Speed Density Explained

You may have heard the term before, but what exactly is speed density (SD)? Well, I'll explain it to ya!

Speed
density is a form of monitoring the air being pulled into the motor by
using a MAP sensor and an IAT sensor. MAP is manifold absolute pressure,
IAT is idle air temperature.

4g63 cars have a MAF (Mass airflow
sensor) to monitor the intake of air. Well, at certain power levels it
can be a restriction, and honestly, its a poor system. On 1g/2g DSM's,
the MAF is before the turbo. With a MAF, any leak in the system will
cause rich conditions, because the metered air is no longer there, and
the ecu doesn't know this, so it will spray the amount of fuel
necessary. You loose air, you have too much fuel. That is why you don't
vent your blow off valve to the atmosphere with a stock MAF, because
while pulling up to a light you will stall, or while shifting you will
have odd problems.

How do I convert my car to speed density you
ask? Well, first, you need a tuning program. Ecuflash with Ceddymods,
Ecmlink, and ostrich with jackal all let you use speed density. You want
to mount your MAP as practical to the intake manifold as possible. The
shorter the hose the better. The IAT, you want to mount as close to the
throttle body as possible.

On 2g DSM's, when using speed density
you can remove the MDP (Manifold Differential Pressure) sensor on top of the intake manifold, and buy an
adapter that RRE sells, it allows you to easily mount a map sensor. 1g
cars don't have this option, as they don't have an MDP sensor. You must
drill and tap the intake manifold or get creative.

And if you turn to running speed density you don't have to worry about boost leaks anymore, as long as they are before the intake and not in or after the intake. (: because it is metering the air in the intake and cyclinder head and not metering the air being pulled into the turbo. Hence being able to run atmospheric with you bov. Also Megasquirt is another tuning software you can use to run speed density.