Sequential Gearbox in Race Car with a Gen3 PCM - How to reduce torque for shifting

[TonyG]

We have a race car with a LSx engine using a 2000 F body PCM.

We are installing a sequential gear box and need a method to reduce torque during shifts.

We are contemplating moving to a Motec which has the torque reduction feature built in specifically for applications like this, but since the GM PCM has served us so well for years, I thought I'd try to keep using it. (not to mention it's a lot less expensive)

Anyway, we discussed interrupting the ignition coil circuits, but that is not the preferred method of torque reduction (like using a sledge hammer to kill an ant), but we also discussed interrupting the IAT, which I believe will throw the ignition into a different map, which could be used to reduce torque.

Is this correct? And anybody know if doing this repeatedly (every time there's an up shift) will throw the PCM into some sort of error?


Any input on this would be appreciated.

Thanks in advance,

TonyG

[Crashgnx]

should be a way to do it by using the clutch switch I would think. I'll have to look to verify but cannot right now.

[Montecarlodrag]

Interrupting the coils circuits will throw misfire DTCs.
Using IAT to lower timing works good. Don't open the circuit, just use a relay with a 10 Kohm resitor. The PCM will use the last column of the IAT, you can set how many degrees to retard until you find the sweet spot. This will not give you any problems at all.

[matty b]

Youll have to try it as I've never done anything with a sequential that wasn't attatched to a motorcycle, but if you wire in a switch imput that replicates a park neutral switch, under the idle spark advance tablles have an in par and in drive table. In a manual, the tables are copies, but you could yank a ton of timing from the in park table when the pcm thinks you are going into park via input from your shifter and will revert to the in drive table when you are back in gear.

[matty b]

Looking at schematics, if you wire in a circuit on C1 pin 34 that grounds while you are shifting (you will need a method to activate the ground as you start pulling the shifter, strain gauge and controller ect) will swap tables. You should also need to go to SYSTEM>GENERAL>PRNDL EQUIPPED>PN ONLY. Keep in mind I THINK it should toggle doing that.

Easiest way to check is just pin in to that connector position with a wire and ground it. If you zero out the in park advance table (leaving in gear alone) when you ground the wire the car should die or want to. If it does that, you should be GTG. Please let us know, if I ever do a setup with an EMCO or the like in it, would be happy to know it'll work.

If it doesn't work just doing that, you may need to set it from manual to non-electric automatic. If it does work, you can actually tune the in park spark map to pull just enough timing to make the shift and no more. That will keep the retarded timing aka glowing header situation to a minimum.

[TonyG]

Matty

These pneumatic paddle shifted sequential transmissions (Albins ST6 with Geartronics controllers) are controlled from their own computer which measures rpm, throttle position, engine load, trans load, and more with very complex 3D torque strategies, recovery ramp times per gear, at specific rpms, tps points, etc.

The trans computer outputs a signal to the PCM to cut torque, when the trans computer needs it in order to shift. So triggering the GM PCM to cut torque isn't the issue.

What is the issue is... > can we map the GM PCM to cut torque to 90%-100% when the GM PCM gets the signal to cut torque, without errors, and how quickly can the GM PCM do this in terms of milliseconds?

Those are the issues.

So I think I might be able to use the GM PCM to do the job, I just don't want to spend the time playing with this on a dyno when the people here with far more experience than I, tell me, "no... it's not gonna happen", etc... :-)

And that's why I'm asking the question to those here that really understand what these GM PCM's can do.

Thanks in advance...

TonyG

Looking at schematics, if you wire in a circuit on C1 pin 34 that grounds while you are shifting (you will need a method to activate the ground as you start pulling the shifter, strain gauge and controller ect) will swap tables. You should also need to go to SYSTEM>GENERAL>PRNDL EQUIPPED>PN ONLY. Keep in mind I THINK it should toggle doing that.

Easiest way to check is just pin in to that connector position with a wire and ground it. If you zero out the in park advance table (leaving in gear alone) when you ground the wire the car should die or want to. If it does that, you should be GTG. Please let us know, if I ever do a setup with an EMCO or the like in it, would be happy to know it'll work.

If it doesn't work just doing that, you may need to set it from manual to non-electric automatic. If it does work, you can actually tune the in park spark map to pull just enough timing to make the shift and no more. That will keep the retarded timing aka glowing header situation to a minimum.

[matty b]

Matty

These pneumatic paddle shifted sequential transmissions (Albins ST6 with Geartronics controllers) are controlled from their own computer which measures rpm, throttle position, engine load, trans load, and more with very complex 3D torque strategies, recovery ramp times per gear, at specific rpms, tps points, etc.

The trans computer outputs a signal to the PCM to cut torque, when the trans computer needs it in order to shift. So triggering the GM PCM to cut torque isn't the issue.

What is the issue is... > can we map the GM PCM to cut torque to 90%-100% when the GM PCM gets the signal to cut torque, without errors, and how quickly can the GM PCM do this in terms of milliseconds?

Those are the issues.

So I think I might be able to use the GM PCM to do the job, I just don't want to spend the time playing with this on a dyno when the people here with far more experience than I, tell me, "no... it's not gonna happen", etc... :-)

And that's why I'm asking the question to those here that really understand what these GM PCM's can do.

Thanks in advance...

TonyG

Tony, I just know that the PCM will revert to that map when it is given a ground signal. How fast that happens, I dont know. What I do know is it will revert to that map given the correct setup in programming so that it pays attention to the P/N switch. An example of these types of maps used is with the ASA LS1's. They used a pit limiter switch to enable the P/N rev limiter. You press the pit limit button, it enabled the P/N circuit to ground and the car sat on the rev limiter that was set. If it works fast enough, you have a full spark map at your disposal to map against, which means you can pull as much or as little timing as you want at the load points you are shifting at.

Again, you are playing with toys I've never had my hands on, but it may work for your application. I wouldn't expect the IAT nitrous trick to work for your setup at all, but it might work for you with this. All it takes is wiring the trans computer to that pin I said and reduce timing to say 10 degs. If it works, fuckin awesome, if not, Motec is in your future. I would say that a 25 cent terminal and some wire is cheaper than a full EMS and wire harness.

ETA: The table will switch as fast as the PCM can, there will be no delay. It will also work as many times as you want it to as you are switching tables so its all digital. The speed it switches is what I do not know. Its all down to the PCM processor speed I suppose.

In regards to the P/N rev limiter, make sure its higher than your shift point, else you will hit hard fuel cut and that is not conducive to what you want.

[GrannySShifting]

Anything ever come of this? There are some other single wire inputs I have used to retard ignition timing (I used to yank timing out with a optical sensor for wheelie control)