Could you clarify that? A strain gauge needs constant calibration or it isn't accurate in the least bit. An inertia dyno never needs calibration because the drums stay the same weight all of the time unless you take a cutting torch to the drum and cut a chunk out. Dynojet inertia dynos are the most accurate, repeatable dynos on the market and have been the standard since they came on the scene in 1990 and revolutionized the dyno world using inertia and a PC. Today they have load dynos as well as inertia only with the ability to run in either mode.

Erik makes a great point though. No matter which dyno you use, as long as you are making increases you know tuning wise you are going in the right direction. Instead of HP you can call it bananas or walnuts if it makes you happier just as long as you use the same one with the same operator. It is really a measuring stick.

you can get at least 10lbs off a hard rev so take into consideration the rotating mass of the wheels and drivetrain and when you strap the truck down you create more resistance on top of that. Sure, the 2700lb roller add to the resistance unlike spinning your tires freely in the air, thats obvious. Anyone that has been around dynos knows that you can easily take that dyno drum and spin it with the flick of one of your feet. I understand the load cells and footbreaking can work but the calculations still arent correct. Many parameters can change your numbers including gears, different tire size and what gear you do your dyno pull in etc.

You are avoiding the question. You said the Dynojet would show more power but in the same paragraph you said the Dynojet would show less boost. I just wanted to know how that was possible.

Actually gear ratio, tire size, etc. are accounted for on a dyno such as a Dynojet because of the circumference and time of the dyno drum that is used in the calculation. On a Dynojet 248, each drum weighs around 2200 lbs. and they are connectoed with a common shaft. See, it's all about rate of acceleration. That's why a Dynojet is always repeatable every time. When Erik was referring to the foot brake he was saying you can use it at the start of the run before you sample to bring boost up and then release the brake just before you hit the sample button on the remote. This is true for an inertia only dyno run and I've done this quite a bit and it helps a lot. The calculation is not affected by this in the least. You say that load cells work but aren't correct. There are two types of dynos in the market currently and one is an inertia dyno and the other uses a load cell and a brake of some kind whether it be an eddy current (best), water brake or hydraulic brake. No matter what brake you use you will have to use some kind of a load cell to determine the torque being absorbed by that brake. So, you don't like the inertia Dynojet (it should be noted that Dynojet has both kinds of dynos and sells both) and you made it clear you don't think load cell dynos are correct either but that leaves no dynos out there you think are accurate. Do you just not like dynos at all?

Well said, Staarma. DieselKid, your "experience" isn't showing.

well staarma, and "erik" at lcd..i understand the types of dynos and how they work. I never said at any point what i thought footbreaking was specifically for and i understand it is to load the truck to bring boost up prior to doing the test but you still have the same amount of load applied while proceeding through the pull so my point being simply that on the top end throughout the pull (when u are not doing anything that has to do with a footbrake) you loose a few lbs of boost due to lack of load) if you do not agree with that point then i would like you too explain how boost isnt lost relative to the amount of load difference between an inertia style dyno and a load control style dyno please. just because i am not being as descriptive doesnt mean my "experience" isnt showing. I could sit here and write a 6 page description of how each dyno works but i dont. In reality you have no idea who i am or the kinds of things i have done in my very short amount of time in the industry

I'm a load cell guy, myself. I like to see a truck pulled down hard and see the run drag out for 5-10 seconds. Plus, if you have a good operator, he can fine tune the load settings for different turbos. Some take alot of load to spool, and others take very little.

On the other side of that, a good operator can fudge the numbers around to make it look like your making more HP than actual.

Inertia dyno's are great if they are operated by the same guy every time and he does the exact same thing, every time. Then yes, you will get very consistent numbers.

Flip side of this one, well you don't have to be a rocket scientist to figure out how to spike an inertia graph. Just pretend your at the drag strip. When your parking brakes are glowing red, pull the lever and mash the throttle.

In all seriousness though. Dyno #'s are WAYYYYY over rated when it comes to bragging rights. If you can't put that power on the track or behind the sled, what have you really got? A NICE PIECE OF PAPER!!
Dyno's are strictly tuning devices.

You are correct, I do not know you, but I can quote what you said. Hence my "experience" comment.
As for my experience, I have thousands of dyno runs under my belt over the past 6 years. When I got into tuning, I invested over $60k into our dyno and related equipment, and before I did, I researched all of the dynos that were available at the time and I chose Dynojet because they were the simplest and, more importantly, most CONSISTENT dynos out there.
I also made the additional investment in the Load Control unit so that I could effectively and consistently load trucks and do cell-by-cell tuning on racecars using systems like Motec, AEM and Electromotive.
Dynojet has one of the more common units available and therefore has the most data points for comparison. If you want to compare #'s to someone in Sweden or on the East Coast, its likely they are going to have access to a Dynojet and that the numbers they can come up with are going to be fairly consistent despite differences in operator, etc. With units like the Mustang, there are too many opportunities for user error and therefore inconsistency.

Non-loaded Dynojets and footbraking can still deliver very good results, though consistency is hard to maintain. As far as lower overall boost is concerned, that is hard to say as many folks who tune on our dyno (loaded) can go run on another unloaded dynojet with footbraking and get the same and sometimes higher numbers. I attribute this to the dyno more than anything else, but they certainly aren't coming up 20% lower on a non-loaded dyno.

Great points and well said Erik.

Here is a graph of my truck that was run twice when stock. The first run was done on 9/14/04 the day after I bought it. The second run was done 3/18/05. As you can see, the Dynojet 248 I ran on was quite consistent even though it was more than 6 months apart. I ran my own truck personally so the operator had nothing to do with it. Both times I just mashed the go pedal once I hit a green button on the dyno remote and this was the result each time. Now that I'm pushing for 700, and am darn close I might add [laugh], I find myslef hitting the brake down low at each run to get boost up. No matter how many runs I do I hit max boost and it maintains it througout the run. I run in 6th gear now as opposed to 5th or 1:1 gear ratio on a NV5600 and can keep consistent boost numbers. I have run on other dynos and I just choose a Dynojet each time as they are the easiest to run and most consistent by far. They have their ducks in a row and they are on top, way on top, for a reason.
Uncorrected numbers
Attachment 73296

Corrected to SAE numbers, same runs
Attachment 73297

Staarm, to compare across that much time, you should probably show it with SAE correction to account for temp/humidity variance. Probably won't change much, but if you don't someone will call BS!

JFlory, totally agree that they are tuning devices, and agree about the operator being important.

For your point about fudging, this comes up a lot, and mostly by people who don't operate dyno's. You CAN fudge a Mustang to change numbers (input diff gear ratio, weight, etc), but the simplicity of the Dynojet basically won't allow it. I can't fake the RPM pickup and I can't fake how fast the roller goes, so basically I can't fake anything since those are the only data points it uses. I suppose I could intentionally mis-calibrate the torque cell, but that would only tweak the torque reading. HP would be the same and TQ would be high or low (and obviously weird).
The "spiking" thing comes up a lot also. I just don't get what people are trying to say here. If there is a spike, you can see it on the graph. I throw out runs with big spikes as they are usually from a crappy converter coming unlocked or something similar. If you footbrake the hell out of it or load it and then release the load you **might** get a spike. If the HP/TQ immediately drops 100 after the spike and then resumes a normal curve, then the spike (big #) is BS and the rest of the curve is reality. If, however, the curve continues in a normal fashion, then the curve/numbers are still real.
Real spikes sometimes occur with N2O on the dyno also. Here again, if the truck can maintain the curve then it is real (its really doing/maintaining the work) if it spikes and drops then its BS as it would have little bearing on the performance at, say, the drag strip.

Edited my post to show both SAE and actual numbers for same runs.

Dang, Son! It must have been HOT and HUMID that day or you are at some serious altitude

4600 feet. Correction factor is usually around 1.18. [laugh]

Ouch, that is brutal! I would imagine that 62 is even pretty smokey up there, eh?

Yep, she's a little smokey down low but the pressure box and some timing helps a ton.