Shift cut - tweaking settings
Posted: Fri Aug 28, 2020 2:20 pm
Hi All,
Was at a practice session this morning at Boyndie kart track - awesome to get back in the car after 11 months. To avoid just wasting fuel/tyres/engine-life going round and round, I decided to look at logging some high-speed gear change data (I also ran the car back-to-back sequential/batch - I'll do a sperate thread for that discussion!).
It was fantastic to get back behind the wheel and it all worked great and the engine pulls and sounds great. I'm still buzzing!
So, back to gear-changes; the settings I've been using over the past 2 seasons are fine - gives reliable gearchanges, but some changes are slower than others, and I get a bit of wheel-spin when the next gear engages. Either way, I am keen to see if I can improve things.
Attached are two screen-grabs from my logged data;
First shows a 2nd to 3rd gearchange.
The top pair is RPM (white trace) and gear (red trace)
The second box has; Ignition (white), gear-shift request (green), gear potentiometer voltage (red)
The second picture shows a 3rd to 4th change (all traces the same as first picture).
These two show a pretty good example of all the upchanges (1st to 2nd is paddock-only as I start in 2nd, and could only get into 5th once during the five sessions).
The traces show that after making the gearchange request (pull the paddle, in green), the gear-pot (mounted on the end of the barrel) moves slightly and stays like this for generally 70ms before making the large movent into the next gear. Now, when I look at the amount of ignition retard at the point the pot moves it's usually around 34 to 37 degrees for 2nd to 3rd, and around 45 for 3rd to 4th changes.
The ignition retard also ramps back in with two distinct slopes, for both gear changes.
Some questions / conclusions I've come up with;
a. I'm curently using a 65 degree ignition retard - the above examples show the ignition only needs to be retarded up to 45 degrees to allow the dogs to disengage; Does this mean I could reduce the 65 down to 45-50? The ignition then has less "distance" to recover when the next gear is engaged - does this imply the gearchange might be a tiny (tiny) amount quicker?
b. I've ticked the "Gear dependant settings" - is the "Retard after cut" column of numbers obsolete because I've also got "Ignition retard if not using cut" ticked?
c. The 70m delay whilst the gearpot waits for the ignition to retard enough to disengage the dogs; Does this imply the 100ms "shift cut delay" time I'm using is too long? I'm thinking it is, and should be reduced to try and eat into the 70ms lag?
d. The RPM jumps when the next gear is engaged - would I be right in thinking if I increase the "retard ramp in time" this may soften off the tyre chirp - OR, is the gear-dependant table's "Retard for ms 0-500ms" column in play? (And likewise increase this time)
I know this all sounds quite pedantic and fiddling for the sake of it, but I am keen to improve the gearchanges if they can be!
All comments welcome; Although I'm running a paddle-shift, I'm sure the same phylosophy should apply if you're shifting with a strain-gauge/gear lever setup so hopefully some of you have played with these settings and can offer some insight.
Cheers
Steve
Was at a practice session this morning at Boyndie kart track - awesome to get back in the car after 11 months. To avoid just wasting fuel/tyres/engine-life going round and round, I decided to look at logging some high-speed gear change data (I also ran the car back-to-back sequential/batch - I'll do a sperate thread for that discussion!).
It was fantastic to get back behind the wheel and it all worked great and the engine pulls and sounds great. I'm still buzzing!
So, back to gear-changes; the settings I've been using over the past 2 seasons are fine - gives reliable gearchanges, but some changes are slower than others, and I get a bit of wheel-spin when the next gear engages. Either way, I am keen to see if I can improve things.
Attached are two screen-grabs from my logged data;
First shows a 2nd to 3rd gearchange.
The second box has; Ignition (white), gear-shift request (green), gear potentiometer voltage (red)
The second picture shows a 3rd to 4th change (all traces the same as first picture).
The traces show that after making the gearchange request (pull the paddle, in green), the gear-pot (mounted on the end of the barrel) moves slightly and stays like this for generally 70ms before making the large movent into the next gear. Now, when I look at the amount of ignition retard at the point the pot moves it's usually around 34 to 37 degrees for 2nd to 3rd, and around 45 for 3rd to 4th changes.
The ignition retard also ramps back in with two distinct slopes, for both gear changes.
Some questions / conclusions I've come up with;
a. I'm curently using a 65 degree ignition retard - the above examples show the ignition only needs to be retarded up to 45 degrees to allow the dogs to disengage; Does this mean I could reduce the 65 down to 45-50? The ignition then has less "distance" to recover when the next gear is engaged - does this imply the gearchange might be a tiny (tiny) amount quicker?
b. I've ticked the "Gear dependant settings" - is the "Retard after cut" column of numbers obsolete because I've also got "Ignition retard if not using cut" ticked?
c. The 70m delay whilst the gearpot waits for the ignition to retard enough to disengage the dogs; Does this imply the 100ms "shift cut delay" time I'm using is too long? I'm thinking it is, and should be reduced to try and eat into the 70ms lag?
d. The RPM jumps when the next gear is engaged - would I be right in thinking if I increase the "retard ramp in time" this may soften off the tyre chirp - OR, is the gear-dependant table's "Retard for ms 0-500ms" column in play? (And likewise increase this time)
All comments welcome; Although I'm running a paddle-shift, I'm sure the same phylosophy should apply if you're shifting with a strain-gauge/gear lever setup so hopefully some of you have played with these settings and can offer some insight.
Cheers
Steve