What MPH are you folks hitting?

kelster1574 · 03-23-2011, 01:56 AM

I was just wondering what kind of MPH you folks are getting out of your 4.3L Mercruisers? I know it's a avague question but I have a 1991 Diablo MX 180 and was just kind of wondering what I should expect when I get on the water. Just an FYI it's an aluminum 14.5x17P prop (I am planning on upgrading to a 4 blade stainless soon).

***mikeyt*** · 03-23-2011, 02:55 AM

You might find that 17" prop will really reduce your top end although you should have lots of low end grunt!. Most here with a 18' will run a 19" - 3 blade. Some of us run a 20" - 4 blade, some run a 21" - 3 blade and there is one of our members that runs a 23" pitch. Your boat should hit between 46-50mph depending on a number of variables such as engine tune, prop used, condition of prop, condition of boat hull, load carried in the boat etc... Your 4.3 is designed to run most efficiently between 4400 - 4800 rpms at WOT so i would suggest you take it out with the existing prop first & record your WOT rpms and top speed preferably with GPS. Then you can make adjustments to your prop selection based on what you want to use your boat for.

I thought i read elsewhere that you have a 'foil' for the outdrive. I wouldn't install one of those things on my mother-in-laws boat but since it's your boat, it's your call. A number of us have gone with Smart Tabs by Nauticus. For less than $150 you get something that you can install yourself, gets you on plane faster & holds plane longer, reduces low speed wander, some report that it increases their top end speed, they are adjustable and i found that mine tend to stabilize the boat at speed. On top of that the manufacturer has very good customer support. Do a site search for 'Smart Tabs' and you will find lots of information on them and what other members have experienced.

kelster1574 · 03-23-2011, 02:09 PM

The Hydrofoil is getting axed. My buddy has a brand new one that he was giving me to replace the small sting ray that is currently on the boat. I already called him and told him thanks but to keep it. I plan on removing the small sting ray and installing the smart tabs ASAP. I have read too many "bad" stories and since the motor is in good shape I would like to keep it that way. Thanks for the heads up. As far as the prop goes I am going to run it with the smart tabs first then make up my mind.

Dredd · 03-23-2011, 02:16 PM

I could usually get 45-48 mph out of my MX-19 at 4800 RPM depending on load and conditions. I was running a 19" SS prop. Mine would easily over-rev with that prop but we wakeboard a lot. If I still had the boat I would have tried a High Five prop on it this year.
30-35mph is what she loved and where she was typically ran for 'running about'.