Loading the Dyno-----

[RustyJC]

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. . . . .

I don't believe your sarcasm contributes to what had been a pretty good technical discussion. I never claimed my truck accelerated harder in 6th than 5th, nor did I advocate throwing out the other 5 gears. I just described an anomaly that is unique to inertial dynos - the difference in my results between 5th and 6th gears. My only point is that the inertial dyno's inherent design produced lower results in 5th gear than 6th, and we made 2 runs in each gear because the dyno operator and I specifically wanted to determine (1. ) that a repeatable difference exists and (2. ) the magnitude of that difference.



I agree - running in direct (5th) would likely produce better results than 6th due to lower powertrain losses on a load-type dyno.



Rusty

 

[banshee]

The rotational inertia issue is one of the main differences between an inertia dyno and a load dyno. Let's take an example of a truck with a given weight (7000lbs) with a lightweight set of wheels and tires (they weigh 50 lbs each), and the same truck with very heavy wheels and tires (300 lbs each... a total vehicle weight of 8000 lbs). If you were to strap this truck to a load dyno and run it with both sets of tires back to back you really wouldn't see much difference, if any, between the two sets of tires. Why? Because it's more steady state... much like towing a heavy trailer up a steep hill. We'll call this "steady state/usable" horsepower. Strapping the same truck to an inertial dyno, however, WILL show a difference in horsepower due to the nature of the dyno... it only shows power due to a change in rotational velocity (acceleration). Such add ons such as light wheels, carbon fiber driveshafts, and lighter flywheels WILL show a gain on a dynojet. Which setup will be faster at a racetrack? The lighter wheels will be MUCH faster, and the dynojet shows that, but the load dyno will drastically diminish the advantage of lighter driveline components. This exampe is exactly what Rusty is trying to demonstrate. The more steady state the runs are the less the driveline's rotational inertia matters. It depends on the case whether or not that is a good thing or not.



John

 

[jetenginedoctor]

Okay Rusty, let's do this. You come to the TDR roundup on October 9th, and I'll test your truck for free just to prove a point. The analogy of the 500 lb wheels is only partially true, as I can make corrections on the dyno that factor them out completely. It's easier for me to show you than explain on the forum. If you want to know for yourself, come to the roundup and I'll show you completely free of charge.

 

[RustyJC]

I really don't know what point you want to prove since nothing we've been discussing regarding inertial dynos has that much to do with your load-type dyno. Most of us have run on Dynojets (as you said earlier), and my discussion was related to anomalies unique to the inertial dyno. No one (at least not I) is challenging your load type dyno - we're just saying that the inertial dyno has some different characteristics by design. Why must that turn into some kind of debate?



As Curtis and Mike are aware, the TDR Texas Rally has been scheduled on the same weekend as the Texas Boomers Octoberfest rally for the last 2 years. Since my wife is wagonmaster of the Texas Boomers, I'll be in Fentress with the 5th wheel that weekend.



Rusty

 

[F8LDOSE]

Will tire size come in effect at all? say 35" tall verse 31" tall?

 

[Hohn]

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.



As for the argument on boost vs. HP, guys please remember that boost doesn't necessarily mean HP. A good example would be if you tow a 10K load up a 6% grade you will make more boost than on level ground with an empty truck, does it make more HP going up the hill? I have seen many times that an engine makes more HP with a lower boost #!



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

Doug, let me go on record as the first complaining about artificially high dyno numbers.



I've dynoed my truck once and only once. Best pull netted 390rwhp and 918 lb-ft. While this is typical of a bombed CTD, it's NOT typical of a truck with only an EZ and 75hp injectors!!!



I'd believe more that I have 350-360hp.



This was done on a dynojet 248C, with the runs made in 6th. Rusty's exactly right about getting better numbers in 6th. All the DEE guys pulled in 6th and got better numbers than 5th.



It's worth mentioning that a CTD doesn't need a load to make HP! That's like saying that if I lightened my truck by 3000 pounds, it would have less power! It doesn't follow.





You DO need boost to burn the fuel, but artificially high loads (and high boost) are not needed to accurately measure "power".





I'd be happiest with a dyno that had rollers that offered 7000 lbs (force) of resistance, simulating the weight of a typical truck.



I don't put much stock in HP as commonly conceived, because most of the time, its measured in a way that doesn't correlate.



A DynoJet may not accurately measure hp, but it DOES give info that's even better-- HOW FAST CAN YOU MOVE THIS LOAD FROM A-B??



Justin

 

[jetenginedoctor]

I really don't know what point you want to prove since nothing we've been discussing regarding inertial dynos has that much to do with your load-type dyno. Most of us have run on Dynojets (as you said earlier), and my discussion was related to anomalies unique to the inertial dyno. No one (at least not I) is challenging your load type dyno - we're just saying that the inertial dyno has some different characteristics by design. Why must that turn into some kind of debate?



As Curtis and Mike are aware, the TDR Texas Rally has been scheduled on the same weekend as the Texas Boomers Octoberfest rally for the last 2 years. Since my wife is wagonmaster of the Texas Boomers, I'll be in Fentress with the 5th wheel that weekend.



Rusty

What are you doing this weekend? Wanna cruise over to Austin for a free in-person demonstration of how a load dyno works? Come on, all it'll take is a little time and a little fuel. . . . you have nothing to lose. . .

 

[offshoreracr]

at an engine makes more HP with a lower boost #



Personally I feel as the dynojet is the best dyno for evaluating our trucks. 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. 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 agree with Doug on this one. I have dyno'd with dragging the brakes, no dragging, on multiple dynos ( 248c) in different states and have always come up within 4 or 5 tenths of a HP between them. Hp has remained constant no matter what, torque has varied , but not more than 80 ft. lbs or so.



Fred

 

[justinp20012500]

I am not quite understanding you...

A DynoJet may not accurately measure hp, but it DOES give info that's even better-- HOW FAST CAN YOU MOVE THIS LOAD FROM A-B??

If I take a stock 2004. 5 cummins 4 x 4 and run a quater mile in 4 high to limit the wheel slip. (Not like it would have much anyway) And then go dyno on Gillette's Mustang M250 (Load Dyno) I will put money on it that the dyno will be within 10 HP of how much HP (a unit of work) it took to move that truck 1,320'. Its kinda funny how every load dyno requires the operator to run the vehicle in a gear that is closest to 1:1...

Maybe I will try the above test this weekend...

 

[Big MAK]

The boost numbers the engnie is making definitely do matter; the boost reflects the work the truck is doing and therefore the HP (aka work) the truck is putting out. 0 to 110 time when boost runs from 0 to 15lbs is not an accurate reflection of the HP capabilities of a truck that can make 60+ lbs of boost -- a reading from 20lb to 60lbs is a-lot more accurate of that trucks work (aka HP) capabilities!



... please correct me if I'm WAY off base; I'm trying to figure this out. But that just makes common sense.

 

[jwilliams3]

Dl5treez,

You ever see anyone put a superstock tractor on a wheel-load dyno?



BTW. . My number came up on a dyno dynamics dyno from a jet.

462hp on a Jet and 501 on a dynamics (this was with the 99).



--Justin

 

[justinp20012500]

I have to agree...

I vowed a long time ago to stay out of dyno discussions around here... my forehead is still sore.

For the record, there is no Dodge pickup on the planet that will slip the rollers on any load dyno, if the truck is properly secured to the platform

If anybody ever gets a chance, go to a heavy truck shop where they have a big tandem bogie dyno and watch them run a class 8 tractor for a session. You'll understand everything jetenginedoctor, etc is trying to say... ...

.

Been there and done that.

I went down to Smith Detroit Allison where they have the twin roller load dyno. They can load a 600 hp series 60 enough to make the turbo glow red. They don't strap the rig down as well as the guy that ran my truck on the mustang.

Dl5treez,
You ever see anyone put a superstock tractor on a wheel-load dyno?

I did see a 1500 HP rail car get broke in on a Mustang M250.

 

[Jetpilot]

jetenginedoctor,



Sorry I have been away for several days and have been unable to post... ... You seem to feel as though my opinions are flaming another product. Let me state why I say what I do and we can go from there. I have not used every type of dyno in the country and I have not personally used the type that you have. My experience with load dynos is limited to the Mustang brand dyno and I have always had tire slip problems. Maybe there is a better way to help with traction but we tried everything we could think of (this included strapping the truck both forward and aft on the rear axles with 8 staps)! So maybe I was premature in saying "load dynos" and should have said Mustang Dynos... ...



Anyway, the point I was trying to make earlier was that I have never had a problem getting a truck to make adequate boost on a dynojet. If someone is having this problem then I would recommend evaluating how the dyno is being operated and the trucks mods. Dynos are great tuning tools but that is how they should be utilized. Doing things to try and produce and inflated number to please somebody in my opinion is not as important as having their truck run the way they want.



Thanks,



Doug

 

[jetenginedoctor]

The dynojet is not as hard on your drivetrain as driving your truck on the street is.

Actually, that's not true. If your truck makes 600hp on the street, it should (and will) also make it on the dyno. In order for the truck to produce 600hp of work, there must be 600hp worth of work for it to do. Whether you're producing that work by accelerating the truck on a flat road, pulling a heavy trailer up a grade, loading the truck with a load bearing dyno, or accelerating a heavy drum on an inertia dyno, 600hp is 600hp and making that power strapped on a dyno is no different than down the 1340.

The drums used just don't cause the same load as you pushing your truck down the street.

Yes it does, or else you wouldn't be able to measure that HP. A dyno doesn't exptrapolate HP beyond the load that it can produce. This applies even to an inertia dyno with a rotational moment of inertia that is less than the linear inertia of the truck by itself.

Still if you run a dynojet correct your truck will produce correct HP. Big Mak what rpm did you start the run at? What gear?

I agree with this one. The trick to this is being able to get ample traction and run the truck in it's highest gear so that the acceleration rate is slow enough for the turbo to spool up.

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.

Awesome!!!! Are you going to be at the roundup at Buckhorn Lake???

 

[Jetpilot]

Actually, that's not true. If your truck makes 600hp on the street, it should (and will) also make it on the dyno. In order for the truck to produce 600hp of work, there must be 600hp worth of work for it to do. Whether you're producing that work by accelerating the truck on a flat road, pulling a heavy trailer up a grade, loading the truck with a load bearing dyno, or accelerating a heavy drum on an inertia dyno, 600hp is 600hp and making that power strapped on a dyno is no different than down the 1340.

Well I have to disagree on this... . Why is it that pulling trucks break things? A truck can make 600 HP on an enertia dyno and not break anything but strap it to a load dyno and haul the load down and see what happens..... I have seen this before, things can go boom. Same thing goes for the track or pulling a sled.



I wish I could come down but with the new addition to the family and all the airline cutbacks I just can't make this one. I would however love to come down sometime and give your dyno a try as it looks like a nice setup.



Doug

 

[jetenginedoctor]

jetenginedoctor,



Sorry I have been away for several days and have been unable to post... ... You seem to feel as though my opinions are flaming another product.

Hmm. . . you are flaming. You make your argument that the DJ machine is the best way to evaluate these truck's performance, yadda yadda yadda. You say you've made hundreds of pulls yadda yadda on different types of dynos yadda yadda and that the DJ is the best. Right. Hundreds of pulls? How many hundreds? On what all dynos have you tested? If you think a dyno that is notoriously a poor performer when it comes to tire to roller traction, one that you have to DRAG THE VEHICLE'S SERVICE BRAKES to get a good number on is the best. . . . then I seriously doubt that you've:



A) Made hundreds of dyno pulls

and

B) Tested on different types of dynos.



I really hope you'll come to the TDR Roundup at Buckhorn Lake because I'd like to show you what you're clearly missing out on.

Let me state why I say what I do and we can go from there. I have not used every type of dyno in the country and I have not personally used the type that you have.

Then come see me at the TDR Roundup nest weekend and we'll fix that for ya!

My experience with load dynos is limited to the Mustang brand dyno and I have always had tire slip problems.

Our dynos feature a unique knurling on the rollers and a patented traction control system that is far more effective than what any other dyno manufacturer uses. The only time I've EVER had a traction problem on our dynos is when testing a FWD turbo car that had just come in from being driven in the summer heat with the A/C on. The condensation from the evaporator was still dribbling out and managed to get on the tire/roller during testing. After some quick mopping with shop towels to take care of the oozing evaporator issue, the car went on to test with no further drama.

Maybe there is a better way to help with traction but we tried everything we could think of (this included strapping the truck both forward and aft on the rear axles with 8 staps)! So maybe I was premature in saying "load dynos" and should have said Mustang Dynos... ...

Yes, you incorrectly generalized all load dynos as being the same as the MD. Come to the Roundup, and we'll make it clear in your mind that you've never tested on anything like this before.

Anyway, the point I was trying to make earlier was that I have never had a problem getting a truck to make adequate boost on a dynojet.

Actually, what you said was, "Personally I feel as the dynojet is the best dyno for evaluating our trucks. 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. " You're mistaken on both counts, and I can prove it.

If someone is having this problem then I would recommend evaluating how the dyno is being operated and the trucks mods. Dynos are great tuning tools but that is how they should be utilized. Doing things to try and produce and inflated number to please somebody in my opinion is not as important as having their truck run the way they want.



Thanks,



Doug

I hear/read all the time people (posting on the internet especially) *****ing about how dyno shop operator X is a real piece of crap because he couldn't make my truck make the same or more power as dyno shop operator Y. For this reason, many dyno operators feel pressured to do every cheat they can in order to please this type of customer and keep them and their friends coming back to use their machine. That's all fine and dandy! I can give you a graph that shows your 300hp truck making 700hp if that's what makes you happy, but you've still only got a 300hp truck.



But the good thing is that more and more people are educating themselves about the differences between inertia and load bearing dynos. They are becoming more and more concerned about accuracy and repeatability. They then see the operators doing all the cheats, and they realize that the test results from such an operator mean nothing. Everything is turning full circle. The dynamometer's original purpose as a repeatable means of evaluating a vehicle's performance is slowly becoming more important than just a source of ammo for showing off to friends. But the facts need to be laid out, and misconceptions need to be dispelled. That's why I'm in the discussion.

 

[Jetpilot]

Jetenginedoctor,



We are putting together a dyno event on October 9th and 10th up here and Iwould love to have you come this way and check out event. I also want you to know that I am not flaming any type/brand of dyno. I stated that I have never used the brand have and I also welcome the opportunity to evaluate one. But you sir seem to take issue with me questioning my experience with dynoing.....



Your above remarks comparing my statement to your dyno is irrelevant due to as I said, I was reffering to a Mustang dyno. One thing I do like about a DJ is the operators inability to run the dyno a certain way to cheat the numbers..... But one thing you said was that you can make a chart to show an inaccurate # if it makes a customer happy but with a DJ the only way to do this would be to alter the atmospheric conditions.



Look I am not looking to debate about a dyno that I am unfamiliar with, I will be happy to give my opinion on a DJ and MD comparision. Like you stated not many have seen the brand dyno you have and maybe its the cats meow of dynos but until enough guys give it a try and we see how it actaully stacks up against other brands I will reserve my opinion.



Thanks,



Doug

 

[Hohn]

If I take a stock 2004. 5 cummins 4 x 4 and run a quater mile in 4 high to limit the wheel slip. (Not like it would have much anyway) And then go dyno on Gillette's Mustang M250 (Load Dyno) I will put money on it that the dyno will be within 10 HP of how much HP (a unit of work) it took to move that truck 1,320'. Its kinda funny how every load dyno requires the operator to run the vehicle in a gear that is closest to 1:1...



Maybe I will try the above test this weekend...

Justin:



My point is simply that often our concept of HP is misleading. More accurately, our concept of power in general is misleading.



This is because we usually think of HP as the formula: (tq*rpm)/5252. While this tells us a hp number, it's really designed for STEADY STATE applications.



Say you have an engine that makes 500 lb-ft at exactly 5252 rpm. By definition we have 500hp, right? Bu this information is only useful if we are holding RPM constant at 5252rpm!!



Because accelerating a vehicle requires a change in RPM (barring a CVT or such), then we HAVE to look a little further into the factors here. We have to be more analytical.



Thus, we are concerned with DYNAMIC POWER! This means how fast can power be applied, not just how much force at a certain rpm. We're not concerned with tq@rpm so much as the RATE OF APPLICATION (CHANGE IN RPM).



There are many documented cases in racing of an engine that puts out higher dyno numbers being SLOWER in the race. I know of a NASCAR example where the engine that dynod 100hp less was actually 2 or 3 tenths faster per lap!!!



Consider the heavy flywheel example that I often cite. If you take two identical engines, but fit one with an excessively heavy (say 200#) flywheel, how does this affect dyno testing?



On a Mustang (load-type) dyno, the heavy-flywheeled engine will show MORE power, because the flywheel effect (inertia) will cause the engine to have a little help in resisting being pulled down to lower rpm.



On a DynoJet, the heavy-flywheeled engine will show less power because the engine has to overcome the intertia of the flywheel to accelerate the drums. The DynoJet can't see this! It only knows the resistance of the drums, so everything before that point is ignored.



Thus, the DynoJet doesn't really do a good job of measuring the actual hp of the engine. What it's REALLY measuring it the rate of application of the torque that actually makes it to the rear wheels!! THIS IS WHAT MATTERS.



So the dyno you test on should be based on what you want the engine to do. If you want acceleration, then use a dyno that tests acceleration-- the DynoJet. If want to a truck that pulls, test it with a load dyno (mustang, etc).



The main point is that THEY ARE NOT THE SAME. The ability to accelerate under constant load is VERY different than the ability to maintain rpm under increasing load. Moreover, it's not linear!!



By linear, I mean this: If you cut the load in half, you should be able to accelerate it twice as fast, right? At least, the "formula" way of thinking would tell you this.



But this isn't true. The Cummins will only rev so fast. If you dropped your CTD into a superlightweight car, you would find that the rate of accleration (rate of work applied) is less than you would think from the "formula".



Scott Bentz is running into this issue right now with the CTD Dragster. He's having to find a delicate balance. If you gear the car too tall, you're slow. If you gear it too short, the rev rate of the engine is limiting you, and you're slow.



You 5600 owners know exactly what I'm talking about. There isn't much acceleration available in the first 3 gears, because redline in 3rd gear tops out around 35 mph! So the first three gears cover 0-35, the next three cover 35-105+. \



Compare that to a quick-revving gasser which is MUCH quicker in the first few gears than in the upper gears.



The best real world measurement of rate of applied tq is drag racing. Unfortunately, variables in transmission, driver skill, shift points, traction, etc make it very difficult to get consistent data.



Thus, the Dynojet is the best approximation out there. It IS consistent, but it's ALSO still an approximation.



Remember: accleration is all about torque rise and the rate of torque application. But accleration isn't the only measure of engine performance.



How well do you think a 600hp CAT would acclerate a 5000lb package compared to a 600hp small block working against that same rate????





Justin

 

[jetenginedoctor]

Heh, that's the same weekend I'm doing the TDR roundup at Buckhorn.



No biggie, we'll get together and have some fun. Where you located? I'm not trying to have a ******* match on this issue, just presenting the facts and dispell any myths. Piers Diesel Research has one of our dynos. I would think that if somebody like Piers (given his reputation in this group) owns one of our dynos, that other folks would take a bit more interest in knowing WHY. After all, Dyno Dynamics is a newcomer to the dyno market in the USA, though they've been building dynos since 1969. I'll take the Pepsi Challenge with anyone else's dyno, and I think after you've seen what we can do that others cannot, you too will understand my position here.



Anyway, no need to feel defensive. I'm offering to show you what I'm talking about as an invitation, not as a challenge. Try to make it down to Austin one day and give me a call. I'd be happy to give you a demonstration of everything I've said in this thread.



BK



(why don't my signatures show up in this thread anymore?)

 

[RustyJC]

(why don't my signatures show up in this thread anymore?)

To save bandwidth, your sig only shows up on your first post on a thread or your first post on each page of a thread (can't recall which).



Rusty