Extra power Mercruiser 3 litre
 

Hello Guys,

Are there any straight forward upgrades to increase the power of a standard Mercruiser 3 litre? I have a new prop to install for the start of the season but was wondering if anyone can advise me on easy power gains (apart from the obvious, buying a bigger boat).

Thansk very much,

Gary

There's not a lot you can do to a 3 litre to provide a 'significant' power increase without going to considerable expense and reducing your reliability. Keeping it tuned and correctly propped, keeping the hull clean and reducing any excess weight in the boat is about the best you can do........ but i would consider swapping your motor for a 4.3 litre. Should be a straight swap and the Alpha one should bolt right on. That will take you from the mid - high 30mph range up to closer to 50mph and provide much more grunt.

Re: Extra power Mercruiser 3 litre
 

I was curious, found this old post and you mention that the 4.3L should be a direct swap? I was just curious if a swap would ever be possible on my 2001 Diablo 180. I don't plan on doing anything like this for a long time... but 4-5 years from now I may be interested in doing such a swap. My plan is to hold onto our boat and just upgrade it over time. I'd like to make the interior a little nicer one day (it's mint now... but could be more upscale with some professional help), although I have to admit that for a base model it looks a heck of alot better than some current models out there.

Re: Extra power Mercruiser 3 litre
 

LOL ,,,,get a bigger motor :)

Re: Extra power Mercruiser 3 litre
 

Get a bigger motor had a 3 liter in my last boat. Not much power top end and terrible resale value. I just got a 5.0 in my new boat.

Re: Extra power Mercruiser 3 litre
 

Unless your in love with your Diablo ng , buy another Mariah when your ready. Between the cost of engine and changing gear ratios in the drive , you'll be money ahead buying a different boat.
However , if you do like your Diablo as I do mine..........it is quite possible to do.
Mercruiser 4.3 package

Re: Extra power Mercruiser 3 litre
 

I would think that it would require a significant amount of work to fit a 4.3 in the place of the 3.0? Wouldn't a modification like this require extensive fabrication to the hull inorder to mount the motor? If going to the expense of modifying to fit a 4.3L why not step up to something larger? Has anyone seen or done a similar swap?

Re: Extra power Mercruiser 3 litre
 

just spit balling here, but how far could you go with this?
what sort of power could you fit in a Diablo
Would she take a small block :rolleyes:

Re: Extra power Mercruiser 3 litre
 

hahahaha!
like minds same times......lol

Re: Extra power Mercruiser 3 litre
 

I agree, i'm in no hurry to sell or upgrade our Diablo. It is in excellent shape, and I could see a motor upgrade being possible in the future. I'm sure I could easily buy another boat - but "if" a swap was possible, why not take my paid off boat and create a river monster out of it. I'm sure a 4.3 would be fine, but i'm not sure how the cost would compare.. seems that it would cost as much as a V8.

Also - I just passed up a deal on a 98 model (can't remember make) boat that had a volvo drive and V8 - I could have picked up this boat (which i understood ran when parked) for around 400.00 cash. The motor probably needed a fresh rebuild to be safe - but i'm thinking having a donor boat would be the best route if you were going to do a swap?

Any thoughts?

Re: Extra power Mercruiser 3 litre
 

Yep, ya gotta remember the max prop horsepower the 180 is rated for is 210. Anything over that might lead to transom issues and the extra weight of a V8 will really make your Smart Tabs work to keep the bow down and the stern off the bottom.

Re: Extra power Mercruiser 3 litre
 

Unfortunately a 4cyl to v6 or v8 swap isn't simple or straight forward, the engine mounts are different and so is the upper outdrive, it has a different gear ratio for the 4 banger. As the owner of an 18 footer with a 3L I can say that having two different props will make the boat much more usable. For cruising and light loads I use a 3 blade 21 pitch, for watersports and and an awesome holeshot I use a 4 blade 19 pitch.. 25-28mph is a comfortable cruise speed with the 21 pitch 3 blade, 22-25 is comfortable with the 19 pitch 4 blade.

Re: Extra power Mercruiser 3 litre
 

4.3 will bolt in with no mods to the hull. All you need is the 4.3 motor mounts , and the drive or regear yours.
Buy another boat.

Re: Extra power Mercruiser 3 litre
 

The 4cyl mount is in the front of the engine, the v6 and v8 have mounts on the sides of the engine.. or am I missing something?

Re: Extra power Mercruiser 3 litre
 

Another issue with over powering a 180 is length,
Stability at the top end of my range now (48-50mph) gets a bit light!
Not sure I’d want to go much faster in this boat! I could see it swapping ends quite easily.

Re: Extra power Mercruiser 3 litre
 

The motor mount towers are there , just not used by the 3.0.
Maybe I'm wrong.......it is early.
Why would they manufacture a hull for each engine/drive package? A lot of extra work.

Re: Extra power Mercruiser 3 litre
 

I agree, it's the same hull whether it's a 4, 6, or 8. Mine being a 4 has nothing there to mount the 6 or 8, so holes would need to be drilled in the stringers for the new mounts.

Re: Extra power Mercruiser 3 litre
 

My Mercruiser 3.0 on Alpha one is definitely under powered for the weight of the Mariah 18 SX,I need to overhaul the engine and I am now considering to upgrade it to a 4.3 V6....from the above thread it seems a straight bolt on right? will we have to do modifications for the exhaust? will the Alpha one sustain the additional power (assuming no modifications to be made on the shaft)

Re: Extra power Mercruiser 3 litre
 

As the previous posts stated, it is a fairly straight forward swap from a 3.0 to a 4.3 and the Alpha 1 will handle up to 300 hp which is far more than the 4.3 liter will put our or the 180 hull can handle. You may though have to change out the gearing in the Alpha 1 because of the increased 'grunt' of the 4.3. Personally..... i would just sell that SX18 and buy something with a 4.3, 5.0 or 5.7 in it.

Re: Extra power Mercruiser 3 litre
 

Thanks Mike.

I did not know the Alpha 1 would be able to handle upto 300 bhp !

Re: Extra power Mercruiser 3 litre
 

Yeah! I'm wondering the same thing.
If a V8 will fit, I have a pile of small block ford motors, including a 351 and a pair of GT40 heads...
I wonder how fast an 18' Diablo would scat with a stroker motor and a bravo3?