Setting Mixture with Nitrous

[David Crocombe]

I wish to know how we can measure the mixture lean/rich on a Drag racing
car that runs leaded petrol and Nitrous Oxide.

What I've heard so far is that the oxygen sensors get ruined by the lead
in leaded petrol; that maximum power (objective) is at a mixture of about
18:1 I think rather than the 14.7:1 for least emmissions.
All sensors I've heard mentioned work around this 14.7 mark. Are there
sensors for those of us who require maximum power regardless of 
emissions?
We (my brother is the Drag racer & I am the Electronics person) are
interested in better tuning without a dyno access and data logging.
At this stage EFI is not allowed in his racing so I figure I'll
just measure everything but not control anything.

Any information or ideas would be most welcome.

Regards,

David Crocombe.
Sydney, Australia.