really bad knock all of a sudden
Japanese emissions testing is done while the vehicle is driven steady at 60km/h. If you look at the JDM exhaust mivec map, the cruise load area has high exhaust mivec retarding. I am almost certain that this mivec map was designed specifically for emissions testing. In the higher RPM range, they also use some exhaust mivec retarding and this was probably done for protection in the high RPM/load areas.
Last edited by SiC; Feb 8, 2010 at 01:56 PM.
Newbie
Joined: Oct 2008
Posts: 55
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From: Houston
I think your missing what I am getting at and there are some flaws in your reasoning there. With aggressive MIVEC you can push fuel out of the cylinders and into the turbine housing, which is typically running temperatures of 1700*F. The flash point of gasoline is -40*F with an (auto ignition) temperature of 475*F. Since you just swept it through the motor with your clean incoming air it has perfect levels for ignition.
So effectively your motor is burning off the air fuel mixture that is measured but only part of it is in the chamber, and whats left in there is lean.
So effectively your motor is burning off the air fuel mixture that is measured but only part of it is in the chamber, and whats left in there is lean.
I was thinking about this today while working on some stuff, and while your theory on this phenominon is sound, in order for this to occur you'd have to have at least a 1:1 pressure differential across the head or better. Basically your backpressure would have to be low enough that the boost and fuel could actually make its way OUT the exhaust. I can garuntee you these motors/turbos in stock form have loads of backpressure, not only from a common sence observation but even from the fact that they move the exhuast cam to achieve EGR like results.
This means even when not in boost the exhaust pressure is great enough to revert back into the cylinder with only a few degree of exhaust retard, imagine how much more pressure there is when you have an exhaust expansion ratio relative to 20PSI of boost pressure and higher RPMs on these tiny turbine housings.. I seriously doubt you are pushing raw fuel into the turbo... I feel pretty sure that the extra knock is from cylinder contamination with those hot spent gasses causing a higher potential for knock..
In your example, you'd have 1700deg exhaust gasses reverting back into the cylinder, that seems to be a more likely cause for increased knock with aggressive mivec mapping.
I'm not saying this IS the anser, but I feel its much more likely with this particular setup. I will still test this theory though, both on a simular to stockish evo and on a really free flowing setup..
I was thinking about this today while working on some stuff, and while your theory on this phenominon is sound, in order for this to occur you'd have to have at least a 1:1 pressure differential across the head or better. Basically your backpressure would have to be low enough that the boost and fuel could actually make its way OUT the exhaust. I can garuntee you these motors/turbos in stock form have loads of backpressure, not only from a common sence observation but even from the fact that they move the exhuast cam to achieve EGR like results.
This means even when not in boost the exhaust pressure is great enough to revert back into the cylinder with only a few degree of exhaust retard, imagine how much more pressure there is when you have an exhaust expansion ratio relative to 20PSI of boost pressure and higher RPMs on these tiny turbine housings.. I seriously doubt you are pushing raw fuel into the turbo... I feel pretty sure that the extra knock is from cylinder contamination with those hot spent gasses causing a higher potential for knock..
In your example, you'd have 1700deg exhaust gasses reverting back into the cylinder, that seems to be a more likely cause for increased knock with aggressive mivec mapping.
I'm not saying this IS the anser, but I feel its much more likely with this particular setup. I will still test this theory though, both on a simular to stockish evo and on a really free flowing setup..
This means even when not in boost the exhaust pressure is great enough to revert back into the cylinder with only a few degree of exhaust retard, imagine how much more pressure there is when you have an exhaust expansion ratio relative to 20PSI of boost pressure and higher RPMs on these tiny turbine housings.. I seriously doubt you are pushing raw fuel into the turbo... I feel pretty sure that the extra knock is from cylinder contamination with those hot spent gasses causing a higher potential for knock..
In your example, you'd have 1700deg exhaust gasses reverting back into the cylinder, that seems to be a more likely cause for increased knock with aggressive mivec mapping.
I'm not saying this IS the anser, but I feel its much more likely with this particular setup. I will still test this theory though, both on a simular to stockish evo and on a really free flowing setup..
I don't notice there is more knock with aggressive MIVEC. I notice that the AFR's lean out more... But even if they lean out lets say to 13's there is no knock... just a lean AFR and a higher PSI (i.e. 26 PSI, 13 AFR, 0 knock)... then the AFR's jump to the correct set AFR. In my case about 11.8-12 AFR on the wideband.
Newbie
Joined: Oct 2008
Posts: 55
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From: Houston
it was kinda in anser to this question and somewhat the other guys statement about fuel going out the exhaust. sorry I usually type in a rush or on my phone and my explinations get sorta jumbled.. haha yeah I re read it all and I kinda mixed up stuff, but the theory still applies in general..
Thread Starter
Joined: Feb 2007
Posts: 9,486
Likes: 67
From: Melbourne, Australia
Your exhaust is ONLY the lookup from #2 table.. so under coldstart it will be wrong.
But yes - both are targets, rather than actual.
