Why 2650rpm max?

[JasonS]

JasonS said it himself when he talked about the wedge of oil. I said it before and I'll say it again, the rods and crank don't ride on the bearings, they ride on a film of oil. And when a engine is over reved it will fling out the oil faster then it is replaced by a stock style pump unable to keep up with the oil lose.
As far as you OLDER and WISER guys on this site knowing everything there is about these trucks, you should remember there are plenty of guys , like me who served in the military (Marines 6yrs) who drove these trucks as part of there daily jobs, worked in the motor pool, repaired them, drove them for days with seized clutches (try shifting with out a clutch) because the Captain said so. Slepted under them at night.
Got then unstuck on beaches with the tide coming in (the Sargeant Major was drunk and decided it would be a good idea to drive into the ocean) Who maybe know a thing or two about these rigs.
Of course I'm probably wrong, you guys know better, my bad.

I think that you are confusing two failure modes. Yes, you need to maintain the oil at the bearing and the lack of this oil will result in wiped bearigns (something not reported by those who have blown up engines). However, once you exceed the fatique strength of the fasteners, no amount of oil pressure or volume will keep the rod from coming apart.

 

[doghead]

I must ask, what is so bad with 2650 as a max rpm?

Why is this a fault?

You need to draw the line somewhere.

 

[m-35tom]

many people confuse high volume pumps. they think it is something special or something very desirable. they could not be further from the truth. you can add a pump that will pump 4 times the volume, but in reality most of the time the oil pressure regulator is just dumping the extra oil back into the sump. it is a proven fact of engine building that all you need is 10 psi per 1000 rpm. with that and correct side clearance on the rod big ends you will always have enough oil to keep the bearings from touching the crank.

there are two sayings about engines: 1: nothing beats cubic inches like cubic dollars. well sometimes, but not here.
2: horsepower lives in the heads. especially true here. the multi with modern head design would be easily 2 to 3 times more hp available.

 

[Jeepsinker]

I must ask, what is so bad with 2650 as a max rpm?

Why is this a fault?

You need to draw the line somewhere.

i don't have a problem with it, but at max speed being close to redline is kind of uncomfortable. That, and just having peace of mind that an accidental overrev once or twice won't cause a catastrauphic failure I think is the draw to this topic.

 

[welldigger]

2500 to 3000 rpm is redline for most OTR diesel engines. In fact even modern diesels 2600 to 2800 is not uncommon. The slow top end if the deuce is directly a result of the low gearing of the truck. Well, that and the low gearing is a nesseity with the MF due to its anemic power output.

I think people forget this truck was designed in the late 40's to 50's with a very specific task in mind. The deuce was never intended to blister down the interstate at 80mph. If over revving the engine is a fear you constantly live with it might be wise to practice driving the truck more or maybe find a different type of truck.

 

[m-35tom]

2500 to 3000 rpm is redline for most OTR diesel engines. In fact even modern diesels 2600 to 2800 is not uncommon. The slow top end if the deuce is directly a result of the low gearing of the truck. Well, that and the low gearing is a nesseity with the MF due to its anemic power output.

I think people forget this truck was designed in the late 40's to 50's with a very specific task in mind. The deuce was never intended to blister down the interstate at 80mph. If over revving the engine is a fear you constantly live with it might be wise to practice driving the truck more or maybe find a different type of truck.

exactly! plus there are affordable solutions. trans OD kit is probably less than bigger tires and does not sacrifice performance but even larger tires on stock rims buy some more speed. speed is expensive any way you do it, given that to make the truck safe at a higher speed there are other issues to address as well. I find that 65 mph at 2500 rpm is completely acceptable.

 

[welldigger]

exactly! plus there are affordable solutions. trans OD kit is probably less than bigger tires and does not sacrifice performance but even larger tires on stock rims buy some more speed. speed is expensive any way you do it, given that to make the truck safe at a higher speed there are other issues to address as well. I find that 65 mph at 2500 rpm is completely acceptable.

I can run 63-65 at 2500 with 395's. I'm more than happy. Nothing against your o.d. kit. Which is considerably cheaper than what I have in my super single conversion.

 

[gimpyrobb]

Yup, buy the OD kit and your wallet hurts once, otherwise you'll be looking for cheap 395s always. If I had the spare cash, I'd go the OD kit.

 

[m-35tom]

thanks guys, I was at least 3 years late getting the OD to market and a lot of people started going to bigger tires. Demand has been a lot less than anticipated, but I didn't do it to make money. Probably have an a/c compressor mount kit in the spring.

 

[gimpyrobb]

Tom, I've always said, why do today what you can put off till tomorrow.

























Well, I thought about saying it.

 

[rustystud]

M-35tom, I'll pass your suggestion for a oil pump on to the racing community. I'm sure they will appreciate all the money they will save from not having to buy high volume pumps (with higher relief valves) and scavenger systems which can cost into the thousands . If anyone really read what I wrote, I said you needed stronger bolts (and bolts that screw into the end caps are much weaker then through-bolts with nuts, Seen any modern engines with this set-up ? I didn't think so) and crank, and rods.
I'm sorry I even replied to this thread. I was only stating why this engine could not rev. It seems though, that there are some here (who think they know all, and must be obeyed) who if you challenge there long held beliefs will attack with a vengeance !
I'm done with this thread.

By the way, that picture is me with my M60A1 Rise Passive Tank.

 

[wb1895]

To quote an old movie.....

Speed is just a question of money, How fast do you want to go?

 

[welldigger]

thanks guys, I was at least 3 years late getting the OD to market and a lot of people started going to bigger tires. Demand has been a lot less than anticipated, but I didn't do it to make money. Probably have an a/c compressor mount kit in the spring.

Out of curiosity, what tire sizes have you tested your o.d. kit with? I know you have used the 14.5-20 size but I wonder how effective it would be with 395's. Since the 395's are so popular right now there may be a few people wanting to run both but are unsure how that would work out.

I'm not advocating running these trucks at an unsafe speed but it is well established these trucks are safe at 60-65mph. It would be nice not to have it pegged at max throttle to cruise.

 

[m-35tom]

how tall is a 395? or more to the point for accuracy what is the loaded radius?

 

[welldigger]

Well they are approximately 46" tall just laying on the ground. I'll have to measure the loaded radius which I can do in a few min. Today is pull injector pump day so I'll be playing with the truck anyways.

 

[JasonS]

it is a proven fact of engine building that all you need is 10 psi per 1000 rpm. with that and correct side clearance on the rod big ends you will always have enough oil to keep the bearings from touching the crank..

Maybe for a SBC but not a universal truth. Look at engines with relatively narrow rod bearings; they need more pressure. It is also misleading to state this suggesting that a multi with worn bearings but still 25 psi at speed is perfectly acceptable.

 

[welldigger]

how tall is a 395? or more to the point for accuracy what is the loaded radius?

Loaded radius of a 395 on the front axle is approximately 22".

 

[m-35tom]

These tires are so close to the same size, 14.5R20 has a loaded radius of 21"
Ok, so at 2500 rpm with the OD kit and 14.5R20 mph = 67.35, changing to 395's increases it to 70.56, 3.2 mph more. I think you will notice a little less power on hills, but on the level it will just about not matter.

 

[m16ty]

many people confuse high volume pumps. they think it is something special or something very desirable. they could not be further from the truth. you can add a pump that will pump 4 times the volume, but in reality most of the time the oil pressure regulator is just dumping the extra oil back into the sump. it is a proven fact of engine building that all you need is 10 psi per 1000 rpm. with that and correct side clearance on the rod big ends you will always have enough oil to keep the bearings from touching the crank.

I know a guy that had a car (don't recall what engine) and he thought it would be a good idea to get a high volume oil pump. The first time he took it out when he really got on it the oil pressure dropped to zero. Come to find out it was pumping so much oil that the oil wasn't having time to drain out of the heads and it was running out of oil in the sump.

 

[Tow4]

All engineered products, whether it is a diesel engine or a suspension bridge, are designed with a set of goals. The bottom line is cost. Anyone can build a bridge. The idea is to build a bridge that will just barely not fall down or in this case, an engine that will meet power and longevity goals without blowing up for the lowest cost.

All the components are designed to work within and achieve the designs overall goals. If rod bolts are a failure point, stronger bolts will only expose the next weak point, and so on. Once you are past changing a bolt, other changes likely become too expensive or difficult.

If you keep in mind the limits of the design, I doubt that there are serious faults in the design of the LDx series engines. For catastrophic failures, I would be more suspect of the assembly process and/or component quality used during assembly, or operation outside of design limits.