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Old 02-12-2017, 09:14 AM   #1
oliviernh
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Default Merc 4.5L 250HP

Went to the Boston Boat Show yesterday. Lot's of beautiful boats. One thing I noticed was that many of the new boats in the 21-23' length were now coming with the Merc 4.5L 250HP engines. My gut tells me that a V6 engine like this just wouldn't be powerful enough for a boat that size. The dealers all assure that they are plenty powerful enough and "you wouldn't be disappointed". Of course they have to say this otherwise they won't sell any boats. Any one have any experience with buying a boat with this size engine or have you test driven one? If you had 6 people in skiing or wake boarding would it have enough power out of the hole? Thanks
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Old 02-12-2017, 01:25 PM   #2
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I have a 21 ft. Crownline with a 6cylinder. I too was skeptical. Boat does 52 mph and my kids ski behind it with no problem at all. My kids are all adults.
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Old 02-12-2017, 02:56 PM   #3
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Merc is pitching the 4.5 250 v6 as an alternative to their 5.0 260 V8. With the weight savings on the v6 I bet the overall performance of the 2 are very similar but definitely better gas mileage on the 4.5. Whether or not either of those are suitable for up to a 23' boat I would agree with you that for 23' that's not enough power especially for 6 people + water sports/towing. You can probably squeeze by with that set up on a 21' but anything bigger definitely opt for more power if that's your intended use case for the boat. If you are really struggling with the decision and are worried that a simple test drive won't give you the answers you need, it may be worth it to rent a boat from one of the marinas on the lake with similar specs to what you are looking for. Load the boat with people and gear for the day and see how she performs.
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Old 02-12-2017, 03:54 PM   #4
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We had a 22 foot Boston Whaler Revenge with a cuddy cabin on Cape Cod.
200 hp Mercury outboard and that boat was very heavy with commercial hull.
WOT at 4400 rpm, cruised at 3700 rpm and 5.5 mpg.Fuel tank 70 gallon. Our neighbor asked to ski one day and after that I was elected the ski boat by everyone. So if 200hp was great for that boat surely 250hp will suit you fine.

I am a retired workaholic and continuing aquaholic.
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Old 02-12-2017, 04:30 PM   #5
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HP is HP, number of cylinders and displacement don't matter. I had a 21 footer with 220 HP; it was quite snappy and topped out well north of 50 MPH. Another 30HP with less weight would be sweet in a 21 footer.
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Old 02-12-2017, 08:48 PM   #6
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HP is HP, number of cylinders and displacement don't matter. I had a 21 footer with 220 HP; it was quite snappy and topped out well north of 50 MPH. Another 30HP with less weight would be sweet in a 21 footer.
That has not been my experience. In my opinion there is no substitute for cubic inches and torque.

Last season I changed from a 26 foot boat with the 8.1 375 HP motor to a 27 foot boat with the 6.2 380 HP motor. The 8.1 seemed to have twice the acceleration and overall power, much more than the boat with the 6.2 that claims 5 more HP. The 6.2 is average at best and works a lot harder to get up and go. The 8.1 never even broke a sweat and even with 15 people on the boat I could hardly tell the difference in performance.
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Old 02-13-2017, 07:34 AM   #7
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Torque gets you going. Horsepower keeps you going.

If one were to look at a graph of the torque curve of both the engines cited above, it might show that the 6.2 has less torque at lower rpm.

There's no replacement for displacement.

One way to make an boat perform better from stationary to plane is to reduce propellor pitch. Top speed will be reduced but boats often have plenty of speed at the top that is never used.


EDIT: A look at Mercruiser's website shows HP specs but not torque.
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Old 02-13-2017, 09:48 AM   #8
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I won't argue with the "there's no replacement for displacement" point, it does play big part in getting a heavy boat up on plane. What also plays into HP / performance differences between one boat and another is hull design. This can include the deadrise angle at the transom, lifting strakes or sponsons included in the bottom design to help lift and so on.

In the case of the 4.5L / 6 cylinder Mercruiser, I believe this is a true Mercruiser engine as opposed to a marinized GM engine that has been the typical choice of Volvo, Mercruiser and Crusader. I think the thought was to have their own engine in place in case large V8 engines go away in the future.
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Old 02-13-2017, 10:22 AM   #9
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That has not been my experience. In my opinion there is no substitute for cubic inches and torque.

Last season I changed from a 26 foot boat with the 8.1 375 HP motor to a 27 foot boat with the 6.2 380 HP motor. The 8.1 seemed to have twice the acceleration and overall power, much more than the boat with the 6.2 that claims 5 more HP. The 6.2 is average at best and works a lot harder to get up and go. The 8.1 never even broke a sweat and even with 15 people on the boat I could hardly tell the difference in performance.
I can totally believe that, but you can't really compare the performance of the two engines unless they are in the same boat, with the same load, with the same drives, both propped correctly, and both running correctly. Way too many variables otherwise.

Additionally, the HP on the 375HP 8.1 might have been under-rated in order to sell more 425 HP versions of the same engine. Conversely, the 380 HP rating on the 6.2 might be over-stated in order to encourage people to pay a premium over the lower HP versions of the same engine.

I'm perplexed by Mercruiser's decision to go away from GM based engines. I think the variable valve timing, that is part of the GM marine engine line, is a massive advantage over the fixed valve timing you find in Mercruiser engines, in a marine application. It allows you to run an aggressive cam to make big HP, but still idles smoothly, pulls strongly from low RPM, and does not suffer from water reversion ingestion due to too much cam overlap at low engine speeds.
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Old 02-13-2017, 12:15 PM   #10
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I'm thinking engine companies are very careful now with horsepower ratings as I remember a company, I think VW or Subaru was sued for overstating ratings and Tecumseh was sued out of the engine business.

I'm amazed at the advances in technologies. Chrysler has a V6 that is rated at 305 hp and will soon make more with direct injection. The big advantage to a v6 is lighter weight. The V-8s are making 465 hp but I think the CAFE increases might be there doom, on the other hand, we have been hearing that since the 70s.
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Old 02-13-2017, 12:35 PM   #11
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I'm amazed at the advances in technologies. Chrysler has a V6 that is rated at 305 hp and will soon make more with direct injection. The big advantage to a v6 is lighter weight. The V-8s are making 465 hp but I think the CAFE increases might be there doom, on the other hand, we have been hearing that since the 70s.
I drove a rental Challenger with that 305HP V6. If memory serves it had an 8 or 9 gear transmission too, so it was always in the power band and was quite snappy. I'm routinely amazed by my wife's 2010 Toyota Rav4 V6. It's a boring looking little soccer mom car, but if you stomp on it, it rips the 1/4 mile in 14.4 @95 MPH. That's right there with many "muscle cars" from the 60s.

Another incredibly impressive car is the Tesla S. The latest one will do 0-60 in 2.3 seconds and cover the 1/4 mile in just a tick over 10 seconds. That's ridiculous acceleration that's on par with modern sport motorcycles and better than most million+ dollar "hyper cars". Not bad for an electric car...
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Old 02-13-2017, 01:44 PM   #12
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The 4.5 engine is a GM engine basically just in print they don't put 4.3 on it. The reason for that goes back to cars,if your Merc Marine and you're selling power plants and say a ford guy or gal comes in are they going to jump at the chance to buy a GM engine? NO and visa versa. As far as HP rating the 4.3 comes with 285 hp and as some us remember the early 70s manufacturers lowered HP ratings so they could be sold and the insurance company wouldn't charge a surcharge for a performance HP engine. Now on getting up on plane it is torque big blocks make stump pulling numbers where as small blocks just rev and make power at higher RPMs. Tesla is a great example electric motors make instant torque. In my current boat I have a 540 and I find it better on gas because I'm barely on the throttle and she's flying. I wouldn't be afraid of a 4.5 in that size boat however if you make a deal it should be predicated with sea trial so you can save now and not be sorry later.
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Old 02-13-2017, 02:22 PM   #13
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I found this link to a review done on the new design 4.5 L V6 vs. a more traditional 5.0 GM based V8, it's a pretty interesting read. The boats used for the "side by side" comparision were a pair of SeaRay 22 Sundecks. The V6 boat out accelerates the V8 boat although the V8 eventually has a higher top speed.

In the article the Mercruiser rep mentions that the V6 was developed due to concerns that many of the commonly used GM engines may not be available to them in the future. They also don't seem interested in developing the GM "LS" 6.2 platform into a marine engine.

http://www.boats.com/reviews/new-mer...8-performance/
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Old 02-13-2017, 02:56 PM   #14
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The 4.5 engine is a GM engine basically just in print they don't put 4.3 on it. The reason for that goes back to cars,if your Merc Marine and you're selling power plants and say a ford guy or gal comes in are they going to jump at the chance to buy a GM engine? NO and visa versa. As far as HP rating the 4.3 comes with 285 hp and as some us remember the early 70s manufacturers lowered HP ratings so they could be sold and the insurance company wouldn't charge a surcharge for a performance HP engine. Now on getting up on plane it is torque big blocks make stump pulling numbers where as small blocks just rev and make power at higher RPMs. Tesla is a great example electric motors make instant torque. In my current boat I have a 540 and I find it better on gas because I'm barely on the throttle and she's flying. I wouldn't be afraid of a 4.5 in that size boat however if you make a deal it should be predicated with sea trial so you can save now and not be sorry later.
I've never seen any Mercruiser 4.3's with 285HP. I believe the high HP rating is 220HP. I have a carbureted version in a 19 ft bowrider that's 195HP and it seems to be plenty of power. I would think a 4.5 with 250HP would be fine up to 21 feet. Over that I think I would go with the V8.
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Old 02-13-2017, 04:01 PM   #15
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I've never seen any Mercruiser 4.3's with 285HP
They don't exist. GM makes a 4.3 LV3 truck V6 that makes 285 HP though. It's got variable valve timing like the current GM V8s. Volvo Penta uses the LV3 GM 4.3 in their 200 HP to 280 HP V6 offerings. Guessing the <280 HP models are just de-tuned with software.
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Old 02-13-2017, 05:20 PM   #16
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Default Lower your HP

So the old saying is... "no one ever says they regretted getting the bigger boat engine". So is that true? Anyone on here ever regret getting the biggest rated engine for their boat? Anyone here have a story on repowering with less HP? How many have regetted getting the smaller engine? I only have a little tin boat but its about maxed out @ 115 hp. Maybe the 90 would have been fine. Until I got passed by a 115?
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Old 02-13-2017, 05:21 PM   #17
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I think the issue with the auto engines is that while they produce huge hp, they generally only need to do it for a short period of time, where as a marine engine needs to produce large number pretty much all the time. Cooling probably becomes a limiting factor plus part longevity issues.
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Old 02-13-2017, 05:38 PM   #18
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So the old saying is... "no one ever says they regretted getting the bigger boat engine". So is that true? Anyone on here ever regret getting the biggest rated engine for their boat? Anyone here have a story on repowering with less HP? How many have regetted getting the smaller engine? I only have a little tin boat but its about maxed out @ 115 hp. Maybe the 90 would have been fine. Until I got passed by a 115?
I have a 27 foot boat with a 425 hp motor. The only time I have regret is at the gas pump, but that goes away instantly when I start that motor back up.
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Old 02-13-2017, 07:44 PM   #19
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GM Powertrain OEM Sales
I called GM in Tonawanda and was told it is a detuned 4.3 due to emissions,tried getting hold of mercury because the last I was aware of after they assembled the last ZR-1 V8 and that was early 90s
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Old 02-13-2017, 08:14 PM   #20
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I drove a rental Challenger with that 305HP V6. If memory serves it had an 8 or 9 gear transmission too, so it was always in the power band and was quite snappy.
I have a Chrysler 300 with the 3.6, 6 Cyl. that is rated at 292 HP, probably the same motor you are referring to. It has an 8 speed automatic. I am amazed at the amount of power and the healthy sound from under the hood. I would never have guessed it was a 6 cylinder if I did not know the car. Typically it gets 30 to 34 miles to the gallon on the highway, excellent for a large car. I had Ford Crown Victoria's for company cars for many years, a 4.6 V8 with 219 HP. Larger motor but much less power. The technology has come a long way for efficiency and power. If only that would translate to boats.

I towed a small pontoon boat to Florida with the Chrysler and got 11 miles to the gallon. The car would not come out of 5th gear at 75 MPH because of the wind resistance from the boat. The cars are very optimized now with the proper gearing to achieve maximum efficiency.
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Old 02-13-2017, 11:13 PM   #21
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In automobiles a lot has to do with the gearing. Something that Mercedes has known for years. we had a Mercedes 420 SL with V8. Averaged over 22mpg on the car over 330,000 miles. Presently have a E 350 Blue Efficiency V6. I don't recall what the Blue Efficiency means but everyone thinks it is a diesel.
7 speed transmission and 302hp verses the other V6 with 268hp. The car has averaged 29mpg since new. On the trip to California against 60mph headwinds averaged 28mpg. Without headwinds averaged 34mpg. With the trunk fully loaded. Back in the days of muscle cars I had a Plymouth VIP with 318 ci engine and 3.72 rear end. It was quite fast for the weight it pulled.
Now I wonder if boats had a 3 speed tranny would it make a difference. I think it is doing a marine engine a disservice to WOT from a standing stop. A lot of dead weight and water to push unlike an automobile.
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Old 02-14-2017, 05:03 AM   #22
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I have a 27 foot boat with a 425 hp motor. The only time I have regret is at the gas pump, but that goes away instantly when I start that motor back up.
You'd have to have operated one of these to cheer you up!



I don't think they'd sell you one with only one gas tank.

BTW: "You can't beat cubic inches" was debunked by Formula 1 race cars in 1966. Formula 1 rules changed to halve cubic inches. "Slowing them" to improve safety.

Didn't happen.



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Old 02-14-2017, 06:19 AM   #23
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I think the issue with the auto engines is that while they produce huge hp, they generally only need to do it for a short period of time, where as a marine engine needs to produce large number pretty much all the time. Cooling probably becomes a limiting factor plus part longevity issues.
That sounds reasonable, but in practice, automotive engines that have been marinized work fine in boat applications. We've been using them for decades and when they fail, it's almost always just due to neglect.

Just to be clear, "marinizing" an engine just means: special gaskets, freeze plugs, raw water cooling and USCG approved external components. The innards are the same.
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Old 02-14-2017, 07:26 AM   #24
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That sounds reasonable, but in practice, automotive engines that have been marinized work fine in boat applications. We've been using them for decades and when they fail, it's almost always just due to neglect.

Just to be clear, "marinizing" an engine just means: special gaskets, freeze plugs, raw water cooling and USCG approved external components. The innards are the same.
I get that, my point is that most marine engines that are modified auto engines are probably detuned from the original auto horsepower for longevity purposes. I have a Grand Cherokee now that produces something like 365 hp, if I used all that HP all the time I'd probably going 110 to 120 mph constantly. I'm willing to bet that engine longevity would be greatly reduced.
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Old 02-14-2017, 07:36 AM   #25
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Torque gets you going. Horsepower keeps you going.
When it comes to engines, torque is meaningless without knowing the RPM. When you combine torque and RPM, you can then calculate HP. Even with a tiny amount of HP, you can use a lever or gearing to multiply the torque. For example, if I use a 36" breaker bar, I can easily apply 500 ft-lbs of torque to a bolt. That's more torque than the 454 in my boat makes, but obviously I don't make more HP than my boat engine.

If I have an engine that makes 300 ft-lbs of torque at 4,000 RPM and I run it through a 2:1 reduction gear, it will make 600 ft-lbs of torque at 2,000 RPM (minus friction losses of course) at the output of the gear set. If I have an engine that makes 400 ft-lbs of torque at 3,000 RPM and run it through a 1.5:1 reduction gear ratio, it will make the same 600 ft-lbs of torque at 2,000 RPM as the smaller engine.

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There's no replacement for displacement.
Using my example above, you can see that's not really the case. Displacement can be replaced by RPM. An 8 liter engine spinning at 3000 RPM moves the same amount of air as a 6 liter engine running at 4000 RPM (assuming the same volumetric efficiency). This is why GM no longer makes big block engines. They get all the power they need from small blocks that just spin faster and they simply adjust the gearing to get the required torque to the drive wheels.

This is taken to the extreme in sport motorcycle engines. My 1.8 liter car makes 130 HP at roughly 6,000 RPM. My .9 liter motorcycle makes 144 HP at roughly 12,000 RPM. You'd think the motorcycle engine wouldn't last long, but with 110,000 miles, it still runs like new.

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The technology has come a long way for efficiency and power. If only that would translate to boats.
It actually has, Volvo Penta uses very modern engines with VVT and high WOT RPM these days and Evinrude has used direct injection for years. Marine diesels have used turbos and common rail injection for years too. Boats are always going to get crappy gas mileage though, they simply require a lot of power to move compared to cars due to drag.
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Old 02-14-2017, 08:04 AM   #26
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Originally Posted by Dave R View Post
When it comes to engines, torque is meaningless without knowing the RPM. When you combine torque and RPM, you can then calculate HP. Even with a tiny amount of HP, you can use a lever or gearing to multiply the torque. For example, if I use a 36" breaker bar, I can easily apply 500 ft-lbs of torque to a bolt. That's more torque than the 454 in my boat makes, but obviously I don't make more HP than my boat engine.

If I have an engine that makes 300 ft-lbs of torque at 4,000 RPM and I run it through a 2:1 reduction gear, it will make 600 ft-lbs of torque at 2,000 RPM (minus friction losses of course) at the output of the gear set. If I have an engine that makes 400 ft-lbs of torque at 3,000 RPM and run it through a 1.5:1 reduction gear ratio, it will make the same 600 ft-lbs of torque at 2,000 RPM as the smaller engine.



Using my example above, you can see that's not really the case. Displacement can be replaced by RPM. An 8 liter engine spinning at 3000 RPM moves the same amount of air as a 6 liter engine running at 4000 RPM (assuming the same volumetric efficiency). This is why GM no longer makes big block engines. They get all the power they need from small blocks that just spin faster and they simply adjust the gearing to get the required torque to the drive wheels.

This is taken to the extreme in sport motorcycle engines. My 1.8 liter car makes 130 HP at roughly 6,000 RPM. My .9 liter motorcycle makes 144 HP at roughly 12,000 RPM. You'd think the motorcycle engine wouldn't last long, but with 110,000 miles, it still runs like new.



It actually has, Volvo Penta uses very modern engines with VVT and high WOT RPM these days and Evinrude has used direct injection for years. Marine diesels have used turbos and common rail injection for years too. Boats are always going to get crappy gas mileage though, they simply require a lot of power to move compared to cars due to drag.
Good points, my 0.8 liter snowmobile engine makes about 155 HP.
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Old 02-14-2017, 08:39 AM   #27
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I think the car/boat comparison gets off track due to the use of multi speed transmissions in cars.

Yes today's cars get great performance with less displacement. Much of that comes from improved valve train and injection technology. The delivery of that performance requires gearing. Does anyone recall cars with a two or three speed automatic? Now it's 6, 7, 8 or a CVT.

I'd like to see some torque curves on the engines in question.
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Old 02-14-2017, 08:59 AM   #28
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How long before we see electric boats? Tesla is developing some of the fastest cars on the road. Will we see some of these engines in boats soon or will electrics not mix well with water?
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Old 02-14-2017, 09:05 AM   #29
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So the old saying is... "no one ever says they regretted getting the bigger boat engine". So is that true? Anyone on here ever regret getting the biggest rated engine for their boat? Anyone here have a story on repowering with less HP? How many have regetted getting the smaller engine? I only have a little tin boat but its about maxed out @ 115 hp. Maybe the 90 would have been fine. Until I got passed by a 115?
Had a Cobalt 250BR with the Mercruiser Big Block, 425HP for a number of years....Loved it. Now have a Formula 270BR, again with the Mercruiser Big Block. The Formula is about 1000 lbs heavier than the Cobalt, and I really can't imagine having a smaller engine. I don't always use all that power, as I find cruising at 25-30MPH is very comfortable, but it's great to know I have it.

As to automobile HP, when I was young and irresponsible, my first new car was a Mustang GT convertible, with the 5.0L V8. The thing was a rocket ship, but with the big tires and big motor, it was pretty useless in New England snow and slick roads.
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Old 02-14-2017, 09:55 AM   #30
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Had a Cobalt 250BR with the Mercruiser Big Block, 425HP for a number of years....Loved it. Now have a Formula 270BR, again with the Mercruiser Big Block. The Formula is about 1000 lbs heavier than the Cobalt, and I really can't imagine having a smaller engine. I don't always use all that power, as I find cruising at 25-30MPH is very comfortable, but it's great to know I have it.

As to automobile HP, when I was young and irresponsible, my first new car was a Mustang GT convertible, with the 5.0L V8. The thing was a rocket ship, but with the big tires and big motor, it was pretty useless in New England snow and slick roads.
When I was a kid I had a 69 Corvette with a 427 engine which I thought was pretty fast. My boss came up to me one day and said, "I'll race you with my ford pick up truck for $100". I said "sure" and he said, "the first snow storm in January".
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Old 02-14-2017, 01:36 PM   #31
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I think the car/boat comparison gets off track due to the use of multi speed transmissions in cars.

Yes today's cars get great performance with less displacement. Much of that comes from improved valve train and injection technology. The delivery of that performance requires gearing. Does anyone recall cars with a two or three speed automatic? Now it's 6, 7, 8 or a CVT.

I'd like to see some torque curves on the engines in question.
The transmissions allow the engines to remain in their optimum power band, maximizing efficiency increasing gas mileage. In the case of the Chrysler ZF transmission, it actually shifts so fast that in the Hellcat Challenger that the 0 -60 and 1/4 mile times are fast for the auto than the manual. These auto transmissions are huge technological breakthroughs and they keep squeezing more and more ratios into those transmissions. I think one company is up to 10 or 11 for an automobile.

Transmissions do not increase engine horsepower, they actually decrease it due to mechanical and system losses.
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Old 02-14-2017, 08:07 PM   #32
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I concur.

My Subaru with its CVT is no race car but it does ok when called on to do so. A rolling start helps get the CVT to perform without wasting high revs.
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Old 02-15-2017, 08:12 AM   #33
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How long before we see electric boats? Tesla is developing some of the fastest cars on the road. Will we see some of these engines in boats soon or will electrics not mix well with water?
They already exist, but are extremely limited in range due to the huge difference in power density between petroleum and batteries. I think the best batteries have something like 5% of the power density of petroleum. Some day, that will probably change dramatically. I think graphene will make batteries, motors, solar cells, and conductors in general, vastly more efficient and compact in the next few years.
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Old 02-15-2017, 08:36 AM   #34
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Originally Posted by 8gv View Post
I think the car/boat comparison gets off track due to the use of multi speed transmissions in cars.

Yes today's cars get great performance with less displacement. Much of that comes from improved valve train and injection technology. The delivery of that performance requires gearing. Does anyone recall cars with a two or three speed automatic? Now it's 6, 7, 8 or a CVT.

I'd like to see some torque curves on the engines in question.
A muti-speed transmission would be a waste in boat, 2 speeds would be more than adequate (well obviously, since single speed transmissions have worked great for decades...). One thing to note, adding gears will not make the boat faster or appreciably more fuel efficient, it will only improve acceleration.

There have been a few attempts at two speed transmissions in boats. I think the luxury brand Riva still offers one. Mercruiser used the planetary gear section of a GM 2 speed powerglide transmission to make a marine 2 speed that fit behind their I/O engines about 20 years ago. If memory serves, they dropped it from their line quickly since it did not sell well.

An ideal solution would be a planetary gear set that takes the place of (and fits in the space of) the coupler on an I/O and uses an external brake to stop the ring gear (and shift into low). The shift to high would be accomplished by simply releasing the brake which would let the ring gear spin freely. With the brake released, the entire gear set would spin at engine rpm with no gear reduction and little load on the oil in the gearset. Planetary gears can handle huge amounts of torque for their size and may work great with today's smaller engines that make losts of HP but not so much torque.
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Old 02-15-2017, 01:05 PM   #35
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They already exist, but are extremely limited in range due to the huge difference in power density between petroleum and batteries. I think the best batteries have something like 5% of the power density of petroleum. Some day, that will probably change dramatically. I think graphene will make batteries, motors, solar cells, and conductors in general, vastly more efficient and compact in the next few years.
I don't even think it's that good, 5%. Once it gets better, I would say even to 30%, the IC engine for road travel will disappear quickly.
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Old 02-15-2017, 03:53 PM   #36
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I don't even think it's that good, 5%. Once it gets better, I would say even to 30%, the IC engine for road travel will disappear quickly.
Considering how small the fuel tank is on a modern car, having batteries take up 3 times the space to give the same range would be fine, IMO. In lab testing, graphene-based batteries, have proven to be rechargeable pretty much as quickly as you can feed them electrons, so recharging could take mere seconds with them, especially if you used graphene-based conductors in the charge cord.
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Old 02-15-2017, 04:19 PM   #37
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I just got off the phone with Merc and the engineer I spoke with stated" We are going back to forging and casting our own engines for several reasons which at this time can't speak about at this time" so there you have it
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Old 02-24-2017, 12:18 PM   #38
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Thumbs up Mercury 4.5L 250 HP

I purchased a 24 foot bow rider in 2015 with the 4.5L and have been very happy with it. It is quiet and smooth with a quick hole shot that gets me on plane fast. Wide open throttle gets me to 48 MPH. I did a little research and found that this is the 1st engine by Merc built exclusively for marine use (rather than a repurposed automotive block). Everything you need to get to is right up front (oil dipstick, oil and fuel filter, all drains, etc.). Additionally the throttle is in the back which cuts down on whine. It has a "season saver" so that you can empty the engine of water by pushing a button to keep it from freezing later in the year. I watched a video on line with two Sea Ray 220 sundecks. One had the older Merc 5.0 and the other the new 4.5. Out of the hole the 5.0 could not keep up. That being said, I have no experience pulling skiers so I can't say weather one would be satisfied with the engine for that purpose. I am very happy so far and it uses less fuel!

Last edited by Old Sarge; 02-25-2017 at 12:24 PM.
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Old 02-24-2017, 03:31 PM   #39
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the 4.5 V6 is as far as I know Mercruiser's first completely original design but it's not their first self produced engine.

Back in the late 1970's when GM stopped making the in line 6 that had been the midrange (165 HP) sterndrive at that time, Mercruiser developed the "470" which was a roughly 225 cubic inch inline 4 cylinder with an aluminum block / cast iron liners and a closed cooling system. I believe they used one of the cylinder heads and possibly the connecting rods and pistons from a Ford 460 V8. Originally it was 170 HP with a 2 barrel carb, later versions did 185 HP and I think they even did a 4 barrel version that was 190 HP. It had an outboard style crank driven alternator (no belt) as well. My parents put around 1500 hours on one over 30 summers without too much drama. It didn't like cold starts (electric choke) and wasn't the smoothest idling engine but it was pretty economical. I do remember hearing some horror stories about them and the alternators were prone to quitting but ours did OK. When the 4.3 V6 became available, they stopped producing the 470. Mid-1980's or so.

Mercury has a lot of high tech casting experience in aluminum, at one point they made the block for one of the high end Corvettes (ZR-1 maybe?) because they had so much experience in aluminum casting with the large outboards. Mercury Racing group makes some pretty extreme engines in house for the racing and sport boat markets, I'm sure they've done their homework.
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Old 03-26-2021, 05:02 PM   #40
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Originally Posted by 8gv View Post
Torque gets you going. Horsepower keeps you going.
.
I apologize for getting techy in my first post =o)
This is a common, and very false, misconception. It makes engineers in the automotive aftermarket cringe.

Horsepower equals torque multiplied by rpm, divided by a constant.
That's literally it. It's just different calculation based on twisting force.
It's all power, and higher HP with the same torque will still accelerate faster and pull better, even if the measured torque remains unchanged.

They both get you going and keep you going, we've just come to associate torque with acceleration, but it's a far over simplified and inaccurate misconception.

At any rate, I've rented a Monterey 22FS 3 years in a row with the 4.5 250 and the thing rips 50+ with no issues and it tows well.
I just bought an M22 with the same engine. It's a good one and it makes a good argument against the 6.2..which is more thirsty and doesn't make a whole lot more power.
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