DIY underdrive pulley?

[serialk11r]

Hey everyone,

I'm getting close to closing the deal on a 2ZZ-GE MR2 Spyder and replacing my FR-S, and like any proper car person I'm already thinking about mods.

The 2ZZ-GE is a pretty good engine considering it was designed before the turn of the millennium, and gets pretty good gas mileage. That said, I can't just leave it alone.

The most obvious bolt-on mod for fuel economy is an underdrive water pump pulley. The pulley is driven off the back side (smooth side) of the belt and has no grooves, so that got me thinking...how hard can it be to make/modify a cheaper off the shelf pulley or stock pulley to a larger diameter?

Monkeywrench Racing sells a 6% underdrive pulley, but 0.94^3 = 0.83 is only a 17% power reduction for 70 dollars. How much power that saves is an unknown, although you gain 3hp at 8000rpm supposedly if you use that along with the alternator underdrive pulley (though I imagine a bunch of that is the fact that the alternator rotor is kind of heavy and has significant inertia).

If say the water pump consumes 6hp at 8000rpm, that's something like 230W at 3000rpm (cruising). The underdrive pulley drops that to 190. If I can bump the diameter up to get 12% underdrive, that drops me to 155W (enough savings to power a pair of HID/LED headlights), and gains me 2hp at 8000rpm.

My thinking is that if some plastic can work as a pulley material, I can buy a section of plastic disk or pipe, machine the center out and epoxy it to the stock pulley for the desired diameter increase. Or, 3d print a plastic ring using carbon reinforced plastic and machine it for a smooth finish. The scary bit is that it has to hold up to 8500rpm...thoughts?

[serialk11r]

Also for that matter, what about paying a shop to directly machine a stock crank pulley down in diameter? I guess that would throw the harmonic dampener off, but perhaps some mass could be added by gluing a steel ring to the rim.

[Baltothewolf]

Tbh it's not worth it, I would never mess with the cooling system on a car, especially when it works. You could take that 70$ and buy a looooot or Coloplast for aero mods that would add significantly more mpg.

[ChopStix]

I would checkout summit racing's website as they have numerous off the shelf pulleys in seemingly every size. I would think it would be easier and cheaper to buy one than have one made.

[serialk11r]

Originally Posted by Baltothewolf

Tbh it's not worth it, I would never mess with the cooling system on a car, especially when it works. You could take that 70$ and buy a looooot or Coloplast for aero mods that would add significantly more mpg.

I've learned that when it comes to car parts, $70 is chump change. Any little part you can imagine on many cars costs more than that.

That's not the point though, my point was more that the $70 isn't buying me much underdrive, and I want more.

The 2ZZ idles at 750rpm stock, and it has a properly shaped impeller that flows much more than a typical stamped steel pump. I think it will be just fine spinning 10% slower. Clearance might be a bit tight since the AC, crank, water pump, and tensioner pulleys are so close together, but I think 10% is pretty reasonable.

Any ideas on how to make this not-yet-existent 10% underdrive pulley? 3D printed plastic parts make me nervous, but maybe I'm too paranoid.

For reference this is what the MWR pulley looks like:

[serialk11r]

Originally Posted by ChopStix

I would checkout summit racing's website as they have numerous off the shelf pulleys in seemingly every size. I would think it would be easier and cheaper to buy one than have one made.

Thanks for the suggestion. I see a lot of pulleys here, but I don't know if they'll actually fit the Toyota pump...

The 5.5" diameter March pulley looks like it could possibly work, but again I don't really know. Most of them don't have diameters listed.

Do all water pump pulleys with the 4 bolt pattern have the 4 holes sitting the same distance from the center?

[serialk11r]

McMaster-Carr

1" sections of aluminum tube for cheap! I wonder if it's strong enough to go on a lathe and trim to the necessary ID to fit over the stock pulley.

[ChopStix]

Originally Posted by serialk11r

Thanks for the suggestion. I see a lot of pulleys here, but I don't know if they'll actually fit the Toyota pump...
The 5.5" diameter March pulley looks like it could possibly work, but again I don't really know. Most of them don't have diameters listed.
Do all water pump pulleys with the 4 bolt pattern have the 4 holes sitting the same distance from the center?

In seeing your example image I'm changing my advise.
I would figure out the diameter that meets your needs. Then I would go to a local auto parts store with your pulley and measure/compare it to a mechanical fan's bolt pattern. This would tell you if common fans, like say a chevy or ford v8 fan has the same bolt pattern. If they do then you know which ones from places like summit would work.

If its not the same then call summit's tech support line and explain all of these requirements and size specs to see if they can find one to meet your needs. I believe regardless of how common your bolt pattern is, that they will be able to point you to finding a solution.

I still think it would be worth buying a pulley before making one. Though making one would not be a big deal now that I've seen your image above. Figuring the load the pulley needs to deal with is the only issue with making one. Programs like Solidworks can calculate the stress load in that application, and thus tell you how strong the pulley would need to be, and all the thickness specs, etc.

[redneck]

.

Machining a sleeve shouldn't be difficult.

What width and diameter is the stock water pump pulley ? (exact diameter - measure with a dial caliper)

What material is the stock pulley made of ?

Will the belt tensioner have enough travel left to make up the difference without changing another pulley diameter ?




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[Daox]

I have a 3d printer. Sounds like a fun project and it would be easy to model up if you got me dimensions. Unfortunately, I think I can only got up to 5" diameter max. Price plus shipping would be nowhere near 70 bucks though. If you're interested shoot me a PM.

I did print out a pulley that I bolted to my water pump on the Metro. It was for an electric water pump conversion. I never drove the water pump with the motor though as I'm getting rid of the Metro hopefully this weekend. I to was worried about it holding up to the heat too. But, The pulley was removed not too long ago as I de-moded the car. It held up just fine. I plan on doing something similar with the Insight which is replacing the Metro. Here is the thread and a few pictures.

http://ecomodder.com/forum/showthrea...eap-29896.html