Mercruiser 5.0L or 5.7L

[moosehunter74]

i have a 2159 bayliner trophy with a 1998 5.0L 2 barrel carb with a bravo3. I'm thinking about replacing the block on it to a 5.7. I cruise at 28 mpr @3700 rpm's. My question is how much better would the 5.7 do? My object is to cruise at 30mpr at a lower rpm. Would i be able to acheive that with the 5.7

 

[thumpar]

Re: Mercruiser 5.0L or 5.7L

I would go with the 5.7. It is a direct swap. You could also put on a 4 barrel while you are at it. With the 5.7l you could probably up the pitch of the props to lower the RPM.

 

[moosehunter74]

Re: Mercruiser 5.0L or 5.7L

I'm assuming that the 5.7 produces more torque at a lower rpm then the 5.0? I'm using 24 pitch props right now, so if I go up to 26 pitch props the 5.7 should do the same speed as i'm doing right now but at a lower rpm?

 

[thumpar]

Re: Mercruiser 5.0L or 5.7L

You will just have to see where you are at after the swap. 26 might be right but maybe 28 would work. You will just have to see.

 

[harleyman1975]

Re: Mercruiser 5.0L or 5.7L

Wow I cruise 28 mph at 3200 with a 19 pitch prop on my 888. what geat ratio are you running?

 

[81 Checkmate]

Re: Mercruiser 5.0L or 5.7L

Keep in mind that your 5.0 has a different advance timming curve than a 5.7 - You proly could use the same ignition... but you would not get the full potental out of the 5.7 motor.

You may have to invest in a different ignition set-up for a 5.7

 

[moosehunter74]

Re: Mercruiser 5.0L or 5.7L

5.0L with Bravo 3 24p 2:20 gear ratio

 

[moosehunter74]

Re: Mercruiser 5.0L or 5.7L

Keep in mind that your 5.0 has a different advance timming curve than a 5.7 - You proly could use the same ignition... but you would not get the full potental out of the 5.7 motor.

You may have to invest in a different ignition set-up for a 5.7

You mean the ICM?

 

[Walt T]

Re: Mercruiser 5.0L or 5.7L

With the 2159 you should see an improvement, but I personally doubt you'll be able to go up in pitch. There just isn't that big a power difference between the two engines. A 4 bbl only helps at WOT, the cruising speed will be the same. If there is a difference it will be shorter on plane times. My guess a 5.7 4 barrel vortech motor with 9.5 compression might get you 3-5 mph top end, you can try a steeper prop just for cruising but keep the lower pitch for skiing.
Since we don't know exactly what results you would like to see, it's tough to recommend the best bang for your buck.

 

[thumpar]

Re: Mercruiser 5.0L or 5.7L

Putting your numbers into a prop slip calculator shows 26%. That is pretty high. Maybe something else is the issue.

 

[moosehunter74]

Re: Mercruiser 5.0L or 5.7L

I'm not trying to go faster by going to the 5.7. I just want to lower my rpm's when cruising to my fishing holes. I cant pitch up anymore as the 24's rev out at 4800 loaded. I travel 2.5-3 hrs to get to my fishing grounds. Main objective is to save fuel so i don't have to carry extra fuel on board

 

[moosehunter74]

Re: Mercruiser 5.0L or 5.7L

I'm not sure what you mean by prop slip

 

[thumpar]

Re: Mercruiser 5.0L or 5.7L

I'm not sure what you mean by prop slip

In a perfect world 24 pitch props would move you 24" per revolution. The slip is the amount you are loosing.

 

[moosehunter74]

Re: Mercruiser 5.0L or 5.7L

In a perfect world 24 pitch props would move you 24" per revolution. The slip is the amount you are loosing.

So your saying i might have a problem with my props?

 

[thumpar]

Re: Mercruiser 5.0L or 5.7L

Probably not the props but could be something like dirty hull.

 

[moosehunter74]

Re: Mercruiser 5.0L or 5.7L

Probably not the props but could be something like dirty hull.

Well I can tell you it's not a dirty hull. I keep it on a trailer.

 

[moosehunter74]

Re: Mercruiser 5.0L or 5.7L

Probably not the props but could be something like dirty hull.

One thing that I've noticed over the years has been the powder coating on the props is worn out. Now the props are shinny. Would that be a concern?

 

[Walt T]

Re: Mercruiser 5.0L or 5.7L

They're right. With the B3 it should be 10-15%. Okay so a good solidly built 5.7 or 383 stroker will get you up a pitch. I have a 22 foot cuddy with a VP duo prop that started with a 5.7 and 1.98 ratio 25 pitch props. (C6) I built a 'stroker' motor specifically for low end torque and mid range cruising. I had a lower pitch propset (C5) that I used for skiing and kid stuff and the stroker motor now overwhelms those easily. It simply climbs past 5000 and keeps going. The C6s load it better but I hit 5200 rpm and it was still slowly climbing so I backed off. Cruising speed is now 4 mph better at the same rpm and it sounds like its not working hard at all. It really sounds sweet. Once I scrape together 1600 bucks or find a decent set of C7 stainless then I am theoretically going to be 6 mph higher speed at same rpm but who knows. You should Google 383 strokers and marine strokers. Summit Racing has them reasonably priced. All your current parts can swap right over. This should be the best bang for your buck and still have a very smooth idling motor with close to big block power.
I really like those Trophy's, how do you like yours? Wifey like it? Sleep on it? Great fishing platform.

 

[moosehunter74]

Re: Mercruiser 5.0L or 5.7L

They're right. With the B3 it should be 10-15%. Okay so a good solidly built 5.7 or 383 stroker will get you up a pitch. I have a 22 foot cuddy with a VP duo prop that started with a 5.7 and 1.98 ratio 25 pitch props. (C6) I built a 'stroker' motor specifically for low end torque and mid range cruising. I had a lower pitch propset (C5) that I used for skiing and kid stuff and the stroker motor now overwhelms those easily. It simply climbs past 5000 and keeps going. The C6s load it better but I hit 5200 rpm and it was still slowly climbing so I backed off. Cruising speed is now 4 mph better at the same rpm and it sounds like its not working hard at all. It really sounds sweet. Once I scrape together 1600 bucks or find a decent set of C7 stainless then I am theoretically going to be 6 mph higher speed at same rpm but who knows. You should Google 383 strokers and marine strokers. Summit Racing has them reasonably priced. All your current parts can swap right over. This should be the best bang for your buck and still have a very smooth idling motor with close to big block power.
I really like those Trophy's, how do you like yours? Wifey like it? Sleep on it? Great fishing platform.

That all sounds good but I might not have enough room. It has a 4.3L and now the 5.0 takes up all the room. Love this boat but like I said I'm trying to lower my rpm's down to gain fuel economy as I usually travel 200 miles round trip. The 5.0 does the job and wide open does 44.5 mpr at 4800 rpm fully loaded and 3 guys.

 

[thumpar]

Re: Mercruiser 5.0L or 5.7L

The 5.0 and 5.7 are the same size. It is pretty much the same block casting. I don't know why they make the 5.0 when they could just make it a 5.7.