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.