Carb and 250 Blower VS Fuel Injection and Procharger
 

Recently had some motor problems. so back to another engine rebuild Motor is a 525SC with an upgraded roller cam. made 570hp. New combo will be going back with alum heads. possible 496 stroker, but not decided yet. i know that since i have a bigger cam and better heads the 177 blower really isnt going to push enough air. and will be more of heat pump. so looking at going with the bigger 250 blower. but since im changing stuff, contemplated going to fuel injection with procharger. would still have good power and slightly better fuel mileage compared to the carb. I know the roots style blowers have a broader tq curve which works better for boats. but whats biggest advantage and disadvantages of each set up?

I'd skip the 250 blower and go right to a 420 or 871. Been there done that. Had 177',s 250's, and now 420's. I have 468CI, Dart 308 Race series heads with a little work, hyd roller cam, JE blower pistons, Manley H beam rods, GM steel crank. Engines made 800HP at 6000RPM, just under 7lbs of boost. Around 760HP at 5500RPM. They run great, sound great. Been running roots blowers for a long time now, properly setup they are just proven reliable in marine.

I ran a 177 blower at 115% over to make 5psi of boost, a 250 blower at 69% over to make 5lbs of boost, and currently a 420 blower at 7% UNDER to make 6psi of boost. Boat ran

77-78 with 177 blower at 5psi (single 950 carb)

78-80 with 250 blower at 5psi (single 1050 carb)

80-83 with 250 blower at 7psi (single 1050 carb)

86-88 with 420 blower at 6psi and still prop testing. (dual 850 carbs)

The air charge is dramatically cooler at 7% underdriven than say 115% over on a small blower. 6psi of cool charge is much better than 6psi of hot air. 12000RPM Rotor speed vs say 5000RPM rotor speed at 5500 Engine RPM, make a BIG difference. The little blowers make nice low end power, and great for a small HP boost on a stock engine. But once you get serious, with good heads, aggressive cam, big exhaust, the large blowers just do so much better.

Parts, accessories, cost, reliability, ease of setup, Im personally a fan of a old fashioned "roots" blower. Theres a reason why you'll see tons of them out there on big boat engines. Some EFI whipples would be better, but a lot more money. Not sure you wanna invest that much into a mill for a 24 outlaw.

ditto

Joe, with so much cooler air charge do you think you could run 89 octane instead of 91 or 93? I am wondering because I am thinking of doing my engines next winter and have only 89 available at Marina Shores.