Need Advice: Repowering 1998 370 Sundancer w/ 8.1Ls

M

MarcOuel

New Member
Sep 23, 2015
6
Boston
Boat Info
1998 370 Sundancer, West Marine dinghy w/2.2 Merc, Raymarine electronics
Engines
8.1L Merc Horizon w/ V-Drives x2
I am strongly considering repowering my 1998 370 Sundancer with new, re-manufactured 8.1L Mercs. Has anyone out there been through this with their 370 Dancer? I am concerned that the extra torque in the 8.1L Mercs (vs 7.4L) may also require replacing my transmissions/V-drives and possibly shafts and propellers. We searched high and low from NY to Maine for this specific model and layout and love the boat!! She is in very good condition otherwise, but is 17 years old at this point, so its a big decision. Any advice and/or lessons learned appreciated!
 
Last edited:
Subscribed. Hope to see the responses on here.

By the way OP....wonderful boat.
 
As with anything, it will depend on how you drive it. You can go up a moderate amount in power and torque and be just fine in most cases if you smoothly apply power as needed. If you have to put the hammer down and come out of the hole like a ski boat, you will add to the stress and wear your components take.
 
First: Congratulations! That's a great boat. If I survive paying for college over the next several years, that's the model that's on my short list when it comes time to upgrade.
Can you check with the manufacturer of your transmissions to see what they say?
You may find that they bolt the same transmissions to the back of 8.1's, or they may be able to recommend something else to you.
The shafts would be the nxt thing I would look at. The transmission manufacturer may be able to give you some info about those too.
If all else is good, the next person you need to speak to is a good prop guy to get his recommendation.
 
Great suggestion to speak with the tranny manufacturer...I have V5000 Velvet Drives and will give them a call for sure! Thx!
 
dpmulvey said:
Do homework and figure total cost of ownership.

There are better options.
Click to expand...

Would love to know what options you have mind. Good 380hp 7.4L Merc engines are scarce. And this would be my 5th engine on this boat since I bought it used in 2007. So I really don;t have much interest in going there, and diesels are out.
 
MarcOuel said:
Would love to know what options you have mind. Good 380hp 7.4L Merc engines are scarce. And this would be my 5th engine on this boat since I bought it used in 2007. So I really don;t have much interest in going there, and diesels are out.
Click to expand...


What was the cause of 4 engine failures? I don't think they wore out. Usually exhaust failure or overheating. I recently had my 454/350hp Crusaders rebuilt to 380 hp. They run great and added that little extra boost the boat needed.
 
No they definitely did not wear out. I'm not the original owner but was told that water ingestion killed the original engines, and the second pair as well with "log style" exhaust. By the time I purchased the boat in 2007, the dealer had just replaced with 2 remans and canister exhaust. One engine burned a quart of oil after an hour of running (no kidding!) and oil would be jet black. Other engine had bad case of "rpm wander" while idling around dock that no one could solve and I was always fearful of stalling while docking in crowded marina ( no bow thruster). So we got Merc to replace both engines under warranty. I had every mod available from Merc installed to deal with water ingestion. Ran great until late last season when #5 piston blew in starboard engine....just black oil again and starboard would not turn 4400-4800 RPM at WOT. If your 7.4L's are running fine then give them a hug, because my experience with Merc 7.4L remans has been a nightmare. And I baby the boat when I run it and take great of her....very frustrating!
 
I'm interested in what you find out. Dealing with college tuition right now, but thinking of possibly going with a 370 of that vintage down the road. They fit the bill for us as far as space, seperate shower, etc..
With one in college and another coming up to the college years, we are probably limited to something of that vintage when the time comes.
 
Joining in on this one. I have the 370 that is rumored to be the first one Sea Ray/Merc did the water lift muffler conversion on, after 2 repowers by the p.o. The third set was put in November 2003, but in most cases all the bolt on stuff is still original, just long blocks that get changed. I have gotten another 12 years out of them, so I too am coming to a decision on repower, or replace.

GEN VI certainly has its issues, and I would love to move to Smartcraft and NMEA 2000 technology as part of the upgrade. I haven't started looking hard at the options yet, but will be shortly. My IDEAL situation would be to incorporate some hybrid technology if it is far enough along yet. A vast majority of our boating life is day trips around the various beaches and bars on the West Coast of Florida. 6-7 knots on generator power would make my day! But, I digress. We'll save that one for another thread.

Here's a quick check on what's happening in 2015...
http://www.michiganmotorz.com/mercr...kage-375hp-inboard-3year-warranty-p-2540.html
https://www.mercurymarine.com/en/us...terndrive/mercruiser/inboards/#specifications
https://www.mercurymarine.com/en/us...rndrive/remanufacturing/plus-series-inboards/
 
MarcOuel said:
Would love to know what options you have mind. Good 380hp 7.4L Merc engines are scarce. And this would be my 5th engine on this boat since I bought it used in 2007. So I really don;t have much interest in going there, and diesels are out.
Click to expand...

Sorry. Didn't see the question.

Crusaders IMHO are a far better built engine. I’ve never heard of one having the ingestion issues Mercs are prone to. Doesn’t mean it’s never happened. I’ve just not heard of it. The RWC impellers are a snap DIY change as opposed to a Merc VLPITA if you can get to it change. They only come up to 6.0L but it turns out 375 HP. It’s a hi rev engine so you would have to check the torque curve. Crusaders were OEM on Sea Rays years ago.

You could go with a reman from a reputable dealer.

If I were made of money there is a fellow in R.I. who makes the meanest small block I’ve ever seen. Pricey, but God what torque. http://boatstoreonline.com/420_MPI.html

Good luck.
 
dpmulvey said:
Sorry. Didn't see the question.

Crusaders IMHO are a far better built engine. I’ve never heard of one having the ingestion issues Mercs are prone to. Doesn’t mean it’s never happened. I’ve just not heard of it. The RWC impellers are a snap DIY change as opposed to a Merc VLPITA if you can get to it change. They only come up to 6.0L but it turns out 375 HP. It’s a hi rev engine so you would have to check the torque curve. Crusaders were OEM on Sea Rays years ago.

You could go with a reman from a reputable dealer.

If I were made of money there is a fellow in R.I. who makes the meanest small block I’ve ever seen. Pricey, but God what torque. http://boatstoreonline.com/420_MPI.html

Good luck.
Click to expand...

The quality of the short block, valvetrains, and fuel systems can't be too different, other than specs, since both are based on GM platforms.
I think the main difference in the two as it pertains to ingestion of water is in the design of the exhaust.
Absent a better alternative, I imagine with a little bit of imagination you would be able to use crusader exhaust manifolds and elbows on a mercruiser motor in an inboard powered boat if you really wanted to.
The exhaust ports on the heads are the same since they are the same castings, so I don't see that as being a problem.
The modifications would probably be in mounting the other stuff that gets mounted to the exhaust, and routing the exhaust to exit the boat after it leaves the elbows.
 
Last edited:
The ingestion issues were centered around the Gen VI valve lash design, and in Sea Ray's case, the original exhaust design. If I repower, the idea will be to get away from the Gen VI block, and get into Smartcraft capable ECMs. Other improvements include dry joint exhaust, and the newness of it all.

Urban folklore was that the cockpit was so inviting, that it was routine to idle around with 10 guests in the aft of the boat, effectively raising the waterline enough to allow backflow through the log exhaust. I think there's some truth to this. I have a deck pad that hasn't seen a butt in years unless the kids are with us.
 
It has been many months since I have posted and just wanted to let you all know that I decided to repower my 1998 370 Sundancer with new Merc 8.1L engines. The project is nearly complete. Both engines have been installed and my mechanic said it was one of the smoothest repower projects he has ever done. Re-used same engine mounts, re-built both transmissions, checked shafts and reconditioned the props. Also removed and serviced/repainted Generator while engines were out. Launch comes in two weeks and I'll let everyone know how she runs! Special thanks to XravenX who gave me the courage to move ahead with new engines instead of trying to keep my old engines going! Speaking of that, I have a very good 7.4L Merc (380hp) on Craig's list if anyone is in need.
 
MarcOuel said:
It has been many months since I have posted and just wanted to let you all know that I decided to repower my 1998 370 Sundancer with new Merc 8.1L engines. The project is nearly complete. Both engines have been installed and my mechanic said it was one of the smoothest repower projects he has ever done. Re-used same engine mounts, re-built both transmissions, checked shafts and reconditioned the props. Also removed and serviced/repainted Generator while engines were out. Launch comes in two weeks and I'll let everyone know how she runs! Special thanks to XravenX who gave me the courage to move ahead with new engines instead of trying to keep my old engines going! Speaking of that, I have a very good 7.4L Merc (380hp) on Craig's list if anyone is in need.
Click to expand...

Way to go :smt038...........you'll be cruising around with a big smile on your face. Yes please report back
 
Awesome.....looking forward to the results and your impressions.

Where did you source the 8.1's? Did you have to do any transmission or shaft work, or was it basically plug n play?
 
I went thru my mechanic who is part of the authorized Mercury network. They use Kellogg Marine to source the engines. I re-used Velvet drive transmissions, existing shafts and propellers. While everything was apart, I checked everything in drive train. I had trannies rebuilt. Props also reconditioned and shafts sent out to check accuracy. Mechanic tells me props may need to be "bent" to add/subtract RPM to get in correct range. Port shaft was 7/1000 out of alignment at tranny end, so fixed that too. Everything else is plug and play. I am thinking of installing Merc VesselView 4 to monitor engines....replace the RayData that is just above steering wheel. Can't wait until the test drive!!
 
You must log in or register to reply here.

Forum statistics

Threads
113,241
Messages
1,429,098
Members
61,120
Latest member
DddAae
Back
Top