Speed Density

[RacerJJ]

Sorry y'all, i'm new to all this high tech stuff and the list...what is this speed density and how do i do it????

 

[TurbochargedBerserker]

There are two basic methods of elec. fuel injection: speed density and mass air.

 

The only hard ware difference is the use of a MAF (and in our case, the MAF houses the IAT). The rest of the difference is in the PCM programming.

 

Speed density systems rely on having a finely tune volumetric efficiency (VE) table to calculate fueling.

 

Mass air relies on the MAF to help calculate dynamic air flow into the motor and helps control fueling to some degree depending on the programming (for example, Ford EECs control most of the fuel based on the MAF, GM uses a strange blend of MAF + VE, straight VE, or straight MAF).

 

In high airflow (like forced induction), GM's mass air can be a limitation (the MAF itself is easily outflowed by turbos, etc). In tuning, GMs mass air is very confusing and tends to blur the effects of tuning changes. On the other hand, mass air is much more adaptive, whereas speed density requires a retuning session if anything changes to the air stream (bigger filter, change in boost level, etc.)

 

For most people, there is no reason to change to speed density. You pretty much have to be a DIY tuner or be completely done with all your mods and know a tuner willing to set you up.

[SSilverad03]

[vette dude]

For most people, there is no reason to change to speed density.  You pretty much have to be a DIY tuner or be completely done with all your mods and know a tuner willing to set you up.

<{POST_SNAPBACK}>

so weather conditions could =have significant effect on a car with speed density, i.e. requiing a new tune?

[zippy]

if you're not maxing out the mass air flow sensor's capabilities, i wouldn't bother with speed density.

[TurbochargedBerserker]

For most people, there is no reason to change to speed density.  You pretty much have to be a DIY tuner or be completely done with all your mods and know a tuner willing to set you up.

<{POST_SNAPBACK}>

so weather conditions could =have significant effect on a car with speed density, i.e. requiing a new tune?

<{POST_SNAPBACK}>

 

 

Yep. Most guys I've talked to around here have a summer and winter tune (we only have 2 seasons). This winter the coldest day so far has been 76... In colder climates it would be a must -- cold weather makes SD tunes run leaner.

[TurbochargedBerserker]

if you're not maxing out the mass air flow sensor's capabilities, i wouldn't bother with speed density.

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Absosmurfly.

[supraman]

With 94-98 twin turbo Supras changing from MA to SD via a "Vein Pressure Converter"(VPC) yields 40-60 rwhp!....52 on mine...whether the stock fuel is maxed or not.

[deezel]

if you're not maxing out the mass air flow sensor's capabilities, i wouldn't bother with speed density.

<{POST_SNAPBACK}>

Too much work when the MAF can handle the flow. Unless you have very radical engine changes - heads, cam, stroker, forced induction... the MAF can handle the flow demand. Stock MAF (with screen) is good for up to around 550hp before it flatlines. Even then, you can program the PCM to provide more fuel above the point where the MAF is maxxed out. Speed density is most useful for setups where the MAF itself is the biggest air flow restriction. If you don't have a 600+hp setup, don't worry about it.