Adjusting Ignition Timing on an SR20DE
Overview
Ignition Timing refers to the point at which a spark plug fires in relation
to when the mixture is released into the cylinder.
Small gains in power and fuel economy can sometimes be gained by adjusting the
timing. Advancing the timing means inducing the spark earlier, thus extending
the period for which the mixture burns in the cylinder.
Standard SR20DEs in Australia are set to 15* BTDC (Before Top Dead Centre)
TDC is highest point that the piston will travel up in the cylinder.
Theoretically, maximum power and fuel economy is achieved by advancing the
timing as far as possible before the engine starts to detonate or ‘ping’.
The timing can be advanced from 16* anywhere up to 26* or more before detonation
sets in. Unfortunately this point can vary greatly and is influenced by
various factors, including fuel quality, fuel octane levels, intake pressure,
intake temperature and air-fuel ratio.
Detonation
can cause serious engine damage!
Pinging is most likely to be heard while accelerating at low revs. It comes
in the form of a metallic tapping sound and is sometimes accompanied by engine
shudder. If you hear you engine start to ping, get your foot off the throttle
immediately!
If you have advanced your timing and you want to provoke detonation, find a
gentle uphill slope on a quiet road and turn off your air-conditioning, fans and
stereo. Accelerating from around 30km/h in 4th gear (1250rpm) should
induce detonation if your timing is advanced too far.
Adjusting your timing
- Borrow or preferably buy a timing light ($40-$50 from Repco or Supercheap).
- Ensure the engine is warm and all components - air con/radio etc are OFF.
- Connect the red and black clips to your battery, and the 'read' lead to
the cylinder one spark plug lead. (Closest to driver’s side).
Be careful, some components will be very hot to touch.
- Disconnect the TPS (Throttle Position Sensor). This is a brown plug
located on the side of the throttle body - passenger side of the engine,
behind the intake. You’ll need to squeeze it a bit (it has a clip release
on the back)
- Start the car, rev it three times past 3000rpm. This should lock the
timing. Release your foot. If it insists on stalling get someone to hold the
pedal down a bit to keep the revs at 700-800 rpm.
- Point the timing light at the crank pulley and squeeze the trigger... the
light will flash very quickly - once per revolution – around 13 times
every second.
The crank pulley will almost appear to be stationary and you will be able to
see the timing marks and the pointer. The pointer should be inline with the 15* mark when it flashes.
The SR20DE crank pulley has small paint filled indentions along the rim as
follows:
| Marks |
| |
| |
| |
Front of car -> |
| Corresponding Figure: |
10* |
15* |
20* |
|
The N15 marks are nice and clear.
The N14 has an extra marker at around 13*.
There is a pointer extending off the block, this should be inline with the
15* mark. This picture shows an N15 crank pulley with timing marks and pointer (Set
to 18*)
- To advance the timing, loosen the bolts on the distributor mount (refer to
first picture) and turn it a few millimetres towards the back of the engine.
- Now go back and check the timing - the pointer should be closer to (or
past) the 20* marker.
- Have a play around until the marker is half way between the 20* and the
15* mark and then tighten the bolts again, recheck timing to make sure it
hasn't moved. Your timing is now set to 17.5*. This should be a fairly safe
level if you are running premium unleaded fuel.
- Turn off the engine, reconnect the TPS.
- Road test your car, listening for any hint of detonation.
You may need anywhere between 15* and 22* (on 98ron fuel only!) to be best
for your car. Timing adjustment may have implications on your factory warranty.
It’s meant to be checked at every service, so always reset it to 15* prior
to dropping your car off if you don’t want to be logged.
This article is a meant as guide only, any engine adjustments are done so at
your own risk.
Joe Perich.
