Replace Mercruiser 7.4 - 5L MPI or 5.7L MPI or 6.2L MPI

[dinopaul]

HI,
I currently have a 1998 sea ray sundancer 330 with two mercruisers 7.4 mpi and two velvet drive 5000v with 1.5.1.
I would like to change my engines because here with the new ecological standards and the taxes on the big engines it becomes complicated.
I thought of two 5L MPI or 5.7L MPI or 6.2L MPI
which of these motors will be the most compatible for my boat without modification of installation and with the wiring harness and other ?
has anyone already made this modification
Can you advise me ?
Thanks
Paul

 

[Golfman25]

Your best bet is probably the 6.2 which is the small block replacement for the 7.4. I think it will be a project due to the different size and configuration. Good luck.

 

[suss1173]

The 5.0 and 5.7 is not gonna be enough power/ Tq to move that boat with efficiency. If anything, I would stick with the 7.4 MPI (380hp) motors, and the 6.2 would be my second choice.

 

[northern]

Can you explain the tax implication of 7.4 engine. I am not sure how true it is but a few years ago I was asking a shop about engine replacement and they recommended a V6 Hyundai marine. Person said it was a good replacement to a 7.4 and the transmission was compatible with an adaptor plate. They said it had similar performance to the 7.4.

 

[dinopaul]

Your best bet is probably the 6.2 which is the small block replacement for the 7.4. I think it will be a project due to the different size and configuration. Good luck.

thank you for your reply,
do you know if for the 6.2 the waring harness is the same and also for the flywheel housing vs the 7.4 ?
can we imagine a (plug and play) ?

 

[Mig22]

Have you explored an electric conversion... 400/800hp options are available today and 250/450hp option are coming online in the next year from Evoy..

https://www.evoy.no/inboard/

 

[Golfman25]

thank you for your reply,
do you know if for the 6.2 the waring harness is the same and also for the flywheel housing vs the 7.4 ?
can we imagine a (plug and play) ?

No clue. But I would doubt it. I don't think you'll find a simple drop in replacement. You might be better off looking for a new boat. The 6.2s where standard power in several models, ie; the 340, in the 2000s.

 

[Captain Spike]

HI,
I currently have a 1998 sea ray sundancer 330 with two mercruisers 7.4 mpi and two velvet drive 5000v with 1.5.1.
I would like to change my engines because here with the new ecological standards and the taxes on the big engines it becomes complicated.
I thought of two 5L MPI or 5.7L MPI or 6.2L MPI
which of these motors will be the most compatible for my boat without modification of installation and with the wiring harness and other ?
has anyone already made this modification
Can you advise me ?
Thanks
Paul

 

[Captain Spike]

I have the 6.2’s and find them equally powerful to the 7.4’s I tested. That being said I feel the redesign of the 6.2s was very good and it allows for the much needed extra engine room space from a practical perspective. Good luck !

 

[dinopaul]

I have the 6.2’s and find them equally powerful to the 7.4’s I tested. That being said I feel the redesign of the 6.2s was very good and it allows for the much needed extra engine room space from a practical perspective. Good luck !

thank you for your reply,
do you know if the 6.2 the waring harness is the same and also for the flywheel housing vs the 7.4 ?

 

[hottoddie]

Sounds like your engines are still in good running condition and the reason to change is only due to ecological and tax reason. Without you explaining what those reasons are in some kind of detail the responses here don't mean much.

 

[PlayDate]

Have you explored an electric conversion... 400/800hp options are available today and 250/450hp option are coming online in the next year from Evoy..

https://www.evoy.no/inboard/

This is a joke.....according to their website....it would cost him $600-750k to go this route to replace his big blocks. And he would only have a 50 nm range. I can't find the battery weight but I'll bet it is at least 50% more than gas engines plus a full fuel tank.

 

[Xplicitlnck]

thank you for your reply,
do you know if the 6.2 the waring harness is the same and also for the flywheel housing vs the 7.4 ?

I can almost guarantee you the harness is not the same. Unless you have carburetor motors and plan to stick with carbs. If your looking for a drop in motor long blocks will be your best bet. I'm assuming wherever your boating is trying to pull back on pollution on whatever body of water your on so there taxing boats with bigger motors more? If that's the case your least expensive way is to go with 2 6.2 383 strokers with carbs. Very simple to wire supply fuel and throttle cable and your on your way. As far as flywheel and transmission I honestly have no clue but I'm sure there's adapter plates to mount. Next problem if you replace 7.4 with 6.2 your rpm range of power drastically changes. The 6.2 revs much higher and produces power at a much higher rpm so transmission gearing will have to change as well as prop pitch and our diameter size. How this helps

 

[dinopaul]

Sounds like your engines are still in good running condition and the reason to change is only due to ecological and tax reason. Without you explaining what those reasons are in some kind of detail the responses here don't mean much.

Hi
thank you for your reply,
my engines are in good condition, the story would be too long, but to make short, i bought this boat several years ago in north carolina, but i can only sail inland water because i cannot have CE certification with these engines.
the ecological standards become like in california, also I must change my engines by more recent ones to be able to have the CE certification.
Regarding the taxes here a 7.4 is considered as 46hp fiscally, each hp costs 50 € (+/- 61usd) X2 for two engines and another tax on the hull and this every year.
I therefore think of changing my engines for two 350mpi or two 383mpi more recent with +/- the same power but less expensive for the taxes.

Thanks

 

[dinopaul]

I can almost guarantee you the harness is not the same. Unless you have carburetor motors and plan to stick with carbs. If your looking for a drop in motor long blocks will be your best bet. I'm assuming wherever your boating is trying to pull back on pollution on whatever body of water your on so there taxing boats with bigger motors more? If that's the case your least expensive way is to go with 2 6.2 383 strokers with carbs. Very simple to wire supply fuel and throttle cable and your on your way. As far as flywheel and transmission I honestly have no clue but I'm sure there's adapter plates to mount. Next problem if you replace 7.4 with 6.2 your rpm range of power drastically changes. The 6.2 revs much higher and produces power at a much higher rpm so transmission gearing will have to change as well as prop pitch and our diameter size. How this helps

I can almost guarantee you the harness is not the same. Unless you have carburetor motors and plan to stick with carbs. If your looking for a drop in motor long blocks will be your best bet. I'm assuming wherever your boating is trying to pull back on pollution on whatever body of water your on so there taxing boats with bigger motors more? If that's the case your least expensive way is to go with 2 6.2 383 strokers with carbs. Very simple to wire supply fuel and throttle cable and your on your way. As far as flywheel and transmission I honestly have no clue but I'm sure there's adapter plates to mount. Next problem if you replace 7.4 with 6.2 your rpm range of power drastically changes. The 6.2 revs much higher and produces power at a much higher rpm so transmission gearing will have to change as well as prop pitch and our diameter size. How this helps

thank you for your clarification, but I wanted to avoid changing the transmissions,
my 7.4 are given for 310HP at 4600RPH
the 350 MAG is given for 300HP at 5000RPM
the 383 is given for 350HP at 5200RPM
Do you think that with two 350s I will also have to change my transmission?
thank you for your help

 

[dinopaul]

Your best bet is probably the 6.2 which is the small block replacement for the 7.4. I think it will be a project due to the different size and configuration. Good luck.

Thank you for your reply

 

[Golfman25]

thank you for your clarification, but I wanted to avoid changing the transmissions,
my 7.4 are given for 310HP at 4600RPH
the 350 MAG is given for 300HP at 5000RPM
the 383 is given for 350HP at 5200RPM
Do you think that with two 350s I will also have to change my transmission?
thank you for your help

Your problem is the different RPM curves.

 

[bfernald0]

I would not replace the 7.4s with 6.2s and certainly not the 383s. The 330 is a heavy boat relatively speaking. The small block V8s cannot come close to matching the torque of the big blocks. They try and make up for it with higher revving engines. In order to move that boat with 6.2s you will be running small blocks at higher rpms for long periods of time, which cannot help but dent the life of the engine. In addition, the 383s specifically are not a good product. My mechanic hates them. They have a high failure rate and I believe Mercury is discontinuing them if they haven't already. I replaced my 7.4s with Mercury's new 8.2l ECT Horizons. They have the same footprint as the 7.4. As with all of these engines, however, the harness, throttle and shift, and the transmissions would have to be switched out. It's not a cheap or easy change. However, the 8.2l delivery great performance and decent fuel economy relative to the 7.4s (which in my opinion are under powered for the 340). If it's between the 7.4s and a small block V8, I would stick with the 7.4s for as long as you can. Change the oil regularly and in saltwater change the manifolds, risers and oil coolers every 3 years or so and they'll run forever.

 

[hughespat57]

There are "CE" requirements for boats brought to or sold in Europe based on the yacht classifications A, B, C, D.
But there are also "CE" exhaust emissions standards for engines.
Are you being forced to meet the current standards to document your bought in France?
Even though it was manufactured in 1998?

Class B yacht (boat) is a vessel built to navigate on the offshore waters (200 miles and less) and can substain UP TO force 8 and waves UP TO 4 meters. (35kts/13ft)
Class C boat is a vessel built to navigate inshore such as lakes, rivers, bays and close to the shore and can sustain UP TO force 6 and waves UP TO 2 meters. (25kts/7ft)

A 330 would be 10 meter length, 3.5 meter beam and about 6,000 Kg with fuel and water.
I don't see how it could be more than a "C" class.
The cost you mention is about 4600 euro ($5500) per year, what is hull tax?

I ask not to be nosy but because there is no "simple" way to do this. It is unlikely anything will just drop in and fit and wire up. Not much of a big block will match a small block engine. You may need gear changes, prop pitch changes. This is very similar situation to people deciding to convert to diesel from gas. It can be done but it is not inexpensive and never cost effective.

My 1994 300DA is slightly shorter and slightly less beam but almost the same weight. I have twin Mercruiser I/O 5.7L/260HP and it performs "well" no race boat to be sure, 30kts is pretty much top WOT, 20-24 kts cruise.

If its costing you enough money to convert I would look at diesel vs smaller gas and how that impacts on your taxes.
That would maintain your current performance, save on fuel, improve the value of the boat (but not going to ever sell it for what it cost you to upgrade) and possibly pay for the upgrade by tax savings.

But given the effort involved in either of these solutions could you just sell it at a reasonable return? And buy something in France that doesn't have these issues?

 

[hottoddie]

Hi
thank you for your reply,
my engines are in good condition, the story would be too long, but to make short, i bought this boat several years ago in north carolina, but i can only sail inland water because i cannot have CE certification with these engines.
the ecological standards become like in california, also I must change my engines by more recent ones to be able to have the CE certification.
Regarding the taxes here a 7.4 is considered as 46hp fiscally, each hp costs 50 € (+/- 61usd) X2 for two engines and another tax on the hull and this every year.
I therefore think of changing my engines for two 350mpi or two 383mpi more recent with +/- the same power but less expensive for the taxes.

Thanks

My math says the "tax" on the engines alone are about $5600 per year, am I right plus tax on the hull. So if you spend $30,000 upgrading to new 6.2s how much would you save? I can't believe it would be worth it. If I were you I'd buy a sailboat (YUK).