"Speed density" explanations please...

[toofastforyou]

Can someone please explain what exactly is a "speed density" system? I'm very confused and a little( maybe a lot! ) explanation would be welcomed... What are it's benefits and drawbacks, which type of car would see an improvement using such a system? Is it something for everyone? etc...
Thanks,

Claude

 

[callmeebryan]

Can someone please explain what exactly is a "speed density" system? I'm very confused and a little( maybe a lot! ) explanation would be welcomed... What are it's benefits and drawbacks, which type of car would see an improvement using such a system? Is it something for everyone? etc...
Thanks,

Claude

There is Speed Density and Alpha-N

In Speed/Density mode, the ECU monitors engine RPM, map sensor, and intake air temperature. Based on these numbers, along with a user-defined engine displacement figure, the ECU calculates the volume of air coming into the motor at any given time. The ECU then calculates the appropriate amount of fuel needed to operate at the air/fuel ratio specified in a target air/fuel ratio table. Because all this continually happens "on the fly", Speed/Density mode provides the highest degree of tunability over varying weather conditions, altitudes, and engine loads.

In Alpha-N mode, the manner of operation is much simpler. An injector pulsewidth is simply looked up from a throttle position vs. engine RPM lookup table. The intake air temperature sensor and the MAP sensor are used to measure ambient air temperature and pressure. There is a user-definable correction curve for adding or removing fuel based on air temperature, and a generic barometric compensation curve is applied internally.

For a turbocharged application, you must use SPEED DENSITY mode. Extreme naturally aspirated applications will use alpha-n in situations where the cam profile makes for very little vacuum.

 

[Blazer406]

For a turbocharged application, you must use SPEED DENSITY mode. Extreme naturally aspirated applications will use alpha-n in situations where the cam profile makes for very little vacuum.

Don't tell our Buicks that..... they are mass air cars.... not speed density cars. They work just fine on mass air.

 

[Blazer406]

IMHO.....

Speed Density: Uses manifold pressure and air temperature with throttle position and engine speed to calculate the load on the engine... and adjust fueling accordingly.

Mass Air: Uses a mass air meter to measure the actual mass of the incoming air to calculate how much fuel is required to burn that mass of air.

Both systems have strenghts and weaknesses. Both systems are found across the OEM's. Most aftermarke EFI systems use speed density for whatever reason. The biggest perk I see for speed density... is there is no mass air meter in the inlet air stream to provide any restriction. Stock ECM'd mass air systems tend to "tolerate" head and cam changes better with a stock computer.... because it still "measures" the amount of incoming air... and adjusts fuel accordingly. a OEM speed density system can't do that.

Once you go aftermarket EFI.... you can take advantage of real-time WOT O2correction based on input from a wideband..... this works fine... even with larger cams...

 

[callmeebryan]

Don't tell our Buicks that..... they are mass air cars.... not speed density cars. They work just fine on mass air.

Well, this "FAST" computer has taken over my car....

 

[johnnyttype]

i got a question... if u r spraying alcohol, would the intake air temp sensor go before or after that? because ive read that it gets relocated when changing to speed density.

i too have been looking into speed density and how it works, how to tune and what not! my brother has a procharged 408CID silverado and the shop that has had it for 3 or more years now just switched it to speed density(HP Tuners unit) trying to get it tuned right because i guess they determined they couldnt do it with the MAF system. they seem to be throwin parts at it and draining my brothers wallet

not trying to steal a thread or anything, just tryin to help my bro

 

[dgoodhue]

Both systems have strenghts and weaknesses. Both systems are found across the OEM's. Most aftermarke EFI systems use speed density for whatever reason. The biggest perk I see for speed density... is there is no mass air meter in the inlet air stream to provide any restriction. Stock ECM'd mass air systems tend to "tolerate" head and cam changes better with a stock computer.... because it still "measures" the amount of incoming air... and adjusts fuel accordingly. a OEM speed density system can't do that.

The biggest advantage to speed density is the ability to fine tune the motor. The MAP sensor is better sense of engine load. The disadvantage is that it doesn't compensate for modification (air flow) changes that well. So 10 Psi @3500rpm on stock heads/cam is not he same 10 Psi @ 3500 rpm with a better set of heads & cam, but the ECM will fuel/time them the same.

As said above MAF systems measure the airflow density. MAF systems work better for the average guy who don't want to get deep into ECM tuning their own systems.

 

[Blazer406]

On the Buicks.... when running a FAST system (speed density).... the air temp sensor usually is located in the doghouse... behind the throttle body... near the coilpack.

 

[Chuck Leeper]

"i too have been looking into speed density and how it works, how to tune and what not! my brother has a procharged 408CID silverado and the shop that has had it for 3 or more years now just switched it to speed density(HP Tuners unit) trying to get it tuned right because i guess they determined they couldnt do it with the MAF system. they seem to be throwin parts at it and draining my brothers wallet"
I'd suggest your bro go get his truck, and find a shop that knows WTF is going on. If they can't tune that combo, with all the info available, + HPT, he needs to "GTFO".
We don't use HPT, but EFILIVE. There's no reason that a SD tune can't be put on that truck, unless something is screwed up in the actual engine build. Did they build his engine, too?

 

[johnnyttype]

"i too have been looking into speed density and how it works, how to tune and what not! my brother has a procharged 408CID silverado and the shop that has had it for 3 or more years now just switched it to speed density(HP Tuners unit) trying to get it tuned right because i guess they determined they couldnt do it with the MAF system. they seem to be throwin parts at it and draining my brothers wallet"
I'd suggest your bro go get his truck, and find a shop that knows WTF is going on. If they can't tune that combo, with all the info available, + HPT, he needs to "GTFO".
We don't use HPT, but EFILIVE. There's no reason that a SD tune can't be put on that truck, unless something is screwed up in the actual engine build. Did they build his engine, too?

no, the engine was built by my dads mechanic who had always done the work to my buick when it was my dad's car. its a pretty radical truck i guess, engine build atleast! ive told him to go elsewhere...in fact i told him to take it to anderson performance before he had even chose a shop! i should have known that the shop was no good, there were mustangs all over the place

 

[Chuck Leeper]

Time to go get it, and spend that $$ on an EFILIVE system. About $700. The EFILIVE forum has ALOT of really astute tuners, that will be more than happy to help. That includes the guys that wrote the programming, and developed the pkge...
That way, the bro can datalog, tune, t/s, and not waste his $$ at a know nothing shop.

 

[SloGN]

there is one thing that is the biggest advantage with a speed density VS MAF


when you snap the throttle the manifold pressure changes instantly so those changes are seen by the computer faster than the change in mass air flow thru the MAF sensor due to the amount of plumbing from the maf to the engine. and i'm talking seconds but this does affect engine response time. yes i know that you can help correct this by adding a larger pump shot etc....


If you will notice that most OEM's that use a MAF they try and place the MAF sensor as close to the throttle body for this very reason.

MY 06 chevy truck 5.3L has both sensors on it.

 

[84BuickGNYorkPA]

With speed density you can eliminate the MAF sensor and it's plumbing if any. My buddie just puts a screen over the turbo inlet at the track and runs no filter, not that I recomend that, but that's how he rolls. Oh yea, he goes alot faster than me too...

Chuck

 

[TurboDave]

With speed density you can eliminate the MAF sensor and it's plumbing if any. My buddie just puts a screen over the turbo inlet at the track and runs no filter, not that I recomend that, but that's how he rolls. Oh yea, he goes alot faster than me too...

Chuck

Speed density completely eliminates the MAF.

There are a couple of ways to achieve speed density setups.

1. You can go with a complete stand alone system such as FAST/XFI, BS3, or many others. As these are stand alone, they completely eliminate the stock ECM and replace it.

2. There is also a piggy back style system such as Translator Pro (becoming very popular), which as said is a piggy back system, which retains the stock ECM and uses the Translator Pro to take over fuel control.

The beauty of 2. for the average "joe" is that it retains the stock ECM that takes care of a lot of the mundane overhead functions that need to be controlled, while allowing total operator control of fuel/air tuning, WOT spark control, closed loop boost control etc.