Steve Baur
Former Editor, Modified Mustangs & Fords
October 12, 2006
ProCharger's D-1SC upgrade uses the same step-up or gear ratio that the P-1SC uses along with some other like-sized components. The impellers are where the significant changes occur.

Muscle Mustangs & Fast Fords currently has four supercharged vehicles in its stable, three of which are running and driving, and each one produces or will produce in excess of 500 rwhp.

These days, modern technology has allowed us to generate these truly impressive numbers with just bolt-on performance parts such as superchargers, and at these power levels, we've generally reached the limits of the factory internal engine components and driveline parts with axles, transmissions, clutches, and so on.

Once you have taken the next step of fortifying these areas, there's little doubt you'll want to take advantage of the beefy parts you just installed and turn up the wick in your ride. A pulley change is usually the easiest way to increase boost levels and subsequently power, but it isn't necessarily the best way to go about it. There's a right way and a wrong way to upgrade your supercharged stallion for more pavement-pounding power.

It's critical to consider that while your drivetrain and short-block may be up to the task, your fuel and ignition systems may not, and spinning you supercharger faster might not be the most efficient way of achieving your goals.

During a recent conversation with Dan Jones and Dorian Comeau of Accessible Technologies/ProCharger, both recommended we upgrade the P-1SC blower unit on our 331-powered '90 Mustang GT with one of their D-1SC pieces. We don't normally say no to bigger and better parts, and this time would be no different, but we wanted to know a little more about why they suggested the upgrade for our Mustang project that was running pretty well already.

While we were at it, we figured we would add an Anderson Ford Motorsport Power Pipe and see where things went. The only problem was that the air/fuel ratio during our last dyno pulls was creeping north, from 11.0:1 at 5,000 rpm to 12.5:1 at 6,200 rpm. Ask any good Mustang tuner and they'll tell you that 11.0-11.5:1 is as high as they would like to see a safe tune go.

With a 255-lph pump in the tank, ATI's pusher pump (rated at 240 lph at 43 psi), 42 lb/hr injectors, and an adjustable regulator, we were reaching the limits of the fuel system, which still employed the tiny stock fuel rails and lines.

Your new go-fast goodies just arrived at your doorstep. Does your ride have what it takes to get the most out of them?

While we had hoped to solve the situation by popping on a set of larger aftermarket fuel rails, a call to Brett Clow at Aeromotive in Lenexa, Kansas, opened our eyes a bit to the fuel-supply issue, and had us rethinking our estimation of the possible power increase.

Sure, we expected a 20- to 40-rwhp increase, but the truth of the matter is that between the Power Pipe and the supercharger upgrade we had planned, it was possible we could see nearly double that.

With the 5-liter supercharger kits still some of the biggest sellers for blower companies, this is a scenario that many 5-liter enthusiasts have or will have experienced at some point. Modular-powered Mustangs have it slightly better when it comes to certain areas, but the same information can be applied to those as well.

We have to thank both Comeau and Clow for pointing us in the right direction with our project, and for spending several hours on the phone with us so we could bring you some of their expertise within their respective fields.

Next month, we will bring you the bolt-on bonanza that started this tech article, and show you how to install the induction and fuel system upgrades, and how our ProCharged Pony faired on the chassis dyno.

Supercharger Head Unit Upgrades
Supercharger head-unit specifications differ with every company, so check with the manufacturer, but determining when you need one and which one is right for you is largely dependent on your horsepower goal and engine combination.

Our ProCharged GT has been the subject of numerous tech stories, including "Blown, Stock, and Born to Rock" (Apr. '03), where we installed ATI's 5-liter P-1SC supercharger system on the stock, 140,000-mile '90 GT, and the two-part "331 Ways to Waste an LS1" combo (Aug. and Oct, '04), which detailed the buildup of our low-compression D.S.S. strokr engine.

The 331 easily put us over the 500-rwhp mark, and the increase in cubic inches as well as the new, larger camshaft is moving a lot more air than we were with the stock short-block and cam. In discussing our project with Comeau, he recommended we move up to the D-1SC head unit. "The P-1SC is our 50-state emissions-legal base unit," he says, "and in the 500- to 600-rwhp range, we recommend the D-1SC as its aggressive boost curve works well with modified motors." The D-1SC should fatten up the low-to-midrange torque curve, which may have shifted upward in the rpm band as a result of higher-flowing engine components, while still producing the hard top-end charge we've come to appreciate.

ProCharger's Pro Flo bypass valve (left) is a bit smaller in stature than its race-tested big brother, but it's still capable and sufficient for most blown street cars. Where it is important to vent the extra pressure from high-boost applications, the race valve is well suited with its larger frame and windowed construction.

The P-1SC can be spun harder with smaller pulleys and is rated to 800 hp, but you can sometimes run into belt slippage issues if you are still running the eight-rib serpentine setup. Smaller pulleys mean less surface area that the belts can grip, and if you use a small enough pulley, the belt will have a harder time overcoming the friction of the supercharger's drive system.

Planning ahead can help avoid this and save you money. If you have an idea at the time of purchase that you may well see 500 rwhp and beyond, you can upgrade the P-1SC kit to a D-1SC for just a little over $400. If need be, ATI can supply a larger pulley to detune and lower the boost of the D-1SC until your engine is ready for it.

ATI estimates the D-1SC is good for 3-4 pounds of boost over the P-1SC when using the same sized pulley. If you already purchased a P-1SC kit and major horsepower was a long time in the making, you can send your P-1 back to ATI, and for a tad over $1,200, the company will completely rebuild and upgrade your unit to D-1SC specs.

Beyond that, the F-1 series ProCharger is the next step, and is more than adequate for the rest of the street car crowd as it is rated to over 1,300 hp. If you're making 800-1,000 hp and drive your car a lot, the smaller F-1 models may be a better choice for such continuous duty.

When planning out your supercharged powerplant, intercooler size should also be considered as there are different sizes that may be better for your application, and choosing the right one from the get-go can save you even more.

To Cog or not to Cog?
Most guys think cog drives are cool. After all, they make loud noises and look racy, but they have their place, and it's not anywhere near a street car. "We don't offer cog drives for the P-1SC and D-1SCs," Comeau says. "We don't recommend them, and oftentimes people use them as Band-Aids for other problems."

This is the P-1SC's impeller. Note the straight vanes, which help produce a linear torque curve.

Deciding on what belt system to use depends on the application, the pulley sizes that are used, and the step-up ratio in the supercharger's drive system (step-up refers to the internal gearing that enables the compressor wheel to spin far faster than the engine rpm). A bigger step-up ratio equates to more resistance and a need for more ribs, i.e., a wider belt.

Cog drives are best suited for racing applications where the chances of missed gear changes are almost nonexistent. Over-revving the engine, whether from a missed upshift or wrong downshift selection is hard on the supercharger's transmission and drive system. Cog belts are expensive as well, retailing for around $125 versus $75 for a 12-rib serpentine belt.

Looking at the D-1SC's impeller here, it is easy to see the difference between the two. Check out the aggressive curve to the vanes. From the tip of the vane to where the slope meets the impeller's face is sized differently as well to alter the airflow characteristics.

With the proper pulley sizes, appropriate belt width, and gear ratios ranging from 4.10:1 to 5.40:1, ATI believes it can provide the street guy with a serpentine system that can get the job done. If you need more than that, you're going to have a bigger problem hooking up the tires

Bypass, Antisurge, or Blow-Off
All three of these terms refer to the same mechanical structure, which is a valve that vents the incoming compressed air when the throttle blade is closed. If this pressure is not released, it can damage the supercharger's drive system as well as the throttle body and other components. For now, we'll refer to it as the bypass valve.

ATI offers four different bypass valves beginning with its smallest, the Bosch valve. The Bosch unit features a 1-inch inlet and outlet and is used on some of the base kits. It is good to about 300-350 hp.

Our project car and the P-1SC system that it currently wears was equipped with the next valve up on the scale, the Pro Flo valve. With a 1.5-inch inlet and outlet, the Pro Flo can handle 600-650 hp. ATI is currently developing an intermediate valve as this article goes to print, but beyond 650 hp, you'll need to step up to the race valve which comes in recirculating and open designs.

The recirculating design can be replumbed to dump the air charge back in the intake stream or vented to the atmosphere in blow-through applications. If you're in need of the race valve for your street car, you'll be moving a lot of air through the motor, which will provide a loud discharge sound when the valve opens.

That being said, the recirculating valve will help quiet the issue, if that's your desire. Some people like loud noises though, and after all, that rush of air is what your average import poser considers the Holy Grail of performance.

"The best place to mount the bypass valve is between the supercharger and the intercooler," Comeau says. This protects the supercharger as well as the intercooler cores from the sudden increase in pressure when the throttle shuts.

The recirculating race valve pictured here is for the Mustang making big power but needing to keep the noise down a bit. The single vent can be connected to the supercharger inlet, hence the "recirculating" name.

But this may not be the optimum place should you be employing a blow-through mass air meter, so consult with the manufacturer for the best place. Comeau also says there is no such thing as having too much bypass valve. It's better to have the extra air out than in, so it mostly comes down to performance and price.

If your ride frequently blows off the induction tubes, you may not have enough bypass valve, or it may not be working properly. "We sometimes get tech calls complaining of poor driveability or tuning issues. Oftentimes it is a result of the bypass valve, whether it is too small for the application, or it is not working because there is some sort of interference with the linkage, or it is not getting a good vacuum signal.

How many bypass valves do you need? Well, one should be enough, but you can double up the smaller Pro Flo to get race-valve performance with a quieter sound.

Rumors, Myths, and the Truth
With the Internet, you can find a lot of opinions about things, but your best resource is most likely the manufacturers, as they spend far more time and money in research and develop-ment testing, and know their products far better than anyone else.

That being said, we queried the ATI guys for some of the most common misconceptions they hear. "People often think the blowers' limitations are a result of the impeller becoming inefficient at a certain rpm," Comeau says. "This is not the case, as it has more to do with reaching the limit of the transmission and bearings."

Evidently, a lot of people believe the adjust-ment on the bypass valves control boost pressure, but in fact it only controls the tension on the release spring. ATI sets the tension from the factory, so you shouldn't have to touch it at all.

"People think engine oil cools blowers better, but the fact of the matter is that engine oil temperatures are actually hotter, and increase far quicker than the self-contained oil temps do," Comeau claims.

Fueling the Fire
Failing to provide the appropriate amount of fuel to an engine modified to breathe more air is a sure recipe to turn expensive parts into a mess of molten metal. Ironically, even though it's the fuel that contains all the heat that makes horsepower, most do not think of their fuel systems as a performance modification. Of course, without a fuel system, you wouldn't have any performance at all.

The classic 5-liter Mustang was factory equipped with a return-style fuel system. In this setup, a pump pushes fuel up to the engine and through the fuel rails, then out into a regulator or relief valve designed to restrict fuel flow just enough to maintain a certain pressure for the injectors. Excess fuel is constantly flowing through the fuel rail, whether it is needed or not, and it relies on the regulator to return it to the fuel tank by way of the "return line."

Aeromotive is one of the only companies that sells a complete system designed specifically for 5-liter Mustangs. All of the measuring, cutting, and component choosing has been done for you. All you have to do is install it, and Aeromotive gives you everything you need.

"A return-style system is superior, providing the most effective fuel flow and pressure control to the injectors" Clow says. "It creates a constant flow of fuel over the injector inlet, at the desired pressure." The major drawback to this system is it can heat the fuel by circulating it through the hot engine compartment, increasing chances of vapor lock and creating more evaporative emissions. "Evaporative emission control is why most new cars built after 1999 are required to use a returnless system instead," says Clow.

He continues, "Today's modern returnless fuel systems are now part of the EEC or evaporative emission control system, minimizing heat transfer into the fuel tank, producing less evaporation, and providing new car makers with a cost-effective solution to comply with the latest EPA standards. Ford was the first to completely eliminate the traditional bypass regulator, replacing it with variable pump speed in order to control fuel pressure. Unfortunately, these new fuel systems leave a lot of performance on the table, providing poor pressure control and flowing fuel only to replace what is lost."

The Upgrade Path
"Whether it's the original return-style fuel system of old, or today's returnless system, the 'stock' fuel system can't be pushed much beyond 500 flywheel horsepower, even with modified components," says Clow. "You can beef up the in-tank pump, add a second pusher pump, and install an adjustable regulator, tweaking it to make 500 hp pretty easily. Some have gone as high as 600 hp, but this is the gray zone, where fuel supply can become unreliable."

To make over 500 hp reliably, the whole system should be reengineered. In order to accurately determine what your fuel system needs are, you'll need to take into consideration your total horsepower goal, if it is drag race only or subjected to continuous duty (street driving or open track), and if you are using a power adder and what type.

Boosted engines have different requirements than naturally aspirated engines. This is because it takes horsepower to turn the compressor wheel of a blower or turbo, meaning a supercharged or turbocharged motor making 500 hp at the flywheel makes a good bit more power in the cylinder than an equally rated engine that's naturally aspirated.

The A1000 fuel pump can supply enough fuel for a fuel-injected, 800hp supercharged or turbocharged application.

So the fuel system needs to be able to support all of the horsepower produced in the cylinder, not just what's left over at the flywheel, and with forced induction you need to be able to deliver at higher, boost-referenced, fuel pressures.

With most "bolt-on" supercharger kits, a second fuel pump, placed in series with the stock pump in the tank, is the standard arrangement. Upgrading the in-tank pump can help to increase available flow. "Two pumps, plumbed in series, are able to maintain the same flow at higher pressure than a single pump alone, but the larger external pump can't make the in-tank unit flow more overall," Clow says.

He adds, "The secondary pump usually fails prematurely in these systems because it starves during normal driving, causing cavitation. This releases tremendous energy inside the pump, shocking parts and shortening pump life. Another quick fix with some systems is a fuel pump voltage booster, used to increase the torque of the pump motor, increasing pump rpm under pressure to provide more flow. Unfortunately, this is yet another shortcut and is just one more thing that can go wrong, and it has shown to reduce the longevity of a pump."

To provide both high flow and long pump life, Aeromotive recommends the opposite approach; that is, installing a pump that is able to supply the engine at normal voltage, then using their fuel pump speed controller to reduce pump speed during normal driving. "A fuel pump speed controller such as our PN 16302, actually lengthens pump life, while recycling less fuel, keeping fuel in the tank cooler," Clow says.

Sumped Tank or Fuel Cell
A proper fuel cell or sumped tank plays a key role in controlling fuel at the pickup point, ensuring the pump always has a supply of fuel at the inlet, which prevents air from entering the system. This is critical to both driveability on the street and all-out racing performance.

If your project expenditures come infrequently, you can upgrade your system as funding permits, though it may be a bit more costly in the long run. Aeromotive's fuel rail kit is a great first step as it provides more volume for the injectors as well as an adjustable regulator to fine tune your combination. Be sure the components you choose will work in concert toward a single goal.

If you will be specifically drag racing, and you want to run less fuel in the tank to save weight (gas weighs roughly 6.2 lb/gal), you should seriously consider installing a smaller, racing fuel cell. This will allow the fuel container to be kept full from round to round, avoiding slosh and a dangerous lean condition, while keeping the car as light as possible. If you do a lot of street driving in your Mustang, consider Aeromotive's sumped tank, or if you're the handy type, you can buy the company's new custom sump-box (for steel tanks only) and install it in your own tank.

Clow also warns against using the drop-in pick-up tubes. "Using a pick-up tube is like sucking through a straw, which most people don't do when they're really thirsty. Plus, the Mustang fuel tank draws from a 2-quart reservoir, and you can run into problems with the fuel not replacing itself fast enough. This sort of setup builds more heat in the fuel by recirculating a smaller amount, too. Our sumped tank eliminates all of this as the sump circulates 3 gallons, holding this at the pump inlet all the time."

FMUs-The Good, The Bad, and The Ugly
FMUs, or fuel management units, have been a staple of bolt-on forced induction since the beginning. The purpose of an FMU is to change the rising rate of fuel pressure with boost. Some offer changeable discs and others an adjustable bleeder valve, to "tune" the ratio of boost to fuel pressure increase. Regardless, all raise fuel pressure greater than 1:1. This makes the injectors act bigger than they really are, reducing supercharger kit costs.

"The FMU is a crutch at best," Clow says. "It uses tremendous pressure to force the injector to be big enough, and it comes with a price. Often, midrange performance is poor due to excessive rich conditions, and the fuel pump becomes smaller as excessive pressure reduces pump speed, and flow, to a crawl."

He also warns, "Be careful trying to lean out the midrange; I've seen many try to clean it up by bleeding off boost or changing the ratio too much. Though crisp in the midrange now, this can make it way too lean upstairs, popping a head gasket or worse, the motor."

More Facts on Fuel Delivery
There's no such thing as having pressure but no flow. Pressure is produced as a result of too much flow. Creating and controlling pressure is an act of controlling flow-just look at your bypass regulator to see this in action. As the engine uses more flow, the regulator shuts down the return line, limiting flow back to the tank, to keep system pressure up. When you're out of flow, and the regulator has virtually closed the return line, then the pressure begins to drop.

According to Clow, 99 percent of fuel system problems people experience, where the system should be big enough but isn't getting the job done, are traced to wiring and plumbing problems. Failing to install the correct line sizes, particularly on the inlet side of the pump, or installing a fuel filter that is not rated to flow with the pump, can damage your fuel system and possibly the engine.

Aeromotive's Fuel Pump Speed Controller reduces voltage and subsequently pump speed during low throttle situations. While the pump will be fully capable of fulfilling all of your engine's needs at normal speed, the controller will bump it down a few notches when you're not flexing your fuel injectors pulse widths.

Insufficient wiring of the fuel pump can cut performance by as much as 30-50 percent. To ensure maximum flow under boost reference conditions, use 10-gauge or heavier wire for the pump power and ground, a 30-40 amp relay, a 25 amp circuit breaker (blade fuses and fuse holders are not recommended), and pull the main power wire to the relay directly from the alternator charging stud.

If you're considering a switch from gasoline to methanol or ethanol, you won't be able to support the same horsepower with the same components. In fact, figure on cutting horsepower in half. Gasoline has much more heat per pound then alcohol-based fuels. The stoichiometric air/fuel ratio for gasoline is 14.7:1, compared to 6.4:1 for methanol and 9:1 for ethanol 9:1. Bottom line, it takes about twice as much methanol as gas to make the same horsepower.

"If you really want to know what your fuel system pressure is, don't use liquid-filled pressure gauges," says Clow. They report differently than nonfilled gauges, as variations in operating temperature change the pressure in the case, affecting the reading on the gauge." The hotter the gauge, the lower the reading, but fuel pressure in the rail hasn't changed one bit. A quick fix is to pull the plug in the gauge case and drain the liquid, or buy an air-filled gauge.