Pulley mean I no longer have to turn off AC to free up hp?

[N8dawg]

Whenever I engage spirited driving I habitually turn off the AC. However I have a Dinan Underdrive Pulley on order. From my understanding, pulleys keep the car from being robbed of power from the accessories. But does the pulley prevent ALL accessory parasitic loss or will I still be freeing up a couple extra ponies when I turn the AC off?

[disapr]

Definition

An Underdrive pulley refers to an aftermarket crankshaft or accessory pulley (such as an alternator pulley) that is designed to drive a vehicle's accessories at a slower rate than stock. Underdrive in general means the input rate of rotation in a system is greater than the output rate of rotation. However, an underdrive pulley is considered to be an accessory pulley that is larger than the stock pulley, or a crankshaft pulley that is smaller than the stock crankshaft pulley, even though the accessory may not necessarily be underdriven with respect to the crankshaft pulley.

Typical Usage Scenario

Underdrive pulleys usually are marketed as a performance enhancing item that increases the torque and horsepower output of an engine by reducing parasitic drag caused by belt-driven accessories, but more importantly by reducing the moment of inertia. Horsepower gains from underdrive pulleys alone are possible. Independent dyno tests have shown up to 15hp increase at the wheels after installing an underdrive pulley.

Usage Concerns

Poorly designed cheap pulleys or copies and knock-offs of major brands can have severe side effects because of too much underdrive of the alternator, power steering, and/or air conditioning units, which are not spinning fast enough. These lead to dips in alternator voltage, power assist, and air conditioning effectiveness that may be noticeable, especially at idle. The headlights may dim when coming to a stop, or the stereo may lower in volume, for instance. Too much underdrive for a race car is not much of a concern, but for a daily driven vehicle it can be a major annoyance.

Changing the original crankshaft pulley can have negative effects if the replacement pulley is not manufactured properly. A crankshaft or accessory pulley that is not machined or balanced properly can cause severe damage. For most American V8s a harmonic damper is necessary to absorb crankshaft vibrations. Early to mid-year V8's kept the pulley and damper as separate components. Most late model V8s now integrate the damper and the pulley into one part. For small displacement engines (4.0L and under) the original crankshaft pulley only serves to quiet noise vibration and harshness (NVH) you hear in the occupant compartment. Although it may look like a damper on V8s engines it serves no protection function to the engine. It is the same as the baffles and resonators found in the intakes and exhausts systems of most cars today that serve to make the engine as quiet as feasibly possible. The first things most enthusiasts do is install high flow intakes and exhausts; the quieting function is eliminated.


And


Air Conditioner Cutout Relay

The air conditioner (A/C) cutout relay is designed to shut off the air conditioner compressor, by disengaging the A/C compressor clutch. Normally, when the air conditioner is active, the compressor users power from a fan belt to convert refrigerant (R12 or R134a, often referred to as Freon™) from a gas to a liquid. This takes a great deal of power. If the air conditioning compressor clutch is disengaged, the pulley will spin but the compressor won't operate, reducing drag on the engine. There are several normal conditions when the cutout relay is activated:

When the throttle position sensor indicates a wide open throttle (WOT) — in other words, when the gas pedal is floored — the logic module sends a signal to the A/C cutout relay to disengage the air conditioning (A/C) compressor clutch, so more of the engine’s power can be used for acceleration.

The A/C cutout relay keeps the clutch disengaged for 10 seconds after the engine has started, partly to avoid stalling, and partly so the logic module can accurately set the target idle using the AIS motor.
If the idle drops below 500 rpm, the logic module disengages the A/C clutch to prevent the engine from stalling.
If the logic module sees any significant voltage when the circuit should be open (on), or does not see around 12 volts when the circuit is closed (or off), a code 33 is triggered. If the car doesn’t have air conditioning, a code 33 may appear, especially on older vehicles; this can be ignored.

[N8dawg]

Wow thanks for all that. So if I'm getting this straight, when I'm WOT the AC is disengaged? So if I were on an oval track and flooring it the whole time I wouldn't get AC?

[J08M3]

Yes

[ADV.1 Matt]

Is that A/C information M3 specific?

[elp_jc]

The main danger of underdrive pulleys wasn't mentioned above, and it's OVERHEATING, due to underdriving the water pump. This is crucial if you live in a hot climate, or if you track the car. And with the A/C cutting out at WOT, it's one of those things like getting rid of the cats, where better driver training would extract more benefits than the few HP gained by modifying cars in the above described manner. Only scenario where it COULD make sense is for a dedicated track car, but with the water pump issue, I'd think twice even in that instance. To each his own though.

[disapr]

Originally Posted by ADV.1 Matt

Is that A/C information M3 specific?

No, it's general info but to my knowledge the key features are the same on pretty much all cars.

[Singletrack]

Originally Posted by elp_jc

The main danger of underdrive pulleys wasn't mentioned above, and it's OVERHEATING, due to underdriving the water pump. This is crucial if you live in a hot climate, or if you track the car. And with the A/C cutting out at WOT, it's one of those things like getting rid of the cats, where better driver training would extract more benefits than the few HP gained by modifying cars in the above described manner. Only scenario where it COULD make sense is for a dedicated track car, but with the water pump issue, I'd think twice even in that instance. To each his own though.

What "benefits" are extracted? Don't you realize how subjective a statement that is?

Overheating in all caps and how many reported instances of it? Asking? I can't recall any, but if it is a real danger, let's get the word out.

The gain from removing the cats is significant, especially with tuning, so I'm unclear why you would make statements to the contrary. The gain from a pulley, if it can even be shown, is pretty tiny.

Yes, becoming an awesome driver is a better way to go faster around a track. No, not everyone wants to, or has time to do that. Some people want to punch it occasionally, others want to take it to the drag strip, some people just polish the car with a diaper. There is no "right way" to experience or use the M3, although I cringe at garage queens ; ) If it's making you happy, then that's all that matters.

[KGB7]

Its always best to turn off A/C before you go WOT.

[Sean05]

Originally Posted by KGB7

Its always best to turn off A/C before you go WOT.

thats what i do... not hard to do...

[disapr]

You guys do realize that these aren't honda civics right? I used to turn the AC off in my 1.6ltr 4 banger when I needed to pass someone - In THAT car you could really feel the boost in available power. I turn my AC off on the track, otherwise I let the WOT relay handle it when I feel the need for that much throttle on the street.

[tom @ eas]

Originally Posted by ADV.1 Matt

Is that A/C information M3 specific?

This has been commonplace on M models for quite some time.

This is also a primary reason why Macht Schnell pulleys are a 2-piece kit, underdriving both the crank and P/S pulley as a system in order to keep the A/C pulley at the same speed.

[turbo8765]

It's not just M cars, most modern cars disengage the a/c compressor clutch during WOT. The clutch is also generally disengaged above a certain rpm regardless of throttle position.