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 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 vs. 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 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 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|