Chassis dyno/engine dyno torque

[1972ho]

Does anyone know if engine torque applied to a chassis dyno would be the same on a engine dyno.The reason I ask is I had a engine that made within 2 ft# on the engine that it made on the chassis dyno so is that real.

[PackardV8]

Generally, an chassis dyno reading is 20-25% lower than an engine dyno, due to installed accessories and drivetrain losses.

jack vines

[F-BIRD'88]

With the various many power correction factor algrythums used you can make the printout read what ever you want it to be.
True real uncorrected chassis dyno numbers will always be LeSs Than engine dyno tested flywheel BHP.
Cause there is no transmission/Driveline /tire friction loss on a engine dyno.

You need to know the weather test conditions and power correction factor method used.
A torque converter creates a initial torque spike because it multiplies tirque output when in "stall mode" during initial acceleration. Then at high speed a torque converter is never 100% power efficient.. The amount of power loss can vary a lot depending on design and set up.

[parkman]

The chassis dynos I have been on back calculate torque from the measured HP via a formula relating the engine rpm to the drum rpm. A significant issue occurs with a race type converter where the stall is above the torque peak and the formula no longer works as the engine and drum rpm are not linear. In that situation the torque reading is unusable as the computer goes cross-eyed trying to assign a linear formula to a non linear function. Power readings do not have this issue

I'm highly suspicious of a calculated torque value from a chassis dyno, and only pay attention to torque values with a stick car.

[panic]

IDK if the dyno operators have a correction for different axles: Ford 9" uses more power than a Dana 60.

[HQM383]

Does anyone know if engine torque applied to a chassis dyno would be the same on a engine dyno.The reason I ask is I had a engine that made within 2 ft# on the engine that it made on the chassis dyno so is that real.

Was the chassis dyno run done in top gear?

[Rick!]

The chassis dynos I have been on back calculate torque from the measured HP via a formula relating the engine rpm to the drum rpm. A significant issue occurs with a race type converter where the stall is above the torque peak and the formula no longer works as the engine and drum rpm are not linear. In that situation the torque reading is unusable as the computer goes cross-eyed trying to assign a linear formula to a non linear function. Power readings do not have this issue

I'm highly suspicious of a calculated torque value from a chassis dyno, and only pay attention to torque values with a stick car.

Do you have the paperwork for this dyno? What does it use to measure power first and then back calculate torque? Pump flow maybe?
Every chassis dyno I have used has a torque arm (transducer) that creates the fundamental Torque measurement which is then mathed out for HP.
Water brakes, eddy current and inertial drum measure torque and process power through basic formulae.
Water brakes and eddy currents measure the torque (F cross r) of the stator as the roll and brake resistance try to twist it.
Inertial drums simply use T = I alpha where I is the inertia of the drum and alpha is the angular acceleration of the drum.
Only once in the hundreds of cars I ran across the chassis dyno did I see an advertised power number match the dyno measured power - a lowly 82 305 HO Camaro that Jerry Hansen wanted to run in SCCA.

[parkman]

The drum also has rpm which gives the actual definition of power, time rate of doing work. Another definition of power is F * v, which you have with the inertia, angular acceleration, and velocity.

To back calculate torque at the engine you have to have an engine rpm signal, allowing T = P *5252/rpm. Problem is this is not linear depending on the converter.

[dynoflo]

when you have an engine on a dyno stand you get flywheel tq and hp. When on a wheel dyno your running thru a tranny a driveshaft and a set of rear gears plus tire deflection and traction. Its a whole different situation. I have a water brake dyno for only carbed engines. Wheel dynos are good for fuel injection and all thier electronics. On a water brake engine stand it is very dificult to hook up all electronics with all sensors. I have only done a few injected engines that were taken to wheeled or drum dynos. They were at least 25 percent less than i would of thought they would be. Both dyno operators made more tq and hp by burning new chips. One engine needed the MAF adjusted. Either one will work but be prepared for lower numbers on rear wheel dyoo.