Loading the Dyno-----

[lmills]

OK you guys are talking in riddles. The turbo needs a load. Which we have all established. The main question that started the thread was how to load up a dyno. So how do you do it?



Just so you know yes, Jetpilot I have been to the same dyno events that you have and personally watched them powerbrake almost every twinned truck to get the most out of them.

 

[robertyoke]

The fueling onthe electronic trucks is tied to boost but the number is very low it is also tied to rpm..... Hence all the smoke with a fueling box. The reason to not drag brakes etc. is to give a constant reading. Dyno's are no good unless they are run correct and consistant. I have run everything form stock to wild, single to twins, N02, and propane so I can be pretty confident when I say that whne you drag the brakes all you are going to do is skew the rpm vs hp data.

I just ran on the dynojet 248c and I got only 35~36 psi of boost my tst box does not full fuel till 40psi so it was not at full fueling. would it make more power?? don't no, I just wanted to hit that 500 mark :{

 

[Jetpilot]

The only truck that has been powerbraked at previous Fall Brawl (according to Dave Kauffmans wheel man) is sleddy's truck..... And Dave said the HP was the same just had a slightly higher torque #.

 

[lmills]

Well, I know for a fact they did more than his. He wasn't even at the last event we had. I don't want to get into a ******* match with people getting upset with the numbers, but if you want names, PM me. I know for a fact that Kauffmans powerbraked more than sleddy's truck. Actually if memory serves me correct I think Sleddy might have been operating his own truck on the last one or two pulls.

 

[Jim Fulmer]

When I run on a 248 I can always get between 73 and 78 psi depending on the way the truck is setup, now having said that it will make that boost late in the band which is not good for max hp but I've only been on one real load dyno and that was at Piers's last fall and I had max boost at 2400.



Jim

 

[jetenginedoctor]

So technically if you can put in any load you chose, then you can skew the results also.

No.



I set the ramp rate in the control software, run the truck up to the engine speed we wish to start the test at in the gear we intend to run at, and set the dyno to load the rollers to hold that engine/roller speed. Then you drop the hammer on the loud pedal, allow two or three seconds for the turbo to spool up (the engine will not accelerate here as the retarder holds the roller/engine speed at whatever it was when I switch the load on) then switch the ramp selector up. The control system allows the engine to accelerate at the rate we specify and draws the graph in real time. Show me another dyno that can do that. We can observe the engine speed, HP, and boost pressure during the entire run as it is graphed IN REAL TIME. We can chose to abort the test at any time due to overboost, runaway EGT, whatever. When the engine has reved past its max HP or has reached its rev limit, switch the ramp switch to hold, release the loud pedal, load switch to nuetral, clutch in and footbrake. Test done. No cheating, no pedal popping, and it'll lay one test down right on top of the other as if it were tracing a stencil.



Other load bearing dynos operate in a similar fashion. Please explain how you think that using an absorber/water brake to hold the engine at a fixed RPM while building boost is cheating? I can make your test results poorer by setting the ramp rate too high, not allowing the turbo to build full boost, but I can't make it artificially high by manipulating ramp rate. I can help you cheat by lying about weather conditions, but that'd be just plain wrong.

 

[jetenginedoctor]

Does this hold true with a truck making 70 lbs of boost? How can the dyno hold the tires till 20-25 lbs of boost? The rear end would really have to be strapped down tight. If you leave the line at 20 lbs, that what you want on the dyno, no?



. . Preston. .

I can hold your truck at 20 PSI no problem.

 

[jetenginedoctor]

I do love the dyno discussions on this board... ... . First off let me say that I have made hundreds of dyno runs and used both load and inertia dynos. The load dynos are not good for evaluating our trucks if what one wants to know is peak obtainable HP. The tires just slip too much under the acceleration.

There's a big difference between what folks are used to and what folks could have if they demanded it. Our dynos have no problem making traction with even the nastiest cars and trucks. The secret is in how we restrain the vehicle. Rather than just preventing the vehicle from moving fore or aft like most dynos, we are actually strapping the vehicle DOWN onto the rollers. As the vehicle loads up and tries to drive up and over the load rollers, the traction system forces the wheels down onto the roller even harder to increase the bite on the tires. We've tested some incredibly powerful trucks where the owners went on and on about how he was gonna break our dyno that day, and that we'll never be able to hold his power with those little bitty rollers. Well, it didn't take any of their friends in the bed to make enough traction for us to be able to turn up the load and bring these fire breathing monsters to their knees. Anything you've seen or heard about wheel slip does not apply to our dynos.

Personally I feel as the dynojet is the best dyno for evaluating our trucks.

Considering the fact that there's probably 20 DynoJet machines for every load bearing dyno out there, I'd be willing to bet money that your opinion is based on what you've seen the most of, rather than really understanding the difference between everything that's out there. This is not a jab at you. This is just to say that you owe it to yourself to take a closer look at things before you declair DynoJet the best suited machine for the task in question.

You can drag the brakes all you want and peak HP remains constant, you can cause a torque spike but the gain in HP is pretty much nonexistant.

Whenever you drag the service brakes on your truck during a dyno run, you're turning HP that should be turning the rollers into heat. That HP is easily measured on our dyno. I'll test my truck tomorrow and show you what I mean.

You will always hear guys complain because their trucks didn't make the HP the expected and then blame the dyno. I have never heard anyone get off they dyno and say "boy that thing is wrong no way I make that much hp", normally its the other way around.



Doug

I can see this has sprialed into a flame war, so be it. I'm not here to argue, just try to set folks straight with facts. If you want bigger numbers than your buddy, go ahead. . . . find an operator that'll use every cheat in the books. If you want to be able to develop your truck into something that YOU KNOW makes more power than your buddy, despite what the other guy's dyno says, you need to aquaint yourself with an experienced load bearing dyno operator, whether it's one of ours or otherwise.

 

[jetenginedoctor]

In my case, making the pull in 6th gear instead of 5th was worth 30 BHP and 100 lb-ft in the dyno results. Not to get into the physics of it, but this is because less power is consumed by the drivetrain's inertia in 6th and more gets transferred to the rollers due to the longer time it takes to make the pull in 6th gear.



Rusty

Not so fast there.



The truck will have more drivetrain intertia and frictional losses in any gear other than what provides 1:1 ratio. If sixth gear "made" more power, it's because you didn't have traction in fifth gear on that dyno. To be quite honest, the difference in frictional and inertial HP losses in the drivetrain are on the order of one or two percent. There's no way in the world that a six speed transmission is going to absorb 30 HP (22,380 watts. . . enough heat energy to weld with) and 100 ft-lb of torque. . . . unless it's full of sand and superglue.

 

[KatDiesel]

Big Mak,



What model dynojet were you running on? I usually run on a 248C, they do make a smaller model and maybe that is the problem.

He was on a 248C. I wasn't there, but been to that particular dyno many times.

 

[Jim Fulmer]

jetenginedoctor



I just looked at your site and the dyno you have, that is the same one Piers has and I know what your talking about on the load issue. Those of you that haven't run on a dyno like this need to, when I was running the machine was set wrong by mistake and my truck did nothing in direct at 1700... ... just sat there at 1700@WOT... ... ... ... uh, that's not going to work.



Have you though about having an event of trucks, cars, mix or whatever... ... . I'd like to run on that type again.



Jim

 

[banshee]

Jim,



Since you've run on both, how did your numbers compare on the Dyno Dynamics vs. the Dynojet? Do you powerbrake your truck to get numbers on the dynojet? If so, howmuch (if any) does it change the numbers?

 

[jetenginedoctor]

jetenginedoctor



I just looked at your site and the dyno you have, that is the same one Piers has and I know what your talking about on the load issue. Those of you that haven't run on a dyno like this need to, when I was running the machine was set wrong by mistake and my truck did nothing in direct at 1700... ... just sat there at 1700@WOT... ... ... ... uh, that's not going to work.



Have you though about having an event of trucks, cars, mix or whatever... ... . I'd like to run on that type again.



Jim

Jim,



If you'd like to test on one of our dynos, consider coming down for the Texas TDR Rally coming up on October 9th and 10th:



https://www.turbodieselregister.com/forums/showthread.php?t=109713



https://www.turbodieselregister.com/forums/showthread.php?t=110653



From the looks of things, Piers and other big names are planning to go, so I expect it'll be a really good time.



Anyway, I find it interesting that a couple guys who are such adimant DynoJet fans in this thread have something about Piers Diesel Research tuned in their signatures. Did you guys realize that Piers dyno IS NOT a DynoJet? If I'm not mistaken, Piers has the big-brother to my dyno, his having two retarders. I'm suprised he hasn't chimed in to make remarks as to why he chose an eddy current absorber equipped Dyno Dynamics dyno. If you guys attend the Texas TDR Rally, I'm sure you'll get a chance to ask Piers about his choice of dynos. In the mean time, we can patiently wait to see if he chimes in here on his own on the subject.

 

[RustyJC]

Not so fast there.



The truck will have more drivetrain intertia and frictional losses in any gear other than what provides 1:1 ratio. If sixth gear "made" more power, it's because you didn't have traction in fifth gear on that dyno. To be quite honest, the difference in frictional and inertial HP losses in the drivetrain are on the order of one or two percent. There's no way in the world that a six speed transmission is going to absorb 30 HP (22,380 watts. . . enough heat energy to weld with) and 100 ft-lb of torque. . . . unless it's full of sand and superglue.

I believe you're missing the point. Horsepower is the rate of doing work. If I move 50 lbs up an 11 ft ladder in 1 second, I've produced 550 ft-lbs of work and 1 HP. If I take it easy and do it in 2 seconds, I've still produced 550 ft-lbs of work, but I've only produced 1/2 HP.



The rotational inertia I'm talking about is coming from the crankshaft, the big ends of the con rods, the engine accessories, the flywheel, clutch disc, pressure plate, transmission input shaft - basically, everything that rotates at engine speed or a fixed multiple thereof. All of these rotate and have mass; therefore, they have rotational inertia and it takes work to accelerate them from a lower speed to a higher speed. The rate at which they are accelerated determines the power required to accelerate them.



Hypothetically, if I can make a 5th gear dyno pull in 5 seconds but a 6th gear dyno pull takes 10 seconds, both going from 1400 to 3400 engine RPM, then the HP required to overcome drivetrain rotational inertia is halved. This HP is now available to deliver to the dyno rollers.



I've worked for a manufacturer of engines, gas turbines, compressors, turbochargers and control systems for over 30 years, 25 of those in technical and engineering management. We use water brake and eddy current dynos for research & development as well as production testing; for electrical power generation packages, we load test using generator output against a resistance bank. My point is - I have somewhat more than a passing familiarity with dynos.



The phenomenon I'm describing is unique to inertial dynos since they determine HP based on the rate of acceleration of a drum of known rotational inertia. Any other rotational inertia in the system before the power gets to the drum should be minimized to obtain more accurate readings - that's what the longer duration of the 6th gear pull does. As I said, 2 runs in 5th were good for about 320/650. 2 runs in 6th produced 347/762, and the results were very repeatable.



Another advantage of the 6th gear runs is that they work the engine harder against the higher 6th gear ratio, allowing the turbo (1. ) the opportunity to produce higher boost and (2. ) more time to spool. To illustrate this from the other extreme, what kind of BHP and torque would you expect from a pull on an inertial dyno in 1st gear?



Rusty

 

[Marco]

they determine HP based on the rate of acceleration of a drum of known rotational inertia

That's the point!

If the inertia ( mass in this case ) is too small, you can't load the engine enough.

Your example would work perfectly for an electric motor, not so for a turbo diesel.



Marco

 

[RustyJC]

Your example would work perfectly for an electric motor, not so for a turbo diesel.

Marco,



For clarification, whose example?



Rusty

 

[BigYellowIron]

Still if you run a dynojet correct your truck will produce correct HP.



I have run a heavily fueled twin turbo truck that the timing was set at 32* on the dyno and I was able to get over 70 psi boost on it.

I hear about " running a diesel correctly on the dynojet" all the time but I have never heard anyone state the correct way. I have a heavy fueled twined truck with high timing and can't spool it on they dyno, I think I've tried everything but giving up. Is there a secret that no one is telling.



Adam

 

[RustyJC]

That's the point!

If the inertia ( mass in this case ) is too small, you can't load the engine enough.

Agreed. To illustrate, what if the dyno rollers were thimbles (the kind thread comes on)? The engine would never even "feel" them on a pull and would think you were just revving it up with the rear wheels in the air - no significant boost or power required.



Rusty

 

[jetenginedoctor]

I believe you're missing the point. Horsepower is the rate of doing work. If I move 50 lbs up an 11 ft ladder in 1 second, I've produced 550 ft-lbs of work and 1 HP. If I take it easy and do it in 2 seconds, I've still produced 550 ft-lbs of work, but I've only produced 1/2 HP.

Trust me, I haven't missed any point. Your understanding of one HP as a unit of work is correct.

The rotational inertia I'm talking about is coming from the crankshaft, the big ends of the con rods, the engine accessories, the flywheel, clutch disc, pressure plate, transmission shafts and gears, driveshaft, pinion gear - basically, everything ahead of the ring gear, axles, and wheels and tires. All of these rotate and have mass; therefore, they have rotational inertia and it takes work to accelerate them from a lower speed to a higher speed. The rate at which they are accelerated determines the power required to accelerate them.

Agreed. All of this means something when testing on our dynos, yet at the same time it means nothing. The total engine and powertrain inertia DOES add to how much HP it takes to accelerate the vehicle at a given rate. It does not, however, make a penny's difference with regards to what HP the vehicle will make when held at a steady speed. Like I've said over and over in this discussion, this is the difference between a dyno that can hold an engine at a steady speed or ramp it up at a given rate and measure it's output during the entire evolution. When you're comparing what's left over after drivetrain inertia and frictional losses between testing in one gear and another, there's maybe two or three percent AT MOST lost between the gear with the least losses and the gear with the most losses.

Hypothetically, if I can make a 5th gear dyno pull in 5 seconds but a 6th gear dyno pull takes 10 seconds, both going from 1400 to 3400 engine RPM, then the HP required to overcome drivetrain rotational inertia is halved. This HP is now available to deliver to the dyno rollers.

Wrong. The relationship between an objects inertia and the accelerating force necessary to accelerate it at twice the rate is NOT directly proportional. In order to accelerate a given mass a given distance from 10 seconds to 5 seconds is not twice the accelerating force, it's four times as much. The relationship is exponential. Otherwise, a car with a 200HP engine that runs 13 second 1/4 mile times would run 6. 5 second quarter mile times when you swap in a 400HP engine. Make sense?

I've worked for a manufacturer of engines, gas turbines, compressors, turbochargers and control systems for over 30 years, 25 of those in technical and engineering management.

Been there, done that, got all the T-shirts, coffee mugs, and mouse pads to prove it. I'm not here to compare credentials, nor am I here to squash anyone's feelings. I'm merely in this discussion to set things straight. So far, there's been a huge measure of misconception exposed, and I'm going to do my best to help folks understand how this stuff really works.

We use water brake and eddy current dynos for research & development as well as production testing; for electrical power generation packages, we load test using generator output against a resistance bank. My point is - I have somewhat more than a passing familiarity with dynos.

I wrote a big thing here and deleted it. If you want to challenge me in a technical dual, PM me your phone number and we'll have a chat. I'll spare you some embarrassment on the forum, but would be more than happy to explain some things for you.

The phenomenon I'm describing is unique to inertial dynos since they determine HP based on the rate of acceleration of a drum of known rotational inertia.

I'm not talking about inertia dynos, and neither were you. You go on and on about working with EC absorber and WB dynos with your work (which you clearly don't) and now you go into rotating inertia dynos. . . . do you use those at work too???

Any other rotational inertia in the system before the power gets to the drum should be minimized to obtain more accurate readings

This is only true if you have no way of measuring and accounting for that inertia. If you have a means to determine this inertia and factor it into the computation (as we can and do) then it's much less of an issue.

- that's what the longer duration of the 6th gear pull does.

No. A longer 6th gear pull on an inertia dyno is simply slowing the ramp rate to allow the engine to make full boost pressure as well as reducing wheel torque which minimises wheel slip. Again, we control the ramp rate on our dynos so we can test in the gear of our choosing, and traction is never a problem.

As I said, 2 runs in 5th were good for about 320/650. 2 runs in 6th produced 347/762, and the results were very repeatable.

Whether you realize it or not, you're losing HP in that overdrive gear, not making more. I can see I'm clearly beating a dead horse with you, however. It's clear from what you're saying that your truck will accelerate harder in sixth gear than in fifth. . . . . why not just make your truck a one speed? You don't need all those other five pesky gears. . . . .

Another advantage of the 6th gear runs is that they work the engine harder against the higher 6th gear ratio, allowing the turbo (1. ) the opportunity to produce higher boost and (2. ) more time to spool. To illustrate this from the other extreme, what kind of BHP and torque would you expect from a pull on an inertial dyno in 1st gear?



Rusty

What would be the point in that? Who would test a diesel truck in first gear on any chassis dyno?

 

[RustyJC]

Actually, I agree with you insofar as a load-type dyno is concerned. Under steady state conditions, rotational inertia is irrelevent since there's no acceleration taking place. Therefore, on a load-type dyno, it doesn't matter.



My discussion was, however, about the role of rotational inertia on inertial dynos such as the Dynojet. Did you miss the following:

The phenomenon I'm describing is unique to inertial dynos...

If you doubt that, look at my signature. The results I discussed are clearly displayed as coming from an inertial dyno.



And, to my chagrin, you're right about the change of energy in the rotating elements - I forgot the ^2 exponent on velocity. My bad My fingers were obviously running faster than my brain.



Rusty