Sports car brakes. Loud as fuck, sounds like a freight train when cold or wet or cold and wet or needs cookies because @puzzled didn't give up any cookies.
It terms of HP? I have no idea. The car has never seen a dyno.
Again, on the meth alone, probably single-digit HP, but meth gives me the ability to dial up the boost to 11 with out maxing out trims.
I can answer the question pretty well for ya though. I run meth, I run a lot of meth. 50/50 WM blend. I get plenty of octane from the meth and cooling from the water to basically run the turbo at the top of it's efficiency range (23psi). With this particular setup, you're not going to see a ton...
Hey! Funny you should ask. I have a throttle body spacer for sale I'll sell ya cheap.
https://www.supramkv.com/threads/fs-bms-methanol-kit-parts-220-190-shipping-obo.11080/
A90/A91 is probably part of your confusion as well.
A91 is just a trim level, not 2021 cars. I have a 2021 A90, it cannot be tuned. Most 2021 Supras cannot be tuned, but a few of the early 2021s can.