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RPM Activated Switch – Good For Camshafts?

ECUMaster DET3 Piggyback ECU

If you have swapped your engine to one with VVL or VTEC, you need some way to change the cam profiles, is an RPM activated switch suitable?

In a word, no.

The decision to change profiles is not solely down to RPM. In lower gears, it is no problem to have the engine at high revs with low engine load. The engine does not need to switch cams when engine load is low, so switching the cams in low gears and low load is not necessary.

To change cam profiles we need an RPM activated switch that can also take into consideration other inputs. The most obvious would be engine load ie the signal from a MAP sensor.

Low gear and low engine load but high RPM will not trigger the cam change, which is exactly what we want.

Ultimately we only want to change the cam profile when engine load is high. And we only want to trigger the larger cam profile when the RPM is high. At low RPM the engine simply cannot make use of the larger profiles.

What Options Do We Have?

There are piggyback and stand alone ECUs which have layered activation ie activation of a 12 volt circuit according to RPM and other 5 volt sensors.

If you need to change your engine program to run the new engine then a piggyback ECU or a standalone ECU would probably be the most straightforward solution. Good examples of these products have layered activation built in.

However if you are using the cars original ECU which you can rewrite, using a Nismotronic ECU for example, then you will need a stand alone device to trigger the cams and this is where the RPM activation switches come in.

The market is absolutely flooded with them but few offered layered activation. For over 250 Euro there are piggyback ECUs which offer layered activation. Examples include Ultratech Chrono and AEM FIC6.

But these are a bit overkill for switching the cams only. Dedicated devices are available which are also cheaper, the MoviChip CamSwitch claims to offer layered cam switching at a price around 30% lower than the piggyback units listed above.

In Summary

Camshaft activation for VVL and VTEC needs to be done primarily according to engine load and secondly according to RPM. It is possible to switch cams according to RPM only but the results will be far from ideal, at best we will see increased fuel consumption.

This page was last modified Oct 28, 2021 @ 8:16 pm

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