Disclaimer

This is a brief guide to tuning the Honda engine. It is a guide only; the final determination of engine parameters is the responsibility of the person tuning the engine. You will need a dyno and lambda meter to tune an engine. While it is possible to tune an engine without either, it is not recommended as there is too much guesswork involved. Forced induction engines should use a detonation monitor (or similar device) to make sure that detonation is detected before it can damage the engine, and an exhaust gas temperature meter.

Before you start

The following is recommended before starting to tune an engine:

• Set the cam timing.
• Set the ignition timing.
• Check the fuel pressure under load.

Set the Cam Timing

Correct cam timing is critical for maximum engine performance. To check the cam timing remove the rocker cover and the spark plug from number 1 cylinder (nearest the crank pulley). Rotate the engine until the cam gears Îtopâ marks are roughly at the top of the wheels. Place a rod through the spark plug hole onto the piston and rotate the engine until the piston is at TDC. This can be done by eye but a dial gauge is preferable for accuracy.

Once TDC is established the marks on the cam gears should line up. Note that the marks when lined up may not be horizontal, but angled slightly. To confirm the cam gears are correct a ruler may be placed across the width of both cam gears so that all 4 marks line up and the rule is over the centre of the cam gear retaining bolts.

A more accurate method is to use the locating holes in the camshafts to check that the camshaft is at TDC. Most camshafts have a hole near number 2 cylinder with a corresponding hole in the camshaft retainer (above the cam). The holes are normally staggered from exhaust to intake cam. When number 1 piston is at TDC a pin placed through the camshaft retainer should slot into the camshaft.

The position of the holes in the camshaft retainer changed between the early and late model engines, depending if the engine has a cast retainer or extruded retainer. Normally this is not a problem unless camshafts from a different model engine are used. E.g. Type R camshafts in an early model engine.

Once the crank TDC and camshaft TDC is found it is a good idea to mark the crank pulley and cam sprockets. For a engines with a stock crank pulley it is unusual for the factory crank mark not to be at TDC. It is also unusual for the centre mark on replacement cam sprockets not to be correct unless the cylinder head or block has been machined.

When setting the ignition timing make sure the idle speed is low enough that the ECU is not adding advance. Otherwise it is possible to set the ignition timing as much as 10 degrees retarded. The ignition timing should be set with the engine at normal temperature.

To find out if the engine speed is low enough put a timing light on the engine and increase the revs slowly by 100 rpm. If the idle speed is too high then you will observe that the ignition timing advancing as the engine speed increases. If this happens then decrease the idle speed. Normally you will need to remove the plug from the idle valve in order for the engine to idle slow enough (usually 500-600 rpm is the right engine speed).

If the crank pulley is non-standard, and does not have the factory timing marks, then new timing marks need to be made on the pulley. If you have a dial-back timing light then only the TDC mark needs to be made. Otherwise measure the radius and distance between TDC and timing marks on the stock pulley and apply the same ratio to the aftermarket pulley. E.g. The stock pulley has a radius of 71mm and the 15 degree reference mark is 18.3mm from the TDC mark. The replacement pulley has a radius of 59.5mm, so the reference mark should be 18.3/71*59.5 = 15.3mm from the TDC mark. It is recommend with replacement crank pulleys that the TDC mark is confirmed using a dial gauge to find TDC for #1 cylinder.

The fuel pressure should be measured and adjusted without the engine running. If the engine is running then the manifold vacuum will cause the fuel pressure regulator to lower the fuel pressure. Since manifold vacuum is dependent on idle speed and cam timing, this is not an accurate and repeatable way to measure or set fuel pressure.

To measure or set fuel pressure switch the ignition key to Îonâ but donât start the engine. The fuel pump should prime the fuel system. You may need to flip the ignition key between Îaccâ and Îonâ repeatedly.

During a dyno run under full load check that the fuel pressure is correct.  For naturally asteriated cars the fuel pressure under load should be the same as the static fuel pressure. For forced induction cars the fuel pressure should be the static pressure plus the manifold pressure.

The normal approach is to:

• Tune the mixture.
• Tune the ignition timing.
• Tune the cam timing.

This process may be repeated if a large change is made tuning one area.

The general approach tuning mixture is to adjust the injector multiplier (overall fuel trim) until the mixture is as close as possible to ideal while the engine is under full load. Normally this will result in the part load settings giving close to ideal mixture as well.

The ideal mixture at full load (for a non boosted engine) is a matter of option but generally lambda 0.88-0.92 (air/fuel 13:1 - 13.5:1) produces the most power. Measurement of the mixture is best achieved with a wide band lambda meter. An exhaust gas analyser may be used, but tend to have a slow response time (although they are more accurate than lambda meters).

With forced induction the ideal mixture will be a richer under boost. Generally lambda 0.82-0.86 (air/fuel 12:1 ö 12.6:1) is suitable for a boosted engine. For engines with a detonation problem richer mixtures can be used.

Once the overall mixture is close to ideal, the fuel table should be adjusted to give an even mixture spread for each cam. The best way to do this is to select the whole of a table (ctrl+A), then apply a percentage adjustment to the table (J).

For stock engines often adjusting the injector multiplier and adjusting the high speed cam table will bring the mixture close to ideal. Otherwise it is best to select portions of the table by revs and adjust the mixture using the adjust function.

As a check as to whether the mixture is correct for full load and throttle two dyno runs can be made with 2% more and 2% less fuel. If the mixture is correct then there should be very little variation in power.

See tuning for boost and wideband tuning.

 

Tuning ignition timing

It is important to set the base ignition timing is a repeatable way before the ignition timing is altered. This is important as ignition timing will need to be reset of the intake camshaft timing is changed.

Like mixture, at first it is best to adjust the whole of the ignition table. With VTEC engines it is a good idea to do this for each cam separately. There are many strategies when tuning ignition timing, but one which works on a near-standard engine is to simply advance or retard the whole ignition table 2 degrees and perform a dyno run. If the torque curve moves upwards, keep adding or subtracting ignition timing until there are no power gains. If the torque curve moves downwards, then apply the opposite change to the ignition table. You should find a point where adding or subtracting 1-2 degrees timing will make very little difference to the torque curve.  You may want to find the centre of this point by performing a few runs either side of the point of maximum output. For naturally aspirated engines you can set the ignition timing at the most retarded position which gives maximum power.  For forced induction it is more difficult as the exhaust gas temperature and likelihood of detonation have to be considered.