2500 #?!?!?! Thankfully they have a regulator on them so you can tone it down some! Also it should come with a selection of nozzles, you don't want the finest or broadest. Experiment with the other one or two. It should also have a siphon attachment so that you can mix detergent with the water stream for extra cleaning ability. Usually a good rental yard sells the detergent too.

Make sure you plug the holes (dist, intake, etc) REAL well, because the high pressure will surely blow out anything you put in that's not secured. Regardless, when you're done, make sure to drain the pan again to let out any water that might get in. Again, after you're done, pull the plugs and rotate the engine to drain the cylinders just in case, then oil them down, turn the crank by hand several times to get the oil on all the cylinder wall surface and into the rings.

Oh, and wear clothes and shoes you don't care about, and don't bother showering before hand.........................the blast back is gonna get ya VERY dirty.