My Intake looks like a cast iron high-rise. But I don't like that it has an adapter. Seems there would be some restriction there with a square-bore carb on a spread-bore intake.

Comp 272 w/1.5..there is no benefit in a marine application running a Vortec SBC to use a 1.6 rocker or I would have...same price.

What rpm are you seeing your max speed at?

Is the speed GPS?

What pitch props and what is the O/D ratio?

RPM was just north of 4500, but did not document exact rpm as my wife was yelling SLOW DOWN in my ear.

Yes speed was with GPS, the speedo pickup was corroded closed at that time (when we first got the boat).

24 pitch stock quicksilver props. Don't know the gear ratio or how to find out what it is.

I'm not really interested in tweaking the props until I have more power to work with. It servs us well in it's current configuration.

do you have serial number for outdrive

I would go with vortecs. Watch craigslist and buy a set off of an old 5.7L engine. I have picked up 3 pair so far, paid $200 to $300 for the whole engine with spun bearings. Take them apart and lap the valves or have them ground in by a machine shop. May want to upgrade the exhaust valves with how new/low hour your boat is.

Like sprink said, compare your cam to what merc offers now. The stock merc cam will give you a 300 hp motor. Get a dual plane aluminum intake for $150 to $200 to match the vortec bolt pattern. Put some richer rods/ jets in your carb. vortec intake manifolds are more coin, so I would guess $600 to $650 for the upgrade plus machine shop time if you use one.

Now, this will be interesting to see what it does with your props. You are not spinning your motor real fast right now, so you may not need new props if you can spool up faster for the higher speed. Plus the torque will help your acceleration I would think.

Plus you get to wrench on you motor!

Brian

The O/D ratio is usually stamped on the drive itself. It's most likely a 2.0:1 or perhaps a 1.81:1. In either case something doesn't add up because 57 mph GPS cannot be attained at 4500 rpm with your prop set. It helps to have good baseline data to aid in performance enhancements.

OK, thanks for the input guys. I'll see if I can figure out what the drive gear is in the next few days. Like I said, I didn't watch the tach closely as I was watching the GPS and boat traffic. It GPS'd at 55 when we tested the boat with 3 people and a full tank of fuel the day I purchased it (last spring) . We did the one 57mph pass a few weeks later with about a 1/2 tank and a cooler full of drinks and just my skinny wife and I with an app on her smart phone which tests out accurate in a car . Not really looking to do 70 mph, but a ligitimate 60+ mph boat with great accelleration would be nice. .. Along with a nice exhaust note.

I have a pair of used Vortec heads traded for and on the way and can handle the machine work and mild port work myself. Will probably upgrade at least the exhaust valves and machine them for screw-in studs. A performer RPM or RPM airgap is on my ebay search list. I like the Carter carb for fuel economy , but will try it with a 750dp holley also.

Merc ran both Quadrajets and Webers on those motors using the same intake. That's why the Weber-equipped motors have the adapter.

An RPM Air-Gap intake will be a nice upgrade. A 750 is a pretty big carb for a stock 5.7L. If you decide to change cams, be careful being that you have stock exhaust and Captain's call. Both would most likely have to go if you choose a cam that would give you the idle characteristics you are looking for. Do you have baffles in your tailpipes or just stainless flappers?

Vortec heads, RPM Air-Gap, and a QF carb would be a good start. Make sure you are turning 4,800 RPM at WOT.