1990 Supra Turbo

[SuperX]

Hi Just got a 1990 Supra Turbo.
I have a question about the boost gauge. It seems to always read -4 on the boost, when driving. I can run down the interstate at 80 and it still reads -4. Now if I jump on the gas it will show boost up to 3 or 4. I haven't driven it hard I just got it and had to bring it home in the middle of the night 250 miles so I was kinda easy. If I get on the gas (hard acceleration) the boost will go up and stay there until I let off the gas and then back down to -4.
Is this normal.
Thanks SupraX