cis 3 pot to map sensor conversion questions

[Alan Pritchard]

This has been talked about on the Megasquirt list, and Javad has also put
some info in his 034efi documentation. I would like to stop using the pot on
my 90q (mainly so its easier to go efi) and plan on using a map sensor (GM
recommended). Firstly, what is the output of these? According to a website,
put 5v into a 2 bar sensor, get 2.5 at atmospheric 0v at vacuum and 5v at 2
bar (If I recall correctly or the other way round). 
034efi recommends a 1bar sensor, which, for my app seems to make sense
(currently NA) so I guess the ecu would see 5v at idle (or there abouts)
Next question, the cis pot gives out 0-5v  across its swing. Is that 0v with
the plate at rest, and 5v fully open?? If so is that not inverse to what the
map reads??
So in theory it would be possible to advance my timing across the range by
raising/reducing the voltage that the ecu sees from that device??? So I
could rig up a sort of "sport mode" button inside the car to use more
advance (where fuel allows)
Thanks for listening to my ramblings!!!!
Alan.