Hey Logical Heritic, I wanted to get your take on these lawnmower illustrations Marine Tinman has been conjuring up. I get the feeling he is trying to point out Ford's superior gearing, but I don't know, maybe he's saying if Ford built a lawnmower THAT would be superior to a Cummins. OR... he's saying the 600 ft-lbs. of torque is impressive in the PSD, but its a joke in the Cummins because its so similar to a lawnmower.

 

So if the Dodge has the same hp and MORE torque, then why does it get OWNED by the PSD in EVERY test. We're not talking about one isolated test. We are talking about every test, no matter the configuration, every time. Has anyone considered that maybe Ford underrated their engine, or maybe Dodge overrated theirs????

 

Actually they have the same hp and the Ford has more torque... but that doesn't much matter the Ford could have half the torque and still win by a huge margin. Its all about the gearing combined with the superior V-8 diesel design. All the power in the world doesn't matter if you can't get it to the ground. Just ask Marine Tinman, oh wait he's already explained it with the lawnmower thing.

 

True, but we've already determined from testing that the PSD performs better in a light duty truck.

This is a technical comparison, as was the "other thread" initially, which compares stock engines. Although I don't own the board, it is typically assumed that the threads will stay on topic. Since I started the thread I should be able to point out that it has gone off topic. If you want to start a different discussion you are free to start your own thread. That's how internet forums work. The longer these threads get the more off topic they get. This seems to be a phenomenon only in this forum. New discussion=new thread. The other thread had very little to do with potential, but that was not the original topic for the thread. It had to do with a simple question on how Ford could call the PSD the most durable diesel engine with the problems the 6.0 had. It turned into a discussion of which was a better engine, PSD or Cummins. That's why I started this thread. For the record, I'm talking about the 1000+ post thread.

Flywheel numbers are meaningless. Bigger numbers don't always win. What matters is the shape of the torque curve, the transmission the engine is mated to, and how much of that power actually makes it to the rear wheels. That's why repeated testing has resulted in the PSD winning over the Cummins.

 

Boys (you've graduated from ladies) ... of course I'm tongue-in-cheek w/ you all. Can't exactly line you up and make you drop-n-gimme-twenty.

Two points, and I'll try to keep'm to the point.

(a) The Lawnmower. Point is that by simple gearing you can get any torque your heart desires. The engine has an inherent capability of torque at "the flywheel" which is your starting point. It's partially determined by mechanical distances of throw on the crankshaft. After that, it's a add-subtract game w/ up/down gearing. ANY engine can move a load. Horsepower determines how much time is needed (rpms per time).

(b) Meaning for PSD/CUMMINS. So, since the Cummins and PSD have same HP they both have the same THEORETICAL limit on how quickly they can move a load from A to B. BUT ... this assumes two things. (1) that they have the HP at the same RPM and/or (2) the gearing makes the output RPM the same at that HP peak.

(c) Actual PSD/CUMMINS design: The Engine - The assumptions above are not true. First ... the peak HP comes at SLIGHTLY different RPMS (400 ain't a huge difference, especially considering it's a V8). If you put each at their max HP, the PSD is, by design, taking BETTER advantage of it's equal horses, and sticking more RPM at the flywheel. This is inherent to the construction of the engine. It is what it is. Cannot change.

(d) Actual PSD/CUUMMINS gearing: Now ... although the RPM for peak HP is different, Dodge CAN make the Cummins match the Ford. From the flywheel back, you can do ANY combination of gearing. So if PSD is 3300 and Cummins 2900, you could gear BOTH to put out the SAME RPM to the wheels. Oh ... THEN, if that were true, you'd have a FANTASTIC argument in favor of the Cummins. Why, the Cummins would ALWAYS be doing the same amount of work for LESS RPM.

Alas ... Dodged has made a POOR design choice on their transmissions. Not only does the PSD start w/ a higher RPM to the rear ... it gives you gearing that is multiplied more in the transmission. Thus, the advantage grows. Well almost always. For example:

6th gear of Torqshift: 0.712
6th gear of NV5600: 0.73
4th gear of 48RE: 0.69

Given a 3.73 rear (you can always get less rpm with a 4.10 rear) ... here is the breakout:

NV5600 makes engine turn more with 2.72 ratio total
TS makes engine turn less with 2.656 ratio total
48RE makes engine turn least with 2.573 ratio total

BUT ... the 48RE has not taken ENOUGH advantage, and still let's Ford stay ahead w/ it's 400 rpm advantage as follows:

PSD at 3300rpm puts out 1242 rpm on the rear wheels
6600 at 2900 rpm puts out either 1066 rpm (w/ 5600) or 1127 rpm (w/ 48RE).

Assuming the trucks have the same tires ... the PSD moves down the road faster. Now, you can calculate this out for every gear, and assume what engine rpm you want to go.

The PSD wins all these things (stock) because, yes ... the INHERENT engine design construction matches peak HP to a slightly ... slightly higher RPM. And then the TS gearing mops up the rest with fantastic optimal choices.

Final note: You can have a MILLION ft-lbs of torque. If you DON'T GEAR IT to take ADVANTAGE of that ... or ... if the horsepower is STILL only 325 HP .... you cannot (I repeat) you cannot make that "system" perform any better than a stock PSD.

Yes, the Cummins has 40 more ft-lbs. Yes, they throw it in the garbage, it is UNUSABLE my friends. Any mechanical engineer can go through this ... set down the pencil and say .... yep. The Ironman is right. It's never USED, even though it's there.

A sad ... but true commentary on the Dodge design. Nothing Cummins can do about it. It's what Dodge does with it.

Have a great day, boys.

The Marine Ironman
(God bless the Marines in Najaf today, and let's hope they kick you know what)

 

I guess I was wrong about Ford having more torque. Must've been going by last years numbers. One thing you forgot to mention there is the curb weight of the vehicles(which doesn't really matter AS much with diesels but can still be a factor). I am curious to know which one weighs more.

 

Check out the Motor Trend comparison thread. The Ford is the heaviest.

 

I have towed with both the ford psd and cummins and i felt that the cummins tows better than the ford. other than towing comparisons i don't know which engine is better.

 

In the towing comparisons the PSD outperformed the Cummins.

 

You pop off with some weird stuff. It is useable just at a lower rpm. It means the cummins makes more hp at all rpms below 2900. More hp equals better driveability. Itll lose the race because of a lack of an additional gear and peak hp is 400rpm sooner.
How many times do you get to race another guy with an identical trailer? Thats the only time it would matter. The cummins launches better. Does low speed manuevers better. Has a history of great reliability and durability.

In fact I dont think anyone has disputed that the PSD is faster. First thing I said was the PSD can take better advantage of gearing. Which by the way you argued. Now your doing the math to support what I said. The PSD is faster always Except with the manual. I supplied three links where it lost with a manual. But whos keeping track. If they are equipped with nearly identical gearing, the 6 speeds. The cummins will outrun the PSD. Even with its gearing advantage. Why? Because the cummins makes more hp at all rpms below 2900. In a manual you have to earn those rpms. Unlike an auto. Because of this. Im under the impression that if Dodge went to a 5 or 6 speed auto. The results would be different. Even with the PSD far superior high rpm torque.
If you had a million lb ft of torque. You could move a stadium. I dont think you could get enough power through the gears because of frictional losses. To multiply a 325hp engine to 1 million lb ft. You can multiply torque through gearing. You cannot multiply hp.

BTW. Your leaving something out of your gearing comparison. The torque at the wheels. If your gonna do the math for each gear you need to figure it in. Its what makes taking advantage of gearing so advantageous.

 

Marine Ironman, how you explained it an Inline engine is like hitting a hammer on a ball straight down, and a V-8 intrinsically has better ballance because its closer to a flat engine which is the best natural balance of all. I was reading the "What was the best overall inline-6" thread and found this post by txtrucker1:

The Inline formation allows for a better cooling system because of the cylinders being straight and next to each other and the block is bigger in size thus more durable. There is less moving parts, therefore less parts to break. Inline engines are difficult to break in general, because of the lower stress on parts. With the cylinders straight up/down, there is no lateral stress as the piston moves. On a V-engine (like a V-8), the piston fights lateral stress as the piston slides upward at an angle. This pushes the piston into the cylinder wall, which in turn wears out the piston rings, which allows oil to blow by leading to engine failure down the road, literally. Inlines don't have this problem. They move up and down and it is extremely rare to have to rebuild one let alone replace the piston rings. When a load is put on the engine, there is no torque lost inside. Again this goes back to the lateral stress in a V-8. When the cylinder burns fuel (diesel or gas) an engine like a V-8 has to use some of its torque to push the cylinder down at an angle. Think of it like this: Ever tried to hammer a nail at an angle without bending it, guarantee it is a lot more difficult then it would be to nail it straight down. Same theory applies to the inline formation. It is easier and uses less engine torque to push the cylinder straight down then to push at an angle. Therefore more torque can be applied to the load being pulled. That is why the inline engines are so much better then the rest as far as durablity and reliablity. They have been proven, tested and NEVER found wanting. Hope this helps you understand the engine a litle better. (any other questions, please ask)

It is an intriguing argument. The hammer illustration seems like it matches with your explanation as well, hitting a ball from the top. Is there more stress on the cylinders of a V-8 due to the angular compression?

 

The Cummins doesn't take advantage of the torque because the automatic transmission is nothing compared to the Torqshift. If you have a manual transmission then you don't have torque multiplication and therefore the PSD is actually producing more low RPM torque at the rear wheels.

 

Thats kinda funny. How does it produce more torque at the rear wheels when it starts off will less? Sorry john. This is incorrect.

The torqueshift is awesome. No doubt bout it.

The math is actually pretty easy. You just need to find the multipliers. Its simpler if you do the math from peak torque but you can do it at any rpm.

So 560lb ft by 5.79 x 4.1= 13294
and 600lb ft by 5.61 x 4.1= 13801

I can do this for each gear. Trust me when I say the cummins puts more torque to the ground.

A transmission IS A TORQUE MULTIPLIER. Thats what it does. If your reffering to the torque converter thats a different story. You can get a tc with a 3 to 1 multiplication if you want. An auto will start out with more torque at just off idle but this quickly dissapears. The more you multiply the torque. The sllllooowwweerrr you move. Cause you be trading speed for torque. So you can multiply all you want. You aint goin nowhere fast.

 

Well, I haven't been in one of these friendly arguements in a while so here is my view of it. The worst environment that any engine can live in is the engine room of a boat. You will find the Cummins 5.9 in boats but you won't see a PSD because of reliabilty issues. Okay, so we aren't driving boats but the reliabilty issues are still there. If the 6.0 PSD is so good, why is Ford already planning its demise? There is a patch of an engine known as the 6.4 in the near future and it won't be there long either. Why, poor engine design. It is not the engine they wanted but had to settle with. The next diesel you have that is a real motor will most likely be made by Ford- not somebody else. So, there it is. Now, which is the better engine? Depends on the workload. Most folks are driving their Cummins and PSDs to and from work, maybe even haul an occasional load. It makes boys feel manly when they have that much macho horsepower. The Cummins engine is speced in light and medium duty trucks, the PSD is not.

 

Flash. They got PSD in mediums. Id didnt used to be but now its standard. I seen one in an 80k app. Seemed a bit absurd but it was there.