[Nightshade]

By the way that dyno run showing the 690 FT LBS of torque is 68.3% above the factory fly wheel torque rating of 410 FT LBS.

It must be the jet chip..

 

[14Hemi]

It must be the jet chip..

Well, actually, we didn't ask the OP if he installed the decals for the mods he did. I'm guessing those added at least 200 lb ft of torque :hah:

 

[spamPALA]

I don't know about that as I have read more than one account of Rams losing a good 30% from drive line loss.

I'm a little curious how that works from a thermodynamics perspective; like for example if the engine is producing a real 390 horsepower at the flywheel and loses 30% of its horsepower somewhere into the transmission and axle that's 117 horsepower.

117 horsepower is 87282 watts or about the equivalent of 60 space heaters or like about 8-10 full size gas bbq grills going full blast worth of energy.

Is that *really* happening? I know the transmission has cooler lines going to the radiator but I really don't think the transmission can shed 8+ large bbq grills worth of heat with its size and a little 3/8" coolant line. :4-dontknow:

 

[Thunderhorse]

30% does sound high, I thought 15 or 20 was more standard

 

[RaceHillFarms]

I'm a little curious how that works from a thermodynamics perspective; like for example if the engine is producing a real 390 horsepower at the flywheel and loses 30% of its horsepower somewhere into the transmission and axle that's 117 horsepower.

117 horsepower is 87282 watts or about the equivalent of 60 space heaters or like about 8-10 full size gas bbq grills going full blast worth of energy.

Is that *really* happening? I know the transmission has cooler lines going to the radiator but I really don't think the transmission can shed 8+ large bbq grills worth of heat with its size and a little 3/8" coolant line. :4-dontknow:

The engine is still making its rated horse power and torque, the drive line loss is what impacts the chassis dyno's read out.

You have the engine connected to the transmission or transmission/transfer case that is connected to the drive shaft some vehicles that can be a two piece drive shaft, then you have the rear end and finally the rims and tires.

Each one of this those pieces results in some percentage of drive line loss of horse power and torque at the rear wheels.

Any point that is a connection point is a potential loss of efficiency.

Some manufactures drive lines are more efficient than others.

Remember bolting an engine directly to a dyno vs putting a vehicle on a chassis dyno are two very different ways of measuring the power. The direct hook up to the dyno will not have anything to cause a loss between it and the dyno, while the chassis dyno has a number of components that do effect the connection of the vehicle to the dyno.

That is why chassis dyno's are rear wheel horse power/torque where an engine dyno is the engines rated horse power/torque.

 

[RaceHillFarms]

30% does sound high, I thought 15 or 20 was more standard

For most vehicles it is but we are adding in transfer cases on 4x4 trucks as well.

I saw a dyno sheet on a 2500 6.4 where both the horse power and the torque were under 300, that is a just over 30% drive line loss.

Don't forget that there can also be programs built into the ECM software that limit torque in certain gears or under certain conditions, does a chassis dyno set off that condition in certain gears? Who knows unless you could get your hands on the code in the ECM which is unlikely.

 

[RayK]

There's a dyno run of a 2014 2500 6.7 Cummins on Youtube where it dyno 346 HP and 64X torque. I thought that was pretty impressive.

https://www.youtube.com/watch?v=V8nCnolDyNc

 

[RaceHillFarms]

There's a dyno run of a 2014 2500 6.7 Cummins on Youtube where it dyno 346 HP and 64X torque. I thought that was pretty impressive.

https://www.youtube.com/watch?v=V8nCnolDyNc

If he had the Aisin transmission that would come to about 25% drive line loss for that run.

But the 2014 2500 did not come with an Aisin transmission it came with the 68RFE transmission.

Rated out put was 370 HP and 800 FT LBS.

That dyno run would indicate a drive line loss of only 6.5% for HP, highly unlikely.

To rate 640 FT LBS the drive line would be giving up a 20% loss.

I have a problem with those numbers.

I would never trust these guys with the traveling dynos as they tend to fudge the numbers. If you really want a dyno run find a reputable shop who has a documented history.

Funny how all these traveling dyno guys produce huge numbers on their dynos even with stock vehicles.

Chrysler seems to have had a larger percentage of drive line loss than Ford or General Motors over the years. They just have not been as efficient.

 

[RayK]

If he had the Aisin transmission that would come to about 25% drive line loss for that run.

But the 2014 2500 did not come with an Aisin transmission it came with the 68RFE transmission.

Rated out put was 370 HP and 800 FT LBS.

That dyno run would indicate a drive line loss of only 6.5% for HP, highly unlikely.

To rate 640 FT LBS the drive line would be giving up a 20% loss.

I have a problem with those numbers.

I would never trust these guys with the traveling dynos as they tend to fudge the numbers. If you really want a dyno run find a reputable shop who has a documented history.

Funny how all these traveling dyno guys produce huge numbers on their dynos even with stock vehicles.

Chrysler seems to have had a larger percentage of drive line loss than Ford or General Motors over the years. They just have not been as efficient.

There were lower dyno runs earlier in the vid. The 346 was an anomaly IMO.
He did have several mods, plus I think he might be running a tune.

I have seen 34 PSI off the line with my truck. Maybe I'll take my truck up and get it on the Dyno-Jet just to see one stock dyno run.

 

[crfq68]

I frequently go to Hypertech's website to look at stock/modified dyno runs. I am always a little disappointed at how low most numbers are( except for the turbo diesels on race tunes).
The op's chart is a joke.

 

[striker2237]

30% does sound high, I thought 15 or 20 was more standard

For most vehicles it is but we are adding in transfer cases on 4x4 trucks as well.

I saw a dyno sheet on a 2500 6.4 where both the horse power and the torque were under 300, that is a just over 30% drive line loss.

Don't forget that there can also be programs built into the ECM software that limit torque in certain gears or under certain conditions, does a chassis dyno set off that condition in certain gears? Who knows unless you could get your hands on the code in the ECM which is unlikely.

I'm suffering 27% so I can see that kind of loss in another 4x4 truck. The ECM is also going to seriously limit things.

 

[spamPALA]

The engine is still making its rated horse power and torque, the drive line loss is what impacts the chassis dyno's read out.

Energy cannot vanish into nowhere.. if you're making 390 horsepower and only delivering 70% of it to the dyno then 30% of it is turning into heat.

I don't think that much heat is accounted for between the transmission, transfer case, U-joints, differential and axle bearings. We're talking 300,000 BTU's worth of horsepower. My house heater is 60,000 BTU's.

I think if the number you're getting is 30% less than the engine's rated power there's something else going on; like either the engine isn't really making rated power or the dyno isn't reading correctly.

 

[RaceHillFarms]

Energy cannot vanish into nowhere.. if you're making 390 horsepower and only delivering 70% of it to the dyno then 30% of it is turning into heat.

I don't think that much heat is accounted for between the transmission, transfer case, U-joints, differential and axle bearings. We're talking 300,000 BTU's worth of horsepower. My house heater is 60,000 BTU's.

I think if the number you're getting is 30% less than the engine's rated power there's something else going on; like either the engine isn't really making rated power or the dyno isn't reading correctly.

You clearly are not understanding how drive train loss works. Maybe this will help you to understand.

http://www.hotrod.com/articles/ccrp-0311-drivetrain-power-loss/

They tested two different cars a Comet and a Buick both ran on an engine dyno first and then a chassis dyno.

With the engine in the car and everything hooked up to make it completely streetable, the car was placed on Flowmaster’s SuperFlow chassis dyno to compare the flywheel numbers with the Comet’s rear-wheel performance. At one particular data point, the little small-block lost a staggering 106 hp, which equates to an astounding 40 percent loss between the engine dyno and the chassis! This was the worst case, but overall the engine suffered from an average loss of over 36 percent across the powerband from 4,000 to 5,500 rpm.

With the powertrain installed in the car, including the exhaust and the stock GS air-cleaner assembly, Kevin ran a series of chassis-dyno tests to compare the power numbers. As you can see from the results in Test C, the combination of the Muncie four-speed trans and 12-bolt rearend exacted a price, which turned out to be slightly more than expected for a manual-trans car. The worst occurred at 5,000 rpm, losing 62 hp over the engine-dyno numbers, which represented a full 25 percent loss. However, the rest of the curve saw rear-wheel power differences between 14 and 20 percent. The overall average power loss penciled out at 21 percent, but if you threw out the number at 5,000 rpm, the average loss drops to a more realistic 17 percent.

 

[spamPALA]

You clearly are not understanding how drive train loss works. Maybe this will help you to understand.

I don't want to get engaged in some big internet argument but around here we obey the laws of thermodynamics.

https://en.wikipedia.org/wiki/Conservation_of_energy

 

[RaceHillFarms]

I don't want to get engaged in some big internet argument but around here we obey the laws of thermodynamics.

https://en.wikipedia.org/wiki/Conservation_of_energy

You just don't have a clue.

 

[14Hemi]

If I ever cite Wikipedia as a source in a battle of wits, I have, in mind, fired a squib. No disrespect meant to spamPALA, just my sentiments for anyone citing Wikipedia, which is a user based encyclopedia, often without verification.


I claim no form of expertise in physics, thermodynamics, or anything for that matter, but, it's important to remember the following:


"In this context, the second law of thermodynamics delivers another dose of bad news: though it is true that energy is never lost, the energy available for work output will never be as great as the energy put into a system. A car engine, for instance, cannot transform all of its energy input into usable horsepower; some of the energy will be used up in the form of heat and sound. Though energy is conserved, usable energy is not."

Read more: http://www.scienceclarified.com/eve...eal-Life-Physics-Vol-2/Thermodynamics-Real-life-applications.html#ixzz4JQV8saI6


That's my $.02- I don't need my change back

 

[spamPALA]

This isn't a "battle of wits", I didn't come in here to battle anybody and if you did, perhaps you've misunderstood what forums are for.

It does appear I'm in the minority as somebody who understands quite well how both wikipedia and conservation of energy work. If you don't know how both of those topics function and can only cast smug, disrespectful comments then we have no cause to keep up the.... conversation if it can be called that.

 

[gofishn]

I think you ALL have your panties in a twist.

Now, play nice or like a monkey at the zoo, I'm going to start flinging poop at of you.

 

[14Hemi]

This isn't a "battle of wits", I didn't come in here to battle anybody and if you did, perhaps you've misunderstood what forums are for.

It does appear I'm in the minority as somebody who understands quite well how both wikipedia and conservation of energy work. If you don't know how both of those topics function and can only cast smug, disrespectful comments then we have no cause to keep up the.... conversation if it can be called that.

My apologies to spamPALA and the members of the forum for my apparent disrespect.


I can be schooled on conservation of energy, and I'm guessing others can as well.


I would like to use the forum as it is intended- to share and learn. If you can put my previous remarks aside, and for the benefit of the forum, engage in a conversation, really, more of a solicitation of knowledge.


If you wouldn't mind, please help me understand how the numbers that the chassis dynos show and engine dynos always vary. I'm not talking about Ram's specifically, I'm asking about the general loss in power from the engine crank to the rear wheels. Is the implication that this is all lost to heat?


I'm truly not being smug or sarcastic here; I find it interesting, as did you in your first comment, and I would like to understand the process from a scientific perspective. If you choose to simply move on from the conversation, I understand.

 

[spamPALA]

My apologies to spamPALA and the members of the forum for my apparent disrespect.

Accepted. I was out of college before wikipedia existed but I know it's not permissible as a citation by most professors; this doesn't mean it's inaccurate nor inappropriate in the context of a forum conversation. Wikipedia is not merely written by random members of the public; it's actively curated and on empirical topics can often be the most ratified source there is - the article on sound masking (one of my professional vocations) for example was largely authored in person by Dr. Chanaud who most consider the authority on the topic worldwide.

If you wouldn't mind, please help me understand how the numbers that the chassis dynos show and engine dynos always vary. I'm not talking about Ram's specifically, I'm asking about the general loss in power from the engine crank to the rear wheels. Is the implication that this is all lost to heat?

The first law of thermodynamics is fundamental to literally everything that exists and can be summarized that energy can neither be created nor destroyed. Here is a non-wikipedia reference describing that.

If kinetic energy is input into a system (engine power) and less kinetic energy comes out of the system (wheel power) then that difference must necessarily be accounted for in some way because energy cannot just vanish. We all know that there are driveline losses because if there weren't any driveline losses then transmissions wouldn't get hot, since they can't generate heat from nowhere.

We know that transmissions get hot, and differentials get hot, bearings get hot - the cause for my initial question is not whether losses exist, rather whether those losses are truly being accounted for correctly. If you're losing more than 100 horsepower into a transmission there needs to be 100 horsepower worth of heat energy dispersed and I argue that there probably is not.

When you convert gasoline into horsepower by running it through a machine like an engine, the conversion is described by what's called the BSFC or "Brake Specific Fuel Consumption" - this consumption rate varies with load and RPM but can provide us with a good enough average to make a few educated assumptions anyway. I don't have BSFC charts or efficiency data on the Hemi but I did find that the *expected* average efficiency for a gasoline engine is about 25% and the most mechanically comparable engine I could find specific data for (compared to a Hemi) is the Saturn 1.9l SOHC engine from 1991 that gets 32.5% quoted efficiency. A Prius gas engine (just the gas engine) quotes a little over 36%.

So turning gasoline into horsepower,

390 horsepower is 290 kW
290kW is 32.5% of 895kW
895kW is in the neighborhood of 3 million btu/hr or about 25 US gallons per hour of gasoline. So far this sounds about right; online horsepower calculators recommend a 190lph (50gph) fuel pump for 390hp - exactly double to make sure fuel pressure/delivery is solid.

290kW is about 990,000 BTU's, so if (at peak horsepower) you're burning 3 million BTU's worth of gas and around a million are turning into kinetic energy then you're shedding 2 million BTU's out the exhaust pipes, through the radiator, and by heating up the engine compartment (and.. the alternator fan and stuff.. )

So we've compartmentalized those losses. We "know" (we assume) that we have 290kW of kinetic energy at the flywheel.

If we only get 70% of that on the dyno then 87kW worth of energy has to be accounted for in some way. If it's heat in the transmission then we need to see 300,000 BTU's worth of heat coming off the transmission.

It can't be explained away with "well it's just lost into the transmission" - the transmission isn't a hole into another dimension where energy can vanish forever. If it's slipping, or creating hydrostatic pressure, or creating shear pressure (in the torque converter), or friction on the bearings, or anything else like that it's going to turn into heat.

Transmissions do get hot for all of the above reasons. I just don't see how they can get 300,000 BTU's worth of hot, that's a LOT of heat. Your engine has huge coolant pipes to carry radiator coolant through the engine plus the huge exhaust pipe that carries much of the heat out in your exhaust... the transmission just has a little 3/8" tube to carry oil up to the wet/wet heat exchanger.

Duty cycle is one way to partially account for it, maybe the transmission really is eating up almost a third of flywheel horsepower but since you're only on the dyno a few seconds it doesn't explode. Maybe if you started pulling a 9,000lb trailer up an endless steep mountain road and held your foot on the gas the whole time the transmission would in fact begin radiating 300,000BTU's of heat and cook itself to death over several minutes. But Ram trucks conform to (SAE) J2807and that would necessitate an extremely long duty cycle at very high engine output.

For that reason I don't think duty cycle explains it, at least not to a satisfying degree.

If I had to guess, I'd say that the most likely explanation might be that the engine is able to routinely produce 390 horsepower SAE J1349 but the ECU is pulling back deliberately when you need it most (or want it, in the case of dyno runs..) in an effort to improve transmission longevity and reduce warranty claims. That's just my guess.
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