your engine vacuum drops, which causes the VOES to open the switch.

The "ungrounding" of the switch causes the C5 to change maps and reduce timing. After the load is gone (climbing a large hill) the VOES once again closes the circuit and the timing goes back to the stock map.

I've been working alot with tractors this year, particularly vintage pulling tractors. With motorcycles we see a wide range of rpm but very little change in load because we can change transmission gears. Tractors must remain in just one gear during a pull. RPM changes very little but the LOAD gets greater and greater.

Using a MAP sensor would be a big advantage and allow THREE of the four timing maps inside the C5 to be used if load becomes high enough.
The rider/driver does not have to do anything...it happens automatically. I believe this would also be an advantage on touring motorcycles.

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How does it work?

An automotive style MAP sensor compares engine intake vacuum to a normal pressure (atmospheric pressure) and outputs voltage based on the difference between the two. We simply feed a regulated voltage in (typically 5.0 volts but I'm using 4.4V) and the MAP sensor outputs a varying voltage based on engine vacuum. That voltage signal is used to reduce timing only when your engine is working harder than normal.

This is an accurate affordable method to convert engine LOAD to a voltage signal we can use. By converting vacuum to a voltage signal we can change our sensor type from DIGITAL (grounded or ungrounded) to an ANALOG signal where it now prompts us for a voltage value.

Example:

You connect a vacuum gauge to your intake manifold. While riding down a flat road you have 18" Hg vacuum. Now you get to a big hill, and instead of downshifting you stay on the throttle and power up the hill. Your vacuum drops to 8" until you reach the top.

Now you do the same thing with a passenger and notice the vacuum drops to 4" on the same hill, because you are carrying a heavier load you are forced to downshift a gear to keep the engine from detonating, and your speed is reduced because of this.

If you had our C5 installed with a MAP sensor you could program the ignition to retard timing when your engine reaches 8" and again at 5" of vacuum. This allows the engine to run more efficiently under load, it will maintain rpm easier, and you might not have to downshift. Plus the engine is working better because LOAD is matched to TIMING.

Once you crest the hill the MAP sensor will read normal vacuum and the ignition will advance timing back to normal.

**KEY POINT** This all happens without you turning a knob, flipping switches, or thinking about it. That is why modern cars use MAP sensors.

Right now I'm testing a MAP sensor and plotting a chart of voltage -vs- vacuum. Next step will be measuring a few vehicles to determine when to reduce timing.
 

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Interesting concept. Seems to me the need will be pretty limited in that most bikes are ridden solo most of the time. Why is Mass Air Pressure better to use than Mass Air Flow? Does this require updating the software? If the advance points are spread out and at the proper increments wouldn't the drop in rpm automatically put it in a more effective retarded timing?
 
Ongoing R&D on the C5 system is making it more and more useful for the masses. :clapping:
This deal with using a MAP sensor is leaps and bounds better than using switches to change the timing. The MAP sensor set-up will control the timing according to what the ENGINE needs, AS it needs it. The only next logical step is a linear programming that will vary the timing across the board, according to engine load through-out the RPM range according to the info from the MAP sensor, which would be an improvement over the "stepped" changes available now. I can see it happening, too, with all of the improvements, and the dedication of the C5 team. Baby steps!
Excellent info, Paul.....youse guys are kickin a$$ and takin names! :clapping: :clapping: :clapping: :thanks:
 
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