[Camstyn]

Ok without turning this into another flame fest by the anti-banks crew, I'm just curious about their torque dyno chart. Why does it look so different from most others that I've seen? For example, I've got to question why both charts start at 1800rpm and not 0, or at least idle RPM's. It looks like if the graph went to a lower RPM they could claim an even higher lb-ft of torque, unless that is exactly where it began to drop.. But looking at how steep it starts dropping there I can't really picture that.


GM claims that the stock duramax makes its highest torque #'s at 1800rpm. Not 2500RPM (as per Banks chart) or 2700RPM (as per Edge's chart).. In the Edge chart it shows it not even making much torque at 1800rpm, whereas it's almost at peak on the Banks chart but not quite.


I'd tend to think that the Banks torque chart is close to correct, due to the peak torque of the STOCK rating being where GM says it is.. Unless GM is full of crap?!? But if this is so, why are all the others' torque charts so different looking in comparison? For example, look at the one that Edge gives us, the stock torque curve is totally different (and the peak ft-lb comes at a higher RPM than what GM states). It makes me wonder if some of these torque charts are just made up in photoshop. Surely there must be an explanation for this, do different dynos read torque in a different manner to make it look that bad?


Damnit I wish they would show the charts from BELOW 1800rpm so that they'd at least be more comparable looking.

Edited by: Camstyn

 

[OC_DMAX]

A thought, not sure if it is the complete answer; GM's torque figures are for the engine alone. The two charts shown above are measured at the rear wheels. So the effects/losses of the drive train (trans, differential, transfer case if 4-wheel drive) are included in these charts. Also, the charts were most likely generated using different dynos, that seems to be a big variable also.


It is unlikely that one would be able to tow using the Banks level 6. I wish they would publish results of a "tow" friendly dyno curve.

 

[Kennedy]

Dunno, but most charts that I've seen for ANY modified Dmax resemble the Edge charts much more closely than the Banks.





Could turn out be the surprise box setup of the year, but to me, the TQ curve looks more like a Cummins than a Dmax...





Should have one here to try relatively soon.

 

[ZFMax]

Judging by the wording on the dyno sheets, neither of those companies apparently understands the difference between "rear wheel torque" and "engine torque as measured at the rear wheels".

By my calculation, even a bone stock truck puts a minimum of 1100 ft-lbs to the rear wheels. Much more in the lower gears.

 

[Camstyn]

That's what I was thinking John, I've never seen a torque chart like that for a duramax. If it makes it feel like a Cummins I'm sold, I love that low end grunt, don't care much about winning drag races or posting top #'s on the dyno. I look forward to reading reviews about this, my trigger finger is itchy but I'll wait until someone else buys it first.

 

[McRat]

I have not looked over a lot of diesel dyno logs, but I have dyno'd/witnessed about 300-500 cars and trucks on DynoJet chassis equipment. I'm a dynowhore


Why no reading under 1800 - If you dyno an automatic, it will downshift if you hit the throttle at too low of an RPM. You could use a manual instead, but autos are more common. It would be nice to "force" a gear in an auto, but I haven't see a gadget to do it yet. You also have 2 other effects that will will wreck low rpm dyno readings with an auto: Torque convertor slip - will falsely inflate numbers, turbo lag - will falsely deflate reading (which will affect manuals as well).


Looking at those charts it seems to me that someone has increased the fuel delivery more in the low RPM than the high rpm. They have roughly doubled the fuel flow at low rpm, but only increased it 25% at high RPM (or the engine is saturated with fuel and needs more boost).


Please stomp on my toes if you see something wrong, as I am new at the diesel thang.

 

[Diesel Tech]

It is pretty easy to get low RPM readings on a D-Max auto on the dyno. All that's needed is a Tech II scantool. Put the unit in Tow/Haul and select 4th gear with the Tech II. The TCC will lock at about 20 mph and stay locked. This will get you about 1250 rpm on the low side with stock tires upto the rev limiter. Take a look at Nick's (Diesel Power) dyno charts.


http://dieselplace.com/forum/forum_posts.asp?TID=3319&PN=2

 

[McRat]

It is pretty easy to get low RPM readings on a D-Max auto on the dyno. All that's needed is a Tech II scantool. Put the unit in Tow/Haul and select 4th gear with the Tech II. The TCC will lock at about 20 mph and stay locked. This will get you about 1250 rpm on the low side with stock tires upto the rev limiter. Take a look at Nick's (Diesel Power) dyno charts.


http://dieselplace.com/forum/forum_posts.asp?TID=3319&PN=2

Thanks! That's a good piece of info to have. Is there anything cheaper than a Tech II that can do it? Or even more interesting, can you remap the fuel curves and injector timing with one? Just curious as to what a Tech II can do, and what it can't do.


Is there anyplace I can find out more about the Tech II? Prices, applications, features, etc?

 

[PeterT]

Camstyn,
In order to completely answer your questions, it is important to provide some basic information about chassis dyno testing in general. There are two basic types of chassis dynos; acceleration and load. Acceleration dynos have rolls that are a fixed mass. The drive wheels of the vehicle are placed on the rolls and the test is performed by starting at a low speed and accelerating the vehicle, and consequently the rolls. Power is determined by measuring the rate of change of acceleration. The faster the rolls are accelerated, the higher the power level. Some variations of acceleration dynos will allow weight to be added or removed in order to more closely match the weight of the vehicle being tested, but the principle remains the same. Readings taken from acceleration dynos are sometimes referred to as “flash” readings, because the engine is only run at any given RPM for a very brief moment while the vehicle is accelerated. In the real world, an acceleration dyno can be compared to an acceleration run on a level piece of road.
At Banks, we use a load dyno. A load dyno provides a resistance on the rolls, either electrically or hydraulically. Power is determined by how much resistance is required at any given speed; the more resistance needed to hold the engine at a given RPM, the more power the engine is producing. Readings taken on a load dyno are sometimes referred to as “sustained” or “saturated” as opposed to “flash”. A typical test that we run will begin by running the engine up to a high RPM, at or near redline. The engine is run there for at least 30 seconds to allow all the engine components to reach an operating condition that is fully heat soaked and stabilized. This eliminates any possibility of error from transient conditions. Load (resistance) is then applied to the rolls, bringing the engine RPM down in incremental steps of 100 RPM. Each step is held for 8 to 10 seconds so that stabilized readings can be taken. This is done all the way down to the lower register of the engine RPM band. Some tests will last 3-5 minutes in their entirety. In the real world, this could be compared to towing a heavy load up a hill that gradually gets steeper and steeper.
Now for why the data is only shown down to 1800 RPM. As Diesel Tech mentioned, we do use a Tech II tool to both lock the torque converter, and to lock the transmission in 4<SUP>th</SUP> gear when we are testing on an automatic. This allows us to take all measurements in as direct a relationship between engine speed and the rear wheels as possible. 4<SUP>th</SUP> gear is 1:1, so the output speed of the transmission is the same as the engine RPM. While running our fully saturated tests, we learned something interesting about the turbo on a Duramax. Around 1600 RPM under full load, the turbo goes into surge, a condition that causes power readings to become very unstable.&

 

[sdaver]

things that make you go hmmmmmmmmf?

 

[Trippin]

PeterT,


Great explanation of the differences in dynos and/or testing procedures. Of course engine dynos would see the same thing based upon whether or not you are conducting acceleration tests or doing "steady state" "step testing". I talked about standardizing test procedures for each type of dyno, Mustang, Dyno Jet, Superflow, in a previous post. I was hoping by standardizing the tests we might be able to get a little better evaluation of product testing that everybody here is doing. Yet no one replied.


I don't have any experience with chassis dynos having conducted all of my research on gas engines using a Superflow 901.


What type of chassis dyno do you use?


Other than what you have talked about in your previous post, can you provide us with a detailed testing procedure, so that we may duplicate your type of testing at other facilities. Perhaps setting a standard that other manufacturers will follow? I realize we may still end up comparing apples to oranges but perhaps we can get closer than where we are now.





Thanks in advance,


Guy

 

[ZFMax]

Peter, my 1100 ft-lb number was based on overdrive and a 3.73 axle and 20% drivetrain losses. If you're testing in direct drive, i.e. the trans is in 4th gear where it's 1:1, you should get a minimum of 1550 ft-lbs of torque to the rear wheels of a Duramax, and again, that's assuming 20% loss through the transmission and differential:

520 ft-lbs at the engine
x 1 transmission ratio
x 3.73 rear axle ratio
x .80 20% loss
------
1551 ft-lbs at the rear wheels

If you notice, the dyno requires a tach signal before it'll show you torque. The reason is that it needs to understand how much gear reduction lies between it's drum and the engine, so it can calculate the torque at the engine. Which it can then plot, not coincidentally, against engine rpm. That's why torque and horsepower cross at 5252 engine rpm, it's engine torque. If it was rear wheel torque, not only would the number be a whole lot bigger, but it'd cross horsepower at 5252 rear wheel rpm.

 

[McRat]

You need to do the wheel radius too.

 

[Amric]

Peter, my 1100 ft-lb number was based on overdrive and a 3.73 axle and 20% drivetrain losses. If you're testing in direct drive, i.e. the trans is in 4th gear where it's 1:1, you should get a minimum of 1550 ft-lbs of torque to the rear wheels of a Duramax, and again, that's assuming 20% loss through the transmission and differential:

520 ft-lbs at the engine
x 1 transmission ratio
x 3.73 rear axle ratio
x .80 20% loss
------
1551 ft-lbs at the rear wheels

You need to do the wheel radius too.

This is only correct with a 24" diameter tire. The 245/75R16 brings it back down to 1200 ft-lbs. If you give up gearing due to larger tires or higher axle ratios, you can just make it up by holding 1st gear longer. Taking axle ratios, transmission ratios, and tire diameter out of the equation makes it simpler to compare apples to apples as far as engine performance goes.Edited by: Amric

 

[ZFMax]

Y'all are confusing force at the contact patch with torque.

Torque is the force at a 1 foot radius, regardless of the actual radius of the tire/wheel. That's the units I used.

Force at the contact patch will vary from that number of course, depending on the radius. Smaller than 1 foot will give more force, greater than 1 foot will give less force.

Look at it this way: you can apply 100 ft-lbs of torque with your torque wrench even though it's more than a foot long, right? Torque describes the force at a 1 foot radius, not the radius at which you're applying the force.

 

[Amric]

IMHO: Who cares about torque of the driveline if you are not considering the tire diameter. I woud either be concerned with engine torque after driveline losses (which is exactly what most people use for comparison), or I would be concerned with the torque that is actually reaching the ground vs. vehicle weight.

 

[White Duramax]

Why is everyone dynoing in 4th gear? I know its 1:1 ratio. But dont you want to know what you are putting down in OD, thats what you are running on the street. Will the tech 2 lock the trans in OD so you can get low rpm numbers without downshifting?

 

[ZFMax]

Amric, I agree ... Engine torque is the meaningful number, doing it any other way causes difficulty in making comparisons due to variations in gearing. Actually, horsepower is the meaningful number, torque doesn't consider rpm and rpm is every bit as important when it comes to how much torque you can get to the rear wheels at a given speed, but I digress. My point was simply that the nomenclature on the dyno sheets is wrong. That's not "rear wheel torque", that's engine torque as measured at the rear wheels, which is something entirely different. Appears neither company entirely understands what they're measuring with their dyno.

WD, dynoing in the 1:1 gear is more or less a standard method, because generally you get fewer losses through the gearbox in that gear.

 

[McRat]

Why is everyone dynoing in 4th gear? I know its 1:1 ratio. But dont you want to know what you are putting down in OD, thats what you are running on the street. Will the tech 2 lock the trans in OD so you can get low rpm numbers without downshifting?

A 1:1 ratio is a straight through ratio, and it will yield the highest numbers.


A dyno is a tool, and the numbers are relative. It does NOT measure real world HP, but instead it measures changes in HP. Unless you put the vehicle in a wind tunnel, and match the load to EXACTLY the way the vehicle is on the highway, you are always going to be off some.


The trick to dyno testing is to be consistant - Same fuel, same dyno, same tire pressure, same starting water temp. I can get a car to repeat within ±2rwhp on different days, and ±1 hp on different pulls. It takes attention to detail. Go beat on the vehicle at WOT for about 5 minutes prior to doing any testing.


What you are looking for is consistancy. So when you make an engine change, you can evaluate it honestly. It doesn't matter whether the engine reads 250rwhp or 400rwhp, the number is relative ONLY to your testing, not someone else's.

 

[Trippin]

McRat,


I agree...a measuring tool. Does it matter if its a metric or imperial tape measure? They both still measures changes/differences. Consistency is the key. Will it measure the same thing on the same truck the same way many times with consistency, should be the key question. If not, then the data is useless.