About Dynamometers

1) Engine versus chassis dynamometers - 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 Dynos*	*Chassis Dynos*
Requires, labor intensive, removal of engine from vehicle	Test right in the vehicle
Excellent accuracy possible	Accuracy subject to numerous driveline-loss variables*
Excellent repeatability possible	Repeatability subject to traction variables
Negligible unmeasured parasitic losses	Significant unmeasured parasitic losses
Excellent access to most engine components	Access to engine components varies greatly by item and vehicle
Supporting ancillary electrical items, pumps, etc. must be replicated	All ancillary electrical items, pumps, etc. are already in place
Excellent range of automated sweep rates and step points available	Available 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 capacity	Relatively expensive for level of precision and power capacity
Generally utilizes a ventilated and sound dampened room	Generally utilizes a standard garage bay
Generally requires water tanks and high-capacity pumps	Generally requires high-volume fans
May require overhead hoist or engine crane	May require a pit or lift (for larger-diameter rolls only)
Well suited for professional engine development programs	Well 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 and tire-flexing considerations.

*Single-Roll (or "Twin-Roll") Configurations*	*Tandem-Roll (or "Cradle-Roll) Configurations*
Each tire sits on the top (12 o'clock position) of a single roll	Each tire sits nested into a pair of tandem (inline) pair or rolls
Requires strapping vehicle in-place for all testing	Strapping 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 Hp	Smaller diameter rolls limit accuracy and safety at higher speeds and Hp
Front-rear roll coupling unnecessary, reduces parasitic losses	Front-rear roll coupling, needed for accuracy, increases parasitic losses
Pit or lift (and high ceilings) needed for larger diameter rolls	No pit or lift required
Typically requires permanent placement in test bay	Often can be rolled in or out of test bay
Larger diameter rolls increase contact patch area and traction	Smaller diameter rolls increase tire deformation losses and heat
Machined in traction grooves & large diameter = best repeatability	Machined 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 models	AWD upgrades less expensive than for single-roll models
Fewer maintenance points	More 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) installation*	*Above-ground (ramp or lift) installation*
Easiest and safest one-man drive-on loading	Requires extra person to guide safe loading
Minimal impact on bay floor space	Fixed models consume significant bay space
Concrete work and minor excavation required	No floor cutting required - great for leased space
Impractical to install in ledge or low water-table areas	Practical to install in most areas
Pits cost more than ramps - about as much as lifts	Ramps cost less than pits - lifts cost about the same as pits
Allows easier access to work on vehicle	Ramps impede access to work on vehicle - lifts are a bonus
Air and electrical supplies must be routed under floor	Air and electrical supplies must be routed across floor or as drops
Floor-level access to vehicle	Elevated 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 dynos*	*Axle-hub dynos*
Quicker mount-test-unmount times	Longer mount-test-unmount times
Traction (slippage) affects results	Zero traction issues
Must be strapped for high-torque transfer	No straps required
Strap-down forces affect parasitic tire losses	Zero parasitic tire losses
Results comparable to other rolling-roads	Results are not directly comparable to other rolling-roads
Reports "wheel" (at-road) power	Reports "in-between" (not wheel or flywheel) Hp
Provides inertia for realistic "off-throttle" simulations	Require AC-motoring option to simulate "off-throttle behavior
Repeatability subject to traction variables	Excellent repeatability possible
Directly accommodates most vehicles	Requires multiple vehicle hub adapters
Inherent left-to-right wheel speed synchronization	No pit required
Not easily portable	Portable
Well suited for fuel mapping, general tuning, and Hp shootouts	Well suited for in-vehicle engine development

6) Docking-station or portable-stand engine dynamometers - which is right for your? 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 dynamometers*	*Engine-stand dynamometers*
More expensive than equivalent portable-stand units	Less expensive than equivalent docking-station systems
Quick-clamp carts speed swapping between engines	Ideal for shops with only fewer engine to test
Drive-shaft connection adapts to the widest array of engines	Requires specific bell-housing absorber mounts
Designed for dedicated test cells	Mobile design (and integral console option) - test anyplace
Boom and patch panel options for dozens of sensors	Self-contained sub-system and sensor options
Integral left and right-hand starter options	Takes advantage of engine's OEM starter
Water brake, eddy-current, and AC absorber options	Water-brake absorbers only
Highest range of absorber capacities and load curves	Single or dual-rotor water-brakes
AC motoring option - for professional road-load simulations	Limited road-load simulation capability

About Dynamometers

Although, as this 1924 photo (at right) proves, dynamometers have been around about as long as automobiles − they have since evolved into much-more complex machines. Below are charts that explain the advantages of various configurations.

"Call for free technical assistance on selecting your own system."