New props after re-power? 5.0L —> 383Mag stroker

[emunns]

Hey all, I’ve done some searching and researching and wanted to post this up looking for more advice.

We have an 2007 SeaRay 240 Sundeck with a Bravo 3 drive. It originally had a 5.0L (260hp) motor but we just re-powered with a 383 Mag Stroker (350hp). We have 22p Mercury Marine props on it still (part #48-823664).

With the extra power we now have we’d like to increase our cruising and top speeds. Can anyone recommend some options for us?

Thank you for the help.

 

[paulswagelock]

Hey all, I’ve done some searching and researching and wanted to post this up looking for more advice.

We have an 2007 SeaRay 240 Sundeck with a Bravo 3 drive. It originally had a 5.0L (260hp) motor but we just re-powered with a 383 Mag Stroker (350hp). We have 22p Mercury Marine props on it still (part #48-823664).

With the extra power we now have we’d like to increase our cruising and top speeds. Can anyone recommend some options for us?

Thank you for the help.

We need to know more specifics. Drive, drive ratio, current top speed on a gps, current rpm at top speed, current cruise speed and rpm.

 

[Espos4]

We need to know more specifics. Drive, drive ratio, current top speed on a gps, current rpm at top speed, current cruise speed and rpm.

Exactly.
Start with some baseline numbers before you make any changes.

 

[ttmott]

It's not so much the horsepower as it is the torque. You should prop the boat based upon the torque curve of the engines. Like said earlier, there are several variables that play into the decision. If it were me I would install the old prop and get a feel what the engine is doing. Then go to your local prop shop (the shop that the bass boaters use is usually the most knowledgeable) and discuss with them. Most good prop shops will loan out props to use and find the best pitch and prop style. For your boat I wouldn't so much care about speed as getting out of the hole and laying the bow down faster. You might also consider a prop that lifts the back of the boat.

 

[emunns]

Thanks all for the reply’s.

The Bravo 3 drive is in good order as are the current props. I’m unsure of the drive ratio (outdrive OW919318)

The old 5.0 was worn out and under powered when we bought the boat over a year ago. Best I could get was ~3800-4000rpm and 39-40mph at WOT. Clean hull, flawless props and minimal weight. It would get up on plane pretty quick, faster than our 185 w/4.3L.

My biggest motivation/thought for swapping props is to cruise at a decent speed, 35-40mph, and a lower rpm to reduce fuel consumption and engine wear.

The new motor isn’t fully broken in yet, only 16 hours so far. I guess I need to be patient, put some hours on it to see how everything lines up before I start swapping props.

I’ll try to find a good prop shop up here in Seattle to help in the future. Unfortunately all our “bass boats” up here are over 100ft long with a top speed of 12 knots and fish for crab, cod & salmon in the pacific.

 

[paulswagelock]

Thanks all for the reply’s.

The Bravo 3 drive is in good order as are the current props. I’m unsure of the drive ratio (outdrive OW919318)

The old 5.0 was worn out and under powered when we bought the boat over a year ago. Best I could get was ~3800-4000rpm and 39-40mph at WOT. Clean hull, flawless props and minimal weight. It would get up on plane pretty quick, faster than our 185 w/4.3L.

My biggest motivation/thought for swapping props is to cruise at a decent speed, 35-40mph, and a lower rpm to reduce fuel consumption and engine wear.

The new motor isn’t fully broken in yet, only 16 hours so far. I guess I need to be patient, put some hours on it to see how everything lines up before I start swapping props.

I’ll try to find a good prop shop up here in Seattle to help in the future. Unfortunately all our “bass boats” up here are over 100ft long with a top speed of 12 knots and fish for crab, cod & salmon in the pacific.

Get the operating data we requested. Anyone with any knowledge that would help you needs that information.

 

[SeaRide]

You should be able to find your gear ratio on the MerCruiser label located on the upper gear case. If not, contact Mercury with the serial number. They will have the info. Sea Ray should have the original build spec as well.

In the meantime, I would have a look at the prop chart for the 6.2 (320 HP). This should give you an idea of what may work for you. Here’s link: 2008 Sport Boat Sport Cruiser Prop Chart.pdf (searayweb.com) Unfortunately, they do not have the '07 chart, but I would be surprised if there are any changes. Also, if you are one of about 10 people who still slalom ski (me), you may want to go a couple of inches lower in pitch if you like popping out of the water quickly.

I would also try searching the site for 383 swaps. I know a couple of members have done similar upgrades. Although, I do not specifically recall one with the 240SD. Another good source may be the shop who performed the swap. They may have a good idea of what may work especially if they have done a number of similar upgrades.

Finally, I had the opportunity to run a 2006 240SD one summer evening when new with your engine/drive set up. Top speed was 44 MPH (GPS) at 5000 RPM, lightly loaded and light on fuel with four adults. Temp was in the low 80s and our lake is around 350' above sea level.

Enjoy and keep us posted. Great engine set up!

 

[Lazy Daze]

Ratio is 2.20:1.

FYI, that 40mph is very close to "normal" for that boat with that engine. Sea Ray always provides a "range" that the boat should run at, depending on conditions and amount of people/gear in the boat. Yours is 40-44mph.

You're not going to get a cruise speed of 35-40mph. Cruise speed is generally around the mid-3,000RPM area. Once you start getting around 4K, fuel economy drops off.

The optional, 6.2L engine (377/388ci) was rated at 320HP. This is propshaft HP. Most likely, the engine you bought was advertised as crankshaft HP. There will be at least a 30HP drop to the prop. BUT, Sea Ray's speed range for the 6.2L adds 4mph to the top speed with 26P props.

Point is, don't go into this expecting to see a huge increase in MPH - this is the wrong style of boat to see bigger gains. Yours is designed primarily for the low to mid-range speeds where most people who buy this type of boat use their boat (family fun). Even with a different hull design, it takes a lot more HP to see decent gains in MPH. It's not a car - boats are a whole different beast.

 

[emunns]

Thanks SeaRide & Lazy Dave, that’s all great info. I’ve been chatting with Ken @ Propgods also. Basically we need to tamper our excitement, get a lot more hours on the motor to really know what we want to change if anything.

I’ll update with real numbers as we get them. Thanks all!!