Would adding a nose cone to a bravo one drive on a boat running under 80 mph cause the boat to lose speed and prop to blow out? I'm running a 29ft scarab with a single pushing 680hp.

If your boat liked a lot of trim and you installed a pointed crescent type nose cone it is possible it wound slow down. The crescent type design is best suited to run A high elevation at near neutral trim. when you trim it out a lot it pushes the stern down. Hydromotive used to make one for that situation. The blow out may be related. Hard for me to say with out seeing it. The original bravos were shorter the current does blow out until mid 90 mph.
Jim

I'm running about 650 in my 29 scarab, I have a standard bravo with a nose cone. I'm running a slightly worked 26p bravo1. I have no issues with blow out. The boat is awsome out of the hole and holds well in turns. As far as top speed I'm getting about 73 with a lite load. Not sure if its been affected or not,never run it without the cone.