I have a 10 gal aluminum fuel cell (trunk-mounted, with sealed sheet metal firewall to the passenger compartment).
It has large blocks of foam inside.

I'm wondering how much gas do these blocks displace? It doesn't seem to hold 10 gallons although measuring the cell and converting to gallons says it should.
Also, what is the purpose of the blocks - to control fuel splashing or something else?

Edit: I've answered my own question. https://buildingspeed.org/2013/04/26/why-you-dont-mess-with-fuel-cell-foam/

Guess it will stay. Maybe I'll change to a 15 or 20 gal. cell... that 451 is thirsty!