An engine dyno is not the "best way" to do it. It's just another way to do it Regardless, if a motor makes 500chp (crank), but only makes 375whp it's better to tune for the drivetrain losses. Of course, this can only be done on a good loading dyno where steady-state tuning can be done.
This brings us to another point. An inertia dyno for anything other than making WOT runs is just an expensive toy. It doesn't have much use other than producing a graph saying you made 'xxx.x' amount of power to the wheels. Even then, the numbers are ordinarily higher than reality.
Inertia only dyno manufacturers eventually got tired of hearing these complaints from their customers and began either incorporating retarders (electromagnetic brakes / eddy currents) into their dynos or simply offering it as an option. There are several problems with this design.
1.) While attempting to hold the vehicle under load, the retarders have a tough job. They're trying to control the entire mass of the roller(s). These rollers can be quite large. You can probably see how this is not a great design? The retarder(s) will do their best to hold at say, 3000rpms, but when modulating through the different throttle and tuning the different load points, the RPMs or wheel speed will have trouble holding and will actually wander around. This makes tuning difficult resulting in longer tuning sessions.
2.) Continuing from above, the wandering gets even worse the longer tuning goes on. The coils in the retarders begin to overheat and you get to a point where they must be cooled down before any more tuning can be completed.
3.) These loading-inertia dynos (some, not all) also can't provide necessary tuning data while holding steady-state like torque or hp. You need this type of feedback so you can see if your increases or decreases of ignition, fuel, boost, etc are making positive or negative gains.
There are several dynos like this on the market. I don't want to get too much into brands, but you'll probably ask which ones they are. Some of the more well known ones offered are; Dyno Jet (retarder offered as an option), Super Flow (retarders standard on inertia units), Mustang (retarders standard on inertia units), Dynocom (I won't even go there LOL), and maybe a couple that I'm forgetting.
So let's talk about low-inertia, loading dynos. These are built around a steady-state design out of the box. Some of these dynos are made by; Mustang, Land & Sea, Dyno Dynamics, Super Flow, Mainline (not well known in the U.S.). The nice thing about these dynos is their ability to hold load in steady-state and do it for long periods of time. They also have a small footprint generally speaking. Some of them won’t give as much data details as others though. For example, Dyno Dynamics will tell you wheel torque, but more importantly will tell you ‘tractive effort’. This is the work that’s being done at the contact patch of the tire. It’s considered far more important than wheel torque. It will also tell you what your wheel horse power is as well all while holding the RPMs steady under load.
Unfortunately, some of these loading dynos have an issue with ‘wandering’ while trying to hold load in lower RPMs. Not quite as important for some of the 4 cylinders (unless running a small turbo), but the big 6s, V8s, V10s and V12s want to tune these areas out easily without the hassle of the load wandering around. The issue goes away the when the RPMs are allowed to be brought up.
Yet, there are more differences. Traction comes to mind first. These low inertia rollers generally incorporate two smaller rollers (rather than one big one). When designed properly, they are able to hold traction better than the large inertia drums and even do it in a lower gear. The reality is that most of these have a belt that connects the rollers. This is why you’ll see some of them state that it is traction limited. It’s not the size of the rollers that’s the problem, it’s the fact that they’re connected together, the knurling design of the rollers, and the strapping method.
Strapping rollers together also creates inconsistent readings. Especially as wheel speed increases, the rollers are forcing the tire to spin at the same speed in between them. This is not desirable since the tire is wanting to turn into (move forward) the forward rollers. The tires then begin to get pinched down between the rollers etc etc.
Dyno Dynamics is designed around a non-belted roller design, meaning that the front and rear rollers are not connected. In fact, the rear rollers are smooth, light, and are independent of each other. While the drive rollers are connected all the way across to the retarder, are light, and have a square cut knurling. The wheels are actually pulled down into the rollers, forcing them to dig. When making enough power, the tires will actually climb up to the 11 o’clock position. If properly strapped down, Dyno Dynamics dynos have held traction to 2000whp and maybe more but no car has ever been able to make more than that (actually 1952whp and the transmission popped).
So why would you want low inertia rollers? For one, some are capable of picking up a single misfire or small detonations. The lighter the roller the easier this is. I can tell you that on Dyno Dynamics, this is the case. Most people are blown away that it can do that. Not to mention, if there's ever a drivetrain malfunction or you pop the motor you can actually slam on the brakes. On an inertia dyno, if you slammed on the brakes to prevent further damage from happening, it would not be a pretty site
Strapping vehicles down on either an inertia style dyno or a loading one is very important for traction. Pretty much, most of the dynos on the market strap the vehicle down by holding it from the front and the rear and the weight of the vehicle is what helps keep traction. Most all of the time, they say you’ve got to be in a 1:1 gear. While true for inertia dynos, not so for most loading ones. On a 5spd, 4th gear would normally be used. Traction is better in 4th than 3rd. Dyno Dynamics dynos are actually designed to be operated in lower speeds, which is impressive since all that power can be held without spinning in 3rd gear.
The next kind of chassis dyno are hub dynos. The most well known is DynaPack. I actually like these a lot as wheel slip is never an issue and is probably the most compact. This is one of the only things I like since getting cars on and off is time consuming. They’re generally more expensive than any of the other chassis dynos and require water hook up. Also, they don’t have the ability to get a good ignition pickup for automatic transmission vehicles. Additionally, they’re reading what’s happening at the hub and not the contact patch of the tire.
Accuracy between all dynos. Some dynos have shown to be very inaccurate. See this article http://www.factorypro.com/maga....html I think most of them can be fairly accurate when following the same strapping procedure each and every time, making sure that tire pressure is up, and testing on the same unit. It’s only when you go from dyno to dyno, same brand everything, but the way one is set up versus another is where the changes begin to happen. On Dyno Dynamics, there’s something called a “Shootout” mode. It fixes all of the variables so that nothing can be changed. This is really nice when you want to compare numbers from one dyno to another. Or even when you have a dyno day and you want the conditions to be the same for each and every vehicle throughout the day.
Numbers. It’s widely known that some of the numbers produced from various dynos are worthless but they do help our egos. I had someone tell me recently that Dyno Dynamics numbers sucked and that the “math” was wrong. He then told me that his Dyno Jet numbers were dead on and how could he sell his customers software with the low numbers like that. I told him that the numbers were real and he said that they couldn’t be because he knows his stuff At the end of the day, what really matters is what the car made, before-and-after results. Those are real-world gains. Besides, take it to the track and see what your trap speed is to back up your dyno numbers. That will tell the tale If someone is supposedly making 400whp (400 real HP to the wheels) then the trap speed should reflect that (providing the clutch is good shape etc).
Graphing. This is huge. To the best of my knowledge, no other dynos out there can produce a live graph as the run is taking place other than Dyno Dynamics. As a matter of fact, I believe it's also the only one that doesn't require 'graph smoothing'. Why you ask? If you need to smooth out a graph, then you've got a problem with the tune. Think about it, if you go back in and 'smooth' out the graph to make it look pretty, you have just hid the important details. Dyno Dynamics doesn't give you this choice, either it looks good or you need to go back and work on it. All the other make you smooth their graph. Generally speaking, the resolution in the graphing is lower on most of the other brands forcing the smoothing issue.
I’m sure there’s a lot more but I don’t feel like typing anymore
Modified by DD Todd at 9:38 AM 2-9-2008
Modified by DD Todd at 9:39 AM 2-9-2008
Modified by DD Todd at 9:45 AM 2-9-2008
Modified by DD Todd at 3:51 PM 2-9-2008