Does anyone have experience of running Avgas 100 LL (100 octane low led)in a scoob without a cat?
or will even the low led content affect the lambda sensor?

Good question! I'am dying to know the answer,would like to run my sti v5(no cat)on it. I know people who run off road bikes bikes on a 50/50 mix and the bikes love it. come on some boffin must know ,even if it means changing the sensor for a lead friendly sensor.

Do not run with Avgas.

I know of a STi3 with some serious engine problems since the owner used Avgas at a track day.

I also spoke to a rallying friend about this some time ago, regarding Impreza's and he uses an ECU set up for it.

You may be lucky and have no problems, but it's a risk I wouldn't take.

David

Lots of reasons not to run 100LL besides lead. Burn rate, boiling point etc are all different. Not to say you can't get good power out of it, but driveability is likely to suffer, as well as starting. For a road car, driven at a wide range of speeds and conditions, it will probably not be such a good choice.