When mapping, at what % of injector duty do back of?
Some say 75% and also heard of some running 95% even flat out in some applications.

Also some injector calculators seems to be very conservative on hp supllied. Like my 403's only suporting fuel for something like (503 * 4 * 0,8)/5,1= 315 hk
503 cc/min
4 nr of injectors
0,8 inj dutycycle
5,1 fuel consumption under load

I know I have more hk than that

You have a better (maybe more accurate) formula?

Link to site http://www.mrm-racing.a.se/index1.htm