What is a speed density system?

[S15SiLVia]

I heard w/ a speed density system you are able to run a car w/o the MAF for those that are equipped with one. I wanted to know what do you need to use this setup, and also the pros and cons about it. Thank you

[ryanman]

When you put speed density in a car, it replaces the MAF.

[S15SiLVia]

ok, what do you need to use a speed density, like what sensors are in involved to replace the MAF?

[davidm_sh]

ok, what do you need to use a speed density, like what sensors are in involved to replace the MAF?

MAP - manifold absolute pressure (I think that is right?) sensor

[hotrod]

Why do you want to replace the MAF with a speed density ?

It seems counter productive to me, as the true MAF (especially hot wire designs) generally does a better job of monitoring air flow.

http://users.wpi.edu/~ktarry/dsmtech/airmetering.html



Larry

[WRX Harvey]

The MAF measures true mass of air without regard to air temp, pressure, altitude.

With speed density the ECU uses a pressure sensor located in the intake manifold along with an RPM signal to approximate the mass of air entering the engine, but the computer needs other inputs such as a intake air temp sensor and an ambient pressure sensor to zero in on a more accurate mass reading.

The upside of the MAP system is that it is not affected by intake leaks like the MAF system. With MAF on a turbo car an air leak will cause a rich mixture.

I used to have an early TPI injector system that used RPM and TPS to figure out air mass and approximate load. An early Holley Pro-Jection unit. Fun and inaccurate.

The closer your engine can approximate the air entering, the better it can figure Volumetric Efficeincy and Load. That means the better it can calculate neccessary fuel and timing for power, economy, emmissions, or whatever you choose to tune for.

[crazycam31]

Well.... there you have it. Now even I understand it.

[saabracr]

It is not a simple conversion. One cannot just swap from one sensor to another. As Harvey mentioned, other sensors are necessary to end up better than where you started. MAP signals are also characteristically a bit different than MAF.

Another advantage to speed-density is that you don't have the MAF posing a restriction to airflow. MAP sensors are also naturally less prone to failure.

Saab's new Trionic 7 and 8 engine management systems use both MAF and MAP. The latter is proving especially hard to crack due to the sophistication. Saab is running some of the most elaborate and effective engine management for turbo cars available. Direct Ignition and ion-sensing "pre-knock" detection, with integral timing and boost adjustment has been in cars for over ten years now.

Take care,
Andy

[S15SiLVia]

Thank you for all inputs. Knowledge went up 5 points :)

[FR Javier]

i would only recommend switching to a MAP based system in you will be making more than 500hp on your nissan. there are quite a few nissan/infiniti MAFS that can measure the required mass flow rate to support these power levels. for instance, the Z32 MAF or the ford Cobra MAF.

if you are going to make more than 500hp, then switch to MAP. there a quite a few standalones out there with 3 and 4 bar map sensors that can handle high hp systems.

personally, i run an Autronic SMC in my 92 SE-R. it's a speed density system...no MAF for me :D

[S15SiLVia]

FR Javier:
How do you like the speed density compared to a MAF? Anything you hate or like about it?

[doctorstupid]

ion-sensing "pre-knock" detection
oh do tell, i am very intrigued :)

[FR Javier]

FR Javier:
How do you like the speed density compared to a MAF? Anything you hate or like about it?

on previous turbo setups (all nissan) i always ran a JWT ecu...it was plug and play. basically plug the ECU in, set the base timing and fuel pressure and your good to go. i didnt have to tune it at all...perfect driveability too.

the autronic took a lot more time to complete. you have terminate the harness, build a base map, basically tune a car from scratch. i wouldnt have it any other way though, it controls anything you can think of 'burnout:

no maf here :)
http://www.full-race.com/images/gallery/javier/images/045.jpg

[THRICE]

Thanks to this thread!!!...






I've now got a headache...

[john]

Speed (rpm) density (intake manifold pressure) replaces all the input which was coming from the MAF (things like air temp, mass air flow / volume, barometric pressure etc) with "other" inputs.

I've done a few speed density on MAF-based cars, and the MAF signal was recreated in a black box by reading inputs from an intake air temp sensor, a MAP sensor, RPM, throttle position sensor, and probably other stuff.

Eliminating the MAF can get rid of a bottleneck both in terms of raw airflow as well as the ability to consume a HUGE volume of air (which the stock MAF would not allow).

[saabracr]

oh do tell, i am very intrigued :)

I cut and pasted this from a Saabnet FAQ. There is more detail out there somwhere if you search. It gets pretty complex.

Saab Trionic Features Powerful Microprocessor

The award-winning Saab Trionic engine management system used for Saab
Ecopower engines was designed and tested by Saab's own engineers. Saab is
one of the few car manufacturers in the world to develop its own electronic
engine management system. The brain of Saab Trionic is a 32-bit
microprocessor, capable of carrying out two million calculations per second.
Programmed with ideal combustion conditions, the microprocessor
simultaneously monitors and adjusts the ignition timing, fuel injection rate
and boost pressure. Control is adaptive, which means that the system adjusts
all calibration points while taking into account variations in engine
parameters, such as temperature, load and even engine wear.

Trionic analyzes the combustion process by using the spark plugs to measure
ionization in the cylinders. A weak electrical current is applied across the
gap of each spark plug after every combustion stroke. The voltage flowing
back to the control unit measures the combustion efficiency in each
individual cylinder. The system continually adjusts the fuel quantity, the
ignition timing or the boost pressure to ensure each cylinder's fuel-air
ratio is as optimal as possible. The result is a reduction in fuel
consumption and exhaust emissions.

Individual ignition timing tailored to each cylinder is possible thanks to
Saab's Direct Ignition (Dl) system, featuring one ignition coil per spark
plug. Introduced on Saab cars in 1985, Dl provides up to 40,000 volts at the
moment of ignition.

The Trionic systems on full-boost turbo engines have an integrated Automatic
Performance Control (APC) function, which helps regulate turbo boost
pressure correctly, regardless of fuel quality or octane. APC allows all of
Saab's Ecopower engines to run on regular unleaded fuel. Premium fuel is
recommended only for the Aero's 225-hp engine.

[slownx2k]

Hey FR Javier , is that car running?? I noticed your turbo is facing the wrong way. I was wondering how you routed the exhaust?? I did the turbo on my Sentra in a similar fashion and I pretty much had to put a big UTurn in my downpipe for everthing to fit...

Josh

[FR Javier]

Hey FR Javier , is that car running?? I noticed your turbo is facing the wrong way. I was wondering how you routed the exhaust?? I did the turbo on my Sentra in a similar fashion and I pretty much had to put a big UTurn in my downpipe for everthing to fit...

Josh


runs great...goes through a lot of transmissions though :ring: im just running a 3.0 in. downpipe right now...

http://www.full-race.com/images/gallery/javier/images/053.jpg
http://www.full-race.com/images/gallery/javier/images/077.jpg