Turbine Wheel The most exciting technology in the EFR package is the turbine wheel material. EFR turbine wheels are made from titanium aluminide. It’s not the first time this material has been used, but it’s the first time that it has been offered to the public across a range of size options. Titanium aluminide (or Gamma-Ti, for short) is a strange compound. One of those nice examples of the result being greater than the sum of the parts; this compound has temperature capability far in excess of aluminum and titanium as individual elements. Very difficult to cast, this compound is actually an inter-metallic which means that it’s not quite ceramic and not quite metal. One major delivery of this project has been to commercialize this material to be able to introduce it at an acceptable price point. The technical advantage is very simple: low inertia. Since Gamma-Ti has roughly one-half the weight of a typical turbine wheel, the reduction in inertia is substantial especially on the larger wheel sizes such as 64mm and above. The turbine wheel is so light, it is very nearly the same weight as the compressor wheel that is on the other end of the shaft. When you feel one of these parts in your hand, it’s hard to believe it’s a turbine wheel. Then you drive the car and you feel what’s been accomplished. When paired with the ball bearing system, it yields a turbocharger that has no rivals in terms of boost response.

EFR Turbine Housings The EFR series uses the most premium materials and processes for the turbine housings that are currently available. The material is HK30 cast stainless steel which is extremely crack-resistant. Having OE-level durability when used in conjunction with gasoline exhaust gas temperatures means never having to give your turbine housing any worry of failure. It is truly fit for purpose whether that’s street use, road racing, or even endurance racing. Another feature of these housings is the investment casting process. This process is the same as what is used for jewelry-making, yielding intricate detail and fine surface finish. The resulting turbine housing is beautiful inside and out. On the outside, it gives a show-quality finish unlike that of a sand casting. On the inside, the turbine flow enjoys a reduction in flow friction due to the smooth surface.

The part can be easily polished if desired, and either way (as-cast or polished) has a very nice color once heat-cycled. It is naturally corrosion-resistant.

All that being said, the design of these housings is all business. There are four castings that make up the initial release of the EFR series, with more to come. The smallest three of the four are wastegated housings. Two of the four are divided (twin scroll) housings. These four castings can be trimmed for the various turbine wheel options yielding a total of 16 turbine housing combinations. These 16 combinations span a PHI range of 0.020 to 0.048 (see BorgWarner Match-Bot turbo matching tool & catalog for details) to give maximum turbine flow options.

0.64a/r Wastegated (A-Type) The A-Type housing is designed for use with our smallest wheels in the range, the 55mm and 58mm. It uses a “T25” inlet flange shape that is industry-standard for this size. The flange is very compact to the body of the housing in the sprit of making the housing easy to package especially on twin-turbo installations. This tightly-coupled flange requires the use of a manifold-mounted stud through the most confined mounting hole. This hole is closest to the wastegate port and due to the compact size makes for a tight squeeze. The stud can’t be too tall emerging from the manifold or it will interfere with the housing’s surface. The nut must be tightened during the process of lowering the housing onto the manifold. The other three are easy to access (by comparison). The housing volute has a 0.64a/r which is nicely optimized for these two smaller wheels. The wastegate port is a generous 31mm port (36mm valve head) which is significantly larger than virtually all aftermarket housings that came prior. The targeted audience is the owners of smaller “street” engines (1.6L – 2.2L) or users installing a twin-turbo system. All four EFR housings have outlet machining that is designed for use with a 3” v-band. The v-band isn’t actually 3” in diameter, but it’s the common size that is used in conjunction with 3” downpipe tubing. The joint is “half Marmon” meaning that half of the flange is on the turbine housing and the other half of the flange (the other angle) is welded to the downpipe.

0.83a/r Wastegated (B-Type) The B-Type housing is designed for the 64mm, 70mm, 74mm, and 80mm wheels. It uses a “T3” inlet flange shape that is standard for this size. The housing is the “big brother” of the A-type and is very similar in design theme, only larger. The a/r is 0.83 which is within the sweet spot for these wheels and is a balance between response and efficiency performance. The B-Type housing has a very large wastegate: 36mm port and 42mm valve head. This wastegate is truly designed for high flow, even for the big-power users. Gone are the days of needing to buy expensive and bulky external wastegates. This is a real “value” feature of the EFR program. A controversial feature of the “B” housing is the offset outlet. This outlet shortens the axial length of the housing by bringing the outlet down and towards the wastegate port. It also tightens the packaging by putting the downpipe closer to the manifold runners. It also has a functional reason: it favors the wastegate flow and makes that an ultra short and direct shot. So, what’s controversial? It looks unusual, and it appears that it would hurt turbine wheel flow. The housing has been tested with and without the outlet offset and results show that no loss results from it. Keep in mind that 30-40% of the flow is through the wastegate port during high-flow conditions.



0.92a/r Wastegated (C- Type) The C-Type housing is designed for the 58mm, 64mm, 70mm, and 74mm turbine wheels. It uses a “T4” divided inlet flange shape that is standard for this size. The a/r is 0.92 which is also within the sweet spot for these wheels. Being a twin-scroll, it is a little larger than the B-Type sibling. Higher flow is the result but the low-end response is retained (and surpassed) due to the divided nature. As discussed in a previous section, the twin-scroll housing and manifold preserves pulse energy all the way from the engine exhaust blowdown event to the turbine wheel, resulting in low-rpm boost response amplification. The C-Type housing also has a very large wastegate: 36mm port and 42mm valve head. This wastegate seals both branches of the twin-scroll volute since each volute has a wastegate channel leading to the Siamesed outlet port. The C-Type also has an outlet offset, but somewhat less than the B-Type housing.

1.05a/r Wastegated (D- Type) The D-Type housing is designed for the 64mm, 70mm, 74mm, and 80mm turbine wheels. It uses a “T4” divided inlet flange shape. The a/r is 1.05 which is on the high end of optimum and is targeted at the big-power users who want maximum flow yet still very high efficiency, especially in the pre-wastegated operating region. Like the C-Type housing, this part is divided (twin scroll) for the best combination of low-end response and top-end power. The D-Type housing is not wastegated, and as a result the outlet length is very short and without any offset. Like the others, it uses a 3” tube downpipe v-band connection.

Integrated Features Why buy an external BOV? Why buy a boost control solenoid? In addition to buying these items separately and spending more money in the process, the user has needed to mount these parts which gives hassle and headache. The BorgWarner EFR turbos have these parts as integrated features. The CRV (compressor recirculation valve) vents boost quickly and efficiently when the throttle closes, and it is internally-recirculated to keep turbo speed high during the shift and to keep engine control systems (especially those with a MAF sensor) satisfied. The boost control solenoid valve (BCSV) is a convenience feature. Integrating the mounting of these valves onto the compressor cover is a trend we observed from the OE passcar side of the business. As such, you can trust that these are proven solutions that have worked for millions of customers for many years. For those that prefer an external blow-off valve, that’s fine too. We will sell a block-off plate that disables the internal CRV.

CRV We have had great success with integrating the compressor recirculation valve (CRV) into the compressor cover for quite a few years on OE gasoline engine applications. The major benefits are of course the underhood packaging space that is freed up by not having an external device and the cost savings from integrating it into the turbo assembly. Recirculating the flow back into the compressor inlet helps keep MAF engine management systems “happy” and also helps keep turbo speeds high during the shift. The only downside of this feature is the fact that it makes the compressor housing about 1” longer in axial length. For the users that opt not to use the internal valve, we offer a disabling cover plate. This cover plate installs in place of the plastic cover and uses the original diaphragm to seal the port. As a service replacement item, spare plastic cover plates (with hose nipple) are sold as part of a CRV service kit. An external valve (BOV) can be used in place of, or in addition to, the BorgWarner CRV if desired.



BCSV Integrating the boost control solenoid valve (BCSV) onto the compressor cover is another feature that has been widely used for a few years on OE applications. Any user of electronic boost control will need a solenoid valve. We use the highest quality part with OE-level robustness for this application. It is a value to the customer to buy it as part of the assembly so that they save money overall as well as have a tidy mounting solution. Loose BCSV’s will also be sold as a service item in case the original one is damaged. The solenoid valve uses an “injector type” connector, and the BSCV connector itself is marked with a polarity symbol. There are two connections, +12V and ground. The valve is pulsewidth controlled and the wave frequency should be less than or equal to 32 Hz. The resistance of the BCSV coil is 23 Ohms.

Speed Sensor Turbo speed sensors are of course not new technology, but the installation procedure has often (or perhaps always) been difficult for the end user. Competing products require the customer to remove their compressor cover and take it to a machinist. This machinist then has to set up the cover at a compound angle to precisely drill the speed sensor bore while carefully hitting the contour area of the wheel bore and at the right angle

The BorgWarner EFR solution provides this precision machining already done to the compressor cover. The hole stops short of protruding into the compressor wheel bore. If a user decides to buy a speed sensor as an upgrade accessory, they can remove the compressor cover and extend the hole the rest of the way through to the wheel bore using a hand drill. A 1/4” drill bit is used and the length required to be drilled is quite short. This hole allows the tip of the sensor to come flush with the contour surface. The hole does not have to be precise, as no sealing takes place in the small hole that the user just created. The hole should be de-burred where it pierces into the wheel bore. The goal is to make sure that there are no sharp edges remaining in the wheel bore that the compressor can become snagged on.

Over the past couple months we have been collaborating with Borg Warner engineers and Full Race Motorsports to Release an aftermarket turbine housing that is a little more mainstream than what Borg Warner is offering for the EFR turbo line up including non-wastegate T3 housings.

After a few months of these turbos being on the market, we have been gathering data from multiple sources who are currently running and testing these turbos, and all of the feedback will be going into our final design. We have multiple designs in the process, and have not finalized a final prototype just yet. The three designs you see here are which will most likely be released as T3 inlet, 3" V band outlet, and a V band in/out style. Optimization of this housing for the multiple size wheels Borg Warner provides is going to be the tricky part, and where spool up vs. top end HP for a particular size compressor/turbine wheel combo will be scrutinized. Stay tuned for a final release date!      

The BorgWarner EFR series is a combination of all the leading edge technology available today. On such combination is there aerodynamics of which inducing the compressor technology known as Extended Tip Technology. There are six compressor wheel sizes within the EFR product range. 62mm, 67mm, 70mm, 76mm, 83mm, and 91mm. The two smallest wheels (62mm and 67mm) offer very large map width while still enabling high-boost operation. Very important for small engines striving for peak torque at streetable engine speeds, these compressors offer surge line positions that are far to the left on the map without needing a cover recirculation slot and cavity. The wheel itself is designed to not need an inducer recirculation slot, but furthermore it helps solve packaging problems due to the 2.5” inlet hose connection. Through a high backsweep angle on the blade outlet and our Extended Tip Technology on the exducer tip, these wheels offer excellent range (flow capacity) while still being capable of high boost at reliable turbo speeds. Both the 62mm wheel and 67mm wheel employ a large 80% inducer trim (64% on an area basis). The rest of the compressor wheels (70mm through 91mm) are of a different design. These Extended Tip Technology wheels are very unique in that they are our highest-boost capable wheels but still give outstanding map width and flow capacity. The compressor cover treatment includes an inlet recirculation groove for maximum width and anti-surge characteristics. A new trim set was developed for this program on these wheels, which is 75% trim (56% on an area basis). This large trim gives up a very small amount of efficiency but for a significant gain in flow capacity. The only trim exception is the 91mm version. This part is released at 74% trim as to maintain an inducer diameter that is compliant to some specific drag racing class rules.

The EFR product line features compressors ranging from 62mm OD (~50mm inducer) to 91mm OD (~68mm inducer). From this, the 70mm through 91mm compressors are designed for high-boost (30+ psi) capability. The smaller 62mm and 67mm wheels are from a different design family, used for “medium” boost but very large flow range. Due to their small size, paired with other technologies like the Gamma-Ti turbine and ball bearing system it yields an extremely responsive system specifically targeted at small engines or twin-turbo installations.

The material chosen for all 6 compressor wheel sizes is forged aluminum, fully milled. Also known as “billet”, these wheels are as amazing in appearance as they are in function. Cut from custom forgings, their strength exceeds that which is available from typical bar-stock and also exceeds the material properties of an aluminum casting. The 62mm and 67mm wheels feature an 80% diameter trim (64% on an area basis), giving them a very high-flow characteristic. They are uniquely capable of having this trim while still having acceptable stress levels, blade frequencies, and boosting capability. The 70mm, 76mm, and 83mm wheels have 75% diameter trim (56% on an area basis) which gives them optimized flow, strength, and high boost capability. The 91mm wheel is trimmed slightly smaller (74% diameter; 55% area) to fit within some specific drag racing class rules. All six EFR wheels feature our Extended Tip Technology. Just as on the S200SX, S300SX, S400SX, and S500SX lines, this feature amplifies the boost pressure and flow capabilities for a given wheel size. This BorgWarner feature has been a segment-leading technology for many years and it is continued here with the EFR series. We investigated the use of an abradable coating on the compressor cover and got mixed results. Sometimes it yielded an efficiency and boost pressure gain but other times it did not. It also had mixed effects during the startup and cut-in process; effects that are all in need of further study. This feature will continued to be evaluated by the BW team and might be released at a future date either on EFR or Airwerks products, or perhaps both.

Three all-new compressor cover castings have been created for the EFR product line. For the purposes of this text, let’s call them “A”, “B” and “C”. All three have some common features: First, they are retained to the bearing housing with a v-band which helps for easy orientation adjustment. Second, they have intregrated CRV (Compressor Recirculation Valve) ports and mounting. Third, they provide a mounting pad for the boost control solenoid valve (BCSV). “A” Compressor Cover This casting is used with the 62mm and 67mm compressor wheels and has a compact non-recirc inlet size. Designed for smaller packaging spaces, a 2.5” inlet hose connection is used. The outlet is machined for a 2” hose connection. As mentioned above, the CRV and BCSV mounting features are included. The volute a/r is 0.46.

“B” Compressor Cover This casting is used with the 70mm and 76mm compressor wheels and features a recirculation (“recirc”) groove. This groove surrounds the leading edge of the compressor wheel and provides an escape path for air on the tip of the wheel. In the process, the surge margin is extended when operating on the left side of the compressor map. On the right side of the map the operating range is also extended. In this zone, air is admitted through the port and into the wheel. The function of the recirc groove is very different than that of the CRV. The recirc groove is in operation all the time. The CRV operates only during a throttle-closing event and helps prevent compressor backflow and related compressor surging. The inlet connection on this cover is sized for a 3.5” hose and the outlet is for 2” hose. Otherwise, it’s very similar in size and shape to the small cover. Again, the CRV and BCSV features are integrated. The volute a/r is 0.5.

“C” Compressor Cover This casting is used with the 83mm and 91mm compressors and also features a recirc groove and cavity. Due to the larger size wheel bore, a 4” hose connection is used. The outlet connection is also larger, being sized for a 2.5” hose ID. This outlet is unique because it can also be modified for a v-band connection. The hose connection can be cut off and then a hard-mount piece (such as an elbow or tube assembly) can be clamped on. The 0.57 a/r volute shape of this cover is one of our long-time staples, having been also used in our popular S300SX and S400SX lines. Again, the CRV and BSCV mounting features are integrated.

Treadstone is offering stainless steel v-band flange and clamp kits in sizes ranging from 2.0" to 4.0"! These kits feature 100% 304 Stainless Steel and are designed from the ground up using a low-profile v-band assembly as well as low-profile male and female interlocking flanges. The clamp features thick heavy-duty retainers and a thick band clamp to avoid stretching and warping from the many heat cycles that the band must endure. The flanges are CNC machined from billet material (unlike cast material like some of our competitors), making them more durable, and more resistant to warping under welding. They are heavier than cast flanges because of the reduced porosity, however they can withstand constant heat cycling without becoming brittle.   -100% 304 Stainless Steel V-Band Clamp -Thick Heavy Duty Retainer -347 Stainless Nut -420/431 Stainless Bolt -CNC Machined 304 Stainless Billet Flanges -Made in the USA!

The EFR line of turbos was born out of an internal BorgWarner Turbo Systems program labeled Advanced Aftermarket Products or AAP. So, the first thing you might be wondering is what does a new product line of high-performance turbochargers have to do with commercial applications? Commercial/industrial turbo products have extreme requirements for durability, reliability, and aerodynamic performance. Since modern passenger car applications use turbos smaller than 55mm in turbine wheel diameter, it's the aerodynamic development from the commercial side of the business (i.e. everything larger) that feeds into what the performance enthusiast wants and needs for big power production. Boost pressures of 45-50 psi (3 bar+) are the norm, not the exception. Also required is resistance to abusive thrust loads, high vibrations, and robustness for a wide range of lubrication conditions. Additionally, our commercial product validation standards are among the highest in the engine boosting industry; all good things that also benefit the performance enthusiast or racer. Those are the commonalities, now here are the differences. Unlike commercial applications, high performance users want lightweight, compact, versatile designs. They also deliver the turbocharger very high exhaust gas temperatures and have high expectations for fast response. They also place value in cosmetic appearance and want integrated features that aid the installation process and remove the need for other turbo related accessories. Those performance and packaging requirements are quite common among the modern aftermarket passenger car turbo customer. So, what happens when you tie together all those necessities and put them in front of passionate car people looking to advance the pace of aftermarket boosting solutions? There is a discovery that something new is needed in order to meet the needs of the next generation turbo consumer. There is the need for an “it” that really changes the game or raises the bar or whatever other metaphor you care to use. Under the product leadership of Brock Fraser, Director, Global Commercial Diesel Application Engineering, a team was assembled and the project began with the proverbial clean-sheet of paper. No legacy products, no preconceived notions of what a turbo could or could not have; no restrictions. The aerodynamics for the product line were selected using a range of optimized combinations that would give users turbo solutions anywhere between 250 and 1000 horsepower capability per turbo. Next, a list of every notable design characteristic for an engine boosting device was tabled. Specific interest was given to new ideas that had never been formed in metal or had never been combined into an aftermarket turbo. Ninety-five percent of the input “stuck” with only the truly exotic being excluded as those elements that would take too long to develop. Moreover, the turbo would be so expensive that the average performance enthusiast who wanted to buy the product could not afford it! After the AAP program took shape, the concept was presented to members of the BorgWarner senior management team. It didn't take long for them to embrace the vision of giving the performance aftermarket something truly remarkable. Management's approval to proceed with our mission led to one of the most aggressive new program introductions in the history of BorgWarner's independent aftermarket. Weeks and months of product development would bring forth a creation that would set a new standard in the performance aftermarket. The result is the new EFR (Engineered for Racing) line of turbos from BorgWarner. These turbos contain a bevy of key attributes such as Gamma Ti turbine wheels, dual ceramic ball bearing cartridges and investment cast stainless steel turbine housings. Collectively, those features help give the EFR line its innovative appeal and will provide a breakthrough experience in durability, device responsiveness and installer/user satisfaction. [gallery] Key Features: - Boost Control Solenoid Valve (BCSV) A boost control solenoid valve (BCSV) is included with every EFR turbo. - Simplified Installation Integrated compressor recirculation valve (CRV) to help avoid compressor surge and backflow during a throttle lift event. This feature helps to simplify the installation task and lowers overall system install cost. - Flexible Compressor Cover The “large” cover has a dual- machined outlet, both for a hose connection and a v- band connection. -Enhanced Turbo Response EFR turbochargers use a dual-row ball bearing cartridge with ceramic balls and metal cage. This bearing system provides substantial friction reduction at low turbo speeds and in the process helps improve turbo response. - High Turbine Efficiency Superback” and “Fullback” back-disk shapes offer very high efficiencies and have been paired with our “. The Superback shape adds a curved profile to the backdisk and has the effect of lowering centrifugal stress and permitting higher rotational speeds. - High Flow Wastegates Purpose designed large wastegate ports give the wastegated EFR turbos the capability of handling the flow requirements of high performance applications - Stainless steel turbine housings Investment cast stainless steel turbine housings improve durability and offer an offer extremely smooth internal flow channel. Turbine housings have thin walls to reduce weight and thermal inertia - Gamma Ti turbine Wheel & Shaft Gamma-Ti turbine wheel cuts turbine inertia by roughly 50% dramatically improving turbo response. Turbine sizes range from 55 to 80mm in exducer diameter - Forged Milled Compressor Wheels (FMW) EFR turbos contain wheels that are fully milled from forged aluminum, commonly known as “billet”. Cut from custom forgings, their strength exceeds that which is available from typical bar-stock and also exceeds the material properties of an aluminum casting

Price, ingenuity, and reliability there are many reasons that the new FRS/BRZ is hallmarked as the revolution/ re-ignition of the RWD platform. One of the many reasons that the BRZ/FRS has been billed as the “dream machine” by many is due to its innovative D4-S fuel injection system. This will serve to inform readers of the D4-S injection system and its use in the FRS/BRZ as well as an over view of the direct injection systems as a whole, the advantages of its use and the difference between both direct injection and port injection. But first some definitions! D4-S: direct injection, four cylinder, superior Direct injection: the act of adding fuel into the cylinder after the valve Port injection: the act of adding fuel into the cylinder before the valve Particulate: when fuel is burned in a low oxygen environment Pre-ignition: Also known as pinging or knocking, occurs when the cylinder pressure peaks before TDC Let's begin, direct injection systems have been around for many year in diesel engines recently have begun to appear in gasoline/Otto cycle engine like those found in most modern cars. Direct injection works by placing a fuel injector directly in the cylinder hence the name direct injection, when the computer gives the command to the injector to fire, the injector opens and releases the fuel which is kept at extremely high pressure (usually several 100 bars) into the cylinder all of this can occur with the valve open or closed allowing the computer to control exactly how much fuel is in the cylinder during ignition. An added benefit of a direct injection only situation is the fact that since there is no fuel in the combustion chambers the possibility of pre-ignition/knock is completely eliminated, again allowing the ECU to have more control of the engine as a whole. Port injection fuel delivery is the most common style used in automobiles today. In a port injection situation fuel is added before air entire the combustion chamber, which means after the valve has closed no more fuel can be added. In this situation the fuel and air molecules mix together better and provide a better mixture and providing better and more constant A/F ratios. Both of these systems offer have positives and negatives but when you combine both systems together the drawbacks of one complement the strength of the other making a more solid well rounded system.

BorgWarner has introduced it's next-generation EFR-7163 turbocharger, featuring an innovative lightweight aluminum bearing housing and mixed-flow turbine, the new turbo combines the responsiveness and compact packaging of a B1 turbocharger with the greater flow capacity to achieve up to 550 horsepower.

"BorgWarner's latest EFR turbocharging advancements are built on our highly successful season as the exclusive turbocharger supplier for the IZOD IndyCar® Series. Our innovative technology optimizes responsiveness and maximizes power output, combining the best qualities of B1 and B2 turbochargers in a small, powerful package," said Pete Kohler, President and General Manager, BorgWarner Turbo Systems. "We are pleased to welcome Dario and the Borg-Warner Trophy to SEMA. Both symbolize achievement, competitive performance and technology leadership—the same qualities and spirit that drive innovation at BorgWarner."

Designed for powerful performance in a compact package, BorgWarner's new EFR-7163 turbocharger achieves up to 550 horsepower while using a small B1 frame size that fits easily into a tight engine bay. Track proven in the IZOD IndyCar Series, an aluminum bearing housing reduces the turbocharger's overall weight by approximately 2 pounds. For fast response, the 63 mm mixed-flow turbine features lightweight Gamma-Ti material and innovative geometry to increase turbine flow capability while providing lower inertia than a conventional radial-flow turbine wheel. To provide the best balance of quick response at low engine speeds with high flow capacity at top engine speeds, BorgWarner engineers optimized the 71 mm (OD) compressor wheel to manage as much flow capacity as a larger conventional wheel. For added flexibility, the turbine housing accommodates either a v-band or T25 inlet connection option for engines using an open manifold or a T4 twin scroll housing for engines using a divided manifold.

BorgWarner's new EFR turbo will be making it's way to Treadstone in the next few months and will be available soon.

SOURCE PRNewswire

Volumetric Efficiency 101 This can actually be a quite tricky subject, mostly due to confusion and differing opinions among many people. Volumetric efficiency (VE) is typically defined as "the actual amount of air being pumped by the engine as compared to its theoretical maximum." Basically, VE is a measure of how "full" the cylinders are. As most of us will know from basic science, gas will expand to fill its container. Seemingly, that would suggest that the cylinder is always full. And, in the pure volumetric sense, that is correct. A 0.5 Liter cylinder will always have 0.5 liters of air in it. The measure we are looking for here is air density. A cylinder with 500 mols/liter of air in it is said to me "more full" than one with 400 mols/liter. Now, where is this air density measured? This is one of the points of disagreement. The point at which air density is measured is crucial. Many will claim that you must take the measurement at a standard, such atmospheric density. This, however, can cause many issues with VE measurements. Forced induction cars will have skewed VE values due to the simple fact that they are forcing more air into the manifold. With more air available to the engine, it will receive a larger/more dense amount. This is not a pure measurement of the efficiency of the engine, To correct for these factors, air density available at the intake manifold should be used. This will correctly measure the VE based on the amount of air available to the engine. As a simple example: Take a 4 cylinder, 2.0 Liter engine (assume even flow to each cylinder) each cylinder will be 0.5 liters. If the intake manifold has a density of 100 mols/liter (this gives 25 mols/cyl), at 100% VE, the cylinder will have 25 mols/Liter. This comes from the equation: VE = Densitycylinder/Densitymanifold * 100% Lets look at this another way. Say the cylinder in a single cylinder engine has 186 mols/Liter. Now, the density of at the manifold is measured at 213 mols/Liter. The calculation of VE gives: VE = 286/213 * 100% or 87.32% It is upon this principle that variable valve timing and similar technologies rely. They will change the flow aspects of the engine to best match the particular RPM range. An engine is typically only maximized for a particular rpm range. By allowing the change in parameters, this can be overcome. This can easily be seen when looking at DYNO charts for any Vtec equipped engine (the S2000 is a good example). In these charts there will be a "double peak." The horsepower will begin to fall off at one point, and then climb again. This rpm point will correspond to the "Vtec" point. Volumetric Efficiency plays a large role in how your engine operates. By understanding this parameter one can begin to grasp the details required to properly tune any engine.