Where does mivec come on anyway?
Aug 21, 2009, 06:05 AM
#1
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Where does mivec come on anyway?
I've always been told mivec engages at 2500 rpm. I haven't found the mivec routine in the stock ECU code yet, nor have I really looked hard. While tuning a car with the RPW cam in it I believe that mivec actually comes on at 3500. Has anyone ever really looked into this? It's not exactly like a honda where VTAAAK engagement is really evident!
-Michael
-Michael
Aug 21, 2009, 06:27 AM
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It is my understanding that in the 2004 and 2005 models, mivec engages at 3500rpms, and in the 2006 model at around 4000 to conserve some fuel at lower rpms.
Imma have a quick look in the service manual too just for ****s and giggles.
Imma have a quick look in the service manual too just for ****s and giggles.
Aug 21, 2009, 06:29 AM
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Oh, actually, when mivec kicks in, I can feel it. When accelerating at medium throttle through 3500rpms, there's a sudden kick and increase in acceleration. Feels like you're stepping on the throttle more, even though the foot hasnt moved.
Aug 27, 2009, 07:07 AM
#6
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I spent a few hours looking at the mivec routine. On the '05 rom I'm looking at the mivec engagement at WOT is 3500 but as you give it less throttle it engages later. This is similar to hondas and vtack! I set up an indicator and was able to get to 5000 with light throttle before mivec came on.
Just another interesting point and yet more fun for the piggyback boys. The fuel maps are different for mivec and non-mivec. I haven't looked at the timing maps in a bit so I can't remember if there are 4 timing maps or 2 plus adjustment maps.
-Michael
Just another interesting point and yet more fun for the piggyback boys. The fuel maps are different for mivec and non-mivec. I haven't looked at the timing maps in a bit so I can't remember if there are 4 timing maps or 2 plus adjustment maps.
-Michael
Aug 27, 2009, 04:52 PM
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I also believe it's when the oil pressure in the head/mivec channels reaches 46psi, it's at that point there is enough pressure to engage the upper lobes.
Possibly why mivec seems to be a smoother transition whereas vtec is a little different in the way it engages - there are pins that engage different rockers that align to the bigger vtec lobe.
Edit: there is an ages old YouTube vid that shows the mechanical differences of vtec, mivec, and vvti too.
Possibly why mivec seems to be a smoother transition whereas vtec is a little different in the way it engages - there are pins that engage different rockers that align to the bigger vtec lobe.
Edit: there is an ages old YouTube vid that shows the mechanical differences of vtec, mivec, and vvti too.
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Aug 31, 2009, 07:01 AM
#9
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Yes, the part I'm working on is the routine in the ECU that engages that solenoid and the sensors and values needed before that happens. Oil pressure is RPM dependant, not load dependant so obviously the computer considers a few things before engaging.
-Michael
-Michael
Sep 1, 2009, 01:46 AM
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so i guess its 3,500 if that what ur all saying i had the understanding it was 3,700 and also why is it vtec somes in so suddenly and you can clearly note the change wear mivec you can hardly tell? is there any way to change this hackish in your tune? so that it comes on suddenly?
Sep 1, 2009, 07:21 AM
#11
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No Joey, it comes on at some point between 3500 and 5000 depending on how much throttle you're giving it. I am going to hook up a light to be sure but I'm fairly certain that's what's going on.
You don't want it to come on abruptly. Even on a honda vtec that's a sign that they've set the wrong engagement point. When I tune I aim to make the engagement silky smooth because it means the torque output on each cam is matching up with the next. Too soon and you drop torque, too late and you have a sudden jump. For performance you want the most average torque so that means picking a point where the two cams match up well. I haven't had the time lately to play with the mivec routine and find the settings exactly but so far I haven't found a car that really needed the mivec point changed.
-Michael
You don't want it to come on abruptly. Even on a honda vtec that's a sign that they've set the wrong engagement point. When I tune I aim to make the engagement silky smooth because it means the torque output on each cam is matching up with the next. Too soon and you drop torque, too late and you have a sudden jump. For performance you want the most average torque so that means picking a point where the two cams match up well. I haven't had the time lately to play with the mivec routine and find the settings exactly but so far I haven't found a car that really needed the mivec point changed.
-Michael
Sep 5, 2009, 10:38 AM
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This is interesing reading. I bought my car recently, used from mitsu dealership and the salesman told me mivec kicks in at about 3000, but we all know they dont know what their talking about lol.
Oct 1, 2009, 03:58 PM
#14
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Small update on this issue.
I've moved from testing the results with a test light to changing the routines in the code.
'04 engages at 3600 disengages at 3400
'06 engages at 4400 disengages at 4200
Earlier testing I did with the throttle position turns out to be incorrect the indicator I was relying on was feeling it in throttle response and that was a side effect of something else I was testing.
Mivec also seems to want 10C engine temp in order to work but I haven't been able to test this yet.
-Michael
I've moved from testing the results with a test light to changing the routines in the code.
'04 engages at 3600 disengages at 3400
'06 engages at 4400 disengages at 4200
Earlier testing I did with the throttle position turns out to be incorrect the indicator I was relying on was feeling it in throttle response and that was a side effect of something else I was testing.
Mivec also seems to want 10C engine temp in order to work but I haven't been able to test this yet.
-Michael
