The MAF Clamp function is probably the slickest yet most under-used function in the application. To illustrate the potential, one of our customers has run a 9-second quarter mile pass on a bone stock 2G DSM MAF using MAF Clamp (previously called Fake MAF for reference). That's pretty cool.
MAF Clamp is basically a switch over to pseudo speed density just before the point where you might not trust the real MAF signal. You run on a nice, smooth factory MAF most of the time with a switch over to speed density only when necessary. The ECU takes care of extrapolating airflow for you based on the VE table you define for your car. This function can also be useful even when running a GM MAF. It can help to smooth out the relatively choppy signal produced by a GM MAF under high boost.
A more detailed explanation of how the ECMLink ECU code runs through airflow calculation can be found on the MAF Comp page. The results of the MAF clamp function can be datalogged as MAFSD. This is true whether the Enable MAF Clamp function checkbox is checked or not. The ECU always calculates MAFSD even if it's not going to use it. This is intended to help dial in the VE table without actually running on the VE table.
To calculate a more customized VE table for your particular setup, first make sure you�re running a boost level low enough to keep MAF Hz below your target clamp point (probably around 2700hz on a 2G or EVO8 MAF and 2100hz on a 1G MAF). Then deselect the Enable MAF Clamp function checkbox, drop the Clamp switchover to a relatively low value like 1500hz, and log both MAFComp and MAFSD. MAFComp is the MAF sensor reading after compensations have been applied to it from the MAF Comp table. MAFSD is MAFComp after VE adjustments have been applied (as well as factoring in pressure if you have Use manifold pressure checkbox selected). Both of these are calculated even when they�re not being used. Adjust the VE table until MAFSD replicates MAFComp.
Changes in the volumetric efficiency (VE) of an engine, by definition, change how much airflow is possible through the engine at a given manifold pressure. This table defines how to adjust airflow based on engine VE while the clamp function is active. The default "stock" table is pretty reasonable for an engine running with a stock intake manifold (IM). By using the Display template drop down box, you can select a reasonable template for a Sheet metal IM as well. Note that a template is a display-only function. To actually use template values as your actual values, click the Use template button while a template is displayed.
This drop down provides a couple basic "templates" you can use for reference. The Stock IM selection would be reasonably close to use while running with a stock intake manifold on 2.0L engine. The Sheet metal IM selection should be more appropriate when running with a sheet metal intake manifold. A selected template is just an overlay on the MAF Clamp VE Table. It doesn't actually change any values used by the ECU. It's a display-only template for reference. To use template values as your actual values, click the Use template button while a template is displayed.
This box must be checked in order for the ECU to actually use MAF clamp results.
This defines the point at which the ECU will activate the clamp function. This is the point where the ECU will sample the real airflow value it'll used to extrapolate the clamped airflow value from then on (up until the clamped airflow value drops well below the clamp point).
In addition to compensating for varying volumetric efficiency, the clamp function can also take into account varying manifold pressure. To enable this function, however, the ECU needs to be told where it can find an aftermarket manifold pressure sensor. You do this in the ECU Inputs tab.
In order for MAP scaling to work properly, the sensor needs to be "zeroed" so that 0v = 0psia. Many sensors work like this already. The GM 3-bar sensor, for example, appears to be zeroed at zero according to most table looks up we've seen for it. The AEM 3.5-bar and 5-bar sensors, however, are actually 4-volt sensors with a 0.5v offset. So for those sensors, you'll need to enter 0.5 into the MAP offset field so that the ECU will treat 0.5v as 0psia.
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