I just bought a 91 scarrab 31 with dual 540's. It will run about 77 mph WOT. I was hoping for 80-85. Long story short, a bad lifter caused a piston to burn up. So now I have to replace at least a piston, valves, and lifters. I'd like to go ahead and add a Vortech blower while it's all apart but I don't know if the motor has the right parts for a blower. It has 10:1 pistons, crower 10404 cam(292 int, 303 ex dur, 110 lobe center, about 600 lift), dual plane manifold, GMPP oval port aluminum heads (110cc), and Demon 850 dp carb. It also has wet headers on it. I'm thinking about getting 8:1 pistons and the Vortech big block chevy carb kit.

Are these heads, cams, manifolds, and carbs good for a blower? Or should I just put it back together and live with it??

Any comments are welcome!

I wouldnt go for the blowers personally. Id keep what you got and make it reliable. You'll end up with a drive bustin combo with blowers along with tuning, and lots of expenses. 77 is a nice speed for that hull.

It sounds like you have a couple of mild 540's. The oval port heads are limiting your top end. If you wanted to go faster n/a you would need a set of AFR315 cnc or Canfield heads, single plane intakes, and new cams. Your exhaust would most likely have to be changed to dry tailpipes. This approach gets expensive fast. Or you can put superchargers on your existing engines. Use pistons with 8.5-8.75 comp. ratio or you'll lose a lot of drivability. Camshafts should be changed to something with 114 lobe centers. This approach is expensive also. Either way you should be able to pick up 10 mph pretty easily.

Yeah to what Patriot said. Blowers would be a real kick in the pants, but I also agree with "Mild Thunder" that your drives will probably last longer by keeping the engines in naturally aspirated form. It seems to me that you would be able to obtain greater speeds than 77mph from your 31' Scarab, and still keep the 540's naturally aspirated, but I agree with what Patriot stated---you'll need better breathing heads, possibly different hyd roller cams, and single plane intakes. I think the Holly 850cfm carbs are fine for a 540cid engine up to 5500rpm range, but I would also swap the 10:1 comp ratio pistons for something safer like a 9:1 to 9.5 comp ratio with aluminum heads. What brand/style of exhaust system does your boat have???

Here's a couple of pics. I don't know the brand of the header. They go straight out the back with no mufflers. What is a good head to use without spending TOO much money? Since I have to buy all new valves anyway and have one head that needs to be fixed, a head/cam/intake swap sounds like a good idea. Any advice on the perfect/affordable combo?

Thanks

Chris

Those are lightning headers.....perfect and affordable do not go in the same sentence.

I have a 79 30 ft. scarab with 540 motors. mine runs right at 90mph. I also use lightning headers. My motors are naturals but i run alum. heads and alot of solid roller cam. I have dart heads and intakes. My motors dynoed out at 668tq. My boat is a trs boat and is alot heavier than the boat you have, so what you have in mind is entirely possible. I agree with patriyacht the heads are hurting you. The speed you have now is good and if its dependable stick with it, it just gets more costly themore you do.

scarrab30 - What heads and what cam are you using? I've been searching the internet and dart 1 heads come up alot. I just don't know what runner size would work best. If I go with a 118cc head, my compression will be about 9.5 which seems more reasonable ( thunderusone, 'reasonable' doesn't belong in my vocabulary either!). I run a solid roller in my car and my jet boat and love them but I am new to this type of boat where you run hard for a long time. Since there's two motors, my usual method of trail and error could get expensive FAST! The first motor is going on the dyno in about two weeks so I gotta figure out what to put in it this week. Help me get to 660+ ftlbs!!!!!

Thanks for the input!

Chris

Canfields are less expensive and more available than AFR's. The Crane 741 hyd. roller is a good all around cam for this size engine. Brodix and Dart make the best intakes. Check with Lightning on your options to reduce water in your exhaust. You may mave some reversion after these mods.