I/o Engine Technology....Outdated?

[dmanmtl]

As I learn more about the engine in my new to me Bayliner (135HP, Mercruiser i/o) I wonder why these engines seem to be using a very outdated technology. From what I read this engine seems to be about the same as it was 20 or more years ago. It's a pushrod OHV motor, similar to what GM was putting in cars in the mid-seventies (is it actually a car motor?). Gas mileage doesn;t seem too great either - however it is hard to make a comparison with a car.

Modern engine technology includes such advances as EFI, OHV, Dual cam, 4 valves per cylinder, Aluminum heads/Blocks etc. If you look at the HP coming out of a modern 3Litre car engine these days it's easily pushing 200HP or more. I also imagine that newer technology engines are much lighter since they use more alloys, aluminum etc. And I am sure gas mileage would be wayyy better, not to mention emissions.

I also wonder why boat motors seem to have such a shorter life expectancy. For example, in another forum I was reading someone referred to a 500hour engine as being "high hour"...Is that an unreasonable statement?

Obviously cost is an issue and using a modern engine would probably push that cost up.

Thoughts welcome ...

 

[rockyrude]

Re: I/o Engine Technology....Outdated?

You don't say how old your Mercruiser is , but newer engines do use much of the technology from the auto world. As far as life expectancy , auto engines don't spent their entire life at full power. Think pulling uphill their whole life.

 

[Yankeyspeed]

Re: I/o Engine Technology....Outdated?

I think think its cost prohibitive to go to a OHV, 4 valves per cylinder ect. I think the power plant of the future is diesel. I dont know how to keep the turbo temps down, but when they figure that out ......LOOK OUT!!!!

 

[Another retired guy]

Re: I/o Engine Technology....Outdated?

Can't answer some of those questions, but a boat engine does work a lot harder than a car engine (3000 to 4000 rpm continuous) so needs to be "beefed up". Also 500 hours is not high - these things can go 2000 hours easily if properly maintained and treated with respect!

 

[GA_Boater]

Re: I/o Engine Technology....Outdated?

Those old, outdated push rod motors sure move the Corvettes around pretty good while getting decent fuel economy. In fact, all of Chevies high performance engines are based on the 1955 265 ci push rod V8 and retain the push rods today.

 

[SWD]

Re: I/o Engine Technology....Outdated?

Look at the Mercruiser page and you'll see some really great engines. Technology has improved. Dont forget that these engines are subject to operating at WOT, nothing compared to what regular cars are subjected to. There are more cars than boats so it takes a while before newer technology arrives to the boating world. 500 hours is all dependent upon the previous owners and how well they looked after there stuff. My boat is 26years old and has compression readings between 145 and 150. Nice and tight!

 

[matt167]

Re: I/o Engine Technology....Outdated?

All of GM's V8's have been pushrod engines, Car, marine or truck it does not matter. The 135hp engine I think is the 3.0L which was never a car engine but it is a larger displacement version of the 2.5L which Chevy designed for the Chevy II Nova and they are both based on the 195-292 CID series of inline 6's. I think they both share most commonalities with the 250 I6. I think it is still used because of the low end torque and how it can plane fairly large boats. Modern 4 cylinders are not 3.0L either. It would take a small displacement V6 to be comparable and the rotating mass and firing cycle is not the same... This same analogy can go for the 4.9L 300 I6 that was popular in the Ford F series, and why it was a prefered hauling motor to the 302 ( 4.9L also, marketed as 5.0L so it seemed bigger ).

 

[Frank Acampora]

Re: I/o Engine Technology....Outdated?

It is simply a cost factor. That engine would be either the old Chevy "iron duke" or a Ford 4 cylinder. Some boats came with sixes or the Chevy 350. All are auto engines modified with special marine components like distributors and alternators. All are cammed differently than an auto engine.

Up until recently there were no pollution restrictions on boats so why spend the extra money for more expensive engines---especially when the American public will willingly buy whatever is offered?

Of course, recently they have had fuel injection and computer controlled EFI in place of carbs but the basic block is the same.

Remember too: Detroit is a sluggish giant that resists change. They are going to sell what they have until forced to improve. To wit: Look back to the 1970s when auto quality was terrible. Detroit sold us crap cars until the Japanese came out with a better product and FORCED the big three to improve--only when they saw sales drop precipitously. Just look how they resisted seat belts and air bags until forced to change their thinking.

Boat builders are a niche market compared to auto sales and are at the mercy of their engine suppliers.

 

[dmanmtl]

Re: I/o Engine Technology....Outdated?

Thanks for you replies - all make sense. 2 More questions: Why would a boat motor have a different Camshaft than a similar car engine? And what would be the difference with the distributor?

BTW: my engine is a 2004 Mercruiser - carb version.

D

 

[GA_Boater]

Re: I/o Engine Technology....Outdated?

Most motors are based on truck variants, so the cam is for torque. A marine distributor has spark shielding so fumes aren't lit off in the enclosed engine compartment, same with the starter. Two other main differences are brass core plug that don't rust in salt water and a fuel pump with venting to the carb in case of a diaphragm rupture. One more, a marine carb has no vacuum ports or any ports with caps. Again in case of a backfire, no fumes ignited if the cap blows off.

 

[crabby captain john]

Re: I/o Engine Technology....Outdated?

500 hours is far from a lot. When I chartered I ran GM engines - mercruisers. It was easy to put 500 hours on every year. Many boats were running well kept engines with well over 5000 hours before a rebuild and 5000 more. Even outboards in saltwater if taken care of are good to go well beyond 500 hours!

 

[carey965]

Re: I/o Engine Technology....Outdated?

generally older is more reliable, personally i would rather have a carb that i can fix with a screwdriver and a hammer then a computer that can get fried from moisture and leave me stranded in the middle of the lake, as the old saying goes a chev will run bad longer then most vehicles will run

also dont forget a marine engine tends to have stronger internal components, better pistons, connecting rods the whole lot, they need to be able to run for many hours at high rpm's

and torque is what moves you in a boat, HP is good when your on plane, but you need torque to get you there

 

[Maclin]

Re: I/o Engine Technology....Outdated?

The duty cycle a boat engine sees is more like a truck sled pull in reverse, where the "pull" would start with the sled weight at the heaviest then work it's way towards the lighter as the boat planes out.

 

[NHGuy]

Re: I/o Engine Technology....Outdated?

If you are interested in modern tech for boats it does exist. Take a look at the newer outboards, they are very developed. And also take a look at the newer EFI sterndrive engines. They are catalyst equipped, fuel stingy, variable valve timing works of modern engine technology. But, as before, they are based on good ol' American engine technology that's a pretty close combination of truck torque and performance car top end. For marine use they add corrosion resistance, moisture barriers, and anti spark shielding because of the reduced ventilation of a boat engine bay.
Light truck and automotive will usually drive discovery in this field. But it will always move forward.
I love my old Chevy motor with a big carburetor. Just redid the carb myself, and I look forward to running it for many years. But I appreciate the later things as they come along too.
When my brother, who's a bigger motorhead than I am, was buying a boat, I recommended fuel injection. They are easier on gas, they run right all the time and they are easy for his non gearhead children and wife to run. His boat is ten years newer than mine and gets the same rated power from a smaller engine. To me that's progress that should yield less fuel use and more dependability.
So sure, your motor is an earlier design, but it's a well proven one that you can expect lots of use from.

 

[Mischief Managed]

Re: I/o Engine Technology....Outdated?

Thanks for you replies - all make sense. 2 More questions: Why would a boat motor have a different Camshaft than a similar car engine? And what would be the difference with the distributor?

BTW: my engine is a 2004 Mercruiser - carb version.

D

Cams for high HP do not work in boat engines like yours because the overlap between the intake and exhaust valves causes exhaust reversion at low RPM. That makes the engine draw cooling water backwards into the exhaust system and that will wreck the engine quickly. The new VP380 V8 overcomes this problem by using a mild cam with a variable hydraulic cam sprocket that changes the cam timing with RPM to achieve a very flat torque curve all the way to 6000 RPM. This results in great low end torque and decent high end HP. I would expect to see that technology available on more marine engines soon.

 

[Silvertip]

Re: I/o Engine Technology....Outdated?

The other missing point in this thread is that boats do not have multi-speed transmissions so the one gear they do have must get the boat out of the hole, on plane, and have a reasonable top end. Small engines with hot cams, four valves per cylinder, and other performance tuning simply does not cut it in this application. Salt water and aluminum don't go well together either. And by the way, GM did have some Vettes with overhead cam V8's. As I remember, Mercury Outboards cast the aluminum blocks for those motors.

 

[matt167]

Re: I/o Engine Technology....Outdated?

The other missing point in this thread is that boats do not have multi-speed transmissions so the one gear they do have must get the boat out of the hole, on plane, and have a reasonable top end. Small engines with hot cams, four valves per cylinder, and other performance tuning simply does not cut it in this application. Salt water and aluminum don't go well together either. And by the way, GM did have some Vettes with overhead cam V8's. As I remember, Mercury Outboards cast the aluminum blocks for those motors.

Agreed. Most of the modern small high horsepower motors are 'soft' below 2k RPM. In a car that can be adjusted for in the transmission and gear ratios.. With a boat, using a steep gear may get it on plane, but it probably couldn't go anywhere quickly with the 1 speed tranamission. Now if only a 2 speed transmission could be developed than the small windy engines might work.. I tried to explain this to someone on another forum who thought 2 tuned up 400hp Honda motors could run a 25-28' vessel as good as 2 V8's. Most of the larger Honda outboards are based on their automotive engines, so it is thoretically possible it could work, but even so, they run a fairly steep gear in the outboards to make them work at their stock HP's
The Mercury marine built Corvette LT5 was in the ZR1's '90-'95 Cool looking motor and from what I've heard they run pretty good too.

 

[Mason78]

Re: I/o Engine Technology....Outdated?

I dont know how to keep the turbo temps down, but when they figure that out ......LOOK OUT!!!!

With environmental controls always increasing I believe we will see turbos showing up in many applications. Its the only way to keep performance and achieve efficiency. It is not longer an option to just "build a bigger engine" and keep feeding it.

Turbos are also better than ever, many made by Borg Warner or Honeywell last 300,000 miles or more in trucks.

 

[H20Rat]

Re: I/o Engine Technology....Outdated?

With environmental controls always increasing I believe we will see turbos showing up in many applications. Its the only way to keep performance and achieve efficiency. It is not longer an option to just "build a bigger engine" and keep feeding it.

Turbos are also better than ever, many made by Borg Warner or Honeywell last 300,000 miles or more in trucks.

Turbos in a gasoline boat engine are a really bad combination, and you will probably never see them in mass production... Couple issues: When you are loading a turbo at high load levels like a boat, a turbo gets far WORSE mileage than a comparable horsepower NA engine. If I'm towing with my turbocharged car, I get 10-12 mpg, with a 2.0liter engine! My SUV which has relatively similar horsepower gets 15-17 while towing the boat, even with vastly worse aerodynamics. Main reason is open loop vs closed loop fueling, basically the ECU dumps in fuel to keep the engine from blowing up. Even ford's ecoboost trucks have the same drawbacks, when you load them up with a heavy load, their mileage drops below what their non-turbo brothers are. Boat engines are ALWAYS loaded.

Also, turbo's need to run hot. Hotter the better, the performance of a turbo doesn't come from the exhaust pressure, but from the heat. That doesn't go well with an enclosed space and gasoline.


Anyway, long story short, turbo's are great in cars where you need short bursts of high performance followed by extremely low engine loading. A boat is different environment.

*disclaimer, i mentioned gasoline, diesel's are an entirely different animal where a turbo in a high-load application makes sense, and is almost required. *

 

[QC]

Re: I/o Engine Technology....Outdated?

These threads are so weird to me. Someone mentions high tech four valve engines, another reminds of OB technology, and then we say those four valve multi cam engines can't work in a boat? Huh?

And someone says that turbos can't be cooled in a boat? Uh, water cooled turbine housings are on every diesel marine engine in the world, even little ones. And turbo engines always get worse fuel efficiency at high load? Huh? smoke is smokin' sumpin', you are so much better than that. One example doesn't a bad technology make . . .

One poster nailed this. Cost, cost, cost, oh and maybe cost.