etec-II underdrive pulley development

[Daox]

I did some more work on the pulley this weekend. But, I also weighed the stock pulley. It comes in at exactly 5.5 lbs. Currently, my pulley is right around 1lb.

[petrified.rabbit]

what software are you using?

depending on price i might buy on just to see if it fits.. but it would be better to try and oem one first.

i imagine the stock on one the ecotec is a little lighter based on the rubber looking insert. but maybe i will take it off for comparison (car is coming of the road next week for rebuild)

[Daox]

I'm using SolidWorks to model the pulley.

Pulling your pulley off would be great to compare. Thanks!

You've probably seen these already, but here are the crankshaft pulley images I took while disassembling the engine. The timing belt section pulls right out of the larger pulley. I'll get some more pictures of it later.

[Daox]

Well, the pulley is pretty much done. I just have one more thing to do, and thats verify the alternator will provide enough output at the new rpm.






I took some time today and ran a couple quick FEAs (finite element analysis) on the pulley to see if it will hold up to the stresses of use. This basically shows me the stress distribution through the pulley. Please note that the deformation of the pulley is for visual effects only, it will not actually deform. I also used very rough numbers for these calculations, so I erred on the conservative side to ensure a good pulley.

[MetroMPG]

Underdrive pulleys designed by Salvador Dali. I like.

[bdc87]

This is coming along well. I can't believe the stocks only weighs 5.5lbs and this one is at 1lb. Can't wait to see it produced and how it effects the rpm's.

[reddemonx92]

So if I may ask what does the underdrive pulley do to the engine?

[MetroMPG]

Underdrive reduces the accessory load on the engine by lowering the accessory RPM. EG: a smaller (underdrive) crank pulley will cause the power steering pump and alternator to spin at a lower rate than stock, reducing drag on the engine.

This frees a small amount of additional power for acceleration. It also marginally reduces cruising power requirements, potentially increasing fuel economy (again, by a small amount).

For more info, wikipedia: http://en.wikipedia.org/wiki/Underdrive_pulleys

[bdc87]

If I can also add to the question above.

The feeling you get from a lightweight crank pulley is not from the hp it frees up but it's ability to spin faster thus pushing you through the rpm's faster. I don't know what it will feel like going from 5.5lbs down to 1lb but, my experience comes from going from a 15lb down to 4lb.

[reddemonx92]

Oh ok thanks for all the info guys. much appreciated. So will it give u like a half a gallon to a gallon more per mile? on the economic side of the pulley