TUNING – SPEED DENSITY vs MAF
BD Turnkey Engines will be SHIPPED with a Speed-Density / CLOSED Loop tune
This topic is VERY debatable. An Internet research will often leave you with more questions than answers. Continue reading, and I will do my best to explain and substantiate why I feel a Speed-Density / Closed Loop fuel injection system is most appropriate for aftermarket projects.
Speed Density / CLOSED Loop Tuning: This is the fuel injection system that I prefer for aftermarket projects. It utilizes every sensor except the MAF (mass air flow). The O2 sensors adjust fuel below PE (power enrichment), and above PE fuel is calculated from a table using the TPS, MAP, RPM, etc. This system DOES adjust with altitude via the MAP (Manifold Absolute Pressure) sensor. The MAP sensor is also used as a BARO (Barometric) Sensor. As you gain or loose altitude the ECM will “shift” the fuel calculations.
NO MAF Reasoning: The MAF sensor accurately measures the volume of incoming air when properly calibrated. Its data helps the ECM adjust the amount of fuel delivered to maximize fuel efficiency and minimize emissions. But, it does this best when at a steady-state, i.e. constant throttle at highway or cruise speeds. In transient situations, i.e. on/off the throttle the MAF becomes inaccurate and the ECM has to calculate or estimate these changes. For offroad, racing, rock crawling, and most aftermarket situations, steady-state driving is minimal. In testing & tuning I have also found the variations in customers intake design to be very problematic. The factory duplicates millions of cars with identical intake designs and has done extensive MAF tuning on that design. I can sell you a duplicate engine & tune, but no one is going to run the same intake design. The slightest variation or change in intake configuration can significantly disrupt the tune, and I have seen this first hand. The airflow through a MAF can be disturbed very easily by 90-degree bends, couplers, etc. A factory tune uses the combination of the MAF and Speed Density calculations and if the MAF does not function properly they battle each other, and poor performance and drivability is the result. It is usually at a specific RPM window where the intake design induces some sort of turbulence. Many drivers may not even notice it, but in some instances it can be quite extreme. FYI, Not all manufacturers use a MAF even today. Without a MAF I can guarantee that your engine will run identical to the test engine that the tune was derived from.
Speed Density / OPEN Loop Tuning: This is often what many are referring to when the term “Speed Density” is used, and it has a somewhat negative connotation to most. It was one of the first injection systems and does NOT utilize O2 sensors and does NOT compensate for altitude or barometric changes. In simple terms, it is an electronic carburetor that injects fuel based on a fuel map relative to throttle position, intake vacuum, & rpm only. It is still used in boats today and some turnkey engine builders still use it.
MAF Tune: If you insist on using the MAF I can incorporate it and supply you with it. If you need to comply with most SMOG laws it is best to run a MAF. You will need to closely follow the guidelines of intake design that is in my manual. This will closely replicate the factory layout and help the data from the MAF be close to factory figures. Despite what many think, MAF tunes on GM cars from 1998-2006 use a combination of “Speed Density” calculations with the addition of a MAF to fine-tune. The base in the tune is “Speed Density”! If you unplug the MAF sensor your car still runs. You will get a “check engine” light, but the system reverts to the “Speed Density” tune and runs fine.
Conclusion: Your BD Turnkey Engine is going to run VERY good when you get it. You will be surprised at how good without a MAF because of the highly polished tune. I run my personal car without a MAF, as do many drag racers, offroaders, etc. This comes from many hours of tuning that particular engine combination. And that is what you are getting – a duplicate engine & tune!