how much rwhp are stock injectors good for?

There's not a hard and fast rule, but if you're pushing 291, you're right on the ragged edge of the 19's. How much fuel pressure were you running? With an adjustable regulator you might be able to extend their 'life' with more pressure. Go to www.pro-flow.com (ProM's website) and click on the meter sizing tab. THey have some calculations showing hp vs. injector size, and what happens as you raise system pressure.

I made 272 with stock 19s, and I know they could handle more (definately not maxed out, but I forget the FP, maybe 40-41 psi). I know Mike Washingtons Factory Stock car runs on 19 lbers, and makes in the area of 340 rwhp. Granted these inj have been tested and Im sure flow more than the 19 lb, but he does use them! I would say your right where 24s would help some...

See http://users.erols.com/srweiss/calcpchg.htm for a calculator that shows flow rate increase with pressure increase.

Acording to the above calculator, with 19 lb injectors at a base pressure of 39 PSI, increasing the pressure to 62.5 PSI makes them flow 24 lbs. Other flow rates can be calculated by changing the pressure.

Use the SOP meter to set the fuel pressure if you think there is more power to be gained...

Get one of your buddies to ride along with you. Find a level stretch of road where you can do some testing. Don't choose a speed range that will make you shift gears, the shift quality & speed will affect your results. Use 2nd or 3rd gear and do a run from 2000 RPM to 5800 RPM. Call out the RPM as it increases and have you buddy record it and the elapsed time. If you have one of those cheap digital watches like I do, a stop watch is built in. Start the fuel pressure at 38 PSI, vacuum off and make a run. Turn it up to 39 and make another. Be sure to reconnect the vacuum every time you set the pressure. Keep turning up the pressure and making runs until you notice a drop off in time. If your bud was careful to record the results, you'll have a nice chart to use to find the optimum pressure.