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-   -   Detroit 8v71TI (http://www.trawlerforum.com/forums/s6/detroit-8v71ti-16475.html)

amelis 09-05-2014 12:37 PM

Detroit 8v71TI
 
Hi all, I'm new to this and switching from a sailboat.
We want a comfortable liveaboard that has good range, at least 700nm.

We have seen a great 1983 Hatteras 53 extended deckhouse but I am concerned that the consumption will make long distance cruising unaffordable. Tanks are 700 gallons and engines are 450hp each so range at the moment is probably no more than 400 or 450nm.

I have read that putting smaller injectors can reduce hp and cruising rpm and consumption quite considerably.
Does anyone have any experience of this? Is it a good or bad idea?

Are there any other ways of reducing the consumption of these big engines?

Thank you!

Ski in NC 09-05-2014 01:03 PM

Injector change will make little if any difference. At any given speed, the boat will require the same hp regardless of injectors.

At speeds down around 8kts, should be better than 1nmpg.

I think there are others on site that have similar old Hatts with same engines, they can give better burn data.

kulas44 09-05-2014 02:21 PM

Compression ratio is lower in the TIs than on a NAs. Low cylinder temps are a problem on TI engines that are not loaded enough (ran slow). Serious cylinder glazing can occur if operated to long at low power. You can remove the turbos and intercoolers and go to a 7E55 injector (318 hp in the NA engine) and reduce or eleminate the low load problems, but you still have the lower compression ratio, which basically just lowers the power output even more. The 7E55 injectors are the latest Calif. bus version and pretty much fix the smoke proble. The timing could be adjusted to partially compensate for the lower cr.

caltexflanc 09-05-2014 02:39 PM

You can also take your question to the Hatteras Owners Forum, where there are several people with the model of engine and boat you are considering.

At hull speed most 53's get a 1nmpg - 1.5nmpg depending on heavy the boat is and what if any generator use is involved. Lots of threads on the subject at HOF.

I could get 1nmpg at 7 knots out of my 8v92ti's , in a much wider and heavier boat than a 53. In reality we got 1 statute mile per gallon, at 8 knots average.

Great deluxe cruising and liveaboard boats by the way.

knotheadcharters 09-05-2014 02:58 PM

I usually run my 6-71Ti's at 11-1200 rpms. I am averaging 7 gallons an hour with a 15kw genny running at about 35-45% load. My temps are right in range and have never had any glazing issues. no smoke, nothing. At this ,I am running 8 kts and getting about 1.3 mpg. The boat is a 48 Californian weighing in at 47,000 lbs wet.

caltexflanc 09-05-2014 03:11 PM

I should add to my answer to cover some of the issues about engine modification the OP had. The short answer is: no. Going slower is the best way to increase mileage. The 450HP version of that engine is about as efficient as it can get. There is no magic bullet that generates the horsepower needed to move the boat a certain speed with less fuel. Make sure you have someone very experienced in the Detroit 2 stroke engines do a complete survey before you buy; this will be someone separate from the hull survey. You can get DD surveyor recs here, at HOF and at boatdiesel.com, which I'd advise subscribing to. Is this boat in Tortola?

amelis 09-05-2014 05:12 PM

Thanks all for your input. The boat we are considering is in the ft Lauderdale area.
We have also seen a 48 lrc with twin Lehman 120hp and that makes more sense for range and cost but doesn't have the great space and layout of the 53.

In the case of the 53 we would cruise slowly to reduce consumption but was just thinking that with smaller injectors we could handle the lower rpms without affecting the engines as much as going slow with the larger injectors.

I did also read somewhere that a 20% saving was possible but can't find the article any more.

caltexflanc 09-05-2014 05:51 PM

No, what you do is run them as gently as you please. To be anal about it, once a day, ok, maybe every other, preferably towards the end, run them up to 1800-2000 for a few minutes. They will live happily ever after. Besides space, one thing the Hatt gives you is the ability to run faster to beat weather or other reason. You have to be careful, there is more urban legend about these engines than any other. The support and parts availability you can get for these old Hatts exceeds any older boat out there.

kulas44 09-05-2014 06:20 PM

I run my 550 hp 8v92s mostly at 8 knots. They are maintained in impeccable fashion. They are in very good condition. They have 115 injectors, most had 120s, so they are a small amount derated. These are in a 48 foot planing hull boat, very similar in form to most boats here. Fairly deep v aft. 32 x 32 props. 2 to 1 gears. Similar to the hatteras 53. It weighs 44,000 lbs. My BEST EVER mpg (statute) was 1.2 mpg, on one engine, no current or wind to speak of. With both engines at that speed they will load up in a few hours and need "blowing out". I removed the intercoolers and it helped some. I know, you're gonna say something is wrong. Well, I am a DD 2 stroke mechanic from way back, back when the oil industry ran on DDs, and I can tell you they are perfect. Just not designed for slow. If a pump or genny required 500 hp these engines would do it for 10,000 hours. In this boat, the way they are being ran they wont go 5000. Just my first hand and knowledgeable experience, if yours do better good on ya.

River Cruiser 09-05-2014 06:40 PM

Moved a 47' Concorde from the upper Mississippi River to Detroit in May. It had twin 8v71 Detroits the the 350 hp version, on the leg from Port Charles marina on the Mississippi near the mouth of the Illinois river to Hammond, Indiana we burned 5.5 gph while getting 1.1 mpg, with the gen running 60% of the time. I don't know what the current we were going against on the Illinois was making, we ran around 1100 - 1200 rpm.

kulas44 09-05-2014 07:34 PM

8v71 at 350 hp is very civilized.

caltexflanc 09-05-2014 07:56 PM

Quote:

Originally Posted by kulas44 (Post 264794)
I run my 550 hp 8v92s mostly at 8 knots. They are maintained in impeccable fashion. They are in very good condition. They have 115 injectors, most had 120s, so they are a small amount derated. These are in a 48 foot planing hull boat, very similar in form to most boats here. Fairly deep v aft. 32 x 32 props. 2 to 1 gears. Similar to the hatteras 53. It weighs 44,000 lbs. My BEST EVER mpg (statute) was 1.2 mpg, on one engine, no current or wind to speak of. With both engines at that speed they will load up in a few hours and need "blowing out". I removed the intercoolers and it helped some. I know, you're gonna say something is wrong. Well, I am a DD 2 stroke mechanic from way back, back when the oil industry ran on DDs, and I can tell you they are perfect. Just not designed for slow. If a pump or genny required 500 hp these engines would do it for 10,000 hours. In this boat, the way they are being ran they wont go 5000. Just my first hand and knowledgeable experience, if yours do better good on ya.

32 pitch and 2-1 gears sound a little big for that boat. What kind of RPMs and speeds is all that taking place at? They certainly shouldn't be "loading up" in a few hours. Going to one engine really doesn't gain anything much. What condition is the bottom in and how new were the props?

kulas44 09-05-2014 09:07 PM

32 x 32 is what she came with, on 2 1/2 inch shafts. On the pins, in the corner, wot, she'll do 29 knots. Its in fresh water at Venice marina (lower miss) so it gets a bit of slime which cleans off pretty quickly at speed. Bottom is slick. Props are fine, had a bent ear on one but repaired at last haulout. Advertized speed was 30 so its pretty close. At 29 they run GREAT, no smoke at all, just that incredible detroit sound. These engines are perfect for the way they were designed. Just not for how they are being used. Running one engine seams to load that engine a little better at 8 knots and loading up is not as much of a problem. It has been a few years since I ran the rack on them so possibly they could use a tune up, but its been less than 300 hours since the last time, so probly not. They do have the air box drains that feed back into the oil, that has been problematic in DDs, I just havent changed it yet. Airseps would help possibly, certainly wouldnt hurt.

Ski in NC 09-05-2014 09:24 PM

The 500 and 550 892TI is one of my favorite DD setups. The 871TI at 450 is in the same class, dang near the same machine. I have a few stories of those that will make a Cap'n or mechanic want to run and hide!!! For another time...

When they went to TA and higher hp, that charge air was just so hot, pistons so hot, you could not get much life out of them. The lower rated TI's would just go and go and go.

I will disagree a bit about the low load running. I am involved with several boats that cruise consistently with their TI's at 1100, 1200 etc. Yes they get slobber in the manifolds and turbos that cooks off with a power up, with the expected cloud of blue stinky smoke. More smoke the longer you run easy. But once cooked clean, these engines still run perfect. No loss of compression, no high oil use, and some have run this way for many thousands of hours. Look in the airboxes, nice crosshatch all over.

Also, some DD gensets are 1200rpm and often run at light load, dang things run forever.

Not saying it is impossible to glaze liners and force a kit replacement, I know it can happen. Just have not seen it at 1200.

Edit: Saw your 115 injectors. The 500hp boats had 9200, the 550's had 9215, and that one we later bumped to 9225 to get about 600. That was on the 92's. The 71 TI's I think were running n90's.

kulas44 09-05-2014 10:58 PM

Right on the injectors. I call them by there sir name. 9215 would be the old 71 series 115s. No difference as far as I know. I do love the old DDs, in there specific applications they could'nt be beat. The 7E series injector is a bit differnt. Made before the ddec for busses in calif. Smoke from inner city transport was a problem. They just dont smoke at lower rpm, like leaving a bus stop. Still about the same hp rating on the top. Much better below 1250 rpm. IIRC they were set at .049

kulas44 09-05-2014 11:02 PM

Wrong again, its 1.496. Thats twice today. I quit.

River Cruiser 09-05-2014 11:05 PM

Detroit 8v71TI
 
Worked several years for a contractor that had a spread of Terex scrapers, dozers and trucks plus other pieces of iron that were Detroit powered. The 12v71 with twin turbos seldom got over 2000 hours, they were either running wot or idling not much in between, the non turbo units in excavators racked up way more hours without problems. The units in the scrapers always ran on the verge of overheating which I think was the culprit to their short lives before rebuild. The turbo 8v71 in the rock trucks ran just as hard and seldom had problems and didn't run close to overheating. On the injector part # most all had the N65 or N70, I had a Chevrolet C60 fix truck with a turbo 4-53 it would hardly go 30,000 miles between major work on the engine, I believe it had the N45 injectors.

amelis 09-06-2014 01:18 AM

So what kind of gph can be achieved at 8kts with these 8v71tis on the hatteras 53 do you think?
Will they run slower than 8kts?
Thanks

FF 09-06-2014 06:33 AM

the problem with 2 stroke DD is no matter which engine is chosen DD expected you to have the correct engine installed.

About 60% of as built HP is required to get the 16 Hp per gal a DD can do.

Running slower is fuelish , but far far cheaper than an engine swop.

If the load requires 300hp DD expected you to use the 8V if it requires 60 hp DD thought you would chose a 3 or 4 cylinder engine .

If you like the boat , and plan on running way over the usual 200 hours a year , a set of Flow Scan and a GPS will help get the best mpg.

With the turbo and after cooler great low rpm fuel burn is not possible , regardless of the injectors chosen.

The NA series can be helped with smaller injectors and advanced timing, but even 20% better is seldom worth the cost and effort for a few hundred hours a year.

Changing the injectors on a DD is not a R&R anyone can do as with other style of fuel systems.

The valves will need to be adjusted and the injector height adjusted , and then the rack run , to get all the injectors working together.

This takes DD experience and hours , as well as a special $20. measuring pin, and did I mention ,DD experience.

caltexflanc 09-06-2014 07:21 AM

Quote:

Originally Posted by amelis (Post 264903)
So what kind of gph can be achieved at 8kts with these 8v71tis on the hatteras 53 do you think?
Will they run slower than 8kts?
Thanks

Yes they will run slower than 8 knots just fine. I don't know if it was you who bumped it, but one of the old threads on this subject re-emerged on the HOF last night.

Great comments Ski. I had my 8v92tis totally surveyed (two day job) at 3000 hours after years of running at below hull speed with the occasional daily or so blowout, and all maintenance done per the book. Came out great, the guy summed it with, "run 'em and take care of 'em that way for another 3000 hours and then lets have another look".


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