What exactly is a Speed Density Tune?

And how does it differ from a regular tune?

What kind of mods work better with an SD tune?

Just lookin for some knowledge...

 

Speed density gets rid of the MAF sensor and calculates airflow into the engine by RPM and manifold pressure (MAP). The MAF is more accurate since it is an actual measurement of airflow, but there are limits to how much it will read. Regardless of the size of your MAF sensor (stock, 90mm, 100mm, etc etc), your PCM will only read up to 512 g/s of airflow with the MAF. Once you get above there I believe the PCM reverts back to using your VE tables only, which is basically SD.

SD is really only advantageous when you are boosted. The other flexibility that SD gives you is the ability to go with a 2-bar tune (meaning you install a MAP sensor that can read vacuum and boost, rather than just vacuum like the stock one). This allows you to accurately fuel the engine under boost instead of just reverting to the power enrichment (PE tables) that seem to me to be just a "best guess" of how much fuel you need to add. You also get the option of using a commanded AFR vs RPM and MAP table.

All in all, for a boosted setup, SD is easier to tune IMO.

 

good to know. I imagine it can get alot more indepth, but that definately asnwered my questions. I got alot to learn...

thanks

 

MAF is also slow to respond. The PCM reverts to VE during throttle transitions.
I don't think there is any reason to have a MAF. Spend the extra time to get your VE and bias perfect and stay in SD. I've had my daily driver in OLSD for 6 months now without a problem.