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Old 04-18-2017, 10:53 AM   #26
gross polluter
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Originally Posted by Dan Stokes View Post
Inertial dynos (like most DynoJets) are simply a heavy drum that times the rate your car can accelerate the drum which is then translated to a simulated HP number.
How is a direct measurement of work performed over time a "simulated" number?
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Old 04-18-2017, 11:09 AM   #27
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How is a direct measurement of work performed over time a "simulated" number?
That is a super poignant question.
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Old 04-18-2017, 04:00 PM   #28
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Never heard it called a PAU before, but the dyno we had at my last job had one, just thought it was called an eddy brake. Was very useful in hurting brodozer feelings, after they get inflated numbers from inertia dynos and think they're getting low numbers from a loaded dyno so it needs more load.. that eddy brake would flat out shut a truck down at anything over 20% load on the brake.
An Eddy current system is one form of PAU - and a good one. It can apply a load electrically with, basically, an AC motor. There are also hydrokenetic dynos that apply load with either a water brake or a hydraulic brake. The downside of an Eddy current is that they can't provide a motoring load (think of decelerating down a hill) but that's not generally an issue for most dyno work.

The Rolls Royce of dynos are either DC or flux-vectored AC - hugely expensive but able to simulate pretty much any on-road situation you can program into the control computer. The EPA and other emissions labs now pretty much all use the flux-vectored AC systems as made by Horiba (what EPA has) and others. VERY cool systems.

As noted, inertial dynos tend to overestimate the HP values and there's no incentive to fix that as most customers like the higher numbers.

As far as "simulated" numbers: Remember that HP is a calculated value from the formula (torque X rpm)/5252. Inertial dynos do not measure load (torque) so they're making an assumption based on the inertia of the drum and the accuracy of the drum speed - wheel slip is ignored. So there are a lot of assumptions instead of actual measurements.

Let me add a note here that no matter how good the dyno is it's accuracy has to be proven regularly with appropriate calibration techniques. The best (most accurate) dynos have been in service for a while and have a long track record of calibrations that demonstrate not only accuracy but accuracy over time. A dyno with a long history also helps the operator know when something is amiss (or going amiss) because the well-known spot checks show a variance from the dyno's history. A good operator will pick up a potential problem right away BECAUSE HE'S LOOKING FOR IT! I've asked at various facilities when they did their last cal and they look at me like my head's on fire - they think the thing holds cal like, say, an anvil. Ain't so and even if it did they can't prove it. I take my business elsewhere.

If you want more info see if you can find a January 2000 issue of Hot Rod magazine. It has an article I wrote as an overview about dynos and lots of folks have found it helpful. I don't know if it's online or not but if anyone is really interested I can send a Xeroxed copy.

Dan
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Old 04-18-2017, 04:57 PM   #29
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I think you are confused on how an inertial dyno works. Horsepower is work performed over time. That's exactly what accelerating an inertial mass is measuring. No fancy calculations from torque, assumptions, or anything like that. A known horsepower measurement is already there.

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Old 04-18-2017, 05:25 PM   #30
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An Eddy current system is one form of PAU - and a good one. It can apply a load electrically with, basically, an AC motor. There are also hydrokenetic dynos that apply load with either a water brake or a hydraulic brake. The downside of an Eddy current is that they can't provide a motoring load (think of decelerating down a hill) but that's not generally an issue for most dyno work.

The Rolls Royce of dynos are either DC or flux-vectored AC - hugely expensive but able to simulate pretty much any on-road situation you can program into the control computer. The EPA and other emissions labs now pretty much all use the flux-vectored AC systems as made by Horiba (what EPA has) and others. VERY cool systems.

As noted, inertial dynos tend to overestimate the HP values and there's no incentive to fix that as most customers like the higher numbers.

As far as "simulated" numbers: Remember that HP is a calculated value from the formula (torque X rpm)/5252. Inertial dynos do not measure load (torque) so they're making an assumption based on the inertia of the drum and the accuracy of the drum speed - wheel slip is ignored. So there are a lot of assumptions instead of actual measurements.

Let me add a note here that no matter how good the dyno is it's accuracy has to be proven regularly with appropriate calibration techniques. The best (most accurate) dynos have been in service for a while and have a long track record of calibrations that demonstrate not only accuracy but accuracy over time. A dyno with a long history also helps the operator know when something is amiss (or going amiss) because the well-known spot checks show a variance from the dyno's history. A good operator will pick up a potential problem right away BECAUSE HE'S LOOKING FOR IT! I've asked at various facilities when they did their last cal and they look at me like my head's on fire - they think the thing holds cal like, say, an anvil. Ain't so and even if it did they can't prove it. I take my business elsewhere.

If you want more info see if you can find a January 2000 issue of Hot Rod magazine. It has an article I wrote as an overview about dynos and lots of folks have found it helpful. I don't know if it's online or not but if anyone is really interested I can send a Xeroxed copy.

Dan
I dont use my flux vector till 88mph.... oh wait, flux CAPACITOR.... I dont doubt your expertise, but in an effort to refocus the thread, got a nitrous redblock dyno sheet?
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Old 04-19-2017, 10:10 AM   #31
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I dont use my flux vector till 88mph.... oh wait, flux CAPACITOR.... I dont doubt your expertise, but in an effort to refocus the thread, got a nitrous redblock dyno sheet?
Sorry, no Volvo N2O dyno sheets - though it seems like someone MUST have one!

Back to your regularly scheduled programming. (Sorry for the threadjack but it sort of grew......)

Dan
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Old 04-19-2017, 10:50 AM   #32
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Don't worry about your numbers - the dyno shop won't. I did dyno work for a living (I'm retired from the US EPA vehicle emissions lab) so I have a huge respect - and knowledge - of the dyno world. The dyno is, of course, just a tool but a really useful one. If possible find a shop with a dyno fitted with a power absorbtion unit (PAU). A PAU will allow the shop to apply a load at a steady state cruise, a big help for tuning. Inertial dynos (like most DynoJets) are simply a heavy drum that times the rate your car can accelerate the drum which is then translated to a simulated HP number. If you aren't accelerating it applies almost no load at all. They're OK but limited in their uses. The only affordable dyno I have access to is an inertial dyno and we do OK with it though I DO wish it had the afore-mentioned PAU.

Anyhow, what you REALLY want to know is the change in the numbers as a result of the changes you made to the car. That's why it's REALLY helpful to have a baseline.

Another FYI - dyno pros call a chassis dyno "The Rolls", NOT "The Rollers". The "roller" thing is a magazine writer thing - again, they don't know no better!

Dan
I just call mine a dyno. I can do pulls with or without the pau being enabled (load cell, eddy brake, atom bomb, whatever else you want to call it). "the rollers" takes too long to say.

interial pulls are alright, but they don't load the car up the same as the street, so you'd expect some variation from dyno to street with that kind of setup.

FYI-if the correction factors are set up correctly for the PAU, the numbers won't change much if at all loaded vs unloaded (but the parts of the map hit may)
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Old 04-19-2017, 11:07 AM   #33
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I just call mine a dyno. I can do pulls with or without the pau being enabled (load cell, eddy brake, atom bomb, whatever else you want to call it). "the rollers" takes too long to say.
Yeah, but you're not a pro. Don't argue with the self-proclaimed dyno god.
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Old 04-19-2017, 01:28 PM   #34
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meh. I don't have time to argue with any form of deity at the moment, self-proclaimed or otherwise.
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Old 04-19-2017, 02:35 PM   #35
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If I find a dyno god I'll have him/her sign in here. I just did that for a living - in no way god-like.

Now let's give this thread back to the OP!

Dan
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Old 04-19-2017, 04:07 PM   #36
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Mmmmmhhhhmmmmmm

http://forums.hotrod.com/hot-rod/70/...-rod-magazine/



Do you always try and duck out for getting called out on all of your BS?
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Old 04-19-2017, 04:14 PM   #37
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That was a bit of humor right there. I know better than to take myself so seriously - and so should you. Why would anyone refer to themselves as a XXXXX "God" other than in jest? We all ought to know better than that.

As long as you're looking at an ancient HRM post you might as well know that I'm no longer the ECTA Volunteer Coordinator and I no longer own the Camaro with a Chevy six. I AM still retired and still do backyard bodywork along with building interesting cars and race trucks.

That said, I do know quite a bit about dynos, just because I worked with them for 31 1/2 years. There are plenty of folks who know more.

Dan
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Old 04-19-2017, 04:25 PM   #38
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You keep talking about all of these years doing something, and yet it does not change the fact that you have no idea what you're talking about. You do not really seem to get that.

I really can't take someone seriously that qualifies their knowledge with nothing other than a timeframe they can't substantiate, and correcting useless nomenclature. But when you're trying to take such limited aptitude and educate an audience with information that is downright wrong, You'll be corrected by those who know better.

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Old 04-19-2017, 05:17 PM   #39
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Why not just whomever does the highest hp number on Kenny's dyno be called King of Dyno! Like King of Kong. No other Dyno's count...
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Old 04-19-2017, 05:31 PM   #40
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Another TB pissing contest? Yawn!!
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Old 04-19-2017, 05:34 PM   #41
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Another TB pissing contest? Yawn!!
Coming from the guy that can't disambiguate a wastegate from a blow off valve.
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Old 04-19-2017, 05:46 PM   #42
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Coming from the guy that can't disambiguate a wastegate from a blow off valve.
Kool aid man will blow anything. Like the Honey Badger, he don't give a sheet.
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Old 04-19-2017, 06:25 PM   #43
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Coming from the guy that can't disambiguate a wastegate from a blow off valve.
OMG Im dead.


In any event, the nitrous outlet wet kit gets ordered friday.
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Old 04-19-2017, 07:28 PM   #44
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Coming from the guy that can't disambiguate a wastegate from a blow off valve.
I could shove a blow off up your ass maybe it would help deflate your fat head?
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Old 04-19-2017, 07:30 PM   #45
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I came here to see melted pistons and windowed blocks. Where are my pictures? TB is dissapoint.
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Old 04-19-2017, 07:39 PM   #46
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I came here to see melted pistons and windowed blocks. Where are my pictures? TB is dissapoint.
Trust me, thats great content.... If i window a block, i only pray the faux pro from PRC is rolling.

Dear God, please only let my ish blow up in 1080p. Until then, help me go faster, hurt feelings and look cool doing it. Amen.....
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Old 04-20-2017, 11:12 AM   #47
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You keep talking about all of these years doing something, and yet it does not change the fact that you have no idea what you're talking about. You do not really seem to get that.

I really can't take someone seriously that qualifies their knowledge with nothing other than a timeframe they can't substantiate, and correcting useless nomenclature. But when you're trying to take such limited aptitude and educate an audience with information that is downright wrong, You'll be corrected by those who know better.
Not taking your bait. I'm out on this thread.

Dan
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Old 04-21-2017, 08:09 PM   #48
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Not taking your bait. I'm out on this thread.

Dan
Awww dont go Dan, experience is what you have in spades clearly. Verbage is debatable as always on the intraweb, but I honestly appreciate your input, as do probably most lurkers of the forum who may not know dynos. I get trolled constantly, because i constantly put myself out there. I also have a jellybean dispenser on my bench. When I get trolled, I just dispense more jelly bellies. The more I get trolled, the sweeter the day.....
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Old 04-22-2017, 08:39 AM   #49
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Awww dont go Dan, experience is what you have in spades clearly. Verbage is debatable as always on the intraweb, but I honestly appreciate your input, as do probably most lurkers of the forum who may not know dynos. I get trolled constantly, because i constantly put myself out there. I also have a jellybean dispenser on my bench. When I get trolled, I just dispense more jelly bellies. The more I get trolled, the sweeter the day.....
Are you related to Ratmonster?
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Old 04-22-2017, 11:00 AM   #50
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Are you related to Ratmonster?
Nope! Why, does he also indulge in Jelly Bellies?
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