coozer
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 posted on 9/4/09 at 06:38 PM |
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Megajolt Q
Been running round on a MJ map for nearly a year now with no apparent problems.
However now looking at my bin values max load (tps) at 7000rpm is 25 advance, yet shutting the throttle at these revs advance goes up to 45.
Is that right? Just looks the wrong way round to me...
Steve
1972 V8 Jago
1980 Z750
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smac
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| posted on 9/4/09 at 06:51 PM |
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Shouldnt advance increase on part / closed throttle as a partly filled cylinder burns slower and hence requires igniting sooner?
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smac
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| posted on 9/4/09 at 07:00 PM |
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Why vacuum advance on a dissy set up then?
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David Jenkins
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| posted on 9/4/09 at 07:04 PM |
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Think of it this way - when at high revs the piston is travelling much faster up the cylinder, so the mixture has to be ignited earlier so that the
pressure wave pushes on the top of the piston just as it's going over top-dead-centre.
When at low revs the piston is travelling much slower, so the mixture can be ignited much later to achieve the same result.
If you recalibrate the tps using the MJ config software it will soon tell you if you've got the wiring the wrong way around.
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smac
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| posted on 9/4/09 at 07:10 PM |
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I understand the revs issue: at higher piston speeds the burn takes the same amount of time and hence must be started earlier in the cycle.
My understanding ( and Ill happily be corrected) is that irrespective of the revs issue a closed or part throttle leads to less mixture in the
cylinder which because it is less dense takes longer to burn and requires more not less advance than a fully filed/full throttle cylinder state
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brianthemagical
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| posted on 9/4/09 at 07:13 PM |
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As above, the less dense mixture takes longer to burn as the flame front can't progogate as effectivley between the widely spaced fuel
particles.
Max advance will be in the bottom right of the map, minimum will be in the top left.
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mediabloke
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| posted on 9/4/09 at 07:43 PM |
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Which map are you running, Steve? I reckon the guys have already identified the cause, but it might be worth posting the map, so we can get a picture
as to where on the map MJ's getting the 45 degs from. Just a thought.
Francis.
[Edited on 9/4/09 by mediabloke]
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paulf
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| posted on 9/4/09 at 09:50 PM |
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It is working correctly, under full load it needs less advance to stop pre ignition.When under low load as with throttle shut and high revs then it
needs more advance to ignite the fuel as it is under less compression due to the cylinder only being partially filled.
This is the main advantage of 3D mapped ignition as it allows the engine to run at a higher efficency under light load conditions.
Paul
quote:
Originally posted by coozer
Been running round on a MJ map for nearly a year now with no apparent problems.
However now looking at my bin values max load (tps) at 7000rpm is 25 advance, yet shutting the throttle at these revs advance goes up to 45.
Is that right? Just looks the wrong way round to me...
Steve
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MikeRJ
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| posted on 10/4/09 at 01:29 PM |
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quote:
Originally posted by Paul TigerB6
Higher revs and higher loads require increased ignition advance.
Higher RPM = more advance
Higher load = less advance.
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