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ignition tuning with an knock monitor

Practical Dyno Tuning

Discussion and questions related to the course Practical Dyno Tuning


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I have seen some of the tuning video’s on youtube of your organisation. Now I’m not tuning car’s but tune single cylinder motocross bike’s. At this moment I can setup the best AF ratio on my own dyno. But I’m still struggling on the ignition timing. I know that I can tune this until I am producing the maximum amount of torque. But there are also my worries because we are running compression ratio’s around 14.5 / 15 to 1. At this point I think with much more advancing of the ignition timing the engine will start to detonate. But I could also be wrong. The engine’s are advised to use 98 octane fuel but we are currently running 102 octane fuel just to be sure and keep the injectors from clogging up. Because of the higher octane fuel and the slower flame front off this fuel I thing there is some power left on the table that i can gain. Now I have seen you are using the plex knock monitor on your tuning sessions and was wondering if this tool could help me out finding the best ignition setting without detonation. I already tried to send an e-mail to the guys from plex but dit not get a reply. I thought maybe you could help me out with your experience of this device. I have only one location I can mount the knock sensor as shown in the image attached. Would this device still be able to help me out?

On the motocross bike I’m running a VORTEX ECU unit witch does not have a wide band lambda sensor connected. It can only control the fuel an ignition delivery. My lambda reading do I get from my dyno along with the torque and hp numbers. The dyno is a eddy current system where I can hold the engine at any given rpm point.

I hope you could help me out.

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With high speed, small bore motorcycle engines knock is often less of a concern than in a conventional road car engine. That's not to say it can't happen but it is less of an issue which is why it's common for motorcycle engines to not use a knock sensor. you've probably helped yourself on this front with the higher octane fuel too although you quite rightly point out that this fuel may in fact need more advance to achieve MBT.

With all that being said I would still advocate fitting a knock sensor for a high comp engine like yours during the tuning process for peace of mind. The location you have indicated would be a good place for the sensor and I believe the Plex would do an excellent job and be a great investment for you.

I still have one more question. Should I tune the ignition timing in a steady state or is it best to run a ramp test? And how is the plex unit connected to the system to obtain a rpm signal. On the mx bike's I do not have an obd2 port to connect to. On my dyno I have a clamp that is placed on the spark plug wire just before the spark plug. Thanks for the help so far you changed my doubts about the plex unit. Do you have an contact person from plex? That way I can contact them directly.

I try and tune the enigne in the way it will most often be used. In this respect I prefer to tune the ignition timing in steady state in the cruise and transition areas (normally up to about 2/3 of the rev limit. The rest is done in ramp runs.

The Plex can derive rpm from an ignition trigger wire or alternatively an injector trigger wire. You don't need an OBD2 port.