NST Pulley Dyno Results

[CASTREX]

Finally some back to back Dyno for the Pulleys!

This is probably one of the more popular mods for the Yaris. NST FTW!


Richard,

Correct me if I'm wrong but some of the benefits from the lightweight/under drive pulleys are not only the power gains (as show in your graph) but also the ability of spin the engine faster and therefore been able to get it faster into the power band?

Same principle as with a lightweight flywheel.

BTW, do you know that Fidanza has a lightweight Flywheel for the Yaris and for the xD. There is another option for the Yaris from SPEC. They run for around $300.
Have you considered throwing one of those into your combo?

Oh, and your observation is accurate the only under driven pulley is the Crank pulley. Is 10% smaller. The Alt and WP are same size as the OE.
NST has an underdrive pulley in the works for the xD as well.

[richardholdener]

This will get a little technical, but the gains from the under drive pulleys come not so much from the chnage in weight but from the change in accessory speed relative to crank speed. You are reducing the parasitic losses associated with driving the accessories. This is a function of the moment of inertia (MOI). Changes in MOI come from changes in weight and changes in diameter (of a rotating object). In the fomula for MOI, the changes in diameter are squared meaning they have much more of a change on MOI than changes in weight. Since you dealing with such a small gain from any change in MOI to begin with on a accessory pulley, the difference in weight has even less effect than a change in diameter (making a small crank pulley). This is why lightweight flywheels usually show little or no gain in power on a dynojet-they are not what is limiting the rate of acceleration of the engine (a change in tire/wheel diamter or weight will have much more of an effect on power than lightweight flywheel). Here is where things get tricky. Lightweight engine components do have an effect, it is just that they have more of an effect when the acceleration rate is increased (free reving the motor for instance) or when a drag race car (a real fast one) accelerates through the gears at a higher rate than can be achieved on a chassis dyno. What all this boils down to is that underd rive pulleys (meaning even larger alt and WP pulleys) will add power more than any change in weight and that a lightweight flywheel would add more power if you make it smaller in diameter, but you are not likely to register any gains with the flywheel on the dynojet. Hope this helps.

Originally Posted by CASTREX

Finally some back to back Dyno for the Pulleys!

This is probably one of the more popular mods for the Yaris. NST FTW!


Richard,

Correct me if I'm wrong but some of the benefits from the lightweight/under drive pulleys are not only the power gains (as show in your graph) but also the ability of spin the engine faster and therefore been able to get it faster into the power band?

Same principle as with a lightweight flywheel.

BTW, do you know that Fidanza has a lightweight Flywheel for the Yaris and for the xD. There is another option for the Yaris from SPEC. They run for around $300.
Have you considered throwing one of those into your combo?

Oh, and your observation is accurate the only under driven pulley is the Crank pulley. Is 10% smaller. The Alt and WP are same size as the OE.
NST has an underdrive pulley in the works for the xD as well.