Dyno Tune Motor

[Brad Pfeifer]

Luke, et al,

An engine, on a stand, unloaded, is nothing more than a very expensive fan!

I used the term 'stand' earlier in speaking of the engine dyno stand. What I meant to say was - "It would be better to have an engine come apart on the engine dyno stand than in the car".

There are folks who put their engine on a stand and run it - only to put time on the engine, break it in, or look for leaks - but this is not a dyno.

Luke - to understand the 'force' an engine can generate, it has to work against resistance. No resistance, and its just running (a fan!). Add resistance and you can measure the force. Most of the engine dyno's I have seen use a water to create resistance against the turning power of the engine. Once the engine is up to proper operating temp, the dyno operator will open a water valve to load resistance against the engine. How the engine responds is measured. Torque is the twisting power that is measured, and horsepower is calculated from the torque numbers. These numbers come directly (Direct) from the engine and are more exact. On a chassis dyno, the tires, axle, rear-end, driveshaft and transmission all tax the power a bit, OR act as a buffer on load placed on the engine (Indirect). You have probably seen a couple of posts on "corrected" dyno numbers where folks try to figure out true engine torque or HP (Direct) from the chassis or indirect numbers they have gotten. Generally, there is a 15 - 25% difference.

Now for Fred question, and how it relates - When you load resistance against the motor, the motor has to work. What the motor does against the load is important, hence your questions about tuning. A motor that runs fine without load may stumble under load if it is either too rich or too lean - a fact that will declare itself in the EGT. If I remember right, a lean engine will drive up the EGT under load.

Does that help?

Brad