Which Dynamometer Type

Read about how and why each type of configuration has its own strengths and weaknesses.

Basics | 07.20.20

Specify the right design and features for your application! Each type of configuration has its own strengths and weaknesses. The information below will help you decide on what matters most in your unique testing situation.

Step through the questions below. They should help you fine tune your dynamometer shopping list. If you have additional questions, and we are sure you will, please give us a call for some personalized recommendations.

Note: Not all of the questions are applicable to every type of dynamometer.

Review “DYNAMOMETER Tech: HOW THEY WORK” article reprint – originally published in the July/August issue of Kart Racer magazine.

Differences between engine and chassis dynos

Which makes the most sense for your testing? There is so much difference between these two dyno categories that, most of the time, you will have already made this choice. Still, as a reality check, it is worth reviewing the strengths and weaknesses of each type. The list below outlines some of the more dramatic general differences.

Engine DynosChassis Dynos
Requires, labor intensive, removal of engine from vehicleTest right in the vehicle
Excellent accuracy possibleAccuracy subject to numerous driveline-loss variables*
Excellent repeatability possibleRepeatability subject to traction variables
Negligible unmeasured parasitic lossesSignificant unmeasured parasitic losses
Excellent access to most engine componentsAccess to engine components varies greatly by item and vehicle
Supporting ancillary electrical items, pumps,  etc. must be replicatedAll ancillary electrical items, pumps,  etc. are already in place
Excellent range of automated sweep rates and step points availableAvailable sweep rates and test points limited by transmission and inertia
Road-load simulation limited by lack of inertia*Great road-load simulation (assuming right inertia and quick controller)
Relatively inexpensive for level of precision and power capacityRelatively expensive for level of precision and power capacity
Generally utilizes a ventilated and sound dampened roomGenerally utilizes a standard garage bay
Generally requires water tanks and high-capacity pumpsGenerally requires high-volume fans
May require overhead hoist or engine craneMay require a pit or lift (for larger-diameter rolls only)
Well suited for professional engine development programsWell suited  for fuel mapping, general tuning, and Hp shootouts

*Note: There are exceptions to some of these issues. For example: high-end AC absorbers allow road-load simulation of vehicle inertia, while tail-shaft mount absorbers allow performing engine dyno like tests right in the vehicle chassis.

2) Power absorption options – which method is best suited to your needs? Click to a chart comparing most popular dyno loading devices.

3) Chassis-dyno roller options – which diameter and configuration should you choose? We manufacture all types, and consequently, are less biased than many of our competitors. Click to a “Tech-Talk” article about roll-diameter vs. tire-flexing considerations.

Single-Roll (or “Twin-Roll”) ConfigurationsTandem-Roll (or “Cradle-Roll) Configurations
Each tire sits on the top (12 o’clock position) of a single rollEach tire sits nested into a pair of tandem (inline) pair or rolls
Requires strapping vehicle in-place for all testingStrapping vehicle in-place not required during very low Hp testing
Slightly lower parasitic tire losses (for a given roll diameter)Slightly higher parasitic tire losses (for a given roll diameter)
Lower complexity and cost (for a given Hp capacity)Higher complexity and cost (for a given Hp capacity)
Larger diameter rolls allow safe testing at higher speeds and HpSmaller diameter rolls limit accuracy and safety at higher speeds and Hp
Front-rear roll coupling unnecessary, reduces parasitic lossesFront-rear roll coupling, needed for accuracy, increases parasitic losses
Pit or lift (and high ceilings) needed for larger diameter rollsNo pit or lift required
Typically requires permanent placement in test bayOften can be rolled in or out of test bay
Larger diameter rolls increase contact patch area and tractionSmaller diameter rolls increase tire deformation losses and heat
Machined in traction grooves & large diameter = best repeatabilityMachined in traction grooves & coupling = good repeatability
Quieter (smooth-surface models – for NVH testing)Unsuitable for NVH testing
AWD upgrades more expensive than for tandem-roll modelsAWD upgrades less expensive than for single-roll models
Fewer maintenance pointsMore maintenance points

4) Chassis-dyno installation options – should you choose in or above ground mounting? Before you grab a shovel or start planning a three-foot tall set of ramps -ponder these points:

In-ground (pit) installationAbove-ground (ramp or lift) installation
Easiest and safest one-man drive-on loadingRequires extra person to guide safe loading
Minimal impact on bay floor spaceFixed models consume significant bay space
Concrete work and minor excavation requiredNo floor cutting required – great for leased space
Impractical to install in ledge or low water-table areasPractical to install in most areas
Pits cost more than ramps – about as much as liftsRamps cost less than pits – lifts cost about the same as pits
Allows easier access to work on vehicleRamps impede access to work on vehicle – lifts are a bonus
Air and electrical supplies must be routed under floorAir and electrical supplies must be routed across floor or as drops
Floor-level access to vehicleElevated access to vehicle – largest rolls need catwalk

5) Chassis rolling-road versus axle-hub dynos – should you consider a true rolling-road or a PTO mount? As one of the first manufacturers of axle-driven dynos, we have plenty of experience with the comparative advantages and disadvantages of both.

Rolling-road dynosAxle-hub dynos
Quicker mount-test-unmount timesLonger mount-test-unmount times
Traction (slippage) affects resultsZero traction issues
Must be strapped for high-torque transferNo straps required
Strap-down forces affect parasitic tire lossesZero parasitic tire losses
Results comparable to other rolling-roadsResults are not directly comparable to other rolling-roads
Reports “wheel” (at-road) powerReports “in-between” (not wheel or flywheel) Hp
Provides inertia for realistic “off-throttle” simulationsRequire AC-motoring option to simulate “off-throttle behavior
Repeatability subject to traction variablesExcellent repeatability possible
Directly accommodates most vehiclesRequires multiple vehicle hub adapters
Inherent left-to-right wheel speed synchronizationNo pit required
Not easily portablePortable
Well suited for fuel mapping, general tuning, and Hp shootoutsWell suited for in-vehicle engine development

6) Docking-station or portable-stand engine dynamometers – which is right for you? While many of our rolling engine-stand dyno systems are upgradeable to full-blown docking stations, it makes sense to start with what you really need.

Docking-station dynamometersEngine-stand dynamometers
More expensive than equivalent  portable-stand unitsLess expensive than equivalent  docking-station systems
Quick-clamp carts speed swapping between enginesIdeal for shops with only fewer engine to test
Drive-shaft connection adapts to the widest array of enginesRequires specific bell-housing absorber mounts
Designed for dedicated test cellsMobile design (and integral console option) – test anyplace
Boom and patch panel options for dozens of sensorsSelf-contained sub-system and sensor options
Integral left and right-hand starter optionsTakes advantage of engine’s OEM starter
Water brake, eddy-current, and AC absorber optionsWater-brake absorbers only
Highest range of absorber capacities and load curvesSingle or dual-rotor water-brakes
AC motoring option – for professional road-load simulationsLimited road-load simulation capability

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