Increasing the power of the Detroit Diesel 6-71

[luvrbus]

Your are going to need the injector and turbo number that engine should have the 3 numbers 1 letter injector like 7C75 and something like S4H-005 for the turbo get those numbers or serial number and we can help with engine power. The after-cooler if equipped is under the blower hard to spot but that year model should have one fwiw it could be 245 hp one never knows without numbers Unlike your Cat engine the 6L71 the peak torque is 1600 rpm or above so keep the rpm up @ 7 mpg it doesn't seem like it needing much attention it is probably a CA smog engine if the truck was based in CA     

The marine world does do 450 hp with a 6L71 problem they are 2000 hr engines which gets you 80,000 miles on the open road.If you are close to Bakersfield Ca ,my friend Don Fairchild can help you he is in the process of moving now so it make be awhile I would stay away from the propane with a turbo 6L71

[wg4t50]

A 200 kw generator on the 6-71T at 345 hp does well with good radiator cooling, we service a few of these, they are now dated, but keep on keeping on.
Dave M

[luvrbus]

Unlike a boat or a generator you are not chasing hp the torque is what you are after

[wg4t50]

Agree, but one interesting point of any DDC 2 stroke 71 or 92 series doing a generator load bank testing, they make the Cat, Cummins and the 60 series look like wannabee contenders when the block load test happens, the 2 stroker only has a very mini blimp in rpm, where the "Big boys" fall on their face big tine, from 1800 rpm 60 hertz down to under 43 hertz. Opps HP or Torque, I call it immediate available HP/Torque, that demo will make a believer out of a hard core Cat/Cummins fan  
The big boys can handle the load as long as it is step loaded, not 100% in one step like the 71&92 can handle so nice.

Dave M

[luvrbus]

I like the 149 series on a generator load those babies up they don't even change tunes

[Audiomaker]

Wow, it's great waking up to a ton of useful information...thanks everyone!

First, ok... now I know that my 7mpg is not *half* of what this rig should get. That helps.

Then I read the part about my 2000rpm idle and thought "wtf is he talking about?".  Ooops..typo.  My bad.  It idles about *1200* rpm.  Sorry about that. I guess I'm excited!

Also, forgive me for using the measurement of hp.  That's just being lazy.  Usually I try to use "power", but I'm aware that it's mostly torque getting me down the road.

I'm kind of getting my feet on solid ground about where to start.  Ya know, this motor is unlike any TD I've owned...even to look at it.
I crawl under there and it's sideways (and cramped)... it's got 3 times the hoses and filter housings, and unfamiliar steampunk looking devices on it than I've ever had.  There's really a lot of it and it's hard to tell what is motor related vs motor dependent (hydraulics and such).

Luvrbus, I will get under there as soon as possible for those numbers.

I'm actually pretty mechanically inclined (in case anyone cares).  I'm a machinist and a fabricator (I own a machine shop).  I've done many engine swaps and mod's...etc etc.  I'm just telling you that if it helps you gauge my ability to work on things and so that when I say things like "this engine has all this stuff I'm unfamiliar with", that comes from a person who has worked on his own diesels (things like changing injector pumps...etc), not from a soccer mom.

Luvrbus, I purchased this rig in CA, but I don't know if it was originally a CA truck... probably so, and I would be interested in meeting this mechanic.
I would trade an 80'000mi lifespan for 425hp by the way.  I estimate 5000 miles per year of driving tops, and 16 years of pulling hard would be longer than I've ever owned a vehicle.  What I couldn't trade in that equation is if it were getting less than 5mpg, and I would imagine that comes with the deal?
The same formula kind of applies for the idea of adding water/methanol or propane.  I have heard stories that either can eat a turbo, or perhaps affect the valves, but if those also would get 80k down the road before servicing, I could stomach that.

I will tell you that I won't go 10kmi down the road the way it is without doing some kind of mod's if it's otherwise functioning properly.
In other words, if I get it to someone with experience, and they find the air leak, or bang on the mystery box until it unsticks, and get it running as it should, then I will do *something* to it if "as it should" is close to this.

Maybe this will help...  running from Los Angeles to Oregon, there wasn't a bus that didn't pass me on any grade, and most of them pulling trailers.  Some of them likely had older DD's so I'm just "feeling" that I'm underpowered.
It's hard to determine "normal" on a new rig...unfamiliar engine... odd chassis and purpose...etc.

I also understand that you guys are giving 100% to try to do the impossible, which is diagnose my issue without standing in front of, driving, or having any experience with the rig, or me as a person.  For all you know, it could just be me.  I really appreciate that effort and I know what's it's like because I've done the same thing helping people with things I do know a lot about.

It might very well just be a combination of things.... CA truck.. the gearing...ridiculously large full time running hydraulic fan, stock injectors, too many auxiliary systems...etc.  I mean, this truck was set up to haul a CT scan machine from hospital to hospital...likely without much freeway time.  It was built by people who build fire trucks and airport emergency vehicles with no regard for the cost of fuel in those equations, nor "giddy up".

So where I stand now with your help is that I'm going to check some stuff as suggested, get some numbers, get to a mechanic who knows the DD like the back of his hand, and get it fixed or Ok'd, and work from there on ways to improve the performance beyond stock if still required.

My experience with the commercial diesels is that getting down the road often has as much to do with the transmission as with the motor.
My 3126 CAT for instance just kind of did its thing while the 6 speed Allison in that rig did all the work.  The tranny made up for a marginally strong motor which is a very efficient setup.   I will have to look into this as well, that the tranny is making good use of the power the 6-71 comes with.

I would like to research the different injectors once I have my baseline.  I've read there is a series that atomizes better.

Also, I'm curious about the blower (err..sucker), which if indeed in an exhaust scavenger, would be a limiting factor in the usefulness of applying more boost prior to combustion.  

Oh, to address some comments on exhaust restriction... I don't need to put a trash bag over the exhaust and watch it fill.  Starting the truck makes enough smoke for the 1st 30 seconds until it stops hunting that I could probably fill a box of trash bags.  Plenty of air moving both in, and out.  No run-away damper that I can find (I have a stainless steel bowl that fits the intake just in case).

One other thing that I'd like to say while I'm here is that I am surprised at the lack of "upgrades" obviously available to this motor.
I don't mean that to sound like a whine, but as an observation.  With so many years of service, I was expecting to see at least a few "kits" or "packages" available on the open market.  Rebuild kits with stronger components that let you get that 425 with some longevity...etc.
It's just something I wanted to mention.

I better get back to it.  I'll have so many more questions as I learn my way around.  Thanks everyone!

Sean

[Audiomaker]

Luvrbus,

I managed to slide this plate off the valve cover.  Maybe it helps?

I can't read any #'s off the turbo yet, but I'll get in there with better light and try soon.

Thanks

[eagle19952]

well the data tag says the turbo is 701
the injectors are 7G75
6A0432271
Model 10678642
My guess is you are not geared for speed.
I think that those numbers will aid the guys who have that info in their back pocket.
PS guard that tag with your life.
Note also outfits like Banks are not any use to you...DD is where you'll find what you need or guys like Clifford or Don Fairchild

Engine model # decoder: Note 42 is not a standard 40 = pre 1991 motor and 45 =firetruck
http://2-cycle.mtu-online.com/extras/engine-model-number-decoder

Your engine details:


1-Engine Series: 71
06-Number of Cylinders: 6 Cylinder
7-Application: FF-Auto
8-Rotation & Type: RD
6-Design Variations: TA
40-Specific Model: Pre-1991 Engine
42-?
45-Fire Apparatus

Heres a better one:
http://engine.od.ua/ufiles/DETROIT-Model-Serial-number.pdf

[eagle19952]

The serial # confirms that it is probably the original motor

6A0432271
431867 being the first produced motor in 1983'

I'm thinking I'd be looking for a metal tag stamped with oversize rebuild data....or think about doing one.

[wg4t50]

More than ever, I strongly suggest he find soneome who loves the DDC 2 strokes, it will then wake up.

I went (15 years ago) over a 6-71 in a 4104 that had about 1500 miles since the big tubeup at Steward Stevenson in Houston,  4 valve head, valve clearence varied from .010 to .032 bridges not close, rack would not fully open etc etc, He claimed it was very weak.  Next time I saw him, he complained about the poor fuel mileage, but it ran & he could pass trucks! Asked if he wanted me to set back to way it was ?  HELL NO, I rest my case.
Dave M

[Iceni John]

You say you want to install a turbo boost gauge.   I did this last year for my 6V92TAC (that's the Californicated version of the TA)  -  I bought a VDO 30PSI gauge from Summit Racing, ran half a mile of 1/4" plain nylon airline from a convenient 1/4" FPT outlet on the side of the blower below the turbo all the way to the gauge, and got a kick from seeing it show 26PSI boost under full load.   At least, until two weeks ago when I was driving along I-15 to Buses Gone Wild 6 for our annual get-together, when there was a loud PSSSST, and after the initial panic of thinking my brake system was kaput I realized that the gauge was showing no boost.   The reason was because the very hot air had melted the DOT fitting's O-ring and the nylon airline.   Doh!   I've now put in a compression fitting (no O-rings to soften) and ten feet of copper tube before the nylon airline, to hopefully cool the air enough that it won't melt the plastic airline.   We live and learn!

FYI, my friend's mid-engine Crown tandem with a 270HP 6-71TA and a non-overdrive 10-speed and 4.1 axles gets 10MPG, but it weighs only in the mid-20s now.   It climbed up Tehachapi out of Bakersfield in 8th and 9th gear, passing every truck on the climb.   As others have said, you have to keep a 6-71 singing  -  it bogs down below about 1500 RPM, so you need to manually shift an automatic to keep it happy (and cool).

John  

[luvrbus]

Sean,it is 285 hp with a after cooler and you have the good injectors the G's are used with std timing no need to advance the cam gear the timing is built into the injectors.  
I would have a tune up done making sure they do the governor setting even the starting aid, with the spring loaded fuel rods the governor should not be hunting as it is called.
Tune it up set the rpm @2500 so it does not faint looking at a up coming grade or hill drive it till croaks and that maybe a long time with a 6L71. The exhaust temp (EGT) will tell you a lot about the engine if you have a good IR temperature gun lay or stand up a board at the exhaust pipe not covering the pipe run it @ 2100 rpm you should have a reading of 760 to 780 degrees

good luck  

[HB of CJ]

Your coach sounds like it may have some Crown Supercoach or Gillig pedigree.  Have you considered taking the Cheap and Maybe Easy way out of this power dilemma and repowering  your coach with a suitable ex Crown Supercoach pancake Cummins engine?

Reason I ask is that right now in California, again lots of Crown Supercoach ex school buses are being placed out of service.  Some have perfectly good 250-290 hp/ 800 tor  Cummins Big Cam or NTC type pancake engines.  Four stroke 855 models.  Available $CHEAP$.

An older Big Cam 2 pancake engine can be easily re configured with factory used parts to as much as 475hp/1500 tor.  With a different turbo and some intake, radiator, charge cooler and exhaust mods, you can get an $easy$ and safe 550 hp/1650 tor.  A tranny change required.

Edit;  I meant a 600 series Allison and NOT a 6000 series.  My bo bo.  Proof reading comes to mind, which I did not.  Sorry for the error.

A 6000 series Allison will not hold up.  You need a HD740 Allison.  Or...with some modifications,  a properly sized New World 6 speed with two overdrives will work and free up some driveshaft length also, plus greatly increase your road speed.   PEM if 'ya wanna.  HB of CJ (old coot)

[eagle19952]

I think the rig has actually some relationship to Oshkosh...probably the most overbuilt chassis imaginable. It sure looks Oshkosh by gosh to me

[Audiomaker]

John, I'll be looking for that fitting myself soon.  Gauges make the truck go faster!

Luvrbus, I'll be right over, how much beer should I bring?  Errr.... how much beer do I need to bring to get 375 with no fuel economy or longevity hit?

HB, I was looking around at what the repower options were for this "L" motor.  Even having done many automobile swaps though, 2 minutes under this truck and I let that fantasy go.  It's just so integrated in there that it would be immense reengineering.  The plumbing alone is daughting.  That said, what is the model of Cummins you speak of?   I might consider it when i blow this one by not listening to Luvrbus's advice (which  everyone tells me is a good idea to do)

A couple quickies...
Are there any electronics in this motor?  I've read about the DDEC motors.  Advantages/Disadvantages?  Conversions?
I have a 701 turbo I guess... which means nothing to me.  Is this the best one? Is there a "best one"?

Also (this should be it's own thread), my hydraulic fan comes on all the time.  However it is "controlled".  After I start the motor, there is a delay of between maybe 3-30 seconds and it kicks in (and it's loud like my forklift steering).  It's pretty random and I can't tie the trigger to anything.
It never shuts off though and it's a big mutha', so I know I'm losing some fuel there.
What is odd to me is that it is controlled, yet comes on and stays on when the engine is cold, warm, hot, whenever.
Before I start tracing this maze of hydraulic lines and magic boxes that they connect to, is there a reason why the fan would be intentionally on all the time instead of thermostatically controlled?
I'm looking for this to be a problem to fix, but I don't want to get it kicking in at 200 degrees just to find out that it needed to be on all the time to cool something else (like the Allison).   Could it have been set that way because it was a CA truck in hot weather that they didn't care about the fuel economy?  Thoughts?