Flatshit on H-pattern synchro gearbox

V3 SOFTWARE
1

Hi,

I’m setting up a flatshift for an H-pattern synchro gearbox. The built-in Flatshift torque cut is a bit too abrupt for my use case because torque returns instantly after the shift. To get a gentler recovery I’m working in the “Gear shifts” section instead.

Problem:
To let RPM drop while the clutch is pressed, I need around 90% ignition cut. That gets the revs down, but it also dumps too much fuel and creates very aggressive exhaust bangs. I use ignition cut because fuel cut feels laggy/weird. I have tried setting second rev limiter to fuel cut, changing rpm limit to something like 4500 and switching to it when gear shift is in progress but it didn’t synchronize well, it switched on couple ms too late and then when limiter switched back to my default one (ignition cut), rpm limit stayed on 4500 for another couple ms, and it was a mess.

What I’d like to do:
Start the shift with a short bot fuel and ignition cut to pull torque and drop RPM cleanly, then restore fuel and set lower ignition cut (~60%) and taper down gradually. The goal is to drop enough rpm, keep gentle pops to preserved spool and have a smooth reintroduction of torque for a synchro box.

Is there a possibility to be able to control fuel and ignition cut simultaneously? Having two “Torque reduction - cut [%]” tables would be perfect.

If this is already doable with existing feature set, I’d really appreciate a pointer to the correct setup. I can share logs and my current Gearshifts settings if helpful.

2

Sorry for putting you on the spot @Jadzwin_ECUMASTER but maybe you only check new software version threads :]

3

There should be ignition restore rate and ignition angle at exit to get always the same result. Then the restoring of torque should be smooth

4

I think it is in ALS section, but I am talking about Gear Shifts. The point is I want to achieve simultaneous ignition and fuel cut at the start of gear shift but with workaround that I have come up with it works wonky. I think the problem is that functions are processed with too low frequency, and as seen in the picture fuel cut starts too late.

flatshift ign fuel cut workaround
flatshift ign fuel cut workaround1544×222 8.8 KB

5

In the previous mail I wrote what I will add :slight_smile: I will check why the fuel is cut with such delay.

6

What input did you assigned for flat shift activation input ?

7

I used clutch pedal input

8

and what was assigned to clutch input ? emu switch input ?

9

I tried to open all the relevant settings in the screenshot

Screenshot 2025-10-18 at 00.03.19
Screenshot 2025-10-18 at 00.03.193004×1586 484 KB

10

The problem is that the functions operates withe the log channel frequency (25Hz / 40ms).

So the delay of function evaluation is 40ms what can be too high for gear cut.

You can use gear shift strategy instead.

11

As I wrote in the OP, I’m already using Gear Shifts. It’s that Gear Shifts can’t do a short simultaneous fuel+ign cut at the very start of the shift.

Without that, ~90% ign cut drops RPM but causes huge bangs from excess fuel. If I lower ign cut, RPM doesn’t fall fast enough for a synchro box.

I tried a function-based workaround, but as you noted functions run at ~25 Hz (~40 ms), so fuel cut comes late and the sequence gets messy.

What would solve it is the ability to start with fuel+ign cut for a brief window, then switch to ignition-only with a restore rate.

Would this be possible?

12

Actually it is not possible to cut fuel and ignition at the same time (there must by synch mechanism that the fuel and spark will be cut exactly for the same cylinder).

Right now you can try strong ingtion retard + fuel cut.