Low speed is a relative term. These are good to ,I would guess, at least 100 MPH.
The bottom inlet angle can be ground to a flatter angle if pressure gets too high.
I have a pressure gauge on the dash and have never seen more than 6 PSI @ over
70 MPH. I also have a relief valve w/overboard dump but it's completely redundant.
The pictures are of my 22C Testa Rossa. There's a heat exchanger hiding at the
bottom of the rear seat also w/an electric circulating pump.

Good luck w/your project.