Shift points too low?
10-25-2012, 10:09 PM
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Shift points too low? Had a friend rebuild the 4l60e at his shop (1yr warranty)
Today he calls me and tells me she's ready and that at WOT she shifts right at 6k...Isn't that a little too low, for my mods?
Today he calls me and tells me she's ready and that at WOT she shifts right at 6k...Isn't that a little too low, for my mods?
10-25-2012, 10:13 PM
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Thinking about manual shifting her on race nights 'til i can either buy a Diablo predator or a custom tune, there shouldn't be any probs doing so? Wondering at which rpms (+/-) i have to upshift to the next gear so she wont bounce of the limiter, or if its a shot in the dark and unknown how the pcm would handle the delay?? Rev limiter is around 7k so i know the tune needs tweaking as far as shift points go...
Last edited by PaSteLaSo4U; 10-25-2012 at 10:23 PM.
10-28-2012, 10:57 PM
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With that converter and gear, manual shifting could bounce the limiter, even if you try to time it precisely. Let the computer do the work, but be conservative. Don't expect it to shift at exactly the way it's programmed. So pick a number, dial it back and run it on the track. If you can record it on video or datalog, measure the difference between the tune and actual. Then adjust closer to where you want.
Here's some food for thought:
Copied right off of Frank's post from Performabuilt
"Bear in mind that while the shift may be commanded at 5100 it could indeed take to 6200 for the trans to make the shift . You see while the electronics are instant hydraulics are not and several things come into play.
One thing is a constant at WOT it always takes the same amount of time for the trans to complete the shift. This time will of course vary from trans to trans depending on condition, Shift kit set up. Line presure.
What does change is the rate the RPM are climbing under various conditions. These numbers are off but bear with me.
Lets say it takes 1 second to complete a shift from 1-2 and at 340 hp NA the RPM climb 300. Ok same time period at 600 hp the rpm might climb 600 RPM during the same period. Other variables would be for instance gear ratio and engine with 4.10 gears behind it is going to climb in RPM much faster that lets say a 3.23 would so then again you might have another 300 or more increase in the RPM during the same time frame between the two gears.I think this is why many times you hear of people boucing limiter after going to lower gears even though they did set up the PCM for the gear change. They failed to compensate for the RPM rate increase. With the stock converter and stock power the PCM can adapt but once you get outside those it cannot do so on its own. Add a shot and the RPM rate increases again even though the time for the trans to shift is still a constant.
I think this is why you hear so many people talk about bouncing the rev after mods they changed something wether it be power or gearing that changes the rate of the rise and fail to realize that all of these things have to be compensated for. Its not as simple as I want it to shift at 6000 rpm and set it that way because to acheive and actual shift at 6000 RPM where you would actually have to command the shift would be different for virtually any mods you make that can affect the rate the RPM rise during the shift.
So realistically every car would be different depending on the POWER/GEAR RATIO/SPRAY.
Then a converter with a high stall is still a further complication and the RPM due to the slip in the converter may be higher that expected for the MPH and this again would vary again with the addition of power adders such as Nitrous or even rear end would affect this too.
So the conclusion I have come to is there can be no one size fits all when it comes to tuning for shifts it would be unique to each set up. A car with 4.10 might take 500-800 or whatever to complete and shift and a 2.73 car might do it in 200-400 and power adders change these numbers around more. So its kinda a trial and error system I would conclude would have to be used.
Also you have to beware looking at the shift completion times with the 4l6x units since the PCM uses the engine rpm verse output speed to determine when the shift did happen and with a stall these numbers can be way off so are useless. The exception would be the late 4lxx with the input speed senor 07 up with these you would get a true time since the converter is not part of the equation.This would be true of the 4l80e also since it does have input speed sensor.
Ramble over lol "
Here's some food for thought:
Copied right off of Frank's post from Performabuilt
"Bear in mind that while the shift may be commanded at 5100 it could indeed take to 6200 for the trans to make the shift . You see while the electronics are instant hydraulics are not and several things come into play.
One thing is a constant at WOT it always takes the same amount of time for the trans to complete the shift. This time will of course vary from trans to trans depending on condition, Shift kit set up. Line presure.
What does change is the rate the RPM are climbing under various conditions. These numbers are off but bear with me.
Lets say it takes 1 second to complete a shift from 1-2 and at 340 hp NA the RPM climb 300. Ok same time period at 600 hp the rpm might climb 600 RPM during the same period. Other variables would be for instance gear ratio and engine with 4.10 gears behind it is going to climb in RPM much faster that lets say a 3.23 would so then again you might have another 300 or more increase in the RPM during the same time frame between the two gears.I think this is why many times you hear of people boucing limiter after going to lower gears even though they did set up the PCM for the gear change. They failed to compensate for the RPM rate increase. With the stock converter and stock power the PCM can adapt but once you get outside those it cannot do so on its own. Add a shot and the RPM rate increases again even though the time for the trans to shift is still a constant.
I think this is why you hear so many people talk about bouncing the rev after mods they changed something wether it be power or gearing that changes the rate of the rise and fail to realize that all of these things have to be compensated for. Its not as simple as I want it to shift at 6000 rpm and set it that way because to acheive and actual shift at 6000 RPM where you would actually have to command the shift would be different for virtually any mods you make that can affect the rate the RPM rise during the shift.
So realistically every car would be different depending on the POWER/GEAR RATIO/SPRAY.
Then a converter with a high stall is still a further complication and the RPM due to the slip in the converter may be higher that expected for the MPH and this again would vary again with the addition of power adders such as Nitrous or even rear end would affect this too.
So the conclusion I have come to is there can be no one size fits all when it comes to tuning for shifts it would be unique to each set up. A car with 4.10 might take 500-800 or whatever to complete and shift and a 2.73 car might do it in 200-400 and power adders change these numbers around more. So its kinda a trial and error system I would conclude would have to be used.
Also you have to beware looking at the shift completion times with the 4l6x units since the PCM uses the engine rpm verse output speed to determine when the shift did happen and with a stall these numbers can be way off so are useless. The exception would be the late 4lxx with the input speed senor 07 up with these you would get a true time since the converter is not part of the equation.This would be true of the 4l80e also since it does have input speed sensor.
Ramble over lol "
