Converted to Vac years ago. The TTA had it from the factory with the turbo engine that doesnt have enough vac to operate
Coverted to vaccuum first. Fine for everyday driving. Horrible at the track...
I can hold 10psi on the footbrake with vacuum at the track, but yes it is good on the street too. I think inadequate checkvalves give vacuum brakes a bum wrap at the track.
10 psi on vacuum brakes??!! I'm not saying you can't but I'd fork up a 12 pack to see that. That is extremely rare.
Boost is relative, actual HP output is the factor. My car has vac brakes and can do 15 psi on the footbrake before the tires break loose. Somewhere in my old Turbolink files (with boost harness) I have frames of my car at 15 psi and the speed sensor reading zero. This was on a slippery oil road no less. BUT, my car runs through the original muffler. Likely making a fraction of the HP at 15psi that the drag strip warriors are making. Now you make me want to open the dump and try it again tomorrow actually trying to set the brakes up to hold good. LOL
Well, that could easilly be explained actually, now that I know you were using turbolink to monitor it instead of an actual boost gauge. Why? simply because there is a full 1.5 seconds in between each frame of data on turbolink and all data doesn't arrive in sync. It's hard to explain but in reality you could easilly have been at 15# of boost on TL, and been moving/spinning and TL still reporting 0 speed.
Try a real test, in your driveway, or out in the street, just start footbraking it and watch a your boost gauge instead of TL. I would be shocked if you could actually hold more than 3-5# on the gauge before things started happening. Most everybody I know on vacuum brakes can't even get past zero, maybe one pound before the rears break loose, and it's even worse with rear disks.