Loading the Dyno-----

[hammersley]

Who knows what one has to do to load the Dyno to get the numbers. A member I know said that when they dynoed with an operator not familiar with the Diesel setup he made under 400 HP! When he told him to put a 25% load it shot up to the very near 600 where it should be.



Now this guy is trusted and a lot of you folk sknow him - but since I didn't ask him if I could use his name - I didn't.



BUT my point is UNLIKE the news folks - on either side - this is a trusted source... ... So experience on LOADING the dyno please... ... . and I'm talking about the Dyno Jet - like at Torque Freaks in Portland.....

 

[lmills]

Some people power brake the truck to make it spool up more boost down low. That helps out quite a bit since the dyno doesn't put enough load on the motor to bring it up to full boost like street driving does.

 

[jetenginedoctor]

Time to find yourself an absorber dyno.



I can bring your truck to its knees. If it makes any power, I'll help you find out. No power braking, no sillyness, no exaggerated non-sense. Are you dissatisfied that your truck hasn't tested with the numbers you expect to see?

 

[Turbo Thom]

Now that sounds a little silly. You want it to read what you what to see? I would want to see what it really is. Or did I read that wrong?



. . Preston. .

 

[Hammer]

Hammersley. .

Do what we did one time with Jetpilot's slick black bottle rocket when it was spinning the tires on the rollers. Find 6 of the biggest guys at the dyno meet,open the tailgate,load them all inside,then do your dyno test. I think the day we did it we only used 4 because 4 was all we needed. I think I counted for the other 2 missing,LOL..... Andy

 

[jetenginedoctor]

Now that sounds a little silly. You want it to read what you what to see? I would want to see what it really is. Or did I read that wrong?



. . Preston. .

Yes, it is silly, and by design. I've read on MANY forums people complaining that they dyno operator didn't do as many cheats as they could to skew the results to produce favorable numbers. I'm not saying that's what's happening here, but I don't think loosely suggesting that dyno operator is at fault is the right thing to be saying here. Powerbraking the truck on a DynoJet is a cheat. It's not the fault of the truck (necessarily) that the turbo can't build full boost on that type of dyno. It's not the dyno operator's fault either. If you want the most reliable power figures, you need to test on a dyno that can apply and hold a load, and control the engine's rate of acceleration. This is why I made the remark about finding yourself a load-bearing dyno.

 

[lmills]

Well then I guess you could consider the load bearing dyno a cheat over the other type? Or how is it right to load the truck up one way but not the other? Cause the way you are talking you make it sound as though I can lay down a 500 hp number on your dyno, but if I have to power brake on the other type to get 500 hp it is now cheating? Powerbraking the motor puts an actually load on the motor to cause the turbo to boost. Most dyno's themselves will not load an engine up like street use would. So I wouldn't call the numbers skewed at all. I definitely wouldn't let it bother me as long as everyone at the event was treated the same.

 

[jetenginedoctor]

Well then I guess you could consider the load bearing dyno a cheat over the other type?

No, a load bearing dyno is not a cheat. With a load bearing dyno, you can control the rate at which the engine is allowed to rev. With our dyno, we can hold the engine/roller speed at whatever speed we choose at the beginning of the test, load the engine allowing it to build boost, then allow the dyno to ramp up at the rate we choose. By doing so, we can load the engine enough to ensure that the turbocharger is able to do its thing while not hindering it to the point of creating dangerously high EGTs.

Or how is it right to load the truck up one way but not the other?

Powerbraking a turbocharged car on an inertia dyno is a very common cheat that will yield brief HP spike that if done 'correctly' will create a nicely embellished test result. Using a load bearing dyno with an advanced retarder/brake control that can properly control the rate at which the engine may rev enables you to load properly load the engine and maintain the appropriate load needed to allow the engine to produce maximum power without damaging the engine by applying too much load. The two techniques are in no way the same.

Cause the way you are talking you make it sound as though I can lay down a 500 hp number on your dyno, but if I have to power brake on the other type to get 500 hp it is now cheating?

Like I said, if the powerbraking is done just right, it can produce an artificial HP spike on an inertia dyno. Is that cheating to you?

Powerbraking the motor puts an actually load on the motor to cause the turbo to boost. Most dyno's themselves will not load an engine up like street use would.

An inertia dyno might not, but an absorber dyno will.

So I wouldn't call the numbers skewed at all. I definitely wouldn't let it bother me as long as everyone at the event was treated the same.

What about side-stepping the clutch during a run? That'll give a nice spike too.

 

[lmills]

I have no affiliation with any vendors. I am a nail banger for a living. However, to put it from the consumers point of view. You make it sound as though we are wasting our time going to any other type of dyno facility except for ones equipped with dyno's such as yours. Not to mention now we have gone from just power braking to load the engine up to dumping the clutch. Like I said I have no problem as long as everyone at the event is treated the same. So how are you supposed to dump the clutch on an auto? Then you said,

With our dyno, we can hold the engine/roller speed at whatever speed we choose at the beginning of the test, load the engine allowing it to build boost, then allow the dyno to ramp up at the rate we choose.

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

 

[Turbo Thom]

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. .

 

[JFinke]

A load bearing dyno is the standard. It's all that is used in the ag applications as you can apply a % of the tractors rated HP and break in a new engine under a controlled load. If you say you have 500 HP at 3400RPM and run on a load dyno the operator can load your truck to 500HP at 3400RPM and it will be at 500, or if you only have 450HP it will loose rpm and fall on it's face. A load dyno will show what HP an engine is capable of running for a sustained period of time, like pulling a heavy trailer up a long hill. Whatever HP the engine being dyno'ed will maintain at WOT at a constant speed is the max HP. They apply a slow smooth load without spikes. If the operator wants to he can kill the engine by overloading it if he has a higher load dyno than the engine being tested. You can also overload an engine and melt it down if it's overfueled. We normally run all new tracor engines on a load dyno for about 5 hours, 2 hours at full RPM and 100% load.

 

[Jetpilot]

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

 

[RustyJC]

Who knows what one has to do to load the Dyno to get the numbers?

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

 

[lmills]

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 #!

Maybe on the mechanically fueled trucks. But remember the newer electronic controlled trucks are all fueled directed with the boost. Most boxes will not allow the full amount of fueling till you reach a certain amount of boost. So technically you are not making more power because of the boost, but you have to make at least enough to get the full potential out of your set up. Granted it should affect it that much but really, what are they hurting if the dyno operator brakes the mtor till it produces 10,15 or 20 psi of boost?

 

[Jetpilot]

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.

 

[Big MAK]

interesting discussion.



I just dynoed on a dynojet. All I can say is we hit max governed speed and were only making 15lbs of boost; essentially free-wheeling. May as well lift the rearend with a floor jack. We had to drag the brakes to get some boost to build then let it rip; at which point the turbos spooled really nice to the range we see on the street. W/o the braking the engine behavior was not realistic at all. And even with the braking the dyno wasn't measuring the power very well since I know at the levels I was running my clutch would be slipping wildly on the street trying to hold that power -- so common sense tells me we still weren't hitting near the power levels I see on the street.



I don't know which way is right; just my observations.

 

[Jetpilot]

The dynojet is not as hard on your drivetrain as driving your truck on the street is. The drums used just don't cause the same load as you pushing your truck down the street. 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 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.

 

[Big MAK]

I didn't drive it... next time I will! The dyno operator was at the wheel. He drug the brakes while maintaining 1500rpm; spooled the turbos to 10/15 (I didn't have a good angle on my gauge for the low side). I think he should have spooled them to the low 20s and I probably would have had better numbers -- low 20s is where they seem to kick in when I'm driving. Ran it in 6th sine it runs out of RPM in a blink in any other gear. I'd like to figure out the 'best' way to get a good reading out of it. Not 'trick' or 'cheat'... just find an accurate top end.

 

[Jetpilot]

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.

 

[Marco]

I know I always sing a different song...



Let me throw in my 0. 2cents here.



Fact #1, all the calculations the ECM does are LOAD related. Then more load then more fuel...

Fact #2, the turbo needs load ( high combustion chamber pressure ) to spool and produce boost .

Fact #3, all engine dynos provide load to the engine in order to measure it's power.



Based upon these three facts (and my experience ) I dare to say that jetenginedoctor hits the nail on it's head.



I've played with several different dynos, none exept the " load bearing dyno "

is trustworthy.



Marco