This has all been discussed before, randomly in threads and sometimes dedicated threads to the actual technology(s).
In effort not to de-rail some other threads, I thought I'd bring this one back up, and kind of put all the thoughts together.

Here's my take. Please interject with your thoughts and any other ideas you may have. This thread is to throw it all out there and see what sticks and what runs down the sewer.

VVT - Variable Valve Timing has become a great way to operate an engine efficiently over a wide range of rpms. Traditional single timed cams had the deficiency of having one range of power. Depending on the cam design, this power could be set at a desired rpm level. The other areas of operation, however, would suffer.
VVT takes this deficiency away by adjusting the timing of the cams to open and close the valves at oppurtune times for increased charging of the cylinders at all rpms ranges.

Superchargers - Superchargers are a forced air system. Thier benefits are that they will increase volumetric efficiency of the engine to over 100%, thereby creating more power. During the compression cycle, the air is heated, but due to the abundance of cooling water around a boat, that air can be reduced in temperature rather easily with the use of an aftercooler or intercooler. Superchargers draw from the power from the engine to operate them, typically in the form of a belt connection to the crankshaft pulley. Therefore, some of the additional power made by the Supercharger will be required to operate the supercharger. The overall efficiency is hindered by this.

Turbocharger - A turbocharger is similar to a supercharger in the respect it force feeds the engine. But instead of pulling power from the engine to operate it, it uses the exhaust gases to spin it. This makes a turbo charger more efficient than that of a supercharger. But one draw back of the turbocharger is its lag. Because it is spun by exhaust, it may take a second or two to "spool up" to begin making its boost. This is typically only apparent on start-out. The other draw back to turbocharging, mostly on a gasoline engine, is the heat build-up during operation. Because the engine will have a heavier boost demand, the turbo will be operating at a higher speed constantly and may have an effect on the units longevity. Why this does not occur with diesels is beyond me. It was said diesels have a lower exhaust temperature, thereby less wear on the turbo, but I do not know.


Very basic info here, just to start a possible discussion.

The cost to get the benifit of the Variable Valve Timing in a given engine is done by GM and then sold within the package sold by GM to a marine engine builder? Or its done by the marine engine maker?

Mutt, I always thought diesel exhaust was plenty plenty hot. I was confused when I read that. Now, the only explanation I can come up with as to why marine diesels work well is that since most diesels don't turn much over 3000rpm, maybe that does keep the exhaust cooler and thus it's easier to raw water cool the exhaust? I have have often wondered why turbos on diesels are "no problem" (if not required) in regards to heat in the engine compartment, but a big problem for gas engines. Is it also possible that since diesel fuel's flash point is so much higher than gasoline that the Coast Guard regulation of under 200 degrees doesn't apply to diesels? I haven't been in a diesel engine compartment while they were running, so I have no idea how warm it gets in there.

Diesels may be built for higher temps, by making them thicker where they need to be. Most diesel engine parts that I have seen and handled are massive in their weight.

That's a good point, seabuddy. And yes, i can see how you could make a water cooled exhaust manifold very thick to cool it. But on the one marine turbo I have been up close to, (Cat 3408) the exhaust side of the housing looks just like the one on a Caterpillar Diesel semi truck engine. And I know they are hot. So how does that not radiate tons of heat in a closed compartment?

The diesel engine compartments that I have crawled around have been hot after a cruise, hotter it seems to me than a gas boat, IMO.

Plus, diesels sometimes have bigger volume air intakes and exhaust systems plus even some have fans to cool down the engine room.

Most diesels also have bigger sized thrugh-hulls for cooling water intake, too.

Okay, excellent information.

If we can't have 496s or 454s, then I think I want a supercharged 383MPI in my cruiser.

I have also heard that due to the turbo size and low rpm of the engines, the diesel turbo does not spin at a high rate of speed like some gas units.

As for the heat produced, most turbo diesels I've seen in marine applications had heat blankets around the exhaust. I can not find the information right now, but ASHRAE has a chart of BTU/hp emitted to ambient. I don't know which is higher, but i do know they are different, gas and diesel that is.

Here is something else to ponder, which is the most efficient as far as BTU of fuel per hp?
Typically a forced induction engine is about 10% more efficient than naturally aspirated, with equal compression ratios at combustion. But this information does not include VVT, and is slightly older, 2001. But for the reasons that Forced induction is more efficient, VVT does not address, so I tend to think that forced is more efficient than VVT.

Yea, the Diesel turbo's get hot. One Turbo started a fire onboard a boat while I was out about 7 miles off Newport Beach, CA.

Direct Injection?

Turbocharging also requires aftercoolers/intercoolers. Compressing air generates heat. Both turbos and super chargers require compressing air.

I'm going to jump to the VVT direction because I don't have enough time to discuss both systems at the moment.

VVT and direct injection allow compression increase on stock fuel. Higher compression=higher potential power, right? Direct injection is the secret to getting the 12/13 compression range on 87 fuel.

VVT, as Mutt mentioned, allows for complete (or higher) compression at lower rpms. This is how the low-end torque is generated with VVT. It keeps the compression high at lower engine speeds. Conversely, as the engine speeds up, VVT adjust something (depends on the particular design we're talking about) to allow more charge to enter the engine, therefore allowing for more (or same if you're at peak) power to be generated. Ya'll already knew that though.

Controlling intake valves separately from the exhaust valves extends that can be corrected for. The first VVT systems where lightyears more powerful then the traditional cam setup. The newer independent VVT system are, well, flat-out amazing.

All of the valve technology in the world won't compensate if the intake and exhaust manifolds cannot handle the volume (both in and out) required to generate X power. A 300hp engine will have to be able to move more air than a 250hp engine of the same displacement.

That factor hasn't disappeared.

Also, we cannot ignore internal strength required to generate such power increases.

More Later. I love this thread.

But VVT does not provide a means to get 100% volumetric efficiency. It gives a higher volumetric efficiency over a wide range of rpms in comparison to naturally aspirated non-VVT engines. To get big power out of limited displacement, I feel you will require 100%+.

DI will provide a more suited control for higher compression, but do not expect a lot of extra power from increased compression. But if controllable, that slight power increase is "free" so to say.

How about DI on a forced induction engine where the resulting compression ratio is high? Less cooling of the air charge would be required, but still helpful.

There's also been talk of eliminating the cams completely for a solenoid actuated valve set up. Reduced friction and full electonic control are a couple attributes. But this technology is years away from automobiles, not to mention making it to marine power.

As a kid, my father had a diesel tractor with an exhaust temp gauge. I want to say under a heavy load it would run continuously between 900-1000 degrees.

Carry on.

How much power are we talking?

Are we considering replacing the 5.7L 300hp engine with a 3.5L 300hp engine?

Are we wanting to replace the 8.1L with a 400hp 6.0/6.2L engine?

Are we wanting to make 350hp from a 2.5L I4?

I think the end power goal depends on what technology is best for the application.

That's the most insightful thing you've ever said, D-Rod! And I agree 100%.

that would be part of the equation, but what about physical size, efficiency, operating performance?

End power is only one variable to the equation. My turbo I-4 is 250hp and 258ftlbs, but I wouldn't want it for a small boat motor. In the same sense, my parent's RV had 330hp and 950ftlbs, wouldn't want that in my boat either.

There are many things to consider. And that is really the reason behind this thread. I feel all of the technologies are viable, some maybe more than others, and that really depends on the application as well. As you can probably tell, personally, I am a big fan of forced induction. My opinion on VVT was to improve a current technology, not a new one. While it is a great advancement, it isn't the end all solution. I think that forced induction is a great way to improve point of operation efficiency and overall efficiency, especially when using variable volume systems like turbos or pressure bypass superchargers. But that overall efficiency decreases a bit for marine application due to the constant heavier loads. But the technology would be very good for a fishing vessel that sees a lot of time at idle for trolling, but then has the power for running on plane. While VVT can provide this somewhat, it doesn't have as broad of operating characteristics.

Mutt I want a Detroit Diesel with VVT, turbo, and supercharger. I guess two out of three isn't bad, right?!

Lets not forget HCCI. It's another technology that could make it to boats in 10 years.

To put a gas turbocharged engine in a boat sounds a bit expensive. I know you like turbochargers, Mutt. I like them better than superchargers in vehicles. I think they're a bad idea for a boat. So, i'm going to put that card back in the cabinet.

Superchargers are viable. But, I do not know of any mass production block other than than the LSA capable of handling the stress produced by the SC engine. The supercharged engine is going to generate more heat then the n/a engine. The power consumed by the SC has to be integrated into the strength of the engine. If we have a 350hp small (3.0L) V6 or I6 engine, that engine has to be able to withstand at least 400, 420hp of internal stress. That's about how much power the engine is making, the supercharger is drinking 50-70hp of it. To be able to engineer this strength with standard block materials, it's going to have to be a small-bore engine. This creates problems valve-train challenges. I'm not sure 2 valves can pass the volume needed without very high charge rate. Now we have to add the cost of SOHC or DOHC and 3 or 4 valves. Lots of costly obstacles to work around. The advantages would be greater power response, especially at lower engines speeds. Also might be able to get away with a more modest 5000 max rpm, which might help save a couple of bucks with the internals. For cost purposes, lets assume this engine uses a basic VVT system, standard port injection.

Now, let's look at ~ 3.5L V6 n/a engines. Let's spend apart of the budget on DOHC with sophisticated independent VVT and direct injection. Let's assume the internals are built with slightly more expensive light-weight materials, so higher RPM's (5750 or so) are not a problem. Let's assume this is enough to generate 350hp. Due to the gearing, the engine is competitive with the S/C engine.

Which is cheaper? I put my money on the 2nd option. I think it is capable.


Thoughts?

While a SC does take some power to operate, and that has to be included into the power internally consumed, you have to remember a forced engine has less internal restriction as it does not have to draw the air in. A naturally aspirated engine has restriction of drawing air in, and inefficiency associated with that. The difference in internal power consumed between the two engines is less than you think.

As for air intake, two valves is fine with forced air typically. While the square area of four valves is more than two, the overall restriction is not much different due to free flow area.

As for turbo charging being expensive, I think you'll find a turbo is less money than a roots/whipple charger we associate with marine applications. Not to mention an external aftercooler on a turbo will be much more effective than the internal units on a supercharger. But I will still concede that a constantly operated turbo may have longevity issues.

As far as overall cost, yes a VVT will be cheaper on a given engine size. But which is cheaper a V8 with VVT or a V6 with forced induction? And say you use a V6 with VVT making 350hp (that is a bit of stretch, IMO) versus an SC V6 making 350 hp, but with lower revs, my money is still on the SC engine as its power generation will be higher in the low end. You can't make a VVT engine flow 100%+, no matter what you do.

Again, a lot of this falls down to what you want in an engine. Many will shy away from an SC engine, just because a supercharger is associated with high performance.

D, I am not trying to change your mind on VVT, not what I wanted to do with this thread. I just want to get all the sides represented, and have a healthy discussion as I feel many of these technologies need to be heavily evaluated to produce an optimum product.

I think that we may want to rethink engines even more than just engine technologies. When you look at how a boat is used, the conventional single engine is not necessarily the best option in the long run. Triple small engines may be the best bet. One for those long periods of idle and slow speeds, and the outer ones for higher speed applications and manuvering. And who is to say that we cannot devise a better drive system? Props and Jets are inefficient. If we can derive a propulsion system that gains efficiency over the old system, it would save a lot of fuel.

Next question: Are we trying to save fuel or are we trying to meet changing emission regulations by adopting new technologies.

I assume we are assuming that current engine technologies will not meet emissions or will be phased out as newer, better automobile technology takes hold.

Increasing efficiency and better emissions are two things that are a must, and almost go hand in hand. Higher efficiency means better/cleaner burn and the use of less fuel, which is the basis to better emissions. Higher compression engines will typically have a better burn because the amount of energy stored in the higher compressed fuel/air will ignite faster and hotter.

seadog, that's a good point. When does multiple engines create a better solution? Obviously a certain sized engine, no matter its technology has a particular hp range where it will be efficient. Multiple engines of different sizes would provide better overall efficiency, but you are looking at a big jump in cost.

I have also been hearing rumors of dual fuel engines. Depending on the loads placed on the engine determines the mixture percentage of the fuels to be used. Using two different fuels provides a better more complete and higher energy burn.