More timing makes the combustion process occur sooner, and will decrease exhaust temperature. It also
makes an engine idle smoother. NO
x
emissions will rise with too much timing.
With increasing RPM, the timing needs to be advanced for optimum power. This is a result of the
available time for combustion decreasing with increasing RPM. The peak cylinder pressure needs to occur
between 10 and 15 degrees after TDC compression for optimum power production, so the timing must be
tuned to allow this to happen. As a rule of thumb, engines with slow-burning (large) combustion chambers,
and/or low dynamic compression (low volumetric efficiency) typically need more timing advance, since the
flame front moves slowly. Engines with fast-burning (usually small) combustion chambers and/or high
dynamic compression ratios need less timing for optimum power, since the flame front moves faster.
Peak timing usually should occur by 3000 rpm on most engines. Load-dependent timing should
always be used, especially on turbo/supercharged engines. With increasing load (i.e. full-throttle or full-
boost), less timing is needed. With decreasing load (i.e. cruising), increased timing is needed.
Rotary engines (particularly the turbocharged rotaries) do not give the tuner a margin of error when
it comes to ignition timing. They will detonate ONE TIME only, and will then be broken. The apex seals
cannot stand up to the huge shockwave generated by detonation. Tune these engines extremely
conservatively!! Start with the least amount of timing possible and the most amount of fuel possible. A
huge power-to-weight advantage is present on the rotary turbo engines, but it will only come to a tuner who
is cautious and patient.
B.2. Establishing Proper Starting Enrichments
When setting up the Starting Enrichments, it is generally best to first use the default settings from
WinTec. If these settings cannot start your engine, there would only be two possible causes: either the
enrichments are not adding enough fuel, or they are flooding the engine with too much fuel. Flooded
engines are easy to spot, since there will be a strong fuel odor in the air around the engine. Alternatively,
the spark plugs can be removed to check for flooding. Flooded spark plugs will be wet with fuel when they
are removed. If an engine is not flooded but still will not start, it is most likely not getting enough fuel.
For engines that will not start when cold, look to SE0 (the Temperature-Based One Second Starting
Enrichment). If the engine is flooding out during cold starting, decrease this number. If this number is
already zeroed out, and the engine is flooding, look to SE1 (the Constant One Second Starting Enrichment).
If SE1 is too high, the engine will flood out during cold AND hot cranking, since its value is added
regardless of temperature. If both of these values are set very low, and the engine still floods during
starting, look to PW0 (the Fixed One Second Starting Pulse Width). Most engines will not need PW0, so it
is generally best to set this to zero. ASE-0 and ASE-1 can also contribute to a flooding problem. If these
values are set too high, there may be too much fuel present at cranking.
An injector that is stuck open can sometimes cause a scenario that can be confused with engine
flooding on start-up. An injector that is stuck open will spray fuel into its respective cylinder as long as
there is fuel pressure. This will fill a cylinder with fuel in short order and effectively lock the engine. The
starter motor won’t be able to turn the engine over, since an engine cannot compress liquid fuel very easily.
Placing a screwdriver on the side of the injector and listening for a clicking sound is a good way to pinpoint
a stuck injector. If the injector is not clicking, it is not opening and closing.
For engines that are not getting enough fuel on start-up, the procedure for tuning the Starting
Enrichments is basically the opposite of that outlined above. On cold engines that are not getting enough
fuel, check the SE0 parameter. If this value is not high enough, a cold engine will not get enough fuel to
start. Coinciding with this, an engine will also need SE1 to be properly established for proper starting.
SE1 has an effect on both hot and cold engines, since it is not temperature-dependent. Some engines may
need PW1 to provide an additional amount of fuel pulse width, particularly on cold starts (temperatures
below CLT0). However, this value is typically not needed for multi-port injection applications.
An injector that is stuck in the closed position can cause a scenario that can sometimes be confused
with a lack of fuel on start-up. The cylinder that is fed by the stuck injector will not be supplied with fuel,
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TECgt Manual Version 2.0
- Page 26 -
©2008 Electromotive, Inc.
