MoTeC Global Forum

Hi,

Car is Evo IX, running M150 with JRR 4g63 custom package. KAPS sequential 6 speed transmission.

i am facing a problem of Boost Pressure drop around 1 Bar after shift. its very annoying.
i have sucessfuly setup a Subaru STI last year, the boost was stable (actually most people complain about boost spike between shift!).

can you please have a look at the log, and any ideas how to get boost stable?

Hi,

Looking at the screen captures it looks to me like the M1 is trying to maintain boost (Boost Aim doesn't drop, Boost Control goes to 100% which should be building boost) when the Boost Pressure is being bleed off. Is the BOV opening at the time? as it looks to me like there has been an external vent of boost pressure causing the Boost Pressure to drop, rather than the M1 commanding a drop of Boost Pressure.

Hi SDean,

throttle is firm at 100%, and there is no way BOV (Tial Sport) will open without seeing Vacuum. I am sure.

i think i found out what is the problem. surprisingly, the "Gear Shift Speed Limit" option, was the reason. settings maybe!

this option, was imposing a 100% ignition cut, and 100% fuel cut, because the engine speed limit was targeting to match the next gear RPM.

i think the cut amount and length to bring the RPM to the next gear match, was too much and too long, that the engine exhaust gas was not enough to maintain turbo rotation to achieve boost.

i found out that car was not following the Ignition Cut, Fuel Cut in the gear Shift tables, but following the Rev Limit settings of next gear.

as you can see, we i switch off the Engine Speed Matching, the drop is minimum and sometime no drop at all.

thanks for your attention

Hi,

Glad to hear that you found a resolution.

I looked through some of the logging that i have from my car, and others that have M1's and use the Gear Shift function and none showed the same boost drop that you have, with most of them remaining at Boost Aim, even with large amounts of fuel and ignition cut. None of the logging that I looked at had 100% cut for both fuel and ignition, so it may be that that combination causes the turbo to drop so quickly.

If I get a chance, I look further into it.

I have experienced boost drop due to gear shift ignition cut events and it's just from the loss of hot exhaust flow, but yours is a lot of boost gone. I suspect the fuel cut is more to blame as it might take a few extra revs to re-establish fuel film and start firing properly again.
You could try using the gear shift rev matching feature just with the fuel margin pushed well out of the way (ignition cut rev limiter only).

We have experimented with gear shift rev matching using ignition retard with very good results. This will build boost on shifts, but it can be balanced with ignition cut also making boost control on shifts reasonably tuneable.

I've came to this post several times already trying to understand how to make best possible gear changes.

I'm really close to and I'm very pleased with it but I have one thing which makes my nights way to long figuring it out.

Car is evo X with JRR firmware with kaps sequential. Right now my gear change takes 40ms of cut and 40ms of recovery. I'm using 100%ign cut to get quiet gear change and 15 retard. I know when I cut all of cylinders there should be none of events happening but with 30 retard I have some pops from exhaust and 15 gives lil bit smoother feeling and very quiet cut. 80% is not enough to pull lever with 90 some pops from exhaust as well. I've tried crazy amount of combinations with fuel ign and retard just this combo for me works best.

It's really fast gear change, car feels great and everything but I know some cars can change gears without any hearable cut something like r5 cars of WRC. So how the hell they do it?
I was thinking on something like very short cut with speed limit function just to be able to pull lever and 20-40 retard to finish gear change and recover all of torque. I don't know if it will work I have to try it but I don't want to drive to many kms on gearbox....

I've done some very short cut with bigger gear tollerance and no recovery and came to 20-30ms of gear change cut but car wasn't accelerating that smooth and could feel slowing down effect on gear change.

I know there is a lot of mechanical stuff to do like clutch and engine/gearbox mounts etc. I just want to get maximum performance I can and understand as well.

Setup Is with small turbo and low boost for ice track. but It will get big turbo and 800+ for hill climb and paddle shift upgrade.
link:
https://www.youtube.com/watch?v=8-HmqZAkgPk
https://www.youtube.com/watch?v=dZC1SZySggE

Thanks for yours feedback

As long as there is fuel going through the engine into a hot exhaust system, you will have the potential to have some pops and bangs on the gear shift, irrespective of the amount of ignition cut/retard used.

The way that the modern rally cars do the cut for shifting is that they take advantage of being direct injected, so they will use fuel cut and ignition cut/retard to reduce the engine torque to allow for the shift to happen. As they are DI, the amount of Fuel Film in the engine is minimal so you don't have the engine continuing to draw the fuel out of the fuel film puddle in the inlet runners as happens with a port injected engine, and they can also reintroduce the fuel quickly when the cut is removed, so they do not lose out on driveability, as can happen with using fuel cut on a PI injected engine as you have to wait for the fuel film to reform.

Stephen thanks for your input.

I perfectly understand it that's why I'm using ign cut because it works faster and lever is softer in feeling.

there is no bangs for me but still I know evo's which sounds like there is no cut at all and producing about 1000hp used in hill climb as well, so I understand it's to be done.

Here you have example of what I have in my mind:

https://www.youtube.com/watch?v=Ak5yJRbBi_g&t=271s w

Going by the colour of the exhaust coming out of that car, it looks like it is quite rich, this can help lower EGT's and reduce the chance of the fuel exploding in the pipe, rather than burning after the valves.

Maybe he is putting extra fuel on shifts but mixture is close to me as I know many cars tuned by this tuner it is 0.77-0.78 he is using Pectel, so maybe.

Thanks again anyway if anyone else will have some experience would be great to hear opinions.