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Marc Haibeck · 10-20-2019

Yes Dominic, the spark advance is retarded by 1 degree when the air horn is at 89 degrees F. And -3 degrees when the air horn is at 110 degrees F. This can take the edge off power on the dyno or at the drag strip. At peak power one degree of spark advance can change the HP by 10 on a 500 hp engine.

To avoid this loss, the table can modified. I recommend relocating the Manifold Air Temperature sensor out in front of the radiator to avoid the negative effect.

When the sensor is relocated the table values are a good feature. I think that it is good for engine safety to retard the timing when the ambient air is 90 degrees or more.

Long ago someone from GM told the group at the Gathering in BG that the sensor was placed in the compromised location to satisfy a requirement to be able to test the engine with all of the sensors that will be used with that engine. Rather than rely on a sensor located on the chassis that is installed at a different time and place.

10-20-2019	#30
Marc Haibeck Join Date: May 2007 Location: Addison IL Posts: 252	Re: Knock. A question for Graham or Marc Yes Dominic, the spark advance is retarded by 1 degree when the air horn is at 89 degrees F. And -3 degrees when the air horn is at 110 degrees F. This can take the edge off power on the dyno or at the drag strip. At peak power one degree of spark advance can change the HP by 10 on a 500 hp engine. To avoid this loss, the table can modified. I recommend relocating the Manifold Air Temperature sensor out in front of the radiator to avoid the negative effect. When the sensor is relocated the table values are a good feature. I think that it is good for engine safety to retard the timing when the ambient air is 90 degrees or more. Long ago someone from GM told the group at the Gathering in BG that the sensor was placed in the compromised location to satisfy a requirement to be able to test the engine with all of the sensors that will be used with that engine. Rather than rely on a sensor located on the chassis that is installed at a different time and place.