VTEC point tuning
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VTEC is one mechanism Honda uses to achieve good emissions, fuel economy and engine power from a small displacement engine. The function of VTEC (variable valve timing and lift electronic control) is to provide two distinct camshaft profiles which are switched electro-hydraulically. The smaller camshaft profile is called the low-speed cam; the larger the high speed cam. The camshaft profiles are switched depending on engine rpm and load, usually from 2500 rpm to 6500 rpm. The main effect on tuning of VTEC is that there are usually two copies of every major table - one for the low speed camshaft, one for the high speed camshaft.
The determine the best VTEC point perform two dyno runs, one with VTEC set low (e.g. 3000 rpm) and the other run with VTEC set high (e.g. 6500 rpm). Set the VTEC point to the intersection of the high speed cam and the low speed cam. Generally if there is a sudden increase in engine output immediately after the cams switch then lower VTEC. Conversely if there is a sudden dip in engine output then raise the VTEC point. Since the VTEC point will be at the intersection of the low speed and high speed cam torque curves, it is normal for the torque to dip slightly around the VTEC point.
Generally the VTEC point will be 5500-5700 rpm on a stock engine, 4500-4800 rpm with intake & exhaust, 3000-3200 rpm for supercharged applications. Aftermarket cams generally require a high VTEC point.
The VTEC window uses a combination of rpm and manifold pressure to determine when to switch cams. This is so that the cams will not switch at light or medium throttle - which is undesirable for fuel economy or driveability reasons. See VTEC parameters for more information on the settings.
Setting the VTEC window
Normally there will be a small dip (less than 5 lbs torque) at VTEC. If there is a greater dip, try changing the VTEC point up, in 100 rpm increments, to see if the dip is reduced.
As see VTEC crossover tuning