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Ask Anything - February 2014

MAF MODIFIERS

Chris Carter; via CarCraft.com: How do mass airflow meter modifiers work? I have a 2006 5.3L truck engine I'm about to swap into an older car. Rather than pay someone to tune my engine, I am thinking of modifying the engine, maintain the stock OE computer and wiring harness, and add a mass airflow modifier.

Jeff Smith: All engines with mass airflow meters (MAF) measure the amount (mass) of air that enters the engine. This allows the EFI to be more accurate because the MAF tells the ECM exactly how much air the engine is ingesting, making a quick and easy calculation for the proper air/fuel ratio. The other version of EFI is called Speed Density where there is no MAF. Without a MAF, the ECU must use input from the manifold absolute pressure sensor (MAP) to determine load and then combine that with the throttle position sensor (TPS) and engine rpm to determine the amount of fuel the engine needs based on a predetermined estimate of the amount of air the engine is ingesting at that given load. Both MAF and Speed Density also rely heavily on the feedback from the oxygen sensor. While speed-density systems are easier to work with and cheaper because they don't use a MAF, they are also less accurate. It might be worthwhile to take a look at how MAFs work so you understand what's involved.

Original MAF sensors used a thin wire stretched across the meter's inlet. A current was applied to the wire, and the amount of voltage and current required to maintain a given wire temperature would change as the mass of air passing over the wire increased. More modern meters divert a small amount of air through a channel and measure the drop in voltage as airflow increases across the meter and use that to calculate mass flow. Early meters delivered a specific voltage output curve that the computer used to determine the amount of airflow. According to Lingenfelter Performance Engineer Jason Haines, GM computer systems after 1994 began using a frequency based output instead of voltage because it offered more accurate information and control at idle and low engine speeds. Now, let's say you've modified your engine and that stock MAF is now a restriction to airflow. This means you need to install either a larger OE MAF or an aftermarket MAF to plug into the inlet system. The problem with using a non-OE MAF is that it may not communicate properly with the existing factory computer. This is where the MAF modifiers come in.

Haines told us that modifiers for late-model GM engines really aren't necessary since all the GM software from companies like HP Tuners and EFI Live (the two biggest) allow you to tune the ECM directly, including MAF frequency. The most popular MAF modifiers were designed for Ford applications that did not have easy tuning access to the OE Ford ECM.

I also spoke to Andy Wicks, who runs DynoTune Speed and Performance in Watertown, South Dakota (DynoTuneUSA.com). Andy is the guy who for years ran the chassis dyno for us at the Car Craft Summer Nationals. Andy has tons of experience tuning all kinds of late-model fuel-injected engines. Andy says the typical GM MAF sensor actually has quite a bit of room for power and that, for a normally aspirated combination, the stock MAF can handle as much as 480 to perhaps 500 normally aspirated horsepower without any changes. He also said the MAF modifiers were actually good for the older Ford systems that still used a zero-to-5-volt scale, where you could use a MAF modifier to increase the voltage reading. For example, you could increase the part-throttle 0.10-volt reading to 0.11 and increase fueling by 10 percent. The down side to this approach is that it sacrifices part-throttle resolution. A far better approach is to go into the computer and adjust the base fuel map tune to compensate for the changes.

To address your specific example, let's say you want to increase the performance on the truck 5.3L engine with a camshaft, ported cylinder heads, headers, and either a passenger-car LS6-style intake, or an aftermarket intake manifold. With all these modifications, you may want to add larger injectors to match the additional airflow generated by the engine's new heads and intake. If you add larger injectors, the original base fuel map will have to be adjusted to compensate for the greater amount of fuel flow. For example, if you added injectors capable of 30 percent more flow, then the fuel map will need to be reduced in pulse width by the same 30 percent to create the same amount of fuel flow at part throttle. The engine will have to be tuned because that simple compensation will not really create the proper fuel curve. Andy told us that his company offers a simple "startup" tune service (for $150), where you send him your stock ECU, along with the specs for your engine, and he will disable the VATS (vehicle anti-theft system) so the engine will start and run, and then a basic file that will allow your engine to run and drive. More than likely, your application will still require further tuning to get the last improvements and better driveability, but this is an inexpensive way to get the car running.

The bottom line is that while the mass air modifier has its place, tuning the ECU's specific fuel and spark maps is still the best procedure for your GM performance application.

More Info
EFI Live; +64 (9) 534 1188; EFILive.com
Dyno Tune Speed and Performance; 605/753-1101; DynoTuneUSA.com
HP Tuners; HPTuners.com
JMS Chip & Performance; 601/766-9424; JMSChip.com


CC Quickies

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