In my 98 ssei the hud and speedo don't match. I was on the interstate on sunday and the hud said 80 and the day said about 77-78. Which one is more reliable? Boy having the supercharger is nice, going up a hill and the speedo and rpm gage doesn't move just the boost gage goes up a bit. Was going up a hill on sunday and a honda accord passes me on the bottom of the hill and when I got up to the top I was back in front of him. Poor 4 banger didn't have any torque.

Mayhem, that error sounds about right. It'* the analog gauge that'* off a bit. Just a function of how they work. The HUD is getting it'* number from the VSS.

My VSS (from the scantool), HUD, and GPS are all within 1mph of each other, while my analog speedo is a couple 'slow' on the freeway.

Sounds like you're right on the money.

Ok then I'll just have to pay attention to the hud and watch the speed from that. I thought the hud was off and I was going under 80 and not at.

yep, its true...
I got pulled over once by a cop, and my HUD said 41mph, and my dash speedo said 39-40mph and when he came up to my window he said i was doin 41 mph, but luckily I got off lucky.
I dont know why its like that, but it doesnt matter to me a whole lot because i rarly look at the dash speedo.