What extra gauge would you add in dash?
 

Besides the usual gauges,
i would like to have some extra reading in my chriscat
that are unusual such as
water pressure
fuel pressure
02 sensor reading
vacuum pressure

what else exist on an engine that could be monitored ?

Oil temp

Definitely oil temp. Pre and post cooler if you've really got the room. EGT as well.

https://cimg0.ibsrv.net/gimg/www.off...4f78070fb.jpeg
You must have more room than me.
Just squeezed in the normal stuff with room for boost gauges later.

A funometer. It’s a combination of boost and trim. The more boost and the perfect trim equals more fun. Of course there’d be something similar to a redline for too much trim.

A rear view camera with a proximity alarm after almost being ran over from behind by a plowing bow high not paying any plucking attention cruiser last Thursday evening at LOTO! :angry-smiley-055::waffen093:

When I got my little old center console bathtub many years back , despite having been re-powered , it still had a functioning vacuum gauge. Over time I came to really like it and what info it could tell.
All the new engine packages now don't have provisions for them , at least an easy provision , and the mechanics/engine sellers all seem to say the same thing now ..with all the computerized crap they come with they're not needed but I beg to differ.

Puckermeter with the sending unit installed in the passenger seat

Good looking dash!

Sounds like you got pretty well covered, but since you asked for unusual....

Cyl head temp/EGT
Drive temp
If twins, a sync-meter
Detonation indicator? (only ones I've seen are home made)
Vibration meter? (I've only seen them in airplanes)

Then there's just downright goofy:
Bilge temp (just made that one up, but what the hell. Could come in handy if suffering vapor lock, or maybe an early indication of fire)
Water level in bilge (made that one up too, but could have come in handy a couple of times:)