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  1. #11
    garyd Guest

    6V92 DDEC 625HP

    Excellent response, Having rebuilt many high powered gas engines and even a jet engine, I appreciated your disertation.

    I have another simple question. When I repitch the props by 2" will the govenor keep the RPM from going tooooo high? I have never run the engines up to WOT not in gear.

    And if I understand it, unlike gas and jet engines RPM in diesel is not really the bad guy its power/load. So I can increase RPM to a point and actually make the engine breath better and get complete combustion. Thus increasing mileage, reducing stress and carbon buildup. This not normal to either gas or turbine engines. This is an insight I was missing and thank you for a new mindset!

    thnaks again garyd

  2. #12
    Walter Pereira Guest

    6/92 engine life

    After reading all the comments regarding 6/92's, I think I realize why when I tell people that I have 6/92's in my boat they sort of give me their condolances (sp). Truth be told, I am guilty of not running most of my boats hard enough. I like to cruise at displacement speeds unless we are on a timetable to be somewhere. We also don't want to be locked into trawler speeds. We like the option as the need presents itself.

    My question is - how can I cruise most of the time at 9.2 K (1200 rpm) and still run up to 16-19 K when I need to, without hurting my engines.

    I presently have 6/92TA's of unknown HP as they have been redone in the past. The history is a mystery, as I only recently aquired the boat. I don't know what sort of maintaince it had (if any). The oil resembled tar both in color and viscosity. One of the engines (port side) was actually replaced with a new long block a couple of years ago and I can't imagine why it is already worn. I need to get them majored or so I was told and I want to be sure of getting the right job for my needs. The boat is a 1982 48 MY with the usual "stuff" that is in the process of a complete rehab.

  3. #13
    Genesis Guest

    Yes, and yes... :)

    Gary, yes. The governor prevents overspeed.

    Indeed, one of the tests you do on a diesel is to confirm the no-load speed. That is, you warm the engine up fully, disconnect the linkage, take it out of gear and advance the "throttle" to full, then measure the RPM. The no-load RPM on a 6V92 in a marine application is typically set to 2500.

    Full-load RPM will be about 150-200 RPM off that, if the boat is propped for full power.

    The DDECs are electronic rather than mechanical, but there is still some "slop" between no load and full-load RPMs - although not as much.

    Typical "spec" from various marine engine people (e.g. Cummins, Cat, etc) is to run at no more than 200 RPM off the maximum for continuous operation. Due to prop demand curves this should result in an injected fuel amount of no more than 80% of maximum. This is for a relatively-conservative rating - for one that's very aggressive, as your boat is, I'd want to be in the 70-75% area at 2100.

    In a marine application the usual arrangement for the governor corresponds the "throttle" (which is really not correctly named, as there is no "throttle" in a diesel!) directly to a RPM setting. That is, you select the RPM of the engine with the throttle lever. The engine varies the fuel injected to maintain that RPM across varying load (e.g. up a wave, down a wave, into the wind, with the wind, etc)

    This is very different than in a "road" engine, where the throttle position roughly corresponds with the power output, with a hard RPM limit at the maximum specified.

    Walter, the issue for these engines in terms of what you want to do is mostly a function of whether they stay fully warmed up. If they do, and you blow them out every few hours with a 10-20 minute run at cruise power (1900ish), they'll be fine. Trouble begins if the temperatures start to drop. Anything below 170ish is bad news; that's the opening temperature of the thermostat, more or less, and the engine has to produce enough heat to keep itself clean. If they run cooler than that its bad news, as you will get incomplete combustion and the carbon will build in the ring grooves. When a ring sticks it will either score the cylinder or break - either is very bad news as it will hose that cylinder immediately, and if you get unlucky with a broken ring the piece(s) can come back into the airbox port and then be trapped, doing catastrophic damage in that cylinder or even worse, wind up with pieces floating around in the airbox and going into OTHER cylinders.

    In older motors one common reason for this to happen is the thermostat housing seals. The thermostats in these motors are kinda bizarre - they are a bypass design, and either run the coolant through the H/E or bypass around it. There are also two thermostats - one for each side of the motor! In the housing there is a seal in which the thermostat poppet rides - if this is worn and leaking the engines will run abnormally cool at part-power settings. If you've got this problem, you need to pull the housings and replace the seals, along with checking the thermostats to make sure they're fully closed at temperatures under 170F. Its not a difficult job but does require partially draining the cooling system.

    The 6V92 is not a bad motor, but you have to be aware of its heritage and what a REASONABLE output level for it is on a continuous basis. Anywhere beyond 300 HP on a continuous output basis is trading power for time in terms of durability. You have a 552cid engine - the general "rule of thumb" is that for really good service life you want the maximum output at WOT to be somewhere around 0.8hp/cid, which would be right around 440HP. This would make the output at 200 RPM off the top in the neighborhood of 300-350 HP.

    0.9hp/cid is the "wall" is IMHO "the line" for good service life in "heavy recreational" (over 100 hours/year) service, which is 500HP.

    Beyond those ratings you're playing with hand grenades with loose pins.

    You can loosely determine output from fuel burn - diesels develop roughly 16hp for every gph consumed, give or take a bit (the newer full-authority electronic motors - DDECs are NOT in this category - do a bit better due to varying injection timing, but for Detroits these numbers are reasonable solid.) So if you know what you're consuming from the tank, you can roughly determine how many mustangs are being requested.

    The final thing to be aware of is that these are "wet liner" engines. The cylinder liners are held in place in the block with O-ring seals. If you EVER overheat these engines, you are almost certain to compromise the seals, which will result in cross-contamination of the cooling and oil systems. As such the cooling system condition is critical, and it is very important to not allow these engines to ever exceed 185F. A wise man installs alarms that sound at 195F, and never hears them ring.....

  4. #14
    DaveP Guest

    Governor?

    Gary,

    The DDEC's don't have a mechanical governor but a microprocessor controlled fuel system. I believe that whatever parameters the tech sets into the computer regarding idle, no load speed, and WOT will not change if you change wheels. The only thing you will do is reduce the amount of fuel you need to run the same RPM's. As Genesis said anything you can do to help your engines live and breathe you should do.

    We have 550 hp 8V92TI's in our 45C and we propped her to run 1900 at cruise because our mechanic told us that was the low end of the best sustained operating speed for these engines. He mentioned EGT's, and Load, and breathing, and increased lifespan if the engine is getting the right amount of fuel and air for clean total combustion. J&T likes you to run 1900-2000 continous cruise with 92 Series engines.

    As for low speed cruising with 625hp 6V92's I am not sure that you are helping your engines out. As long as your water temp is around 180 you should be OK, but I know even with my detuned engines and small injectors I load up after trolling at 900-1100 RPM's for a few hours. My engine temps drop down to 165-170 and I smoke when I accelerate. I changed my thermostats to 180's and that helped but J&T said to put back in 165's because the 180's will be constantly opening and closing and will mess up the cooling if I tried to run with the thermostats in the closed position. If you look at your DDEC readout for EGT, just make sure they don't rise above normal temps. I will say this...at those slow speeds you aren't letting your engines breathe, in fact your turbo boost is probably in the neighborhood of 5-8% if that.

  5. #15
    garyd Guest

    6V92

    Ran the boat last night. at 2000 rpm white/clear mist exhaust. At 1900 a very slight smoke at 1800 a little more, nothing major. It looks like I can run about 1900 at 26.5 kts and accomplish what everyone is saying until I get a chance to reduce the pitch. Turbo boost is: 1800 13 p 16 stb. 1900 17 p 19 stb. 2000 20 p 22 stb.

    Trolling doesn't really load them up I guess the ddec system takes care of that for the most part.

    Temps stay at 170 at just about all RPM's.

    Someone told me to let them cool down about 15 minutes before shutdown due to fuel cooling the injectors. I figured he really meant to cool them down so I let them drop until they stabilize around 145 then I shut them down. See any problem with that?

    thanks gary d.

  6. #16
    garyd Guest

    6V92 DDEC cool down procedure

    When shutting down I let the engines cool down to around 145 degrees it takes about 15 minutes. Is it necessary or harmful to do this? thanks for your responses, learned abunch so far.

    garyd

  7. #17
    Genesis Guest

    Good idea....

    .... to cool them down before shutdown.

    15 minutes is more than you probably need, but won't hurt anything.

    The big deal is don't shut down hot.

  8. #18
    divernc Guest

    Engine temps

    First year of Hatteras ownership. I have 450hp 6V92TAs in a 1979 43C. Engines have 2050 origianl hours. As winter water temps have risen from low 50's to low 80's, both engines' temps have risen from 175 to 181-182. These are from bridge gauges and mechanical gauges in engine room. Is this normal?

    Last Friday, the port engine overheated, but resumed normal temp when I pulled it back to 1000 RPM. Hours later in a heated engine room, I found the pencil zincs in the Jabsco raw water pump broken off and laying on the intake strainer fingers of the pump. This seems to resolve the issue.

    I have cleaned and replaced all parts of raw water cooling system except exhaust showers. The exhaust shower can is welded to the exhaust piping coming off both turbos(about 5' long with a Y for both sides of engine). There is not enough room to slide the rubber coupler downstream to get a look at the shower head while in place. I tried to remove by taking off the clamps holding the female to female mating of the turbo and exhaust tubing. I could not ge them loose with a rubber mallet or steel hammer on a 2X4. There is a set screw or gauge sensor port on top of the exhaust tubing immediately downstream of the turbo, which I could not free either. Any hints on how to get access to the shower head for cleaning? Is there a way to tell if these are obstructed without disassembly?

  9. #19
    Genesis Guest

    Exhaust issues....

    OK, you have the old style (original) single-piece exhaust collectors.

    You have to dismount them to get them out.

    To do so:

    1. Remove the blankets over the turbos and the collector. Close the seacock and remove the raw water hose going to the shower head. This will make a saltwater mess - have a 5gal bucket handy.

    2. Remove the Monmon (V-Band) clamps on the turbine exhaust outlet. DISCARD THESE. It is very important that you NOT reuse these clamps - they heat-harden and if one breaks underway you are almost certain to have an engine-room fire. New clamps are roughly $10 (each) These clamps also use castellated nuts which self-lock but are not nylon-based (too hot for nylocks)

    3. You should now have the exhaust collector attached to a brace that goes to the transmission rear housing and bracketing system roughly in the center, and at the shower head in the hose that goes to the elbow leading out of the boat. If you have Pyrometers (wires coming out of the collectors just behind each turbo), remove them. PB Blaster is likely going to be required on these connections - be careful, however, not to get too much of this on the pipes in general, as it contains an oil and is flammable! Take your time on those lest you break the probes and get to buy new ones or worse, shear them off leaving you with no pyrometers.

    4. Loosen the clamps on the hose on the shower-head end. Using 409 (yes, the cleaner!) and a straight-blade screwdriver, work the screwdriver between the hose and shower head, spraying 409 in the gap. Work around the entire shower head to free it up as much as is reasonably possible. This will take some time, be careful not to damage the hose.

    5. Place your FEET between the turbos on either side of the flex section in the collector pipe while sitting on the airhorn. Try to avoid pressing on the flex section - you may not be able to, but do your best. Kick STRAIGHT BACK with moderate force - not too hard! The collector should separate from the turbos. The idea is to just break the joint loose - don't go nuts with the force here or you'll bend the support bracket at best and could rip things up in the exhaust beyond the shower-head at worst.

    6. Now get some help to support the pipe. Its kinda heavy and awkward (perhaps 50-60lbs, long, etc) With the turbo end supported by a helper, unbolt the support and remove it.

    7. You now have the pipe held on one end by the hose, and the other by your helper. The helper now must push his end aft while you use your legs to lever the pipe forward and up slightly to clear the hose. Beware that if you have blower-mounted alternators that there is a hot 12V lead back there that is on EVEN WITH THE MASTER DISCONNECTS TURNED OFF AT THE PANEL! It should have a boot on it, but..... Don't short it! Once the pipe is free you can maneuver it out of the engine room.

    Installation is more-or-less the reverse of removal. Use Silkolene on the turbo-to-collector joints, and use NEW band-clamps. The first time you put the engine under load the Silkolene will smoke like hell - do your sea trial after repairs with the floor up and all windows open! Silkolene seals during that heat-curing process and will prevent exhaust leaks, which is very important to avoid serious engine damage due to ingestion of "recycled" exhaust.

  10. #20
    Genesis Guest

    Temps...

    181-182 is normal, provided those are real temps (get an IR thermometer or mechanical gauges if you don't have them - electrical gauges are notoriously unreliable)

    Do not allow these engines to run over 185F. That is "thermostat fully open" temperature, and you will quickly get overheats beyond 185F, as you have effectively reached the end of the cooling system's reserve capacity.

    Thermostats start to open at 170ish; so normal range is between 170-185. These engines have marginal cooling systems for hot raw water (over 75-80F); be wary and attentive, as regular maintenance is required to avoid disasters.

    Overheats are DEATH to wetliner motors, and the 92s are. Check those zincs regularly, at least every three months, and replace long before they get worn and can break off.

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