Would super unleaded + Proboost be a more effective replacement to Optimax? (MY98 STi 4)

Cheers.

SUL plus the right amount of booster would probably be better than Optimax on its own, but you shouldn't really be using Optimax on its own in the first place.

Why not optimax by itself?

Japanese fuel is over 100 octane. Optimax is something like 98.7 fresh out the refinery. Thus, it still needs a bit of help to match what the ECU expects the car to be running on.

What sort of booster should you use, how much, what kind and how much does it cost?

I use millers, 1 bottle per tank full, cost vary depending where you order it from, anything from £2.30 to £3.00 a bottle.
I think Scooby mania are the cheapest.

simb

Youve got to look at whats available and how much it can up the ron by. I use nf race myself..:D

ok, it's optimax rather than SUL then ('cos it's cheaper) and proboost I guess!

What octane is LRP?