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This was something interesting on the Matrix site. Anyone know about this sort of thing? I like the idea, and I can understand why an automaker would not opt for more expensive lightweight parts, but does using an under drive pulley cause issues with the accessories being driven? If not, why wouldn't all the automakers do this too? Must be some trade off in the balance?http://matrixowners.com/index.php?showtopic=77959

Quote, originally posted by Kincaid »This was something interesting on the Matrix site. Anyone know about this sort of thing? I like the idea, and I can understand why an automaker would not opt for more expensive lightweight parts, but does using an under drive pulley cause issues with the accessories being driven? If not, why wouldn't all the automakers do this too? Must be some trade off in the balance?In terms of cost the numbers ordered by a auto manufacture for OE equipment would make the cost difference within pennys. The issue is that these pulleys under drive the accessories such as the alternator, power steering pump and AC compressor for example in addition to be ligter weight. By slowing the rotation less power from the engine is required to drive them at higher rpms. For example the average P/S pump requires about 1-2hp to turn at idle. At highway speeds this loss could be as much as 3-5hp in a straight line and 7hp when the wheel is turned. In some cars the volume of fluid being pumped by the P/S pump can exceed the volume the by-pass valve can bleed off at over 6500 rpm and loss could spike to over 12hp. Fortunately this is not an issue in the '09 corolla/matrix/ vibe because the power steering is done with an electronic servo eliminating the hydraulic system all together. The next issue is the alternator. Underdriving the alternator reduces the voltage output at any given rpm meaning at idle there would only be enough power made to keep the car running but not charge the battery. While driving the losses for the engine would be lower once the battery is charge back up as if the the engine were running at a lower rpm. If there is a high electrical load the alternator will suck back a lot of power from the engine as it increase electrical output to generate the electrical to meet demand. On a car like the TC with conventional P/S this may not the that big of an issue but on the Vibe with the electric P/S and all the extra power equipment like Onstar, T/C, ESC and ABS as standard equipment the electrical load may put a lot of additional stress on the alternator causing it to fail pematurely if under driven as well as taking more hp to drive it that stock loosing any benefits. Finally many engine are designed to use the mass of the pulley to dampen crankshaft vibrations. They are very sensitive to over and under tightening of accessory drive belt. Light weight underdrive crankpulleys have been know to prematurely cause crank seals to fail, crank bearing to fail and in the worsts case the actual end of the crank to break off. Whether any of this would happen with the engines in the '09+ Vibe has yet to be seen. Manufactures will always tell you the best case storey about there product never about the issues caused by their product.

Thanks for the information. I knew there had to be a downside. I will stay with the well-engineered stock system.My engine mods will likely begin and end with a cold air intake.

Didn't 1st Gen 2zz owners who installed pulley's have their engines go kaput due to damaging the oil pump?Eh... Not worth it in my eyes.

pulleys are safe on the 1zz cause its an interenally balanced motor unlike the 2zz it uses the pulley to make it balancei have been runnning the unorthodox crank and the aem alt pulley for a year and love it but i just swapped out for the matching unorthodox alt pulley just this week to have a matching set