S13 Silvia Tuning

Advancing the base ignition timing is a simple modification that can be done to almost any car. This is diffrent to adjusting the ignition timing in the ecu, which varies according to load and rpm, but it will affect it directly. Say at 4000 rpm at 100% load (open throttle) the mapping inside the ecu might electronically run the car at 18 degrees Before Top Dead Centre. If the base timing is forward 3 degrees, then the actual timing will be 21 degrees BTDC.

Advantages and Disadvantages

Advancing the timing has the effect of increasing the efficieny of the engine by optimising the timing of the spark. The further forward is set, the more power the engine will make, and responsiveness will also be improved. The danger however, is that the engine will be closer to detonation, which spells doom for any engine. Detonation is uncontrolled pre-ignition in the combustion chamber, where at least one additional flame front ignites with disasterous consequences. Most of the time this flame ignites too early and then collides with flame produced originating from the spark plug. The piston may stll be travelling up the bore in its compression stage, and is suddenly met with the force of the flame fronts trying to push it downwards, leaving no where for it to travel. The result is the piston rattling from side to side, which after not too long has the nasty effect of smashing the rings on the piston. This will result in loss of compression and increased oil consumption, if the engine will run at all. Another cause of detonation is lean fuel mixtures, which raises cylinder temperatures dramatically. Detonation resulting from this can be intense enough to melt pistons.

It is obvious then that detonation must be avoided at all costs. The easiest form of identification is a metallic rattling sound that is not entirely consistant with engine rpm. It can be hard to hear whilst driving, as the many other sounds around may drown it out. Special microphones can be made for little cost that clip onto the engine block, and amplify the sound for the listener. Several designs are outlined on www.autospeed.com.au, one of which I made with the provided instructions. This is highly recommended for the safety of your engine.

It may seem daunting after reading about the severe impact of detonation, but good gains can be made if the process is performed careful. Two tips are to use the highest octane fuel available as this will increase the engines resistance to detonation, and to make little changes at a time until the final setting is known.

The Process

	Before you can ever think about checking the timing, you have to borrow or buy a timing light. These should be available from generic automotive stores such as Auto 1, Super Cheap Auto, Repco, etc. The unit pictured cost me around $50 and is a basic timing light. This is all that is required, so try and get the best value for your money.
	The base ignition timing is controlled by the distributor on the SR20DE. Other engines may be controlled by a Crank Angle sensor, which works on a similar principle. To simply check the timing neither will be needed to be altered, as you will be essentially taking a measurement. Timing is adjustable with both a distributor and a crank angle sensor by rotating the unit. To change the timing, the bolts holding the distributor to the engine need to be loosened. Not so loose the unit will move by itself, but just loose enough so that it will turn by hand. Note that base bolts are those requiredto be loosened, not the screws or bolts which hold on the distributor cap on. It should be obvious which is correct though, as the hole in which the bolt resides should be an arc, therefore allowing adjustment.
	Fitting the light is simple. Clip the positive and negative leads onto the battery terminals (left highlight), and put the last clip around the wire going to cylinder number one (right highlight). The inductive clip is often fragile, so take car. During use the timing light does not rest in position shown (centre highlight), this is just for illustrative purposes to show where to point the light. Before starting the car, don't forget to pull all wires out of the way of moving engine components.
	This picture shows where the timing light is to be pointed, as shown in the picture above. Inbetween the engine and the fan shroud is the spot on SR20 engines, and with better light than in the photo, you will be able to see pulleys. The marks will be on one of the belts or pulleys.
	Start the engine and make sure it is up to the correct operating temperature before measurement. All accessories should be off, including stereos, air conditioning and headlights. This is because the engine must be at its correct idle speed for the timing light to be accurate. A sticker like the one pictured may be found somewhere in the engine bay, and the ever important factory ignition timing setting. For the SR20DE it is 15 degrees BTDC.
	For the SR20DE, the timing marks are as pictured. Only the lines are visible, so this picture is a handle guide to the actual values of the lines. The second from left is coloured slightly yellow, but this may be hard to see. A fixed notch will protrude above the markings on one of the pulleys. Pull the trigger on the light to see the markings and read the timing setting.
	If you want to change the ignition timing, then you must turn of the engine and disconnect the Throttle Position Sensor. This will be the only wiring going into the throttle body, so it should be easy to spot, if not easy to access. Once it is diconnected, start the engine and make sure it is still up to temperature. You must rev the motor three times to above approximately 3000 rpm, which settles the computer for the change. Now with one hand on the loosened distributor, and the other working the timing light, turn the distributor slowly to see the timing change before your eyes. Once the desired setting is selected, turn off the engine, tighten the bolts and connect the TPS and then double check th timing again to make sure it hasn't moved. Repeat as needed to obtain the best setting. Done!

I personally advanced my ignition timing to 20 degrees BTDC, which has ran perfectly for months now. Please note that 98 octane unleaded petrol is now always needed for safety. I never struggle the car up hills in high gears either, some similar sympathy may be required. Seat of the pants impression is slightly increased abilty to rev, and a tad more throttle response. Considering the timing light is the only cost and be used on any car, and that the timing can be changed an infinite number of times, I feel the modification was worth while.

UPDATE!

After speaking with a friend I decided to further advance the ignition timing to 25 degrees BTDC. This sounds silly, but has been like this for a few thousand kilometres now without trouble, with varying weather as well. Seat of the pants impression is that the car has that little bit more pace up top, jut enough to warrant the settings to be permenant.