Timing and... - Diesel Truck Forum - TheDieselGarage.com
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post #1 of 6 (permalink) Old 02-13-2007, 07:46 PM Thread Starter
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Timing and...

Optimized timing is that which results in the most fuel combustion energy being delivered to the crank in the form of rotational torque, and ultimately to the wheels. It is where our 35% engine efficiency comes from at WOT. (2/3rds of fuel running through the motor is wasted heat.)

I have been doing some research and it seems we often overadvance our tuning.

Timing and boost. Adding boost, speeds up the flame front, so timing must be retarted to prevent that coveted efficiency from going south.

Timing and IAT. Same thing

just starting a discussion thread. The moment you jump off the 5 second dyno, everything changes. Intake charge might be 100 degrees for a race launch, but after 5 minutes towing up a grade, 200 degrees. Yet no timing change. Add the increasing cyl head temp. Fuel with increased Cetane. Dry environments, even a free flowing exhaust. All these factors add to the requirement to retard for optimization.

I just seem to have it stuck in my head, advance is possibly overused, particularly when dyno tuning.

Timing and ....

Michael
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post #2 of 6 (permalink) Old 02-17-2007, 05:24 AM
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Where did you get your info that warm air advances timing? It is very much the opposite. That is the reason for a pilot injection pulse. That warms the air and makes the fuel/air mixture less volatile. The mixture starts to burn sooner and lasts longer with warm air.

In Lehman's terms, increasing boost increases the compression ratio. These motors are compression ignition.....you get the idea.


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post #3 of 6 (permalink) Old 02-17-2007, 01:04 PM Thread Starter
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I think we agree Bob. My terminology may have been poor.

-Increasing IAT has the effect of advancing ignition.
-Increasing boost has the effect of advancing ignition
-The pilot injection pulse permits the main charge to be retarded, when optimizing timing

Diesel or otherwise. Better?

Michael
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post #4 of 6 (permalink) Old 02-17-2007, 01:07 PM
 
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pilot inj is for noise reduction, multiple small shots to quiet down combustion process, so it does not sound like a 24v isb cummins.by the way our trucks turn off the pilot inj when its revved above 25-2600 rpm because of federal mandated emmisions it does not pass at those rpms with pilot inj on.
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post #5 of 6 (permalink) Old 02-17-2007, 03:06 PM Thread Starter
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Quote:
Originally Posted by dmaxvaz
pilot inj is for noise reduction,
true, as well as nox production, but pilot inj has an impact on timing optimization. Pilot inj reduces main ignition delay, requiring the tuner to retard timing for optimization.

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post #6 of 6 (permalink) Old 02-17-2007, 04:33 PM Thread Starter
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Timing and...coolant temperature

ECT is more or less, engine temperature. If engine temperature increases, say from 190 to 230, this has an impact on final charge temp. So we would need to retard timing as ECT increases, to maintain optimized timing.

Michael
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04.5 GMC 2500HD SRW LLY

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