map sensor should ideally be upgraded once boost is above 1 bar as that's when the standard sensor has no more measurement left, and so when remapping you cannot add any more fuel at this point so either have to turn boost down to stop damage to the engine or put enough fuel in for 1.5 bar at the 1 bar map point which means that between 1 bar and 1.5 bar it'll be overfuelling and making less power than it should.
as for injectors, you'll definitely need some bigger ones yes, not optional really once you get to about 165-170 bhp you are maxing out the standard ones at high rpm. This was witnessed years ago on Paul Borthwick's g40 saloon. For 190bhp you'll get away with 250cc ones I'd have thought.
I reckon 190 will be possible with a standard head and bottom end, just about. Mine has standard bottom end with big valve, ported head and made 194bhp. Robin's car made exactly the same power on the same rollers on the same day with standard head but 1341cc bottom end. Both with approx 1.5 bar. Although you might struggle beyond 180bhp with both head and bottom end standard, if you push the mapping to the limits and dont map in any safe guards (i.e. push ignition advance to the limit, keep AFR a touch leaner than might be safe at top end, andy mapped mine to run a touch rich at the top end so as to keep the bottom end cooler) then you might get 190 out of it. The head seemed to be worth 10bhp at the top end, the 1341cc bottom end worth 10bhp everywhere else until you hit the max flow limit of the standard head higher up the RPM range.
