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Best Dyno's?

Discussion in 'Technical Q&A' started by ernie, Mar 11, 2004.

  1. ernie

    ernie Two Time F1 World Champ
    Lifetime Rossa Owner

    Nov 19, 2001
    22,022
    The Brickyard
    Full Name:
    The Bad Guy
    Okay, I was wondering with all of the different types of dyno's out there, which ones are the most accurate? Now the most accurate way to get the engine power numbers, would be to remove the engine and get it dynoed. But as for getting the wheel hp/torque numbers, cause that is were the power meets the asphalt, what is the most accurate way to get it dynoed? I have read that different dyno's give misleading numbers, as well as some shops that cheat the results. So which ones are the most accurate?
     
  2. Matt Morgan, "Kermit"

    Matt Morgan, "Kermit" Formula Junior

    Nov 12, 2003
    405
    Ferndale, WA
    In my experience, you are more correct than you realize on the differances between the static Engine Dyno than you think, but there are problems there a well. Haveing run 10,000 HP engine dynos, I can fill ya in on how it is done.
    First off, all accesories are usually left off. That is to say there is no water pump, water is taken from the buildings supply, run thru the motor, then dumped. Secondly, ther is usually no alternator either, an outside power source, needed only to power up the ignition is used. This is why most of the old stats given for a car always read higher than an inertia, or chassis dyno. Simply put, no parasitic losses, so natureally the numbers are more impressive.
    An inertia type dyno uses a precisely weighted roller (usually 850 lbs) that the rear wheels drive. The time/RPM achieved figures are read and calculated in the control computer give it a reasonably accurate method of reading out the HP.
    Now comes the part that really can screw it up for a comparison. Most Dyno operators will have the driver use 4th gear as the choice in which gear to run,as they know that 5th is an overdrive ratio, or over a direct 1 to 1 drive, like .86 to 1. Now they ASSUME (and we have all seen that word broken down) that 4th is direct or 1 to 1, and it is not, in fact different models will have a different drive ratio. Euro models, and Mondials feature different drive ratios with the same basic motor, yet the operator dials it in as a 1 to 1.
    This is the reasoning behind the often drastic differances between advertized HP, and tested in the car. Secondly, it is common for a shop to use its's own "parasitic loss factor" to calculate the crank shaft HP, ergo some use 18% and some perhaps 16% as the loss factor. You can easily see how these variables are easily going to have a direct effect on what gets printed out.
    The "Roller type" dyno is however the most common, and easier to use, as it is simple to take a run, and the #'s are a very valuable source of info on showing impovements, based on runs on the same machine, but motor items changed,such as fuel, ignition, etc.
    HTH
    Kermit
     
  3. Ksullender

    Ksullender Formula Junior

    Sep 3, 2003
    883
    USA
    Great information.
     
  4. ctkellett

    ctkellett Karting

    Jan 2, 2004
    236
    Havertown PA
    Full Name:
    Chris K.
    I worked @ a shop that had a chassis dyno and I can tell you first hand that the dyno # are to taken with a grain of salt. We could make the number say what ever you wanted it to say. This was not our style and we did not do this but the point is that it is not hard to come up with a # first, and then run the dyno to get that those #'s. There are many, many, many factors that go into making up the torque and hp #'s. Instead of repeating or missing some points, here is a link for a fantastic run down of dyno differences and what factors go into it.


    http://www.awe-tuning.com/pages/faq/awefaq_main.cfm?FAQ=22


    All the best

    Chris
     
  5. mk e

    mk e F1 World Champ

    Oct 31, 2003
    11,505
    The twilight zone
    Full Name:
    The Butcher
    To the best of my knowledge, none of them have any real problems. It you just want to make a run, pick the shop you like the best, a good dyno operator is what makes the difference. If you are planing the do turning, ask if they can give you A/F ratio. It helps to get yopu close with less runs. If you are tuning a car with EFI, a brake dyno is a little easier/faster than an acceleration type, but either will work. Then, if you make changes to the car and want to see what how they work, go back to the same dyno or at least the same type dyno.
     
  6. Mitch Alsup

    Mitch Alsup F1 Veteran

    Nov 4, 2003
    6,973
    I will mention that the SHAPE of the curves are MUCH more important than the numbers (peak TQ, peak HP). You should be looking for smoothness in the TQ curve, a broad plateau aroung the peak TQ number, and a slow decent on either side of the plateau. Any dips in the TQ curve are indicative of something not being right (Ignition, detonation, octane, fuel pressure, cam timing, intake and exhaust system flows.)

    If you are simply tuning a car, use the dyno (the same dyno run after run) to see whether any one modification made forward progress or backwards progress or was irrelevent. Look at the shape of the curve not the peak numbers. Use like this requires no calibration to any universal standard, and only requires the operator not to change the dyno calibrations from run to run (days lates).

    Only if you want to compare different cars on different dynos do you need to calibrate the dyno to a reference. This is known as benchracing.
     

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