more stupid questions!

[sracing]

Good on the steam engine. It fools most people.

I see the point you were trying to make with "inertia". As a matter of fact, it is one way brake dyno operators fool the customer re: hp of an engine. If I make the run downward in RPM when applying the load I can use that extra stored "inertia" to pick up a few extra lbs of torque (ie HP) at the RPM range I want.

Jim
SR Racing

[buymeabmwm3]

An electric motor produces max torque at zero RPM. If i remember correctly, it actually produces infinite torque at zero RPM.

[psychorallyfreak]

I think you may have missed the point...
Creating maximum torque at zero RPM, because it has no balls.

[buymeabmwm3]

What?

[sracing]

Originally Posted by buymeabmwm3

An electric motor produces max torque at zero RPM. If i remember correctly, it actually produces infinite torque at zero RPM.

Infinite? Nope. I can hold a 1/4 HP motor back by hand from 0 RPM.

Jim
SR Racing

[CBFryman]

Well just to let you all know. HP is totaly reliant on torque.
Torque is Work. Horsepower is work done over time with speed. HP is a fine way to measure an engines performance. only thing is you also have to look at what RPM that HP is at. sure an S2000 makes 240hp but its at well over normal operating range.
people always say "has good botom end torqe, so it gets off the line quicker" well this is true. if you launch 2 cars from the same RPM. but if you make peak power at 6000RPM then you should launch from there. because This is where you are going to do the most work the quickest. so this is where you are going to accelerate the quickest. good low end torque is great for everyday driving because this means you have more low end HP. but as far as for pure pwerformance a smaller amount of torque doing its work quicker is more valuable.
also, all of the formulas above are for 33,000 lb/ft seconds and Lb/Ft. other ways to rate "Horse Power" often used in europe is in KiloWatts. 1 Hp=746w. and N/M (neuton meters) and Kilogram/Meters is used in countries other than america.
Damn our standard system.
as for the BHP. BHP stands for Brake Horse Power as has been said. this measures horsepower and torque to the flywheel. it uses a brake to put anti rotation force (counter torque) on the flywheel to simulate a load. these are more acurate compared to a cyntrifical or jet dyno but they only rate to the flywheel. what matters is what yo uget to the wheels.
a Cuntrifical dyno measures how quickly an engine can accelerate a very heavy cylender. a Jet duno uses a stream of fluid to create counter torque. both will give a very close figure but if you dyno a car once and then dyno it 5 seconds later on the same dyno it may be a few HP points off and it can be as much as 20hp off between dyno's. Jet Dynos are largely used to measure WHP but cyntrifical dynos are also used.

[sracing]

Well just to let you all know. HP is totaly reliant on torque. Torque is Work.

Nope. Torque is Force only. Usually used in reference to rotational force. It is NOT work.

..also, all of the formulas above are for 33,000 lb/ft seconds and Lb/Ft. other ways to rate "Horse Power" often used in europe is in KiloWatts. 1 Hp=746w. and N/M (neuton meters) and Kilogram/Meters is used in countries other than america.

Nope. HP can be converted to Watts, BTU or Calories / sec, but they all come out to the same when converted. Some countries do use watts interchangably. I think what you thinking of is other countries use of different correction factors. DIN, vs. SAE, STP, etc.

BHP stands for Brake Horse Power as has been said. this measures horsepower and torque to the flywheel.

Often true. But it really refers to the meaurement via measuring torqe(force) with a brake. It can be rear wheel brake horsepower just as easily and flywheel brake horsepower.

it uses a brake to put anti rotation force (counter torque) on the flywheel to simulate a load. these are more acurate compared to a cyntrifical or jet dyno but they only rate to the flywheel.

Nope again.

Actually a brake dyno is usually a bit LESS accurate than an inertia dyno. (What you are calling a jet dyno is probably a Dynojet dyno. This is a brand name. Which can be either a brake or inertia dyno.)
A brake dyno is a bit less accurate in most cases due to it being used to run an engine up and/or down it's RPM range. This is prone to operator error and will measure differently depending upon the rate that the engine is accelerated at as engine component inertia will cause errors.
An Inertia Dyno is all other things equal the most reliable for the actual HP as far as repeatabity etc. It simply measures the amount of time it takes to accelerate a known mass. Usually drums or rolls that equate to about 2000-2500 lbs of rolling mass. This makes calculations very precise with little chance for operator error.

a Cuntrifical dyno measures how quickly an engine can accelerate a very heavy cylender.

Actually it's called an inertial dyno.

..a Jet duno uses a stream of fluid to create counter torque.

Actually it uses a hydraulic brake or eddy current brake to simply hold the engine back. The hydraulic type is usually an impeller in a seal container called the load cell. The Edddy current type is sort of an electric brake.

The brake dyno measures Torque and RPM and computes the HP based upon that. (The Torque is measured with a Strain Gauge or Pressure Transducer of some type. This tranducer is also one reason why it is sometimes not as accurate. They are sensitive to environmental conditions and noise.)

The Inertia dyno simply measures the time it take to accelerate the drum. An accurate timer is all that is needed. It has no other dependencies other than RPM measurement.

..it may be a few HP points off and it can be as much as 20hp off between dyno's.

Then one dyno is simply WRONG and/or the correction factors are wrong and/or the engine is broke. (heat swamp, etc.)

Jet Dynos are largely used to measure WHP but cyntrifical dynos are also used.

Brake Dyno and Inertia Dyno, not "Jet Dyno and cyntrifical" dynos.

BTW, Good dyno shops use wheel dynos that have both Brake (Eddy Current) and Inertia Dynos integrated. It is the ONLY way to accurately test and tune a vehicle.

Jim
SR Racing
(Owners of Chassis Dyno's Eddy Current and Inertia and Engine Dyno's, and lots of other neat toys.)




Jim
SR Racing

[bjdm151]

Jim,

Stop playing so rough,

The word of Jim Schings is law........almost always......... but especially when he signs my pay check!!!!!!