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No Device: Why Decrease Timing in High RPM Range???
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I have a question related to timing..In all the tunes that I've seen, what I don't understand is why do they decrease timing as MAP and RPM's go up.. Doesn't that leave power on the table? I know with any other motors like Evo's, Shovels even SBC's we've never decreased timing going up into the power band.. As far as 42* on my well built SBC's.. Why it's it different with fuel injected TC's.. Why are the timing curves decrease as MAP and RPM's go up
Depends on how you look at it. As rpm's go up, and kpa stays the same. So does timing. As kpa increases and rpm stays the same. Timing is taken away.
In the ideal world. We want the most pressure in the cylinder when crank is so many degrees past TDC. Let's use 15 degrees. This is decided by leverage of crank vs flywheel, crank angle. Flame front travel and AF burn is dependent on several things. Pressure is one of them. AFR is another. 50 KPA will have a different pressure at the same rpm as 100 kpa. Flame front will travel faster the higher the pressure. At the same time. The time the engine takes to rotate 40 degrees changes from 2000 to 5000 rpm. (I'll save typing out the math)
We have control when the burn starts but what we are really trying to do is control when or at what crank angle most pressure is created. Of course, this is perfect world. With a knock limited engines on pump gas. Sometimes knock occurs before hand and you can't get highest pressure at the best leverage. This limits power output.
Okay here's where I'm at with my PV-2b tune. I've been slowly trying to make changes both to timing tables, AFR's and VE's.. I'm closing in on a really good running bike.. My temperatures are coming down but I don't like my 2000 to 2200 rpm heat ranges at lower speeds 30 to 40 mph.. At 50-60 mph it's great but at lower speeds less air, less cooling, I don't like going up to 265* to 270*.. So what I did was, look at my timing tables in that range.. I lowered the timing a little bit. At 40* to 45° of timing at a light tip in is a hell of a lot of timing, to me.. So I knocked it down a little hoping it'll decrease temperatures in that range at lower speeds we'll see what happens... Gonna take it out in a little bit. Current OAT is 82*.
Well I'm finding out just how much the knock sensor is taking away timing up top.. I had to take away as much as 7° in the 90-100kpa range in the entire rpm range.. I guess the TC's don't like a lot. I've created a couple of tables as well as increased the front cylinder VE's. It appears the front cylinder is running a little hot.. got a new set of plugs and will do some days logging this next week to see if there's a difference.. Here's what the old plugs looked like.. The right is rear and looks pretty good.. The left of front and not so good.. to much heat and timing..
Hey Jamie (FuelMoto),.. I didn't do a couple of screenshots.. Anyways I did do 3 different data logs with 3 different tunes all within the same day and all at least 20 miles, same heat and riding conditions.. I am working on lowering the timing in cruise as well as WOT.. Yes it is a good thing that the ECM pickups on detonation.. I will find the right amount of timing and fuel, most likely in the next 3 tunes that I just readjusted.. And again I will data log all 3 tunes to see where I'm at with detonation.. It is my primary goal.. I will also add the bike screams... One more thing I would like to is lower the heat in the motor, I'm trying to tune to get that down as well.. So far the cruise range is awesome 237*-255* it's the slow speed low RPM that builds the heat and I'm still working on that...
Last edited by 98hotrodfatboy; Jun 27, 2022 at 08:17 PM.
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Why Decrease Timing in High RPM Range???
