Tuning your vehicle

Basics

First it is important to understand how the Honda ECU determines the appropriate settings for the engine. The Honda ECU uses the speed/density method of calculating these values. The ECU uses the intake manifold pressure and engine speed to index lookup tables for ignition and fuel (amongst other things). Other parameters such as coolant temperature, battery voltage and intake air temperature are used to compensate the table lookup values for the engine. To tune the engine we alter the main tables (fuel and ignition) to suit the particular configuration of the engine.

A typical fuel table is shown above. The indices used are rpm (along the bottom) and intake manifold pressure (along the side). The ECU uses interpolation to calculate valves from the table which do not fall exactly on a row or column index. e.g. if an ignition table contains 20 degrees advance at 2000 rpm and 10 degrees advance at 3000 rpm, when the engine rpm is 2500 rpm the ignition advance will be 15 degrees. The interpolation actually occurs in two dimensions (engine speed and engine load).

VTEC

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. Another tuning consideration is the point at which VTEC switches (see Tuning the VTEC point).

The Tuning Process

The best process is: