Why no supercharged diesels
 

Why is it that diesels all seem to be turbo charged? It would seem that a supercharger would work well. With the new quite and clean fuel efficient diesels from GM and Ford, do they have a future in performance boating?

The "roots" style superchargers originated (I believe) on 2 stroke diesel engines on the exhaust side. Turbochargers are lower in cost, lighter in weight and don't rob a lot of power.

Most of the early 2 stroke Detroit Diesels were supercharged, I believe. Some even supercharged and turbocharged.
Gary

I always figured it was because turbo chargers use the exhaust gas to produce the boost so you dont have to use any power initially to turn a pulley. I think it is more efficiant for a diesel. My.02 cents

Check out this site. www.marinediesel.nu They sell diesels with screwtype compressors ( branded whipplechargers in the US.)

Roots blowers were used on the intake and exhaust of GMC/Detroit (I have no experience with the others) diesels. The size of ther blower was indicative of how long the rotor blades were and from what I can tell denoted whether the supercharger fit 4, 6, 8, etc. cylinder varieties.

Most V8 gasoline retrofits used either a 6-71 or 8-71 type supercharger. Nitromethane guzzling fuelers used 14-71 superchargers (until the hi-helix rotor roots-type superchargers appeared). We make roughly 55psi of boost with our hi-helix setup on our FM/A Olds (big Chevy) dragster. :D

More Detroit Diesel info...

The models numbers refer to:
Number of cylinders and cubic inches per cylinder or 6-71=426Cu in.

Models were and some still are:
3-53, 4-53, V6-53 & V8-53
2-71, 3-71, 4-71, 6-71, 6V-71, 8V-71 & 12V-71 s)
6V-92, 8V-92, 12V-92 & 16V-92
8V-149, *12V-149, *16V-149, *20V-149
Note* a 20V is one V8 and two V6's bolted together and so on.
Many models share common (4 exhaust valve only) heads as there are CW
and CCW rotation drive models that are mirrored. The big 149's have a
single head assembly for each cylinder.

Many have N, T, TA, and DDEC added. N=normal aspiration but still have
over pressure with the scavenging blowers. T=turbo,
TA=turbo+inter+aftercooling, DDEC= Detroit Diesel Electronic
Controlled. All have roots blowers but turbo's use both and do a
functional bypass on the blower, when on turbo boost.


GMC 6-71's and 8V-71's were the most common. These were and still are
used in 'then' general motors GMC two cycle diesel engines, developed
in the late 30's and for the most part still in production, albeit in
smaller numbers and very specific applications, where their
compactness and high output per liter are required. I believe
Hildebrand (sorry spelling) is now building their own Hot Rod roots
blowers based on the Jimmy design. The drive ratios and other stuff
had to be modified for high RPM automotive engines.

Penske bought Detroit Diesel in the 80's, bailed them out and made
them profitable again, after that GOD Awful sorry ASS American icon,
General Motors, ran them into the ground, like so many other once
profitable industrial divisions.

I remember installing a V-16 diesel generator. That engine had dual everything. Dual oh cams, 4 valves per cylinder, dual superchargers AND dual turbo chargers.

Now having my own diesel with a turbo, I become a believer that the turbo and the diesel are a perfect match.

The new high horspower diesels seem like they would be great for performance boating. Is it just that people dont like the sound and smell, because that has changed. I would love to have 450hp and 700ft pounds of torque in my boat and get triple the fuel consumption and four times the longevity.

My dad taught diesel mechanics in the Navy, after he retired, he taught for Cummins for a few years. I once asked him about Cummins engines and his reply was "They ain't no Detroit Diesel".

Keep in mind in the Navy they used very few diesels for proplulsion, but mostly for running pumps, generators, and the like that ran 24 hours a day, seven days a week, so reliability was the main concern.

Diesels can't match the power to weight ratio of a gas motor. Internal parts just too heavy to turn high rpms, plus the burntime of the diesel limits rpm also (it is compression ignited, not spark ignited).

Economy is dramatically better than a gas motor, and longevity is usually much better. Cruise speed is often higher than a comparable gas motor cause a diesel is happy running at 80% of its max rpm for long periods of time - this would be like putting 1,500 hours on our HP500's at 4400rpm.

I see more and more mega yacht tenders (19 footers) running small diesels (in the 200 horse range). They perform very well, accelerating like the same hull with a 300 horse gas motor, providing the same cruise speed and ski-pulling ability, returning double the fuel economy, and only giving up a few mph on the absolute topend.

For us speed freaks, though, gasoline rules...

If your making the power why would you worry about the rpm's? Is their no way to prop and gear for a 3500rpm redline?
I know its not a boat, but these new diesel trucks haul butt. I can outrun most any gas powered truck with my lightly modified diesel. I understand that if your talking about huge horspower motors then the availability of resources for gas big blocks rule. But for stock power like a 3-400hp engine, why not?
I'm going to see if I can find some specs but I did read somewhere that a Ford PSD is lighter than a 454.

Heres the only thing I could find that is related:
http://popularmechanics.com/outdoors...er/print.phtml

Couldnt find any weight info but I would be suprised if the diesel was in fact lighter but I imagine they are getting lighter.

The "Tigershark" model from MarineDiesel
( www.marinediesel.nu ) is supposed to crank out 400+ horsepower and weighs less than 1000 pounds (430 kg). Thats a better power to weight ratio than a stock 454 or 502. Also they are based on the GM 6.5L truckdiesel and bolt right in place of a bigblock.

Sorry, here´s the link to the english version. www.marinediesel.nu/index_eng.htm

Another place that i used to look at was --boatdiesel.com--- they're usually talking about cruisers, fishing, and work boats, but there's a fair amount of knowledge on diesel powered and repowered boats on that site, lots of classifieds also.
I looked into it last year-- repowering the scarab with powerstrokes, had a line on 2 for $ 11,000 each with 140hrs complete. Decided it was too rich for what i was looking for once you change everything like, Trannies, props, fuel system, fluish tank, etc. A local guy here is repowering his 50ft scarab with twin cats right now, it had triple fords with arnesons on it, so it should be about the same weight if not lighter. I think i heard it's supposed to be filmed and shown on the boating channel/show.

Another boat here has twin supercharged Volvo's -- runs 40mph -- not shabby for a 30' aluminum tug, and talk about take rough water:eek:
It would seem to me that the 6-71's were designed with the superchargers originally because they were 2 strokes. Pretty hard to power a turbo down low without that exhaust stroke. Pretty amazing motors really, we've got 2 of them in equipment and they'll rev to 32-3400 all day long. I've never seen too many of them that didn't leak more oil than they used though. Still pretty good for 70 year old technology:)

Horsepower generates speed. Horsepower is a function of torque multiplied by rpm. If a given engine has enough torque to pull to its power peak, it will move a given craft at a given weight faster than a lower horsepower engine, even if the lower horsepower engine can generate a significantly higher peak torque (assuming that propping and gear ratios have been optimized for each combo).

1000 pounds at 400 horsepower is nice, but doesn't compete with a supercharged 502/540 at 700 horses and 850 pounds. Sorry, but it still ain't even close. If you want to compare the diesel you are mentioning with stock 454/502's then that is an unfair comparison. A stock 502 bobtail is around 450 horsepower, 800 pounds, and $9,000. The hotrod 400hp diesels you are speaking of are most likely around $35,000 each (I'm just guessing). At that price point, you have to compare them to a KE 600.

Speaking of dragracing trucks against cars, a diesel's TORQUE works well indeed in providing impressive acceleration, especially on heavier vehicles. Works the same way in boats. My 20,000 pound diesel cruiser will CRUSH the same boat in gasoline form hopping on plane (it is available in gas form with 380 Mercruiser Horizons). It cruises 8 mph faster, burns half the fuel, but runs within a mile an hour on top end. The horsepower advantage (350 vs 380) and lighter weight of the gas "toy" motors cannot be overcome by brute force of the Cats, cause when SPEED is the issue, HP is KING.

Take your 290 horse powerstroke and race a 320 horse Navigator (add weight to whichever one needs it to make them the same). Your diesel will most likely outdrag the Navi. The Navi will most likely catch and pass the Powerstroke on the big end (assuming no speed limiters).

There's a good reason we don't see Diesel Vettes...

Oh, this whole thread was about SUPERCHARGING.

Turbocharging has long since been proven to be a far more efficient method of scavenging (pressurizing the intake). Turbo's drawbacks are that the turbo needs to build speed before it makes boost, versus a mechanically-driven supercharger. This is not considered to be a drawback in a marine or a trucking application, because the intention is to provide pulling power, not instant throttle response. The efficiency advantages far outweigh the drawbacks regarding response.

Turbo Lag can be significant on nonwastegated turbo diesels. I have been on boats that took 13 seconds to build boost if you simply firewall the throttles from idle speed. Still, this is not a big deal cause you should ease the throttles forward to mid-displacement speed for a minute or so to stabilize coolant temps and stuff anyhow before calling for boost - at that point, boost is only two or three seconds away.

Mechanical superchargers are still used on some diesels, but usually as a low-speed aid. They typically are disengaged as soon as the turbos build speed and provide boost.

Electronic engine controls and electronic injection, combined with wastegated turbos are the more prevalent answer to the diesel boost question. These turbos are designed to spool up faster, and are bypassed to some degree to keep from overboosting the engine once proper boost levels are reached. Injection timing and volume are also mapped much more closely and work to virtually eliminate the diesel "throat clearing" we all are so fond of (think heavy black cloud of stinking, clinging, diesel smoke and soot) that our mechanically injected diesels like to do.

Hey, its my thread, I'll make it whatever I want ;)
I did ask why there are no performance diesel boats in the original post.
Thanx for the info.

I would like to see a 2-stroke supercharged Diesel with direct fuel injection(injection after the exhaust port is closed). That should give a reliable, fuel efficient package with good power to weight ratio.

Mr. Demeanor
Cost and weight. Even a pair of little Yanmar 6 cylinder turbo diesels will set you back more than a pair of new Merc 525hps.
Gary

Actually ---look at the big performance boats there's quite a few that have come out with Yanmar options in the last couple of years. Before that the biggest problem was getting the power to weight ratio in line. There's 38 cigs out there with 3208 cats v-8's but they're just too damn heavy for the power they put out. The yanmars are only like 250 lbs more than a dressed BBC, and can run close to WOT all day long and still pass some fuel pumps at 75mph.
Yes they are expensive but a 420 hp diesel isn't that different in price compared to what you would buy from Merc that could give you that kind of performance. And maybe in 30 years when these diesels are being rebuilt by shops all over the country and there are all kind of used/ and aftermarket parts like there are for the BBC maybe they will be cheaper-- I know they will require alot less maintenance!
Mcollinstn--You're right we won't see any diesel vettes, but in a pleasure/ performance boat it's not about accelerating quickly, rather it's fast and steady wins the day! For me at least:D
I know if I was buying a 47 ft fountain or similar I'd be eyeing up the diesels---

Oh hell just get the turbines:p :p

Hey, I LOVE diesels.
I'll never consider buying a boat over 15,000 pounds without them.

If I lived on the Florida coast, I would be riding in a 42 plus foot performance hull with hotrodded diesels and surface drives.

Performance, economy, the ability to run at 85% all day long, beefy transmissions to harness the torque, and a bunch of stout stainless steel sticking out behind the boat that won't corrode off of it or blow the floors out of the pinion gears every time you fly off a big roller.

Question#1: (Why no supercharged diesels.) We have addressed this. Turbos are more efficient.

Question#2: (Why aren't more lightweight highpower diesels used in performance boats?) Because you do, indeed, give up performance over a comparably-rated gas motor. You also have stink, fuel that foams out all over your hands when you go to the pumps, and soot. They also add, on the average, $40,000 to the cost of a twin engined boat, and can't be bolted to an outdrive, which forces the installation to a more unconventional (read expensive) surfacing drive. They are also very long and force boatmakers to scrimp on interior cockpit size to fit them in. THIS, I believe, is the strongest set of reasons why we don't see more of them.

That, and the fact that there are more people capable of buying a 26 foot boat with gas power than a 45 foot boat with twin diesel surface drive power.

Not to say they aren't out there, just that they are a tiny minority of the whole of the performance boating pie.

I agree totally!!!

Here is a v hull with a diesel, this vent 85mph aprox, it has a sea tek diesel 650hp, the boat is 36feet.

Another pic

last one

cobra 860
 

WOW -- That looks like a pretty trick set-up, do you have any info on that single engined wonder boat?? 85ish is moving for a single 36 fter. What kinda drive is that and what the hose coming into the top of it??
I wonder what it would be like docking though--probably not extrememly manouverable...

What are the details on that set-up.
The beam looks very narrow.
Do you know what hull and drive that is?

I've heard horror stories about Seateks.
Running on the ragged edge, from the info I received.

If you've got em, I've heard that you shouldn't expect them to last more than 250 hours between major teardowns.

Course this is not experience talking, only repeating hearsay.

650hp diesel prolly 1300ft lbs no wonder it needs rebuilt every250hrs. I'd like to hear more about the rigging of that boat also, pretty cool looking.

In Europe they race those big trucks, with c12 cats that make 1000 HP.

I wonder what the rebuild interval is?

When comparing the price of diesel vs. gas you must analyze the total cost over the life of the engine. Diesels are more money initially but have a longer service life.


Here's a good article on hot rodding diesels.

http://www.dieselinjection.net/articles.html

Re: Why no supercharged diesels
 

This is a thread that may have been ahead of it's time.

However,with technology that is being touted as coming in 2007,the diesel may well take on a whole new profile.

Re: Why no supercharged diesels
 

Please expand....