DIY underdrive pulley?

[Baltothewolf]

Doax, how well would that hold up over time though...?

[Daox]

Well, it was on the car all summer attached right to the water pump. Its been spun up and down all through the rev range. Upon removal there were no signs of deterioration or melting/softening. That is about as much as I can say as that is the amount of experience I have with it. If it were my engine, I'd give it a try. I'd also probably run around with the stock pulley, belt, and a wrench just in case until I got comfortable with it.

I also have sold a few other products that easily hold up to engine bay temps that have been in cars for longer than that, but they're farther away from heat.

[Baltothewolf]

Well, I might need a pulley for a supercharger I'm working on so, I'll hit you up when I know more.

[mwilliamshs]

Originally Posted by redneck

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

Fixed it for ya!

[serialk11r]

I don't have my new car yet, but I have calipers I can go measure it with when I do. The stock crank pulley is supposed to be 133mm diameter or so, eyeballing it the stock water pump pulley is something like 105mm

The MWR pulley is still slightly smaller than the stock pulley, so 5"=127mm is probably a greater diameter than the MWR pulley.

I believe the stock pulley is steel since every picture of an old engine has rusty pulleys, so it should be more than strong enough to hold a plastic or aluminum sleeve.

The MWR pulley is aluminum, but thicker than the stock pulley (as it should be). The guy who runs MWR got back to me and said they only went 6% because clearance is tight, so I guess that means I should attempt to make this a cost saving exercise hehehe. @Daox are you interested in some carbon fiber infused filament?

Originally Posted by Baltothewolf

Well, I might need a pulley for a supercharger I'm working on so, I'll hit you up when I know more.

Superchargers typically need quite a bit of torque to drive, are you sure a plastic pulley is a good idea for that? I would go metal for peace of mind.

[mwilliamshs]

A metal rim fixed to an interchangeable hub, perhaps 3D printed, might be a good blend of options. The metal rim would be in contact with the belt so would see the most heat and hold up to the friction there better, while the hub could be designed with a reinforced structure to better resist twisting forces. The water pump is directional so the pulley hub could be made very strong in one direction without concern for its strength in the opposite direction. This also simplifies the matter of diameter, as a large diameter, thick wall piece of say, aluminum driveshaft from the junkyard, or other scrap, could be turned on a lathe to whatever diameter you like, maybe even incrementally.

For that matter, the OE pulley, usually stamped steel with a machined center bore, could be turned INTO a hub just by parting off its rim on a lathe then attached to a separate rim of whatever other diameter would fit. Perhaps find a pulley of the correct outer diameter and take it with your original pulley (or a spare from the junkyard) and have the rim turned off yours, the hub removed from the other, and the two combined by welding or bolting through the resulting flanges. An interference fit here would be very easy to achieve without fasteners but I'd want things at least tacked to withstand vibration. This is how these things were done before there was an automotive aftermarket.

[MPGeo]

For around $130 - $150 you can find you a good quality, good flow rate 12v electric water pump... why not eliminate your pump pulley all together?

[serialk11r]

Originally Posted by MPGeo

For around $130 - $150 you can find you a good quality, good flow rate 12v electric water pump... why not eliminate your pump pulley all together?

Nevermind $130, I'd direct drive the stock pump with a $20 electric motor if I could.

Unfortunately, this is what the serpentine belt looks like:


If the belt skips the water pump, the alternator pulley would have very little belt to pull it since it would only have maybe 100 degrees of wrap. I am not going to take that risk.

[MPGeo]

Can't see the pic... but I you remove your impellers, the pump essentially becomes an idler pulley. Add to that an inline electrical wp and you have essentially removed the wp losses completely... and transfer them to the electrical system...

Your under drive pulley, if you can get away with doing it cheaply, seems to be the best route to go... Keep at it!

[serialk11r]

Originally Posted by MPGeo

Can't see the pic... but I you remove your impellers, the pump essentially becomes an idler pulley. Add to that an inline electrical wp and you have essentially removed the wp losses completely... and transfer them to the electrical system...

Your under drive pulley, if you can get away with doing it cheaply, seems to be the best route to go... Keep at it!

Oh I see, that's a good idea.

However the 2ZZ water pump is a pretty good design (the impeller isn't one of those crappy straight stamped steel vane ones, it's a properly shaped plastic part), and you always need some water flow regardless so I'm more okay with the small amount of energy waste at the water pump.

If we were talking about a Honda S2000 with 9000rpm rev limiter I would probably go electric pump though, since at 9000 the pump is sucking down 30% more power than it is at the 8200rpm Celica rev limit, probably like 4-6hp after you put in a big underdrive pulley.

Contrast that with a power steering pump, which is completely useless 99% of the time. Thankfully, the MR2 has an electric PS pump (which I might remove and make it a manual steering car). The other day I turned the wheel on a Mercedes S550 while it was off, and honestly it was not as bad as I thought. With 1/3 the weight over the front wheels, I'm sure the MR2 can do just fine with manual steering, and that would save ~55W of electrical power or 100W at the crank required to keep the electric pump idling.