Different types of tunes

[Ted Y]

Noob question here. I see talk about speed density tunes vs. 2 bar and 3 bar tunes. What do these terms mean and how are they fundamentally different?

[ChadC]

the basic (from what I understand) is that a Speed Density tune is using the MAF (Mass Airflow Sensor) to measure the the volume of air entering the engine. From that it determines the amount of petrol to add for maximization Ya Hoo. The drawback is that once a SuperCharger is added the Volume of Air that is sucked in exceeds the MAF sensors capability. in most cases that build is leinar and the Tuner can add the correct amount of gas based on how the car is behaving. a better approach is to replace the MAF with a 2 bar/3bar sensor (bar meaning atmospheric pressure) so it can still measure airflow (now actually boost) and add the correct gasoline with out 'guessing' 2 bar works for cars with X amount of Boost say 10PSI? 3 bar works for cars with XXX amount of boost say 20PSI? please correct me if im wrong.

[Two Fangs]

Speed density (also known as low speed strategy) is a method of determining engine load (and therefore engine fueling and spark requirements) by using the pressure in the intake manifold via the MAP sensor. Since the MAP sensor does not typically cause an inlet restriction, it is a very popular method of tuning high performance vehicles. Additionally, MAP sensors can be purchased in a wide variety of measurement scales that allow for proper measurement of high levels of manifold pressure over atmospheric, also known as boost.

Since a MAP sensor measures absolute pressure, it does not read zero when in the open air, but rather reads the air pressure. A two BAR MAP sensor then, is capable of reading the atmosphere surrounding us, but also one atmosphere (14.7 PSI) of boost pressure. A three bar MAP can read up to approximately 30 PSI of manifold boost (two boost atmospheres, plus the absolute atmosphere that makes up the 14.7 PSI found at sea level at 32 degrees Fahrenheit). Therefore the MAP sensor does not measure manifold vacuum, but rather the difference between 0 PSI absolute (also known as a perfect vacuum, only truly obtainable in space) and the pressure above this point in the intake manifold.

For a PCM to accurately determine the amount of load an engine is producing based on the pressure in the intake manifold, it must look at other sensors, such as engine coolant temperature, air temperature, and a also bevy of coefficients that can have an effect on air density.

Installing a big cam in a car, can greatly change the manifold pressure in the intake manifold at idle, skewing the load and fueling tables greatly. A speed density car will freak out when a cam is installed without a tune. The old speed density 5.0 Mustangs from the '80's were often a tuners first experience with tuning this phenomenon.

The other means of measuring airflow and determining load is the Mass Airflow Sensor or MAF. Many vehicles use one or the other, but in the case of GM, many of their cars have both. The PCM looks at both sensors, but it uses one against the other as a sanity check. Low speed operation is typically the realm of the MAP strategy, and higher RPM uses the MAF strategy. Tuners can change the point in engine RPM where the strategy is changed, up to the point of eliminating a strategy completely by changing the RPM setpoint to zero.

If this doesn't confuse the shit out of everyone, I guess we can go further....

[Blk n Blu]

Thanks for the added headache Michael.

[HOXXOH]

Speed density (also known as low speed strategy) is a method of determining engine load (and therefore engine fueling and spark requirements) by using the pressure in the intake manifold via the MAP sensor. Since the MAP sensor does not typically cause an inlet restriction, it is a very popular method of tuning high performance vehicles. Additionally, MAP sensors can be purchased in a wide variety of measurement scales that allow for proper measurement of high levels of manifold pressure over atmospheric, also known as boost.

Since a MAP sensor measures absolute pressure, it does not read zero when in the open air, but rather reads the air pressure. A two BAR MAP sensor then, is capable of reading the atmosphere surrounding us, but also one atmosphere (14.7 PSI) of boost pressure. A three bar MAP can read up to approximately 30 PSI of manifold boost (two boost atmospheres, plus the absolute atmosphere that makes up the 14.7 PSI found at sea level at 32 degrees Fahrenheit). Therefore the MAP sensor does not measure manifold vacuum, but rather the difference between 0 PSI absolute (also known as a perfect vacuum, only truly obtainable in space) and the pressure above this point in the intake manifold.

For a PCM to accurately determine the amount of load an engine is producing based on the pressure in the intake manifold, it must look at other sensors, such as engine coolant temperature, air temperature, and a also bevy of coefficients that can have an effect on air density.

Installing a big cam in a car, can greatly change the manifold pressure in the intake manifold at idle, skewing the load and fueling tables greatly. A speed density car will freak out when a cam is installed without a tune. The old speed density 5.0 Mustangs from the '80's were often a tuners first experience with tuning this phenomenon.

The other means of measuring airflow and determining load is the Mass Airflow Sensor or MAF. Many vehicles use one or the other, but in the case of GM, many of their cars have both. The PCM looks at both sensors, but it uses one against the other as a sanity check. Low speed operation is typically the realm of the MAP strategy, and higher RPM uses the MAF strategy. Tuners can change the point in engine RPM where the strategy is changed, up to the point of eliminating a strategy completely by changing the RPM setpoint to zero.

If this doesn't confuse the shit out of everyone, I guess we can go further....

I'm only confused about one point.

What set of air density standards did GM and/or HPtuners use, when they determined which sensors to use and the associated calibrations and programming to ensure proper AF mixtures?

You stated 32*F at sea level, which is what the air conditioning industry uses to adjust Freon pressure (a not very precise requirement). So how does that relate to the EPA standard of 68*F at 29.92" Hg and 20%H, or the AMCA standard of 70*F at 29.92" Hg and 0%H, or the FFA standard of 59*F at 29.92" Hg and 0%H?

It's been a day or two since my physics/chemistry classes, but I think I remember using the same one the EPA uses to calculate molecular weight. It also seems very logical to use the FFA standard when dealing with air density in DA calculations.

[Two Fangs]

I'm only confused about one point.

What set of air density standards did GM and/or HPtuners use, when they determined which sensors to use and the associated calibrations and programming to ensure proper AF mixtures?

You stated 32*F at sea level, which is what the air conditioning industry uses to adjust Freon pressure (a not very precise requirement). So how does that relate to the EPA standard of 68*F at 29.92" Hg and 20%H, or the AMCA standard of 70*F at 29.92" Hg and 0%H, or the FFA standard of 59*F at 29.92" Hg and 0%H?

It's been a day or two since my physics/chemistry classes, but I think I remember using the same one the EPA uses to calculate molecular weight. It also seems very logical to use the FFA standard when dealing with air density in DA calculations.

When I stated 14.7 PSI at 32^o at sea level, I was basically working to convey a measure of atmospheric pressure I thought a lay person could understand.

MAP sensors by nature are not exactly laboratory precise. They are essentially an inexpensive strain gauge, which by nature commonly have tolerances around +/- 3%, therefore they have a fairly wide acceptable range and changing from one MAP to another will likely give you a different atmospheric and manifold pressure readings when datalogged. Using adaptive strategy, the PCM has the ability to make determinations and adjust operating characteristics based on algorithms within the software.

While I am certain they are held to the EPA standard, or a derivative thereof, I would not expect the sensor on your car to hold that tight of a tolerance.

We can, within the tuning software, adjust the slope and offset of the sensor output. Then, when the sensor output voltage or frequency is compared to valid atmospheric pressure data, there will be a close to perfect match.

[LastC3]

Sometimes I wonder if we don't make it more confusing then it needs to be ..... understanding the basis of the sensors is very cool, and probably need to be understood .... but at the end of the day isn't the AFR what we're really concerned about ????? ( to Tom's point) ((( this may be a very dumb question .... but #justsayin )))

basically I'm working toward an AFR of about 12.5 for our overall conditions herein AZ .... ????? (understanding its a moving target) and to take into consideration overlap as well ....

the real question is .... getting that calculation as close to reality as possible, considering baro pressure, temp and keeping in line with mechanical specifics ...... (ie overlap, flow, etc) What should we really be shooting for ....... but then .....

It has occured to me that "giving the engine what it likes" is sometimes contradictive to some of these base calculations ...... case in point ...... my motor (at least right now .... in very early stages.... (OL, 0-2200 rpm) seems to like closer to 11.0 or so AFR based on WB readings .... but the math calculations read closer to the 12,5 mark ?????

Sometimes I wonder if I;m over thinking the process ..... ???? (( I know, I know .... the dyno will tell me for shure )) (( oh yeah, a mic term vs motorise ))

I guess the question is ...... what is more important ..... the calculations ...... or the response /?????

Holy Crap ..... just re-read Ted's OP ,,,,, this could certainly be *(((sorry)))

[Two Fangs]

I am not certain that without a thorough knowledge of the sensors, their function, and how they affect the output controls, that one can truly generate the results they would like to achieve. I kind of got lost in the "what the engine likes" section, I am much more interested in making the engine do what I like.

[HOXXOH]

I'm only confused about one point.

What set of air density standards did GM and/or HPtuners use, when they determined which sensors to use and the associated calibrations and programming to ensure proper AF mixtures?

You stated 32*F at sea level, which is what the air conditioning industry uses to adjust Freon pressure (a not very precise requirement). So how does that relate to the EPA standard of 68*F at 29.92" Hg and 20%H, or the AMCA standard of 70*F at 29.92" Hg and 0%H, or the FFA standard of 59*F at 29.92" Hg and 0%H?

It's been a day or two since my physics/chemistry classes, but I think I remember using the same one the EPA uses to calculate molecular weight. It also seems very logical to use the FFA standard when dealing with air density in DA calculations.

When I stated 14.7 PSI at 32^o at sea level, I was basically working to convey a measure of atmospheric pressure I thought a lay person could understand.

MAP sensors by nature are not exactly laboratory precise. They are essentially an inexpensive strain gauge, which by nature commonly have tolerances around +/- 3%, therefore they have a fairly wide acceptable range and changing from one MAP to another will likely give you a different atmospheric and manifold pressure readings when datalogged. Using adaptive strategy, the PCM has the ability to make determinations and adjust operating characteristics based on algorithms within the software.

While I am certain they are held to the EPA standard, or a derivative thereof, I would not expect the sensor on your car to hold that tight of a tolerance.

We can, within the tuning software, adjust the slope and offset of the sensor output. Then, when the sensor output voltage or frequency is compared to valid atmospheric pressure data, there will be a close to perfect match.

So you're saying that even though the software may be highly capable, the method of air density being used is immaterial, due to the inability of the hardware to measure it with precision. AKA the sensor sucks.

[Two Fangs]

Precisely

[Drewstein]

the basic (from what I understand) is that a Speed Density tune

is using the MAF (Mass Airflow Sensor) to measure the the volume of air entering the engine. From that it determines the amount of petrol to add for maximization Ya Hoo.

Speed density (SD) doesn't use the MAF.

In general the addition of the MAF made it easier on the car to determine the volume and temp of the air entering the car.

When you add a lot more air like us FI guys do, we toss the MAF as it can't handle the volume we need it to. When then use a proper MAP sensor and SD tune it. It's not as finely tuned as a MAF car, but it works where it matters most. This is when you hear about 2BAR and 3BAR tunes.

I refuse to speak in BAR as the Supra guys douched it up too much in the early 2000s.

[Guest Mikey]

SUCK - BANG - BLOW Oh, now I get it!