What can I expect?

[rch105]

As my engine froze and cracked 2 winters ago, I'm finally getting a replacement Mercruiser. The oroginal was a 4.3L with 190hp.. The new one is Mercruiser's 4.3L with 225hp. All being equal except the engine swap, what changes could I expect to see as far as top end, acceleration, etc?

 

[gm280]

Probably not much. It takes a LOT of extra HP to see much of a different in top speed...

 

[Bob_VT]

Well you have increased over 10% and I bet you might see a HUGE improvement from a 18 year old motor to a newer one. It will be a new awaking for the boat! I bet the handling and economy will be changed too. As mentioned it won't be a big increase in speed but I bet you will be happy!

 

[ahicks]

What can you expect? This engine will run for starters.

From there, watch your max rpms. If you had the right prop on it originally, one that would allow the original engine to turn right at max rpms, this new engine, having more power, should turn up even higher rpms - to the point you may need to be careful what you are doing possibly.

 

[roffey]

I would go with a new prop as ahicks said more power and likley more RPM. I bet you can get an extra 5-10 MPH with a different pitched prop... now the big question is what prop do you get, lol. Props are a whole science in to them selves...

 

[Scott Danforth]

if your new one is a reman....remember that 225hp is at the flywheel

your original was 190 at the prop...

taking into consideration the driveline losses. your new motor is 200-205hp at prop

so that 10-15hp wont amount to much noticeable change other than the new one runs

 

[rch105]

Thanks for the replies everyone!

 

[QBhoy]

I’d say she will go a little better. But as said. Anything over the 50 mark in speed takes ridiculous hp increase to see any real margin. It gets worse over 60 haha.
At a push. You might be able to turn an inch or two more pitch to a better tune than before. But 10mph speed gain...you won’t see. 2/3 would be a good result.

 

[QBhoy]

I remember as a younger man going from a 150v6 merc outboard to a 200v6 outboard on my old ring 18 (racing derived hull in U.K.)...expecting a massive gain. Wasn’t the case. The difference was 2/3mph tops and only on occasion. Same prop.

 

[Lowlysubaruguy]

Chances are the hp difference was mostly achieved by fuel delivery and newer spark controls anyway so the gain will most likely be minimal. As far as your old 4.3 unless it had a wear related performance issue it probably hasn’t or hadn’t lost much top end mine has not still dead on with it from when it was new.

I think the the thing you need to know is how to pull all the water drains easily. I pull mine at the boat launch and twirl a screwdriver in each one any time the temp could get cold enough to freeze the block. Takes me a couple minutes now. Make it habitual enough your can do it with your eyes closed which is basically how it’s done anyway can’t see them anyway.

 

[Scott Danforth]

Lowlysubaruguy this is the motor the OP is re-powering with https://www.mercruiserparts.com/4-3l-alpha-4v

it is a 1996 or newer vortec headed 4-barrel carbed 4.3.... rated 225 at the flywheel (in a boat it would have been 205hp)

the 190 that was on the boat originally was a 1996 or newer vortec headed 4.3 with a 2 barrel TKS carb and rated 190 at the prop when in front of the Alpha drive. (about 210-215hp at the flywheel)

the difference in HP is the 4 barrel carb (as they both have the same ignition) and how they rate the motor.... nothing more.... nothing less.

you are correct, the gain will be minimal

 

[rch105]

And again... my thanks!