LDS VS LDT and the real differences

[JasonS]

Merry Christmas!

Just a suspicion, backed by the wrist pin talk we had here, but I thought hollow pins were LDT and solid were LDS. I'll look it up when I have time if one of you doesn't beat me to it to verify, but I remember thinking the solid (heavy) offset the lighter weight of the LDS piston with the cooling channel. (less mass) I could be wrong.

Sure would be nice to be able to balance, stud, and blueprint one of these and then torture test it with modern lube. But the cost just wouldn't justify it.

I'm still waiting for some bright and connected individual to take a 6BT and install new pistons and injectors modeled after the MAN Hypercycle and see what is possible there. Maybe me someday.

The LDS Troubleshooting manual shows both solid and hollow pins. Why would you want to ruin a cummins?

 

[JasonS]

Tom,
Don't you think the LDS/LDT will be able to tolerate 250hp and 700 lbf-ft torque or so??

If I recall correctly, Continental demonstrated this horsepower level "while maintaining multifuel capabilities" meaning that they kept the high compression level. Whether or not it is a good idea ??? this was never a factory horsepower rating.......

 

[Heath_h49008]

The Cummins? Because you could modify the injection timing so easily to compensate for different fuels. Maybe even a dual or triple injector system. One "normal" diesel mist injector, one liquid MAN style injector and one gaseous injector in the intake for propane or natural gas and a nice computer to control all 3 at once. Plenty of aftermarket interest and support for anything you want to do.

If you want a base to play with, I think it has to be about the out there.

 

[m16ty]

I've always contended that the best way to get higher HP out of these engines would be to lower the compression. You'd loose your multifuel capability though. The high compression generates a lot of heat and puts more strain on the lower end.

 

[hornetfan]

I would grudgingly admit that it is a very very close relative to what we normally call a Diesel - but just as a 2 stroke marine engine does not use the Diesel Cycle (it uses an Otto Cycle) although most people call them diesels - the hypercycle is different mainly because of the high compression ratio - 16 or 17:1 is common on most diesels and we have 22:1 here

Also the way in which the fuel is atomized makes a large difference in the dynamics of the air and fuel interaction inside the combustion chamber, the multifuel uses a fairly basic injector which does not make a particularly fine mist or atomized spray because it does not have to... the turbulence in the chamber makes up for this fact - the long delay in ignition and the slow rise in peak pressure also make these engines different - close cousins for sure but different.

As for the other styles of multifuel engines there are many ways to skin a cat - some use a precombustion chamber which acts like a little rocket nozzle as the fuel in the prechamber burns, some use shrouded valves, or specialized inlet ports, and some just use a different style of piston...

I think the thing that sets these engine apart is the injection style and turbulence generating features engineered into the combustion chamber...

It comes down to nomenclature in the end - when I think of lower case "diesel" I lump all compression ignition engines together - where as when I think of upper case "Diesel" as in Rudolf's engine I narrow the scope...

Riddle me this - what would you call an EMD 645 engine - it has exhaust valves and liner intake ports but is a trunk style engine...

Sorry, I'm just buying that these aren't diesel engines. 22:1 compression is high for a turbocharged engine but not THAT high. And my NA 6.5L GM/Detroit diesel has 21.5:1 compression. The unusual swirl chamber is a bit different and appears to be what gives it long-burn characteristics which allow these engines to be tolerant of a wide variety of different fuels from gasoline to pretty heavy oils. But the multi-fuel engines are a diesel cycle engine e.g. COMPRESSION ignition engine. It shares the same suck-squeeze-bang-and blow of any 4-stroke whether Otto cycle or Diesel but the mechanism which initiates combustion is the heat of COMPRESSION.

This aspect of this discussion thread might make sense in an engineering class but this thread is about differences between LDS and LDT engines and has added "what makes a multi-fuel engine a multi-fuel engine" which I have personally benefited from. But let's not get too bogged down in the weeds, ok?

 

[hornetfan]

Having custom rods made is no big deal, and we've talked about having ARP make some studs for the stock rods to see if that might be a step in the right direction.

And polish the rods to remove the stress risers guys! I've built many an engine on a budget -- e.g. street racer's budget. Simple way to drastically increase rod strength is careful use of a grinder and polishing wheel. The get ARP studs and you've probably doubled rod strength. Street racers and moonshiners started doing that stuff way back in the 30s and 40s long before you could buy custom rods.

 

[m816]

This as far as i can follow this thread. You guys have shown me ho little I know about Multifuel engines. I have to stop now, my brain has been reduced to mush. Have a Happy New Year everyone.

 

[hornetfan]

Heath,

IMHO, your are focusing on the wrong things. The LDS's cooling channel is designed to cool the top ring land and does it at a 100F maximum! The LD, LDT, and LDS all have the piston cooling valve and oil galley in the block (at least all of the ones that I have seen). It seems like a sure bet that they all have piston cooling. Most of the piston failures that I can recall were damaged either due to a leaking injector or damaged when the rod bolts failed. The wrist pins are a ruse as well. I can't recall anybody reporting a failure of the hollow type.

You should read up on the multi's common failulre points and focus on those instead.

Jason, I think that's a really good point re: common modes of engine failure. Inexpensive stuff to enhance longevity include carefully balancing the rotating assembly, removing stress from the rods (polishing them), changing to ARP bolts and studs for the main caps, increased air intake flow and low restriction exhaust (which may mean using Donaldson air filters and larger tubing. I like a quiet truck so intend to fit a muffler but it will be very low restriction and the air cleaner will be as large as I can manage. Then make sure to add extra instruments for boost and EGT and carefully crank up the fuel to safe limits.

None of these things I just mentioned are very expensive and when rebuilding an engine it just makes sense to do this stuff.

 

[hornetfan]

C or D or the old LDS turbos will all make more boost than the engine can handle.

This thread is supposed to be about the differences in an LDT and an LDS motor.

The turbo has nothing to do with the differences in the motors.

That's an awfully definitive statement that does not seem to be backed up by what I have read in this thread in the past two days and certainly not backed up by any of the TMs mentioned so far. From what I can see these engines are starved for intake air and constricted with exhaust system. The injection pump, fuel delivery lines and fuel filter system are restrictive as well. The differences between the engines is being covered over because the whole engine system is held back to "military power levels" by various restrictions which are difficult to suss out which is causing what symptoms. Making a flat statement that the differences between a turbo that does move more air but may be constrained on the exhaust side as well as at least partially starved for intake air just isn't sound engineering analysis. At least not in my opinion as a mechanical engineer. Shoot, I don't know, you may be a P.E. mechanical engineer that teaches at MIT for all I know but if you were I would have dropped that class when I was there.

These guys may be taking various shots in the dark but they are actually making an effort to understand what is going on a very compliced engine system which is further complicated by lots of common parts and interchange of parts which may never have been intended for the engines they are found on because of Army logistics priorities. Give 'em a break. And yah, I know my comments are being offered over a year after the time of your post and haven't gotten to the end of thread. If I see something to change my mind I'll apologize and kiss your arse in the middle of Main St.

 

[gringeltaube]

Basically we are trying to find an explanation for those 50 extra horses. Mechanical engineer - or not, anyone experienced with these engines can feel (in that body part closest to the seat upholstery) the difference between a stock LDT465-1D and then a 5ton LDS465-1A, pulling the same truck. Air filter, primary fuel system, exhaust... all remained the same! And what if both engines even had the same model (D) turbo?? That's why Doghead says it is not the turbo!
I completely agree with him and I know I'm not alone...


G.

 

[JasonS]

We can get the same HP out of the LDT by simply turning up the fuel. Why does anything else really matter?

 

[hornetfan]

Basically we are trying to find an explanation for those 50 extra horses. Mechanical engineer - or not, anyone experienced with these engines can feel (in that body part closest to the seat upholstery) the difference between a stock LDT465-1D and then a 5ton LDS465-1A, pulling the same truck. Air filter, primary fuel system, exhaust... all remained the same! And what if both engines even had the same model (D) turbo?? That's why Doghead says it is not the turbo!
I completely agree with him and I know I'm not alone...


G.

I'm certainly not arguing that their is a seat-of-the-pants difference and if anyone in the past three yrs of this thread had measured the right things we might have found it -- but the turbo IS putting air in which lets the fuel burn and produce torque and hp -- from what I can see the likeliest component is the IP head which nobody seems to have taken apart and compared yet. But the extra fuel without the additional air (whether from a C or D turbo) will just shoot up EGT and fry pistons and turbo both. And a low restriction exhaust helps the turbo -- and low restriction intake air give s the extra air needed because all diesels really extra air -- they are happinest when lean burn.

It seems that all this talk and all this effort HAS produced some tangible results and the answer is right there close by -- just not spotted yet lol

Don't mean to be insulting or condescending to anyone -- engines are pretty darned complicated but they really are engineering and science -- not magic

 

[gringeltaube]

We can get the same HP out of the LDT by simply turning up the fuel. Why does anything else really matter?

Agreed the first sentence. Now IMO, it matters because we have learned that for the LDT you'd better install a pyro and boost-meter, after doing that... like probably the same if we turned-up a 5ton MF, now delivering 230Hp, instead of 175Hp in stock form.... !?

So again the same question: what makes a LDS465-1A -repowered M35A2 run like a scalded ape without having to fear for the pistons to melt-down at any moment?


G.

 

[Csm Davis]

Did anyone verify the rocker arm difference? And this is just a stab in the dark but the two hole injector might keep temps lower by hitting more surface area of the piston there by cooling quicker?

 

[Squirt-Truck]

Do not forget that the LDS-1A uses the ONE-HOLE injectors with the Code B pump. The LDS-1 uses the TWO-HOLE injector, which was a change and not done initially. The TM (226-34) is very specific that the -1 must have two-hole injectors installed. The pumps (Code B and Code F) are interchangeable but have to the specifically identified as calibrated for B engines (-1A) or F engines (-1).

So...is it just fuel delivery and timing?
More timing reduces EGT, and puts the heat in the piston and block, it also reduces smoke, but makes for a rough idle. I believe that Gimp made the comment early in this thread that there is a distinct difference in the sound of an LDS465 and a LDT465. I agree, it is dramatic.
Has anyone that has turned up the fuel added any timing? Say 5 degrees more advance?

 

[JasonS]

So again the same question: what makes a LDS465-1A -repowered M35A2 run like a scalded ape without having to fear for the pistons to melt-down at any moment?
G.

I would offer this:

1) Based on what I have read here, most LDT owners turn the fuel up well beyond the LDS ~10 psi setpoint. The higher fuel rate makes it easeir to get too hot, fast.

2) We really don't know how hot the LDS runs. This question has been asked here before but no answers....

 

[hornetfan]

Agreed the first sentence. Now IMO, it matters because we have learned that for the LDT you'd better install a pyro and boost-meter, after doing that... like probably the same if we turned-up a 5ton MF, now delivering 230Hp, instead of 175Hp in stock form.... !?

So again the same question: what makes a LDS465-1A -repowered M35A2 run like a scalded ape without having to fear for the pistons to melt-down at any moment?


G.

The simple and smarta$$ answer is air and burn timing. The timing of the burn is <mostly> determined by injection timing but actual intake pressures affect it, too e.g. how much pressure has already built from the turbo and whether you are in the lag rpm range or above it and have pressure building. This is what I <think> several others earlier in the thread meant re: dynamic compression ratio. Determining exactly what is different between these IP pumps seems pretty critical to answering this question. Has anyone compared the LDT vs LDS IP heads one-for-one? I didn't see it in the thread and I read the wqhole bloody thing over the last couple days -- maybe I missed though.

 

[Squirt-Truck]

The pump TM lists different part numbers but identifies no differences for the HH. It is not considered a serviceable component and is to be replaced as a unit. This is due to the lapped fit of the piston. With the exception of an older model that has an extra oil passage and that can be plugged. Hornet you may be onto something, just not sure what, if the head makes pressure and has flow capability, what else is there?
The head does not set the timing, it is just the distributor and the high pressure pump.

 

[hornetfan]

How many folks are running EGT gauges on both LDT and LDS engines? What are you seeing for max temps at what IP settings? Can we regularize some of this data so we have apples-apples points of comparison? I KNOW I'm not the only one interested in the question of not only what is different LDS v LDT but also what hp levels are safely attainable. From another thread (forget the userid but hilarious BC comic animation of the pegleg guy making the first snowboard) he asked the question what are max temps and what are people seeing and nobody responded to him -- back in '09. The question still stands.

Can anybody help here? This definitely isn't in the TMs for turned up engines.

.22 Hornet Fan

 

[hornetfan]

Question to moderators

Several parts of this thread have dealt with turbo differences and injection pump differences between LDT and LDS engines. The LDS 465-2 engine seems to be set off to one side as unique but I'm not so sure it is and I wouldn't mind seeing it included but they seem much less common so maybe irrelevant.

I'd like to broaden the discussion to a wider discussion of the part that the different IP heads play as well as turbo differences and include the rest of the intake and exhaust systems -- e.g. replacing an A2 air cleaner or substantial changes in the exhaust system such as adding muffler or dual stacks or ... ? And include as much gauge data as possible.

The internal components seem to be pretty much the same or else so mixed up by logistical considerations that various internals spec'd for LDT can be found and in LDS and vice versa. And they don't seem to really make any substantial difference when installed in an LDT it is still LDT power levels -- installed in an LDS and you still have LDS power levels. Have I got this correct? Anyone?

Am I trying to broaden this thread too much and getting out of line here? Should this be a different thread? This seems a good place for the discussion because the thread has durability and many of the same folks are still hanging in to find real answers. But I don't want to get my cherry butt chewed by brass either <bg> My tigerstripes are faded but they didn't get faded in this AO.

Just asking gents

hornet