Why no supercharged diesels
06-02-2003, 04:40 PM
#11
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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.
06-02-2003, 11:54 PM
#12
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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...
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...
06-03-2003, 12:50 AM
#13
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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.
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.
Last edited by Mr. Demeanor; 06-03-2003 at 01:48 AM.
06-03-2003, 02:30 AM
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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.
( 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.
06-03-2003, 03:12 AM
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06-03-2003, 04:45 PM
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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
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
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
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
06-03-2003, 11:11 PM
#17
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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...
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...
06-03-2003, 11:22 PM
#18
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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.
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.
06-04-2003, 03:59 AM
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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.
