Wilford Brimley
Is posting from the grave
- Joined
- Jun 26, 2008
- Location
- Marysville, wa
BIG TURBO! HUGE! GIANT! IMPRESSIVE! <a
Hello Guest, welcome to the initial stages of our new platform!
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Thank you for being a part of our community!
Just a "BTW" - NOBODY who actually works with these systems EVER calls it "NOS (naws)". That's a trade name for a company called Nitrous Oxide Systems which is a perfectly decent organization. They DO NOT call the gas "NOS", either. That comes from movie references when writers, clearly not car people, were trying to make the characters sound cool by uttering sounds that simply showed that the writers didn't know the car world. Sadly this has caught on with folks who mostly saw a movie but really aren't car folks either.
So it's N2O or (usually) just nitrous. You'll sound cool and not like a wanna be.
Dan
BIG TURBO! HUGE! GIANT! IMPRESSIVE! <a
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?
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
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?
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.