MoTeC Global Forum

If the engine on downshifts struggle to hit the calculated rpm before the shift is completed?
Where to look?

I have been testing and reading about it but still feel downshifts especially from 2 to 1 gear is not smooth.

Also. When I look in the gear timing settings, what is correct? You have all gears specified. And if I want to extend the timing from 2nd down to 1st, is it the settings related to first or second gear that’s controlling it?
When I check the logs. It looks like even if I’m targeting first gear from
Second it’s still the timings on the seconds that’s active? If so. Why does even first gear have settings for blip etc?

Also is there a blip setting that holds the blip active a little bit after the gear is engaged to smooth out the transition? Or is that not necessary if the engine reach the calculated target in time before the shift is finished.

Looking in my logs it seems like tbe calctilate target for a shift is about 4500 and the engine only reach about 4000 before the shift is done. Therefore it’s not as smooth as wanted.

I guess you can accomplish it in more than one way, but where would you more experienced tuners start off first?
My settings is about the same as in the motec help document.

I would add more Blip (Higher Throttle Aim in Downshift cases), and more Pre-Shift time -- then see what happens -- better, worse or the same?

If the pre shift is longer, would this make it tougher to get it out of gear?
If it messes up the timing to unload the dogs.
With cold gearbox it failed to downshift a few times. Haven’t noticed that before.

I hade a pre shift of 250ms now.

For sure need to test more with this. But it felt like the blips where a little longer.


If you are in 3rd gear and want to downshift to 2nd, is it still the settings for 3rd gear that controls the shift?

You really need to log all the relavent channels at the highest possible rate, and study the data. If you want help you will have to share it with those that help. Otherwise we can only provide general guidance.

If increasing Pre-Shift made it worse, then try making it shorter.

Doesn't sounds like mine was very useful. Good Luck!

The Gear Shift Timing table uses "Gear Shift Current" as the axis. The help for Gear Shift Current indicates this is the "Gear at the start of the shift".

As David has said, without any logging it's hard to advise on anything.



As covered in the help, you can see how the each phase of the shift implements various settings.

The goal of the Preshift is to generate negative torque to allow the dogs to unload, and to charge the inlet with air (which on a short runner ITB setup isn't a large volume, but it can quickly draw air from the plenum.) to allow for a crisp blip.

For this to all work correctly, you need to be running enough ignition cut or retard to minimise the engine making power during the blip. As you have an S54, I would avoid excessive cut if you plan on keeping the shims where they belong. If you are not doing enough in this regard, the engine will accelerate when the blip occurs. You do not want to use fuel cut however, as you will need the fuel film present to ensure the blip is works when the gear shift state changes to shift.

Depending on your actuator settings, your shift actuator is activated before the gear shift state changes to "shift". This is determined by the gear shift actuator timing.

Once the "shift" phase begins, the retard and cuts are removed, allowing the engine speed to increase, whilst if the timing for everything in the early stages is correct, the actuator should be helping the gearbox start engaging the next gear. If the engine does not increase in speed quickly (provided you don't have any filters on your pressure sensors) you can take a look at the lambda for an indicator if there is enough fuel present.

Post shift is then used to help being the engine speed back down before the recovery phase to re introduce torque. Depending on if you are using gear shift engine speed limit mode or not will vary what your trying to acheive here, but the main purpose is this helps "catch" the blip to help match the engine speed for when the recovery phase occurs.

As you are working with shifts where everything can occur in well under 100ms, you need to log things as fast as possible. Gear shift state, Gear Position sensor, Throttle Servo Position, Throttle aim state, Ignition timing, Engine Speed, Inlet manifold pressure, fuel and ignition cut average along with paddles, actuator duty lambda and everything else are needed to determine what changes are needed to improve shift quality.



As you have an ITB car, my first instinct is that your air/fuel balance is not allowing the engine to blip cleanly. Commanding a massive blip with that much throttle area will need a lot of fuel to make the engine respond, otherwise you will find the engine runs lean during the shift phase and splutters.

Here is the logfile from the last drive.

If i remeber correct the last drive is with longer pre shift. The log include both the last test and the one before. You can look at the transmission temps to seperate them.

Hi Mobne,

Nobody will be able to give you any constructive advise from that log file.

You cannot correctly use Dash logging to determine Paddle shift settings. Channels are also logged far too slowly to work out how the engine is responding to anything.

With dash logging, if events occur other than at the sample point of the logging, they won't be captured, whereas in certain channels of ECU logging, they will be shown at the next sample point so that you know an event has occurred.


A prime example of this from your logging sample is the gear up shift. The paddle has clearly been used 50+ times, but not been captured in the log.

Dash logging is also only capable of 100hz for most logging instances, as well as the ECU transmit not occuring at a high enough speed for meaning logging for sub systems such as paddle shift.

Channels such as gear position voltage, Gear shift state, throttle servo position need to really be logged at 200-500hz. You need manifold pressure, ignition timing and engine speed at 100hz. As David has previously directed you, many of the channels need to be logged at the maximum available rate.

Gear position/gear position voltage are your only real way of determining how the shift barrel is responding, in regards to moving between the gears. This needs to be logged at high speed, so you can see the when the shift actuator is applying a bit of preload.

Sorry my bad. Posted the wrong file. Will get the one from ecu tomorrow.

Btw, the channels you want logged, are they logged with the standard logging? Im not sure but i don't think i can change whats logged in the ecu with the basic gprp license?

Hi,

It is highly recommended to have at least level 2 logging in the M1 to be able to correctly setup a Paddle shift system. Level 1 and/or dash logging will not provide the resolution needed.