LDS VS LDT and the real differences

[m-35tom]

if you want more power (HP) just run them at higher rpm since the formula for HP involves rpm and torque. and that is just what the military did since the engine in its most reliable form, low rpm, did not make enough power. hence the higher rpm of the LDS. but it's not gonna last as long before it breakes. however the military did not care if it broke, they had plenty of 'our' money and spare engines. if you will read the operators manual you will see something to the effect of ' max rpm is just for short periods of time when you need absolute max power' not for continous operation. when this same engine was used commercialy, the rpm was limited to 2200.

 

[Heath_h49008]

Another good reason for overdrive.

[/shameless plug]

 

[m16ty]

wow i have read through 25 pages n am almost more confuzed than when i started"thnx dh for trying to keep thread on track" as from what i have "understood" lds makes more hp/torq from more air / fuel? has anyone checked the intake plenum and exaust size? more air / fuel=more power right? mabe its not just a 1 thing deal that makes the engines different ok ie the intake rocker may be a touch bigger. pump may put a little more out but as i read earlier the air filters tm was also different . lds has larger cfm's than ldt. parts are interchangeable, are the intake and exaust the same as well? i dont really know but that would make sence 2 me. normally if someone hops up a engine, 1st thing is a intake and exaust mod then fuel and so on right?

The multifuel breathes fine. You have more than enough fuel and air available to melt down the rest of the engine. The main obstacles with increasing hp in a multifuel is heat melting the pistons and the weak bottom end.

From all available data, the engines are functionally identical except for the pump/head, timing of that head, the extra cooling in the LDS pistons, and the bigger turbos on some LDS to deal with the increased fuel/power.

The LDS/LDT are the same engine in different tune and with different accessories to deal with the increased fuel/power/heat.

Tubos do not increase power per se. They allow the engine to remain cool while the extra fuel that makes the increased power is burned. Any change in timing would also effect the burn time and heat produced.

The reason it seems so hard to find the difference is, there really isn't one more complicated than more fuel and more cooling.

I agree with everything except adding a turbo will help the engine run cooler. When you compress air it heats up and when you restrict the exhaust you increase heat, a turbo does both.

I know all the literature says that a turbo was added to the multifuel to reduce smoke and not add hp but that's not entirely accurate. The military actually had two choices to decrease the smoke of the multifuel, they could either de-fuel the LD to decrease the smoke which would result in lower hp or they could add a turbo and keep the hp the same or a little more. Both options would decrease the smoke. Smoke is too much fuel. The only way to decrease smoke is have less fuel or more air.

 

[mudguppy]

intake rockerarms(ratio). It's like having a "hot cam".

that isn't correct. higher ratio rockers simulates higher lift but doesn't change duration or lobe separation. a 'hot cam' has changes in all these areas, which makes an engine's idle characteristics change.

in these two engines, the changes in injector and IP are the only things that can account for any descernable differences.

 

[JasonS]

and the bigger turbos on some LDS to deal with the increased fuel/power.

That "bigger" turbo uses a nozzle ring to spool up what is otherwise too big of a turbo for this engine. The D is supposedly capable of the same boost.

 

[Heath_h49008]

That "bigger" turbo uses a nozzle ring to spool up what is otherwise too big of a turbo for this engine. The D is supposedly capable of the same boost.

Yep. More boost at lower RPM levels to compensate for the increased fuel.

I'm actually considering finding a "D" myself and dumping my "C" just because the "D" has a more robust design. Not really interested in a wastegated pinwheel though, the D will do me fine.

The pump pushes more fuel, and the Turbo/pistons/timing/etc are all changes that help the engine deal with it. I was under the impression that we had only found 1 rocker ratio, and that the differing part numbers were simply individual arm vs arm/kit. Also, IIRC the injectors are either two hole or one hole but are also interchangeable.

It's almost a non-subject... want to make an LDT an LDS? Turn up your pump. The factory just used a marginally "bigger" one on the LDS. You will have a hot running LDT/LDS without the cooler pistons and with more smoke. There is no magic LDS part required.

 

[Katahdin]

FYI, this was the Army's idea of an endurance test for the LD/LDT-465. They were run at 2600rpm for up to 2 hours at a time with one hour periods of idle in between.

 

[Csm Davis]

Okay just read all of this and in three years or more no one has answered the question of what makes the differences. Some have posted parts that are listed as different, and some have cited those parts on both engines. As to rebuilt engines the military does dyno them, there's one at Camp Shelby, but they are looking for minimum numbers to pass not maximum as much, think they will turn down a real hot one, so to say that your ldt runs like a lds might be because it is running those parts. They will up grade parts to improve reliability so lds pistons in ldt engines maybe the rule.
As to the extra horsepower I would say the IP would be the number one part, and has anyone actually checked the timing on both side by side?

 

[m-35tom]

seems to me the question has been answered over and over again. but as heath says there is no real big differance just as there is no big differance in power. the LDT is set at 9 psi boost and the LDS at 14. that takes more fuel, and fuel = power. any good LDT turned up to 14 psi will run as good as a LDS.

 

[JasonS]

seems to me the question has been answered over and over again. but as heath says there is no real big differance just as there is no big differance in power. the LDT is set at 9 psi boost and the LDS at 14. that takes more fuel, and fuel = power. any good LDT turned up to 14 psi will run as good as a LDS.

I agree with everything you said except that, according to Continental's LDS465-1 Troubleshooting manual, the maximum LDS boost is 20" Hg which is equivalent to an even lower thresholod of 9.8 psi. Which means that almost anybody who has turned up their LDT pump has LDS power.

 

[sandcobra164]

I'll add this after reading the content of this thread. My LDT-1D turbo will blow a pile of smoke out of the stack under acceleration. I turned it up and it's now mostly on filtered WMO. I would bet it is turned up past "factory" LDS settings and has been running that way for years. I know for certain it will out accelerate an M923 on 14's but of course is out matched on "road speed" once it get's going. It doesn't back down on hills and pulls most hills at 45 MPH indicated or so, it's has 11:00's but I think it could pull 395's just as well. An LDS is a nice motor but the more I read, I think it's all in the pump.

 

[hornetfan]

good point on the CR - i was trying to recall (without going back through all 90 posts) whether the rotating assembly was the same.

if the crank and rods are the same part #'s and the piston pin heights are the same between the two motors, then CR should be the same unless there are differences in the head chambers.

however, i don't see a CR change being responsible for adding 50-70+ horsepower over the LDT.


my opinion based on what i've learned: diesels make power based on fuel. and you can alter fuel delivery to make more power without changing any other aspect, including air. fuel delivery pressure, fuel delivery velocity, injector orifice count and size, spray pattern, combustion bowl design, and other things can be altered and have affect on power without increasing EGT or putting combustion pressures above safe levels.

that's my theory without know much about anything.

Before any body jumps my butt -- I realize I have NOT gotten to the end of this thread yet. However Travis' comments need a comment or two, to whit:

As I read the thread to this point there IS a lower compression black-topped piston that is a late replacement piston for the LDS.

The LDS has longer length rockers for the intake side (this CAN make a big difference in breathing and YES, an IC engine is first and foremost an air pump)

Travis is forgetting the differences in the size of the central bowl cavity in the head of the piston with regard to CR. Bigger cavity with same head = lower compression but perhaps more fuel for a multifuel based on larger area to evaporate the injected liquid fuel. The black coating may increase heat absorption by the piston and thus increase heat available to evaporate the liquid fuel pooled in the bowl cavity. But it also might be a thermal rejection coating to allow higher EGTs without damaging the underlying aluminum (which I think more likely). If it is Type III MIL-spec hard anodize then it will reject heat. The higher area would still increase rate of evaporation and thus amount of available fuel per stroke (assuming the IP is delivering the increased amount of fuel).

More air flow is REQUIRED to keep EGTs low. This includes plenty of intake air but also important is lower restriction exhaust including turbo and exhaust tubes downstream of turbo. Excess fuel for a given amount of air flow (exhaust and intake alike) = high EGTs and melted pistons.

So now that I've jumped the gun I'll finish the thread and see if someone corrects me before I even wrote this. What the heck, some days you have to pays your money and takes your chances.

 

[hornetfan]

it's amazing how much crap people believe. ok,maybe the 465 can put out 400-500 hp for 5 or 6 seconds. so what? we need a reliable engine that will run for 100,000 miles minimum. it ain't gonna happen. if you use a different block, different heads, crank, pistons, rods, etc, it is not the same engine. no one here is gonna pay for that kind of engine when they can just put a 8.4 cimmins in.

Tom,

I think you will agree that doing things like polishing and balancing rods, deburring everything inside the engine to promote oil drain, carefully blueprinting the engine during rebuild, etc. -- all the kind of stuff that Smoky Yunick did way back in The Day can't possibly hurt and will probably increase the longevity of the engine correct? And will allow some serious increases in power. Don't you think the LDS/LDT will be able to tolerate 250hp and 700 lbf-ft torque or so??

 

[DUECE-COUPE]

does the cam make the difference between the LDT and the LDS. I have all the parts off an LDS motor (motor was left outside and the ants took up residence in one of the cylinders) so what I am asking, is it worth my wild to swap heads, cam, injectors, and injector pump, or can I get by with just replacing the injectors, and turning up the fuel?

 

[Heath_h49008]

Same cam.
Same rockers.
Same heads.
Same injectors.
The two pistons have the same compression ratio, and have been found in either engine.
The difference between the pistons is the internal oil cooling channel and the wrist pin.
Same block.
Same crank.
Same rods.

Read the whole thread... we had a LOT of ideas, and we fleshed out a lot of misinformation.

It's the pump/HH and enough cooling to help it live at the higher fuel rating. That really is all there is that matters. (Wastegate turbos do build pressure lower in the RPM range, but the effect is marginal on overall output.)

 

[DUECE-COUPE]

So now I have this stuff off of an LDS motor, heads, cam, injectors, and injector pump, that is really the same as what I have in the truck, except for the Injector pump, which may or may not be the key to the whole "where did the extra horse power come from" question, and all I really need to do is tun up the fuel and get a pyrometer to keep from cooking the pistons. 28 pages later we come the answer.

 

[sandcobra164]

I think alot of us came to that conclusion a few pages back Duece-Coupe. I don't even have a pyro yet, I followed the advice of "turn the fuel until you get a nice puff of black smoke when you floor it at idle but soon clears up" when I turned my pump up. I've towed some heavy stuff behind it and it's lasted 3 years and countless miles in that state and I'd bet it could hang with a stock LDS just fine. It's an LDT-465-1D that came with a D turbo but I've since put a C on it. Didn't notice any difference with the turbo swap other than the "whistle" that I was wanting to hear.

 

[gimpyrobb]

So now I have this stuff off of an LDS motor, heads, cam, injectors, and injector pump, that is really the same as what I have in the truck, except for the Injector pump, which may or may not be the key to the whole "where did the extra horse power come from" question, and all I really need to do is tun up the fuel and get a pyrometer to keep from cooking the pistons. 28 pages later we come the answer.

Personally, I think its more than just the pump. One of these days, I will pull parts off both motors to find out. Once in a while, I get busy and don't have time to do it.

DEUCECOUPE, look in the LDS troubleshooting TM and it will outline the steps you need to take to make your motor as powerfull as an LDS.

 

[m816]

When we rebuilt the LDS in the Untouchable, we ordered parts from Memphs. The manual and part number for the wristpin on the LDS said we would have a solid wrist pin in that can. Memphis said they no longer have the solid ones in stock and they have had no trouble using the hollow one from the LDT's. When we opened the parts box we found a solid wristpin. Go figure. As far as adding a pyro and boost gauge, we have both. It seems to get to 1200 so fast that we now have to feather the accelerator and baby the thing up to get any speed out of it. Before I blew the truck all to ****, It was possible to get nearly 70 MPH from my LDS. I also run an over drive trans so you guys can calm down now. I know everyone wants to jump all over that statement. Any way before the catastrophy I never had any pyro's or boost gauges. I do drive em like I stole them. Now with the new engine, gauges and orders from my nephew. I may as well have the standard trans and grandma behind the wheel. I can't get it up to 48/54 MPH unless I have straight flat ground for a lond way and it is a dog on the hills? I will leave the IP at its factory settings cause at $3000 for a rebuild I am not looking forward to doing it again.
I bought a "new" M54 this year. Everything is standard on this truck and it runs and handles like a new truck back in 67 so I like it so much, it will be my favorite driver.. It is just a cargo truck and I never drove those back in the day but I had plenty miles on M52,M543's and big cranes. I really like the Cargo to drive. Now wonder they towed so well. Those are my ramblings for Christmas morning. And I wish everyone a Merry Christmas. Gonna go take pictures of the grandkids now.

 

[Heath_h49008]

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.