Can anyone tell me, at roughly what throttle position is 100% MAP achieved? I’m trying to compare AFR fuel maps between TTS and Tmax.


Thanks

 

MAP stands for manifold air pressure....100% map does not have a linear relationship to throttle position,,,,in general larger throttle openings will get to 100 map quicker,,,the map value is a value trying to describe the load that the engine is under.
m
lower map values=less load on engine, like cruise,,,,,,,higher map values=more load on engine.

 

@marcodarq Thanks for your explanation. I understand the difference between the two, in your opinion do you think you can reach 80MAP at 40% throttle? I am trying to establish a good AFR curve in the Tmax, almost all of the maps I look at transition from cruise AFR to WOT AFR around the 40% throttle position.

 

A MAP sensor sends a voltage or frequency signal representing engine (intake) vacuum to the Engine Control Module (ECM).

It's not pressure or load. Now it is determined by how far the butterfly is since vacuum drops as it opens.

Dan, now when you compare fuel Maps to it, not a clue. With a wide open throttle, there sill is a slight vacuum. Surely that's 100 isn't it.

Now there is still some atmosphere pressure at manifold levels of vacuum that increase as throttle opens. So pressure does rise at WOT.

Remember I am just trying to learn.

So, Marco, you need to step in here..

 

To really understand MAP ya have to quit thinking vacuum. 0'' of vacuum = current atmospheric pressure or approximately 14.5 psi. So a 0 inHg reading on a vacuum gauge is approximately 14.5 psi of Pressure in the intake manifold. MAP stands for Manifold Absolute Pressure. Absolute being the keyword. so if your current atmospheric pressure is say 980mb the best you can achieve is a MAP reading of 98KPA at WOT. if its 1020mb then you can see 102 kpa at WOT. This is important because the pressure entering the cylinder is going to affect Volumetric efficiency of that cylinder. the complicated Ideal Gas law computation that the ecm uses to calculate VE requires the absolute pressure variable as part of its equation.You cant have 100% VE in a cylinder if you only have 7psi or 50kPA of air entering the cylinder. Once you adjust your thinking from vacuum to pressure a lot of things start making more sense. Throttle position is not directly tied to MAP. If you've ever seen a vacuum gauge on an engine MAP behaves the same way. Why Harley has us tune using throttle position based VE tables instead of MAP based VE tables I have no idea. I'm sure there is a good reason for it. Maybe its because of the short intake with no plenum which would cause erratic MAP readings at lower engine speeds. But I'm just guessing here.

 

I would guess roughly on a straight road , about 65-70%. if uphill or under hard accleleration, it would be very hard to estimate. The Map would heavily depend on the engine speed , air temp, air density, airflow ( due to pressure difference) and throttle % open at the time of measuring . There is no scientific way to give you an accurate answer, but for your intents of comparing aFR maps, its about 65-70% straight road.

 

Op, yes you c reach a map value like that. CSt gave a great description of the map values. If you are tuning a T-Max, throw all thoughts of MAP out the window. It has no one to sense or correct for it
m

 

Here is a plot I made in XLS to better understand the relationship. It is data from my 114 with Woods 22XE logged on a powervision.

 

Nice, just saw this today, this helps immensely!

 

Note that the camshaft will cause the reading to change quite a lot. At lower RPM, say 1500 RPM you will reach 100 kPa at roughly 35% TPS. At 4000 RPM you will reach 100 kPa at 95% TPS. At various different altitudes it all changes. MAP stands for Manifold Absolute Pressure, it has nothing at all to do with vacuum. At sea level the absolute pressure is 101.3 kPa under normal conditions and this is the rate as the standard pressure. Now when you at an altitude of ~8000 Ft above sea level that pressure changes to about 82 kPa, so it's impossible to get to 101.3 at that altitude yet you can still go to 100% TPS. So what I am trying to say is that you need to know the data before you can correctly use it, and as you can see it needs to vary based on the conditions the data was taken in.