3.7 to 4.3 swap

[Dubed]

post 1996

Thanks!
Out of curiosity, any particular reason 96 and up? What changed?

 

[Scott06]

Thanks!
Out of curiosity, any particular reason 96 and up? What changed?

Vortec heads were introduced adds about 20 hp vs non vortec

 

[achris]

post 1996

Post mid-96 (also known as 'Gen+').

Beware, the pre-96 4.3L engines (also know as 'Gen II') also have 'Vortec' on the rocker covers, but they are NOT Vortec heads. You can pick the difference by the intake manifold bolts.

Vortec intake has 8 bolts going straight down.
Non-Vortec intake has 12 bolts that run in at a 45° angle.

Chris.......

 

[Dubed]

Post mid-96 (also known as 'Gen+').

Beware, the pre-96 4.3L engines (also know as 'Gen II') also have 'Vortec' on the rocker covers, but they are NOT Vortec heads. You can pick the difference by the intake manifold bolts.

Vortec intake has 8 bolts going straight down.
Non-Vortec intake has 12 bolts that run in at a 45° angle.

Chris.......

Awesome. Will keep that in mind.
If I get a donor boat pre-96 and just buy a reman vortex long block, everything else will be good? Except the intake will be different?

 

[achris]

...Given that a 190 hp 3.7 pushes the boat fine ...

And that's 190 CRANKSHAFT hp. A 2bbl Vortec 4.3 produces that at the prop! The 4bbl is 205 at the prop (probably around 230 at the crank)...

Chris....

 

[nola mike]

Awesome. Will keep that in mind.
If I get a donor boat pre-96 and just buy a reman vortex long block, everything else will be good? Except the intake will be different?

No, some accessories will be different as well as the balancer, starter, some metric bolt... Vortec block will be serpentine instead of v belt drive

 

[Scott Danforth]

Awesome. Will keep that in mind.
If I get a donor boat pre-96 and just buy a reman vortex long block, everything else will be good? Except the intake will be different?

what makes a vortec a vortec is the heads

and the vortec heads will fit on the earlier balance shaft and non-balance shaft motors

 

[Rick Stephens]

While the recommendation is to find a '96 or newer, nothing wrong with an earlier 4.3 if you find a nice one as a donor.

 

[Lou C]

True the only downside to the older ones other than condition is that the ones without the balance shaft don't run as smooth, but they used softer engine mounts to compensate. You will feel a harmonic vib at about 1700 rpm or so. The ability to run a mechanical fuel pump on a carbed engine in my mind is a plus. Cheaper, more reliable.

 

[jimmbo]

Bollocks! 4.3 propped right is plenty good enough. And with the want of passengers to head aft, you'll be grateful not carrying that extra 100kg!

Small engines have to spin higher Rpms to get the same power that a bigger engine gets at lower rpm. The Extra Torque from the greater Displacement is what bigger boats need most. Given a Choice between a 220hp 4.3 and a 220hp 5 Liter, I will take the 5 liter(though I consider it too small for anything over 18ft) in a heartbeat. The 5.7 is about perfect for a 18 1/2 ft

 

[nola mike]

While the recommendation is to find a '96 or newer, nothing wrong with an earlier 4.3 if you find a nice one as a donor.

I think he was talking about pre-96 donor boat + post-96 longblock, in which case he'll run into the same complications that I did. The swap will definitely not be as straight forward. Don't know what the price difference is, but if you're going to do a reman anyway, might be worth it to just spring for a bobtail. Or find a newer donor boat. Other thing to mention is that at least in my neck of the woods, a 4.3 marine donor is a lot harder to find than a v8.

 

[achris]

.... The 5.7 is about perfect for a 18 1/2 ft

That combination would require quite a large prop (pitch) to keep the revs in check, and at normal cruising speeds (16-23 knots) is going to be out of the bottom end of the power band, and hence a dog to drive. And when the seas kick up and cruising speed is down in the 12 to 15 knot range, the thing's got nothing in the torque department. You'll have an extra 100kg of dead iron dragging the boat's backside down for no reason and it would have no response, at all (and in an 18 foot boat, 100kg at the back is anything but insignificant). How do I know this? Been there, done that...
I don't think you understand about the torque curve vs cruising speed. Sure, that combination as a small (waveless) lake speed demon would be perfect, but in the real world, I'll take a V6 over a V8 any and every day of the week for boats in the 19 to 23 foot range...

Unless.... You're one of those lake people, in which case, knock yourself out. But for sea and ocean, bad idea! No seriously, such a large engine in such a small boat is a very bad idea.

 

[jimmbo]

Lake Boating where the waves get a little nasty is where I boat. The Boat actually holds 22(statue)mph very well. I run at that speed a lot as it allows me to stand up and get some cooling on Hot Days, 20c and above. It is propped to hit the upper end of it's rpm range, with a 1.51:1 gearbox. It has great Acceleration, almost as good as an Outboard

 

[Dubed]

Thanks guys!
You've given me loads of information to dwell on and managed to confuse the crap out of me at the same time...

I think a good vortex 4.3 would suit my needs and give me better weight distribution, be a bit less cramped in the engine bay, better fuel ecomy (huge plus right now), and be more economical to purchase, maintain, etc.
Knowing how a 4 cylinder powers my boat now, I can only imagine the 4.3 being so much better and reliable.
Now to find a donor that makes sense.

 

[Scott Danforth]

I think a good vortex 4.3 would suit my needs and give me better weight distribution, be a bit less cramped in the engine bay, better fuel ecomy

marine spark-ignited I/O motors burn 0.4# of fuel per HP per hour. so fuel consumption is solely dependent on load and commanded throttle. if you load a 5.7 liter motor and a 7.4 liter motor and a 4.3 liter motor to 150hp for an hour, they all burn 60# of fuel in 1 hour (8.8 gallons)

 

[jimmbo]

The only time you will save fuel with smaller engine is idling in Neutral. The larger engines will match the smaller one's WOT Speed, at part throttle and usually be burning less fuel doing so.

 

[achris]

The only time you will save fuel with smaller engine is idling in Neutral. The larger engines will match the smaller one's WOT Speed, at part throttle and usually be burning less fuel doing so.

Maybe true in a car, but in a boat you also have to consider the not inconsiderable extra water drag created by carrying 100kg of dead iron around, especially at the back of the boat... If you're on a lake (like you are) then maybe you have the sort of waters where you can use the extra power more often than not, but in larger bodies of water like Oceans, the opportunities to use the extra power granted by a V8 are so few that it really is dead weight. And dragging that dead weight around costs $$$. Yes, I agree that the other end of the scale is also a bad idea. Seen a lot of people get into some fairly serious trouble because of a lack of power, but if a boat (in the 17 to 25 foot range) can achieve 35 knots top speed and comfortably cruise between 15 and 25 knots, while still in the power band, then THAT is the right power for the boat. In boats (in oceans), too much power is just as dangerous as not enough.

Chris.....

 

[jimmbo]

The fuel economy of WOT on a small engine in a Boat, vs a bigger Engine at Part Throttle, has be discussed/documented for over the past 70 yrs. All of them have concluded that the Bigger engine did better. The one time I was on Salty Water, not true Ocean water, was in Vancouver BC, Burrard Inlet, there were no boats on plane, every one of them was just puttsing along and I could understand that a larger engine wasn't of much use. I kind of like going around 70mph.

 

[achris]

.... I kind of like going around 70mph.

Thank you...

 

[Dubed]

Where I spend most of my time fishing is usually the sweet spot between the boat staying on plane and dropping off plane, any faster and the sea will beat the snot out of me. Where I could use more power is in the bay and rivers however when we go outside that extra weight would offset my balance of planing or not (in my opinion). I am simply looking for more reliability than the old discontinued 3.7 can give me. I have had this boat since 2008 and have never been disappointed in its performance inshore or offshore. But am tired of digging for good used parts and the feeling that I'm stuck with this motor eventually leading to the demise of my boat which I love. Just trying to get ahead of the inevitable