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microsquirt trans tuning advice/experience for a newb?

740atl

740atl

Gear acquisition syndrome
Joined
Apr 17, 2010
Location
USA
Preliminaries... I have a 4r70w from a 2000 v6 stang installed behind a 302w in a 242. The engine is currently being controlled by a megasquirt 2 extra system.

drumroll.. sitting next to the car is an uninstalled microsquirt v3 whose purpose in life is to control said 4r70w.

I'm hopeful to have it wired up in the next week but I have never "tuned" a transmission before.

Anyone out there have relevant transmission tuning experience? I'm looking at the tunerstudio configuration page now and there's quite a few blank windows. I downloaded someone else's tune file from msextraforums but still have questions...

The Questions

  1. How do I go about setting up a shift curve? Just copy/paste what someone else has and roll with it?
  2. How do I know what line pressure curve that the transmission needs? This is a mostly street car (maybe 250hp) that will very rarely see the strip.
  3. What are recommended lockup settings for the converter?
  4. I get tuning air fuel ratios and VE bins, but what exactly am I looking for when I am logging data from the microsquirt?

I suppose I'll have more questions once the thing is running but any pointers/advice beforehand will be appreciated.
 
it's a lot more feel in this case than science as it is with an engine. with line pressure, until you can get definitive data from someone about that specific model of transmission, I'd leave it on the high side but not so high that part throttle shifts are violent (here comes the feel part lol).
As far as when to shift at what throttle position vs speed, feel.

lockup? if the converter clutch is stout and you've got enough line pressure in it (start high and work backwards, not the other way around), you can probably leave it locked up in higher gears to 60-70% throttle. Unless you know for sure, I wouldn't leave it locked up at WOT (or, work your way up to that point)

since you can link the two ecu's via CAN, set up a timing retard on shift if ms2 supports this, and make sure it's active long enough to cover the entire shift. should be able to determine that with data logs.
 
Awesome! Thanks Kenny! Looking forward to getting it running.
 
does anyone know if there's any math/log channels for slip? this would be useful for line pressure adjustment
does the ms2 trans software calculate trans input RPM from engine rpm and do you have some sort of driveshaft or wheelspeed sensor? does the 4r have a converter tooth sensor like the 4l80 and so on
 
I don't know off hand if they have a slip % to pressure table (it's been a while since I've updated or even looked at mine), but it will log the slip difference.
 
Ok... been about a year and finally got this heap running... turns out the microsquirt TCU needed dedicated 12v and not 12v switched and it was giving me all kinds of config errors.... I was powering the TCU from the megasquirt "fuel pump relay" instead of the main relay... duh... It didn't help that my laptop at the time as crapping out and was periodically corrupting my msq's. Such is life.

Took me a while to figure out the shift curve... I was using the stock curves which was putting me into overdrive by 20mph... Car never felt right until I actually read the manual and figured out how the shift curves worked, but not before I uploaded someone else's shift curves and figured it out.

At any rate, now this heap is running... I freaking love the transmission control features, but... have two... three main questions.

1. what is the difference between RPM-based up-shifting and well, not RPM based upshifting? Y'all know the manual was written by engineers and not literature majors... can't quite make out what this means and I haven't found clues in MSEXTRA forums... Does RPM based upshifting use the shift curves as shown to the right or does it negate them and solely rely on RPM? I currently have it set to RPM based but it just feels funky in WOT shifting. I am going to turn it off and try again but wanted a little advice before I do.

My hunch is that it will use the shift curves up until a given TPS percentage, then it changes over to RPM ONLY to judge the shift point... sound about right?
1690470072707.png

2. I have a shift delay of anywhere between exactly 0.4 seconds and exactly 0.466 seconds between when the shift is commanded and when it actually happens.. This is shown in the 2nd image... is this normal? Can I reduce it? It doesn't seem to be causing any problems... just noticing it's happening. In this image, I'm in 3rd gear, let off the throttle which induces the shift to 4th gear, but it takes 0.4 seconds for that gear change to occur.... it's not like the transmission is slipping, else I'd expect to see the RPM's shoot up... which... they're not.

I don't have any shift delays programmed... except for the stock shift delays in the 3rd image below.

1690469326077.png1690469976572.png


3. How well does (should?) VSS speed match up with the actual vehicle speed...
Many thanks.
 

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Ok... disabling RPM based shifting was the key... it followed the shift curve exactly.

How much shift retard is necessary? I am pulling up to 6 degrees at 100% load. Is the shift retard only necessary under WOT shifts or is it important under part throttle shifting as well?
 
It really depends on the amount of engine torque that must be reduced to help with unloading the "stack" to reduce friction on shifts/loading/unloading (if I think about this correctly in this way, I don't typically work with automatic transmissions) . there is no real way to quantify that in terms of basic offsets of ignition since there's no relation to actual engine torque on MS (unless you do maths).

Thinking about it that way may help quantification in that relationship. that being said, I typically reduce 200NM of torque (in a lower power engine) in a DCT application (timing reduction and fuel/spark interruption). I use math channels to show exactly how much torque is reduced by way of fuel calculations in the Maxxecu fuel model. Note: Constant A is theoretical maximum torque at atmospheric pressure, Constant D just turns VE into a percentage

Something like that looks like:

1691432267329.png

So using MLV, you could do some math channels to show how much power your engine makes (via VE and fuel calculations) and then compare to engine torque output with reduced timing (just by playing with the amount of timing reduced on a shift, or by using cuts) and it should give you a decently close figure to work with. I might also do some time measurements on the transmission side to see how long it takes to shift, any slippage that occurs, ect. (I don't work with MLV much anymore, but I think everything is there to be able to do it)

the obvious idea is safety and not frying things internally, so I really don't have any personal issues with going as soft on the shift as possible within reason.

I hope this helps!
 
WillettRun? said:
what transmission are you thinking of running?
Click to expand...
I was thinking of a ZF 4HP24, still have to find out if it will fit though. Should be a relatively cheap and easy swap. I made a thread about it:

Swapping a ZF22 automatic into a 240

This may be an unusual one... But would it be possible to swap the ZF22 automatic from a 740 into a 240? Do they use the same driveshaft as the AW7x automatics? And what about trans crossmember? It seems that the Volvo 740 used a ZF 4HP22 gearbox in some models. Later on, ZF produced a 4HP24...
turbobricks.com turbobricks.com
 
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