[UnixHH]

How Your Drivetrain Handles Boost

The short answer to this question is both yes and no, so let's start with the basics. (See a comparison of supercharger types here!)

Drive train defined:
The system that transfers power from the engine to the wheels is known as the drive train or driveline. It includes the clutch or torque converter, the transmission, differential, ring and pinion gears, axles, and where applicable drive shaft(s) and transfer case, universal and/or CV-joints.

Power train defined:
The complete system of the engine and the drive train.

Understanding Factory Drive Train Limitations

The drive train in your car or truck is designed, by the manufacturer, to be strong enough to handle full engine power at the vehicle’s load and gross weight limits. Safety margins are factored into each component so that the entire powertrain will survive moments of particularly strenuous conditions. (ex: Shifting an automatic transmission into “Drive” and applying power while the vehicle is rolling in reverse). In some cases, the vehicle’s Powertrain Control Module (PCM) is programmed to identify stressful drive train conditions and take actions electronically to reduce them. One such example of this is where power is reduced during down or up shifting to extend the life of the transmission.

Many systems can also limit torque taking off from a stop. Abusive situations can also be identified by the PCM, such as a driver shifting back and forth between reverse and drive to create a rocking motion, or a high throttle position when putting the vehicle into gear - also known as “the drop shift.” The manufacturer knows exactly how much stress each component can handle under various conditions before it fails. The onboard computer (PCM) provides a way to extend the safety margins of the drive train without installing larger, heavier components. This contributes to higher fuel economy and lower cost.

Are Supercharger Kits Designed With Drive Train Limitations in Mind?

A Supercharger kit is the single best power upgrade you can make to your vehicle. Every supercharger manufacturer goes through extensive design, prototyping, testing, tuning, and qualification of each system before it can ever be brought to market. Most kits are tuned to be installed on otherwise factory-equipped engines. Power levels are specifically tuned not to exceed the critical thresholds of the OEM drive train components. An example of the Supercharger industry’s engineering confidence in their products' effect on powertrain lifespan is MagnaCharger’s 3-year/36,000 mile limited powertrain warranty.

What Affect Do Other Upgrades Have?

As explained, a supercharger kit installed to the manufacturers' specifications will not exceed the factory power train’s capacities. Problems will start to appear as other engine parts are upgraded to increase power even more. There are a few upgrades that will have an adverse affect on the drive train when combined with the supercharger. Here are some examples:

1. High-Stall torque converter. A torque converter multiplies torque from the engine to the transmission by a factor proportional to the rotational speed difference between them. Basically, a higher stall converter alone will cause the transmission to experience momentary input torque levels much higher than a stock converter would.

2. Boost Upgrade. Installing a smaller pulley on the supercharger is an easy way to get more power if detonation can be controlled. This extra power may be in excess of the drive train’s capabilities.

3. PCM Reprogramming. A popular performance modification to the PCM is to remove the Torque Management subroutines that reduce power in favor of drive train preservation.

4. Wider or larger diameter tires. From a drive train’s perspective, larger tires or wider high-traction tires have a similar effect when launching from a stop. Either tire upgrade will reduce wheel spin. Wheel spin actually reduces stress on the entire drive train once it begins. Increasing traction with a tire upgrade will increase driveline stress if the previous tires were able to break traction before.

These upgrades are so effective that together, with the supercharger, failure of a major drive train component is just about guaranteed to happen sooner or later if these components are not also upgraded to handle the additional torque.

Back to the Original Question:

In the never-ending quest for more power, it is this torque that ultimately dooms the weak link. Twin Screw and Roots superchargers make full boost right off idle when you jab the gas. At this instant, the engine may reach its torque peak just as the vehicle begins to move forward. The torque peak of a centrifugally supercharged engine would be seen in the higher end of the RPM range. Launching a centrifugal vs. twin-screw or roots with the same peak boost is therefore less stressful on the drive train and less likely to cause a failure for that reason.

It takes lots of torque to break parts, and twin-screws and roots superchargers make more of it. It is typical to see peak boost levels of centrifugal supercharger kits calibrated and tuned to one or two pounds greater than a roots or twin-screw kit for the same engine. The centrifugal supercharger kits do not have to be de-tuned to keep power levels manageable at low RPM.

Conclusion

Adding power, in excess of what the supercharger kit provides on a stock vehicle, is possible as long as attention is paid to the limitations of the transmission and the rest of the drive train components. If you’re building a torque-monster for towing and the best possible hole shots, driveline upgrades will be required.

Detonation

As you probably have already figured out, detonation (aka "knock") is a big issue in the world of forced induction. You probably know that detonation is a bad thing, and that by adding a supercharger (or any forced induction power adder), you must take additional measures to avoid detonation, especially if your engine has other modifications. Normally the simple solution to stop detonation is to run higher octane fuel... but before we get ahead of ourselves, let's start from the beginning.

What is detonation / knock?

Under normal conditions, the combusting air and fuel mixture inside the combustion chamber ignites in a controlled manner. The mixture is ignited by the spark, normally in the center of the cylinder, and a flame front moves from the spark towards the outside of the cylinder in a contolled burn. Detonation occurs when air and fuel that is ahead of the flame front ignites before the flame front arrives because it becomes overheated. Under these conditions, the combustion becomes uncontrolled and sporadic and often produces a pinging noise, or a "knock" noise when the conditions become worse.

So far, detonation sounds cool... why is it bad?

Detonation is definitely not cool. Detonation causes sudden pressure changes in the cylinder, and extreme temperature spikes that can be very damaging on engine pistons, rings, rods, gaskets, bearings, and even the cylinder heads. Even the best engine components cannot withstand severe detonation for more than a few seconds at a time. More severe detonation obviously leads to more severe forms of engine damage. If there is enough heat and pressure in the combustion chamber, detonation can begin to occur before the spark plug even fires, which would normally initiate the combustion. Under these circumstances, known as "pre-ignition", the piston may be travelling up towards a wave of compressed, exploding gas. These are the worst kinds of detonation conditions, and can bend con-rods and destroy pistons.

What causes detonation?

Detonation occurs when several conditions / factors inside the combustion chamber exist at the same time. Increased compression, high temperatures, lean fuel/air mixture, advanced ignition timing, and lower octane fuels are all factors that PROMOTE detonation conditions. The good news is that, because there are so many factors in play, you can always find a way to eliminate detonation if it exists.

So, where do superchargers fit in?

A supercharger increases the amount of air inside the combustion chamber (see "Bye Bye 14.7 psi"), which in turn increases the compression inside the combustion chamber. Along with increased compression comes higher temperatures and higher pressures, which as we know, tend to increase the chances that some form of detonation will occur. In order to compensate for the increased compression and heat, we must change one or more of the other factors / conditions to move us away from our detonation threshhold. Tuning the supercharger system to the engine in this way for maximum performance without detonation is something that supercharger manufactuers do so, chances are, you won't have to worry about it unless you do other modifications to your engine that place you closer to your detonation threshhold.

How do I get rid of it?

The two most common tricks used by supercharger manufactuers and engine tuners looking to obtain maximum performance without detonation is 1. use higher octane fuel, and 2. retard the ignition timing.

Higher octane fuel burns more controllably and is not as likely to combust before the flame front. This is why racing engines use 100+ octane gasoline. The ONLY benefit of racing gasoline is that it moves you away from the detonation threshhold, which allows you to be more aggressive with power producing factors - i.e. raise compression, advance timing, etc. This is why you'll be disappointed if you put racing gasoline in your mom's bone-stock '82 Toyota Cressida thinking you'll turn it into a race car. If you don't have detonation, the increased octane will do you no good. For cars designed for daily street driving, you obviously won't want to fill up with 100+ octane fuel every week at the tune of 5 bucks a gallon. This is why supercharger manufactuers tune their supercharger systems to run properly without detonation on 91 octane fuel - aka "premium" at your local gas station (in some states premium gasoline is around 93 octane).

Retarding the ignition timing will delay the timing of the spark, which also moves you away from your detonation threshhold. Most popular "power programmers" or "chips" increase engine power by advancing the ignition timing, and requiring you to run a higher octane fuel to avoid detonation. These work great, except the advanced ignition timing is NOT compatible with most superchargers, unless you're happy to run 100 octane fuel. In fact, many supercharger systems include an "ignition boost retard" that retards the ignition timing when it senses boost from the supercharger. This allows you to maintain stock performance while not under boost, yet still remain safe while the supercharger is making its boost (and power).

Another way to avoid detonation is to cool the incoming air charge to lower the temperature inside the combustion chamber. On a supercharged application, this task can be handled by an intercooler (see "Let's Talk Intercoolers") or by a water injection system (less common). The intercooler takes the incoming air charge and passes it over a series of air-cooled or water-cooled fins and ducts, thus cooling the air in the same way that a radiator cools your engine's coolant. Intercoolers are thus very popular in higher output supercharger systems, where detonation becomes more of a problem. Often times, the intercooler allows you to run more boost and also allows you to eliminate the ignition boost retard, meaning you'll notice increased performance, and still experience no detonation. Another way to lower the temperature of the combusting air and fuel is to run cooler heat range spark plugs. Many supercharger manufacturers will recommend cooler plugs for you supercharged engine.

Because lean condition (fuel starvation) also contributes to detonation, it is important to make sure that the fuel system (pump, injectors, etc.) is capable of delivering the increased fuel requirements of the supercharged engine. Often times, an otherwise perfectly tuned engine will experience detonation just because the fuel pump can't deliver enough fuel to the engine. Upgrading certain fuel components is almost always necessary when supercharging an engine. Most supercharger systems normally include the upgraded fuel components if they are necessary. If you are installing a supercharger on an engine with other modifications, make sure you consider the additional fuel requirements and compensate with larger injectors and / or a bigger fuel pump.

Some modern vehicles come with "knock sensors" that listen for detonation, and automatically retard the ignition timing to eliminate detonation. Although these devices are effective in preventing engine damage, they are not tuned for performance, so you should not rely on the knock sensors and expect your engine to run its best.

Conclusion

Altough detonation can be potentially damaging to an engine, a simple understanding of what it is, and what causes it, will help you stay away from your detonation threshhold. Pay attention to "knock" and pinging noises that come from your engine becuase they could indicate detonation inside the combustion chamber and should be dealt with immediately. If you're looking for a new supercharger system, don't worry too much about detonation - the manufacturers have designed the system for use on your stock engine, and if you follow the manufactuer's fuel recommendations, you will not have a detonation problem. If you ever do notice detonation, perhaps from bad (low octane) gasoline or extremely high air temperatures, just drive with a light foot until you are able to resolve the cause of the problem.

--------------------------------------------------------------------------

What is an FMU?

Horsepower is a result of two key components: air and fuel. The supercharger itself, whether a centrifugal, roots, or twin screw, really only provides one of the two major ingredients for making more power. Each supercharger kit is a complete system that increases both air and fuel flow into the engine. A supplemental fuel system upgrade must complete the package.
The FMU Explained

There are several methods used by various supercharger kit manufacturers to deliver supplemental fuel to the engine under boost. An FMU, or “Fuel Management Unit”, is the chief component used for one of these methods. An FMU is often referred to as a boost-dependant fuel pressure regulator. The FMU is essentially a variable fuel-pressure regulator that automatically raises fuel pressure as boost rises.

Depending on the capabilities of the stock fuel pump, a booster pump may be used in conjunction with the FMU. The FMU is downstream (after) of the stock regulator. As boost pressure begins to rise, the FMU starts restricting the flow of fuel returning to the gas tank. Like a garden hose, if the flow is restricted, the pressure increases. The increase in restriction results in an increase in the pressure of the fuel being delivered to the factory fuel injectors. Higher fuel rail pressure enables the fuel injectors to deliver more fuel in the same amount of time than they do at the static stock fuel pressure.





The FMU is calibrated precisely for each supercharger system - a rise in fuel pressure equals a directly proportional rise in boost. The ingenious simplicity of the system means that no computer recalibration is required. Without the FMU, the stock fuel system would not be able to maintain an air-to-fuel ratio low enough to prevent a lean condition. FMU-based systems are the most popular with supercharger kit manufactures.



Other Types of Supplemental Fuel Systems Used With Supercharger Kits

Some supercharger kits take a different approach to supplemental fuel supply. One of these alternate methods, to an FMU-based approach, uses an auxiliary EFI computer. This computer is connected to one or more separate fuel injector(s) installed just before the intake manifold. The auxiliary injector(s) work like a TBI to provide additional fuel to all cylinders. These systems do not require an increase in fuel pressure over stock and, therefore, the fuel flowing through the factory injectors is not increased.

On most supercharger systems, booster pumps are not needed unless the supercharger kit manufacture determines (through testing) that the stock fuel pump is not able to provide enough volume to supply both the factory and auxiliary injectors. These kits do not require recalibration of the factory computer.

The most effective way of compensating for the additional fuel required under boost is to replace all of the factory fuel injectors with higher-flowing ones. This method requires recalibration, or replacement, of the factory computer with a new fuel map appropriate for the new injectors. Replacing all of the fuel injectors is expensive and labor intensive, thus making this fuel system upgrade the least popular among supercharger kit manufacturers.



It should also be noted that some engines are designed with proprietary fuel injection that makes swapping out injectors impossible. Just like the others, supercharger kits getting this fuel system treatment may require a booster pump or replacement of the stock pump depending on the application.

For specific information about which fuel system upgrade is included with each kit, start with our Shop by Brand page and select an application.

Conclusion

So, that's the bare-bones of an FMU. In the next installment, we'll get into more the more detailed and technical aspect of this darling of the Fuel Management program - the FMU.

Getting Technical

The FMU, also know as a “boost dependant fuel pressure regulator,” only increases fuel rail pressure when boost is applied to the reference port on the FMU. This regulator is in the return fuel line and is downstream of the static fuel pressure regulator. The FMU is a simple mechanical device that can be calibrated by changing the internal ring and spacer. Inside an FMU is a piston. The boost pressure comes from the manifold to a fitting on the FMU and applies pressure to a washer sitting on the piston. The larger the washer, the more pressure it applies on the piston. The piston pressure blocks the flow of fuel down the return line. This backup creates a higher line pressure because the fuel cannot freely pass through.

As explained in the previous article, there are two key ingredients to making horsepower: fuel and air. We are going to discuss the most popular methods of increasing the quantity of fuel, to support the air entering the motor under boost, and its relationship to the amount of power you are trying to make.

3 Steps to Delivering More Fuel

Traditionally, there are three most common ways to deliver more fuel to your engine. They are:

Upgrade Your Injector Scenario
Utilize the Power of the FMU w/ Existing Injectors
Use a Computer Programmer to Regulate Fuel Management With Upgraded Injectors
Upgrade Your Injector Scenario

To get more fuel, you can run larger injectors, increase the pressure to the injectors you already have, or add an auxiliary set of injectors. The auxiliary set of injectors usually squirts fuel into the manifold and requires a secondary injector driver to tell the injectors when to fire and for how long. This method is effective for street cars because it lets the car run like normal with smaller injectors. It is also good for cruising because it prevents the motor from overloading with fuel and stumbling. It then allows the second set of larger injectors to give more fuel when you are trying to make power. The major downside is that this method is very expensive because of the additional components required. Furthermore, it can be very difficult to tune because of the wide adjustment range of a completely separate set of injectors. This common dilemma led to the eventual creation of the FMU.

Utilize the Power of the FMU

The FMU is great because it allows the car to run normally on a small injector, but can also increase the rail pressure under boost which, in turn, forces more fuel through the same size orifice. The fuel that the FMU adds has a direct relationship to the boost pressure. The proportionality is usually stated in a ratio, for example 12:1. This means that the FMU will add 12psi of fuel for every psi of boost. (For example, 10psi of boost will add 120psi of fuel pressure.) When all is said and done, this could net a total of about 140psi of fuel pressure which is often too much for a little injector to handle. It is also the reason most people opt for a combination of larger injector and lower ratio of FMU. This is an ideal setup because it allows the same quantity of fuel but at a lower pressure which is more constant for tuning and less fatiguing on the injectors.

Computer Programs and Fuel Management

The third most popular method of increasing fuel is to add larger injectors and use a computer chip to calibrate and control them. This often can cause the car to run great under boost. However, it is often harder to mange when the car is a daily driver or when cold started. Even this method only can supply enough fuel to support a given amount of pressure. Eventually it, too, requires an injector so large that it would not be suitable for any type of street driving - just racing.

Conclusion
This is why the FMU has become so popular. It offers great versatility for street and strip use. You get the ability to support horsepower and still have the street ability of a daily driver. It is also mechanical and not very complex, so there is little chance of having any reliability issues. The final attribute of an FMU, that has make it popular, is its ability to be easily recalibrated (for a relatively low cost) to match the injector choices you make.

[lyobov]

>with the supercharger, failure of a major drive train component is just about guaranteed to happen sooner or later if these components are not also upgraded to handle the additional torque.

Any clue about how many lbs they're talking here before having to upgrade?

[MATT02GT]

[BakerFX4]

dude unix... where you been? Havent seen you on in a while. Ever get your car tuned right?

[lyobov]

Originally Posted by MATT02GT

original.

[03SonicBoom]

The only issue I have w/ this is your bit on the factory drive train limitations. Factory drive train limitations are designed for two failure modes.

One failure is instant failure. This is where one applies a lot of power to a component and it breaks instantly. This failure requires a lot of torque or power. This is the failure mode that the average joe tries to avoid. As long as the manufacturer can avoid this failure for a year or so the average joe will say the part is "reliable" and doesn't really affect the vehicles reliability.

The other failure mode is fatigue. This failure mode is actually harder to design around. This is the most common failure mode out there. This failure is caused from the repeated application of SMALL forces on a material. Think about it; I would bet that one couldn't break a paperclip from just twisting it with such force that it breaks w/out repeated bending. But, one can apply a small bending force over and over again to get the paperclip to break. With an engine operating at several thousand revolutions per minute, these small forces can quickly become a problem due to there frequency.

Now, how does this apply to the supercharger? Well, the factory designs there parts to withstand immediate failure and to withstand fatigue failure for a set lifetime of the vehicle. Now, one can add a supercharger and stay clear of immediate failure of parts by properly tuning the supercharger. This is due to the factor of safety built into this failure mode.
But, the increase in forces is going to increase the rate of fatigue and cut down on the vehicle life. No matter how you want to try and word it, the increase in power is going to cut down on the life of the factory components.

Basically what I'm saying; it doesn't require large forces to break factory components and adding a supercharger is going to reduce the life of factory components.

[~C~]

Down with superchagers!!!!!





Great posts by Unix and Sonic.

[UnixHH]

Originally Posted by 03SonicBoom The only issue I have w/ this is your bit on the factory drive train limitations. Factory drive train limitations are designed for two failure modes. One failure is instant failure. This is where one applies a lot of power to a component and it breaks instantly. This failure requires a lot of torque or power. This is the failure mode that the average joe tries to avoid. As long as the manufacturer can avoid this failure for a year or so the average joe will say the part is "reliable" and doesn't really affect the vehicles reliability. The other failure mode is fatigue. This failure mode is actually harder to design around. This is the most common failure mode out there. This failure is caused from the repeated application of SMALL forces on a material. Think about it; I would bet that one couldn't break a paperclip from just twisting it with such force that it breaks w/out repeated bending. But, one can apply a small bending force over and over again to get the paperclip to break. With an engine operating at several thousand revolutions per minute, these small forces can quickly become a problem due to there frequency. Now, how does this apply to the supercharger? Well, the factory designs there parts to withstand immediate failure and to withstand fatigue failure for a set lifetime of the vehicle. Now, one can add a supercharger and stay clear of immediate failure of parts by properly tuning the supercharger. This is due to the factor of safety built into this failure mode. But, the increase in forces is going to increase the rate of fatigue and cut down on the vehicle life. No matter how you want to try and word it, the increase in power is going to cut down on the life of the factory components. Basically what I'm saying; it doesn't require large forces to break factory components and adding a supercharger is going to reduce the life of factory components.

very true man! thats why modding is so expensive. 1/4 of the money is actually for parts that give you more power and the other 3/4 is on parts to withstand the new power. ie. input shaft, clutch, u-joints,axles, etc......

[BoCFes]

Sticky?!

[lyobov]

Much thanks. So basically anything over stock hp will kill it faster...what is the life of a car these days, provided it's taken care of - 10 years or so? Cuz they sure don't make em like they used to.

[Ke^in]

I guess one could say that a CAI and a tune will make your car not last as long as well..

BTW you can find this exact info here. When copying/pasting another person's text you should always give credit to the original writer. It's just good manners. (BTW I am not trying to accuse the OP of trying to say he wrote it etc)

SuperchargersOnline.com :: Detonation, Knock, and Pre-Ignition 101

And yes, this should be a sticky.

[Eagle2000GT]

Originally Posted by lyobov Much thanks. So basically anything over stock hp will kill it faster...what is the life of a car these days, provided it's taken care of - 10 years or so? Cuz they sure don't make em like they used to.

Sarcasim? You're right, they don't make them like they used to. I remember when a motor with 60,000 miles was considered worn out, when using one quart of oil per 1000 miles was a tight engine, when body rust was common after three-four years, when brakes, tires and shocks needed to be replaced every two-three years, and a tune up (points, plugs and condenser) lasted 12,000 miles at the most.

Even though increased horsepower reduces the life of the motor and drive train, I still expect my motor to last until 180,000-200,000 miles. I'm glad they don't make them like they used to.

[UnixHH]

Originally Posted by Ke^in I guess one could say that a CAI and a tune will make your car not last as long as well.. BTW you can find this exact info here. When copying/pasting another person's text you should always give credit to the original writer. It's just good manners. (BTW I am not trying to accuse the OP of trying to say he wrote it etc) SuperchargersOnline.com :: Detonation, Knock, and Pre-Ignition 101 And yes, this should be a sticky.

i actually do give credit to the ORIGINAL poster which was not the one you posted, but chip wrote it back in 06' Forced Induction (FAQS) - SVTPerformance theres the link.. i just wanted it available for people here as well