Terrorist 5.0
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So it is no secret that the 5.0L is a dinosaur of an engine, and leaves some to be desired in terms of performance. One of the first modification people do to take their baby steps in making some more power is an (or a set of) underdrive pullies. However, there are many questions people always ask, and side effects they may be unaware of. I wanted to make this the end all thread on underdrive pullies for newbies (like myself) in the Mustang (or Ford for that matter) world who want to feel a little more kick in the Mustang's step. This will cover mainly 1994-1995 V8 Mustangs, but I will explain some aspects of the earlier ones as well
I ordered and installed an ASP (PN: 523500) underdrive crank pulley and short belt on my car about 5 months ago, and have been daily driving it with no side effects what so ever. Let me begin this by saying, if you have a 94-95 Mustang V8 (so long as it is not a Cobra because those have underdrive pullies installed from the factory), buy yourself a crank underdrive pulley. Yes, it is worth it, yes you will feel it some. It is not earth shattering, but it is noticeable.
So what do underdrive pullies do? They change pulley sizes to change the ratio between the crank (drive) pulley, and the accessory (driven) pullies to change their speeds. To put it simply, the goal is to spin the accessories slower, to reduce the amount of power they are sucking from the engine to drive them. This will allow the engine to use more of its power to spin your wheels, rather than your accessories. There are side effects to this, and they can cause serious engine damage if not considered. Understand that the water pump, alternator, A/C, and power steering are all accessories. Spinning them slower can effect their operation. The smog pump is also an accessory, but most people took that off forever ago. It will not be effected in any noticeable way, although an emissions reading before and after the underdrive pulley would be interesting to see. I doubt it would be an issue anyway. The power steering will feel slightly heavier if the pump is turning slower. A little reduction in pump speed is all fine and dandy. Too much and you risk causing damage to your rack and pinion. They are designed to work with power steering fluid circulating in it under pressure. If that pressure drops too much, it will wear out your rack and pinion faster, or damage it in extreme cases. The A/C compressor does not really have any consequences in regards to turning slower, but your A/C will not be as effective. The two important accessories are what you really need to be considerate of.
The alternator needs to spin to produce voltage and cool itself. Spin it too slow, and it will not produce (or produce enough) voltage and will overheat. If your alternator is always switching back and forth from not being able to produce enough voltage, to working harder to make up for said voltage, as engine RPM moves from idle to cruising or accelerating, this can wear out your alternator. Of course, all parts have some give. They are designed for this to some extent. This doesn't mean it should though. Luckily, the SN95 5.0L's get a 130 amp alternator. The Foxbody 5.0L's only got a 65 amp alternator. The SN95's can handle the alternator being underdriven significantly. As a result of this, you may notice all the lights in your car will dim slightly at idle. This is the effect of the alternator not producing enough juice to keep things running 100%. This upgrade to 130 amps from 65 amps is a good thing though because SN95's have something that the foxes don't. Electric fans, which leads me to my next point.
The water pump is perhaps what you need to be most careful of. Like the alternator, the water pump needs to spin to do its thing, which is circulate coolant through the cooling system. If it does this too slowly, the fluid will not be circulated fast enough through the engine, and will begin to get too hot. You will overheat the engine. Luckily again, all SN95's have electric fans. The foxes don't. They have a clutch fan. This is where the common misconception that the 5.0L is really sensitive to overheating. It isn't. When the car sits idle without air blowing through the radiator, the engine heats up. It needs some sort of cooling. This is accomplished using fans. The issue with clutch fans, apart from sucking power (more on that later), they are directly attached to the water pump, meaning any air the fan pulls in at idle is directly proportional to water pump pulley RPM. Slow that pulley down, and you also end up slowing down the cooling fan, which further reduces cooling, at a time where it is needed most. This is not a problem with electric fans. Again, a lot of this is common sense, if your cooling system is in bad shape, slowing down the water pump is asking for trouble. If it is decently maintained, you should have no issues.
The information above should tell you that while the Foxbody can be temperamental with underdrive pullies, the SN95 will take it with no issues so long as the impacted systems are in decent shape. What kind of gains will you see? You will see more with a Foxbody due to the clutch fan, but on a dyno, anywhere from 4-10 RWHP has been documented. On a stock motor SN95, expect 4-7 RWHP. Again, a Foxbody will show more than that due to the clutch fan.
So if you've decided that you want to install an underdrive pulley (or pullies), there are a couple more things. You can buy a set, which typically comes with a smaller crank, water pump, and alternator pulley to maintain the proper pulley ratio (and thus their full or extremely close to full capacity), or just buy an individual pulley, and experiment yourself. I believe the individual pulley is the way to go. It is cheaper, and will yield more gains by not using other pullies to speed anything back up. This is fine as long as the car can take it. My pulley is a 26% underdrive crank pulley. It spins everything 26% slower. I have my smog pump deleted so I ended up using an AC DELCO 2226MM belt. It was on the looser side but it worked fine. I swapped everything over in the parts store parking lot, and after doing pulls on the same day, about same time, same weather, so basically no variables, I felt a little extra. Nothing much, but for the money, can't be beat. Technically, better fuel mileage would be a result of this modification, but it would be extremely miniscule. Not noticeable. One thing I would suggest, and what I did, is that before you drive your car after the install, start it and let it run. Monitor the temp. Wait for the fans to cycle on and off a couple times. This ensures that the car can self regulate temperature and won't overheat in traffic.
Another thing I did was turn up the idle some. This essentially cancels out any effects at idle by increasing engine RPM, which would bring accessory speed back to normal. I turned my idle up from 600, to 800. It is a number that I feel is perfect for the car. Not low, and not high. Follow the appropriate idle setting procedure when doing this.
I ordered and installed an ASP (PN: 523500) underdrive crank pulley and short belt on my car about 5 months ago, and have been daily driving it with no side effects what so ever. Let me begin this by saying, if you have a 94-95 Mustang V8 (so long as it is not a Cobra because those have underdrive pullies installed from the factory), buy yourself a crank underdrive pulley. Yes, it is worth it, yes you will feel it some. It is not earth shattering, but it is noticeable.
So what do underdrive pullies do? They change pulley sizes to change the ratio between the crank (drive) pulley, and the accessory (driven) pullies to change their speeds. To put it simply, the goal is to spin the accessories slower, to reduce the amount of power they are sucking from the engine to drive them. This will allow the engine to use more of its power to spin your wheels, rather than your accessories. There are side effects to this, and they can cause serious engine damage if not considered. Understand that the water pump, alternator, A/C, and power steering are all accessories. Spinning them slower can effect their operation. The smog pump is also an accessory, but most people took that off forever ago. It will not be effected in any noticeable way, although an emissions reading before and after the underdrive pulley would be interesting to see. I doubt it would be an issue anyway. The power steering will feel slightly heavier if the pump is turning slower. A little reduction in pump speed is all fine and dandy. Too much and you risk causing damage to your rack and pinion. They are designed to work with power steering fluid circulating in it under pressure. If that pressure drops too much, it will wear out your rack and pinion faster, or damage it in extreme cases. The A/C compressor does not really have any consequences in regards to turning slower, but your A/C will not be as effective. The two important accessories are what you really need to be considerate of.
The alternator needs to spin to produce voltage and cool itself. Spin it too slow, and it will not produce (or produce enough) voltage and will overheat. If your alternator is always switching back and forth from not being able to produce enough voltage, to working harder to make up for said voltage, as engine RPM moves from idle to cruising or accelerating, this can wear out your alternator. Of course, all parts have some give. They are designed for this to some extent. This doesn't mean it should though. Luckily, the SN95 5.0L's get a 130 amp alternator. The Foxbody 5.0L's only got a 65 amp alternator. The SN95's can handle the alternator being underdriven significantly. As a result of this, you may notice all the lights in your car will dim slightly at idle. This is the effect of the alternator not producing enough juice to keep things running 100%. This upgrade to 130 amps from 65 amps is a good thing though because SN95's have something that the foxes don't. Electric fans, which leads me to my next point.
The water pump is perhaps what you need to be most careful of. Like the alternator, the water pump needs to spin to do its thing, which is circulate coolant through the cooling system. If it does this too slowly, the fluid will not be circulated fast enough through the engine, and will begin to get too hot. You will overheat the engine. Luckily again, all SN95's have electric fans. The foxes don't. They have a clutch fan. This is where the common misconception that the 5.0L is really sensitive to overheating. It isn't. When the car sits idle without air blowing through the radiator, the engine heats up. It needs some sort of cooling. This is accomplished using fans. The issue with clutch fans, apart from sucking power (more on that later), they are directly attached to the water pump, meaning any air the fan pulls in at idle is directly proportional to water pump pulley RPM. Slow that pulley down, and you also end up slowing down the cooling fan, which further reduces cooling, at a time where it is needed most. This is not a problem with electric fans. Again, a lot of this is common sense, if your cooling system is in bad shape, slowing down the water pump is asking for trouble. If it is decently maintained, you should have no issues.
The information above should tell you that while the Foxbody can be temperamental with underdrive pullies, the SN95 will take it with no issues so long as the impacted systems are in decent shape. What kind of gains will you see? You will see more with a Foxbody due to the clutch fan, but on a dyno, anywhere from 4-10 RWHP has been documented. On a stock motor SN95, expect 4-7 RWHP. Again, a Foxbody will show more than that due to the clutch fan.
So if you've decided that you want to install an underdrive pulley (or pullies), there are a couple more things. You can buy a set, which typically comes with a smaller crank, water pump, and alternator pulley to maintain the proper pulley ratio (and thus their full or extremely close to full capacity), or just buy an individual pulley, and experiment yourself. I believe the individual pulley is the way to go. It is cheaper, and will yield more gains by not using other pullies to speed anything back up. This is fine as long as the car can take it. My pulley is a 26% underdrive crank pulley. It spins everything 26% slower. I have my smog pump deleted so I ended up using an AC DELCO 2226MM belt. It was on the looser side but it worked fine. I swapped everything over in the parts store parking lot, and after doing pulls on the same day, about same time, same weather, so basically no variables, I felt a little extra. Nothing much, but for the money, can't be beat. Technically, better fuel mileage would be a result of this modification, but it would be extremely miniscule. Not noticeable. One thing I would suggest, and what I did, is that before you drive your car after the install, start it and let it run. Monitor the temp. Wait for the fans to cycle on and off a couple times. This ensures that the car can self regulate temperature and won't overheat in traffic.
Another thing I did was turn up the idle some. This essentially cancels out any effects at idle by increasing engine RPM, which would bring accessory speed back to normal. I turned my idle up from 600, to 800. It is a number that I feel is perfect for the car. Not low, and not high. Follow the appropriate idle setting procedure when doing this.
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