185/4.3 Alpha One Cruise Speed

F

firecadet613

Well-Known Member
May 10, 2007
5,253
Indiana
Boat Info
SOLD - 2007 Four Winns V358
Engines
Twin VP 5.7GXi V-Drive / ZF63s
What is the best cruising speed/RPM for my boat? I've seen people say anywhere from 3000-4000rpm. I've got a Michigan Wheel Rapture 21P SS prop.
 
I think this is from the same year as yours...

Test Power: 1 x 190-hp MerCruiser 4.3L MPI
RPM MPH Knots Total GPH MPG NMPG Range NM Range dBa
1000 5.2 4.5 1.0 5.42 4.71 127 110 77
1500 7.1 6.2 2.3 3.09 2.68 72 63 82
2000 9.0 7.8 3.5 2.56 2.22 60 52 81
2500 20.9 18.2 4.3 4.86 4.23 114 99 83
3000 27.7 24.0 5.7 4.85 4.22 114 99 85
3500 34.7 30.2 8.6 4.03 3.51 94 82 85
4000 42.0 36.5 11.1 3.80 3.31 89 77 88
4500 45.6 39.6 14.5 3.14 2.73 74 64 95
4750 45.6 39.6 15.1 3.02 2.62 71 61 98

Speeds measured with Stalker ProSports radar gun. Fuel consumption (gallons per hour) measured with Floscan digital fuel-flow meter on gas inboards, sterndrives, and outboards, TechMate electronic scan tool on gas EFI inboards, Caterpillar digital fuel-flow meter on diesel engines, or permanently installed fuel-monitoring equipment. Range is based on 90% of published fuel capacity. Sound levels determined using Radio Shack digital decibel meter on A scale. 68 dBa is the level of normal conversation.

Performance Chart

Test Conditions
Test Power: 1 x 190-hp MerCruiser 4.3L MPI Time To Plane 3.9 sec.
0 to 30 6.9 sec.
Test Power 1 x 190-hp MerCruiser 4.3L MPI
Transmission Alpha One
Ratio 1.5:1
Props 14x23 3-blade aluminum
Load 1 person, 3/4 fuel, no water, min. gear
Climate 91 deg., 45% humid., wind: 10 knots; seas: 1 foot chop
 
Looking at the data, I would say 2500 to 3000 rpm.

In reality. . .the peak efficiency for the engines and boat is the slowest where you can comfortably stay on plane. As you accelerate from that point. . .the engine power needed vs speed follows a geometric rather than linear relationship.

This sad relationship continues until weird things start happening with the props (they start cavitating, and are no longer spinning efficiently). . .which from this data would suggest happens between 4000 and 4500 RPM.

The data from this test boat looks very similar to my boat. . except that my 280SS will sink off of plane at about 2800RPM/25mph or thereabouts.
 
I've heard high RPM usage can dramatically shorten engine life. I'm assuming thats more like WOT? I've been reading some threads about the 240DA where they cruise at 4000RPM. Do their engines have a similar redline to mine?
 
I have always heard that operation at 3/4 throttle setting or lower is recommended and you should refrain from prolonged operation at WOT RPM
 
Running WOT wears out the engine. Yes.

Engine life is measured in hours, right?

In reality, engine wear is more a function of total revolutions - all else being equal. And all is NOT equal. At high RPMs, you are "pushing" components in the system. Oil circulation and water circulation in particular. The revolutions at WOT are *harder* on the engine.

Put it another way: These are (more or less) car engines. Car engines generally tend to run at 30%-40% load. My V8 runs at 2000rpm at full highway speed. Marine engines run much higher load all the time.

Aircraft engines run at much higher load. . but are built a bit different (i.e. redundant ignito's and such) and I think get more maintenance.

_____________________

I recently had an issue with my boat, and took my mechanical out for a seatrial. He got antsy when I pushed the boat WOT for more than 1 minute -> and thats when he thought the engine was running perfect,
 
I run at 3000 rpm which is about 30 mph. I have ran at 2500 rpm but that is a much slower cruising speed. When I run at 3000, I have the drive tab 1/4 of the up. At 2500 I have the drive tab down or almost all the way down.

This past friday, I had it up in the 3500 - 4000 rpm range when rain was just starting. she was real comfortable at that rpm range.
 
My 2004 185 Sport 4.3L calls for 3500 @35 mph, I can get that with just me on board, but when you add 1 to 4 more people and gear for the day then I could not quite get the 35 mph. 3500 rpm is the sweet spot for mine.
 
I push my engine all the time, WOT and planing as fast as possible. I think the out drive will take a dive before the engine ever will. These engines are built a bit different than car engines. They have better (sometimes forged) rotating assemblies. My 4.3 must be balanced, because it runs smoother than any S10 I have ever seen. Also these engine are redlined way early in my opinion. I have seen numerous SBC and SBFs turn many more RPM than 4800 to 5000.

The short of it: These engines run at realatively low RPM, with beeter rotating assemblies, and less dynamic loading (no stop and go traffic)

Life is short, run hard have fun!
 
DAVECS1 said:
I push my engine all the time, WOT and planing as fast as possible. I think the out drive will take a dive before the engine ever will. These engines are built a bit different than car engines. They have better (sometimes forged) rotating assemblies. My 4.3 must be balanced, because it runs smoother than any S10 I have ever seen. Also these engine are redlined way early in my opinion. I have seen numerous SBC and SBFs turn many more RPM than 4800 to 5000.

The short of it: These engines run at realatively low RPM, with beeter rotating assemblies, and less dynamic loading (no stop and go traffic)

Life is short, run hard have fun!
Click to expand...

I disagree with you on this one. If I recall you purchased your boat last year and it has a low 142 hours on it. The difference between what you do in your car and your boat is your car does not have sustained high RPMs. Maybe your S10 (I think that is what you said you have) is set up different than any vehicle I have ever had but WOT for sustained amount of time in a boat is not good for your engine. We usually cruise at 3000 to 3500 RPMs for sustained periods of time and I do not recall ever doing that in a car or truck. You manual should also state that long WOT usage is not a good thing. I agree life is short but replacing your engine is no fun!!! Again this is just my opinion and enjoy your boat the way you want to. But I do feel it is a bad idea to be telling other new boat owners who read your post that it is fine to push their engine all the time for sustained amount of time. :smt009

Wesley
 
pushing at full trottle

to Davecs1,
please define you wot, at what rpm, lenght of time per run, sea conditions, mph.
:smt001
How long is day of outing, going point to point or constanting on the move.

is there a rescue service nearby or do you have to depend on yourself to rescue youself. Safe boating has a lot of considerations besides going fast all the time. Please explain further your burst of speed. :smt101
 
I wouldn't run WOT for a long distance either, it's okay for short runs, but is definatly harder on the engine. A good example would be race car engines, they are built way better than our engines, run wide open for several hundred miles then they are rebuilt. I've run long distances at 4000 rpm when in a hurry ie. weather or something, but I have to slow down to no wake speed several times due to all the no wake zones on the ICW around here. This puts the out drive back in the water an cools it down and also gives the engine a little break. I'd agree with First Born that 3000 to 3500 rpm is a very good range for cruising with our engine/boat combo.
 
Well I agree with you guys, that everyone must be responsible when boating. That was never a question. I also agree that when running the 4.3 with a 21-23P prop, 3000-3500 RPM is right around optimal for fuel usage and wear on your boat.

I guess the point I was trying to make, was that these engines are not that fragile, and that there is a big difference in the wear and tear of your engine versus your sterndrive.

Charlie L. Stated the following:

"A good example would be race car engines, they are built way better than our engines, run wide open for several hundred miles then they are rebuilt."

No, really these engines are no that far from race car engines. I am not talking NASCAR, but go down to your local dirt track. You will find that most of the rotating components, and the heads you have in your boat are the same thing they run every sat or sun night. And these guys are on a budget, so they can't afford to rebuild after every race.

When I talk about WOT in my boat, that is about 4500 RPM at 52 mph. I usually run the Peoria and Pekin pools in the Illinois river. So there are some things to consider. I am never that far from shore, and the river has a long way to run. I usually run WOT for 10-15 minutes at a time

Another thing to consider is that I am maticulous on maintaining my boat. I change the fluids twice during the boating season, and before and after winterizing. I use only Mercruiser fluid and filters. I also clean and inspect my boat and stern drive after every outing. I have a log book of all the parts and fluids I have changed and it stays under the dash in the boat. Also I change the cap rotor and plugs for every boating season. In my mind there is not much difference between driving a boat and flying an airplane, if it fails you just can't stop and get out like an automobile.

As far as cars turning 3500 4500 RPM cruising. If you drove autos before the 80's. It was common to have cars roling down the street at these RPM's. We did not always have overdrive transmissions. I have had several cars that turn almost 4000 RPM doing 75 mph. Did it waste gas? Did I have more maintenence? Yes, but the engines were not always being pulled.

I guess my point is, I would not be afraid to lean on your 4.3L if it is well maintained.

No offense to S10 owners, but I do not own one of those bucket of bolts. I have a GMC Sierra Denali with Quadsteer (best thing since sliced bread)

Please read this as a friendly discussion as this is all it is meant to be. Life is too short to argue, but am always up for discussing the technical merits of big boy toys,, especially over a couple of ine belgium beers :smt001
 
What kind of top end GPS speed and WOT RPM are you getting with that prop? We have about the same boat, and I've got a 21P Apollo on there after all, originally purchased a 23P Rapture but exchanged for the Apollo. I turn 4800 at WOT and about 50 MPH.
 
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