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| slight warm up miss is back. https://www.slantsix.org/forum/viewtopic.php?t=25990 |
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| Author: | Sam Powell [ Tue Nov 27, 2007 6:27 pm ] |
| Post subject: | |
Quote: Oh, KEEP IN MIND: the Iron conducts heat less than aluminum so count on having much HOTTER combustion chambers while rest of head and coolant isn't warm enough to equalize the temps quickly enough. I have played with these Intake Port Temperature tables a little bit, and have gotten the engine to be less lean when restarted after driving and then sitting a short spell. It seems as if variance in the IPT was at least partly to blame for the variability of the AF ratio over time. When I came back out from a short stop off the IPT temp had gone up 20 degrees between the time I cut the engine off and restarted it, from 50 to 70. This made the mixture go from 14.8 to 16:1. On the lap top, I bumped up the IPTvs ET coefficient for that higher temp, and the AF ratio went back down to 14.8 where it was when I cut off the engine. AS delivered for a SBC configuration, the default curve for the IPT compensation starts with more fuel at cold IPT. Fuel was then reduced as the IPT approached 50 degrees, and was increased again as the temp went above 50 degrees. I suspect this basic idea is right, and that I need to just tweek this for proper AF ratio for a slant. So it seems emsvitil's genralization is correct up to a point, and then goes back the other way. The explanation I have heard is that once the temperature gets above a certain value, the air gets into the cylindar more easily. So even though is is less dense, more of it can pass through the valves, requiring more fuel. Very interesting. I am no expert here. Just reporting. And it seems to be born out by my experience today. I am certain this behavior effects carbs as well. And I am certain that this is why the engine , when it was carubureted ran poorly when exiting a highway after an hour or so cruise. The high volocity of the intake air at cruise kept the IPT down, and then when slowing down, the IPT went up at the first light, and the mixture would lean out. Sam |
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| Author: | Wizard [ Wed Nov 28, 2007 10:44 am ] |
| Post subject: | metal types of heads in coolant's point of view. |
Alum head tracks the coolant temps closer than iron/steel heads. Iron heads chambers get hotter quicker and coolant yet to get warm enough and effects the warm up curves of the mixture ratios in warm up phase. On carbed vehicles with heated plenum by coolant can screw up the drivablity due to mixture requirements not met and need bit of extra twreak to work around this. Intake of course needs heat especially for TBI and carb to keep mixture in suspension and is not the reason for the combustion processes IN the chambers. Port injection does not need that heated plenum. Note that air temperatures (density changes with temp, that why hot air balloons floats and cold air sinks causes room drafts, winds are the work of heat/cold that makes air move due to density differences) have effect on the fuel mixture ratios to some percentage. Alum transfers heat more efficiently means coolant get heated sooner than iron/steel do yet the iron/steel heads combustion chambers get hotter far sooner (heat transfer travels far more slower). Toss few grains of used coffee or tea in a glass pot or like (heat resistant) with water and set it on stove and heat up the water, you'll see water circulate in a pattern made visible by the grains. Cheers, Wizard |
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