MAY DAY ! Repower a FWC 7.4 Mercruiser with a new 383 Stroker or a 8.1 CPO Mercruiser

[Pour Bouy]

I purchased a 2000 27' Sea Ray Sundance powered by a FWC 7.4 Mercruiser in July of 2010. I had a favorable survey and sea trial but the surveyor recommended replacing the risers, manifolds and elbows before any prolonged use. I had this done before traveling by water from Parker Marine in Bristol RI to Onset Bay Marina in Onset Mass. where I keep the boat at a slip. The engine had 251 hours on it when I bought the boat and has approximately 370 hours at present. I had a swamping incident in Buzzards Bay in August 2014 and the engine started to run rough and stall out shortly afterwards. I made it back to Onset Bay Marina and had hem check out the problem. I had them do a compression test and it was determined that the heads were damaged and that the risers, manifolds and elbows had corrosion in them. There were no outward signs of corrosion or rust stains on any of the components. I filed an insurance claim with Boat US Insurance but have been denied after 2 insurance surveyors stated that the swamping incident had nothing to do with the damage but rather it was due to a lack of maintenance and water intrusion through the riser gaskets. I did some research on my own and found that between 1998 and 2001 there were problems with the 7.4 Merc engines involving water intrusion / ingestion due to a valve overlap issue. I am still fighting Boat US Insurance around this issue. In the meantime I have to repower ad my choices are to rebuild, go with a new long block, a certified pre owned 8.1 Merc or a new 383 Stroker. I have been advised that the 8.1 Merc is the way to because it would add power to what is considered to be an underpowered boat to begin with. Any one have any thoughts on this situation or experience / problems with repowering with the 8.1 Merc or 383 Stroker in a similar sized single engine boat ?

 

[hottoddie]

Re: MAY DAY ! Repower a FWC 7.4 Mercruiser with a new 383 Stroker or a 8.1 CPO Mercru

First question is what was the cause of the swamping? Can't figure what the manifolds/risers/elbows have to do with swamping. The 7.4 water ingestion problem I thought was confined only to inboard boats that had the poorly designed exhaust in the mid sized Sundancer models but could be corrected by adding 3" risers between the manifolds and elbows and the changing the mufflers to water lift type. Lastly if this FWC 7.4 has 1/2 fresh water cooling the after 4 years they will show signs of corrosion but it should not be enough to cause a failure. I would not change from the 7.4 but instead have a proper valve job done with new exhaust components. Do t yourself for $1200-$1500 or pay $3000-$4000 to have it done.

 

[Pour Bouy]

Re: MAY DAY ! Repower a FWC 7.4 Mercruiser with a new 383 Stroker or a 8.1 CPO Mercru

I had a following sea on my stern, the bow went down, the transom door opened and my friend got up to close it. He fell down so I throttled back and went into the wave behind me a huge amount of water came through the transom door and into the cockpit also some of the water got into the engine compartment. The engine ran fine up until this incident !

 

[2000SR380]

Re: MAY DAY ! Repower a FWC 7.4 Mercruiser with a new 383 Stroker or a 8.1 CPO Mercru

The 8.1L swap had already been done on our 2000 380DA before we purchased her, and she came into our family with 8.1L engines. I did the same research and was looking for 8.1L V8's. So far they are really good engines, running right on spec. The install appears to have been done by a good shop and the exhaust modified for the new engines. Only time will tell, but after 15 months with pretty heavy use they seem to be awesome engines. As far as the swamping incident : If enough water got in the engine compartment to cool down the engine too rapidly, there could be cracked or damaged components. If the engine attempted to ingest water, while running, that can also be really bad. Water will not compress, so connecting rods will twist and bend, bearings can flat spot, and the engine can be stopped dead. I once worked on a Corvette that ingested water at speed (dove through a big puddle with an aftermarket air scoop), the engine was not only destroyed, the starter had broken itself out of the engine block when the owner had repeatedly attempted to restart it with the intake full of water.

 

[Henry Boyd]

Go with the 496. For starters you can upgrade the gauges to SmartCraft giving you a huge improvement in engine management.

I do know from the PO's records that our 280 had increased height exhaust spacers installed by SR/Merc under warranty to prevent water ingestion, you might look into that.

Henry


Sent from my iPad using Tapatalk HD

 

[Jimmy Buoy]

Re: MAY DAY ! Repower a FWC 7.4 Mercruiser with a new 383 Stroker or a 8.1 CPO Mercru

You say that the manifolds, risers and elbows were replaced when you bought the boat in 2010 and that you have only put 71hrs on it in the 4 yrs since that time? If so, were the replacement risers the same height as the original ones?

 

[Xplicitlnck]

Re: MAY DAY ! Repower a FWC 7.4 Mercruiser with a new 383 Stroker or a 8.1 CPO Mercru

I had a 99 270 with the 7.4. I dont think the boat was underpowered but I do think it was stern heavy. Long plane time and the boat really liked to squat. I changed the props out to a set of 4 blades and I loved them. Still liked to squat but cut my plane off time in half. If i ever had to repower it I would have went with the 383. More power and a couple hundred pounds lighter. Also they claim its more fuel efficient. Everything SHOULD bolt right up and i dont believe you have to change the gears. My boat neighbor did it in his 29 amberjack and raves about them.

 

[dcpringle]

Re: MAY DAY ! Repower a FWC 7.4 Mercruiser with a new 383 Stroker or a 8.1 CPO Mercru

+1 on the 383, A friend of ours replaced his 7.4 with the 383 in a 28 maxum. What a difference it made in the boat. He used to have to use tabs to get up on plane, but after the 383 swap, the boat would jump out of the water. I know he need to put riser blocks or something like that on to elevate the height of the risers... Fuel injected, but like i said what a difference it made for them.

 

[Jon stark]

Re: MAY DAY ! Repower a FWC 7.4 Mercruiser with a new 383 Stroker or a 8.1 CPO Mercru

First question is what was the cause of the swamping? Can't figure what the manifolds/risers/elbows have to do with swamping. The 7.4 water ingestion problem I thought was confined only to inboard boats that had the poorly designed exhaust in the mid sized Sundancer models but could be corrected by adding 3" risers between the manifolds and elbows and the changing the mufflers to water lift type. Lastly if this FWC 7.4 has 1/2 fresh water cooling the after 4 years they will show signs of corrosion but it should not be enough to cause a failure. I would not change from the 7.4 but instead have a proper valve job done with new exhaust components. Do t yourself for $1200-$1500 or pay $3000-$4000 to have it done.

I had the same problems brand new in 2017 less than 15 hrs water intrusion through exhaust had riser blockes plenty of pitch disgusting now they don’t run rite ,mercuiser did nothing to help ! Still under warranty still nothing pissed

 

[Jon stark]

I had the same problems brand new in 2017 less than 15 hrs water intrusion through exhaust had riser blockes plenty of pitch disgusting now they don’t run rite ,mercuiser did nothing to help ! Still under warranty still nothing pissed

Both motors the center exhaust ports loaded with salt and crud plug fouling, not a happy boater