The Basics of Turbocharging and Supercharging

By popular demand: a Q&A on supercharging (and turbocharging).

Q: What’s a supercharger?
A: An internal combustion engine works by drawing a mixture of air and fuel (the intake charge) into its cylinders, compressing that mixture, and then burning it. The more air/fuel mixture that can be crammed into the cylinders to burn, the more power the engine produces. You can increase power in three basic ways: you can improve the engine’s ability to draw more air and fuel into the cylinders and expel its burned exhaust gases (its volumetric efficiency, or ‘breathing’); you can increase the swept volume of the cylinders (the engine’s displacement) so you can fit more air and fuel into each cylinder; or you can pump the intake charge into the cylinders under high pressure, squeezing more air and fuel into the available volume.

Forcing air (or air-fuel mixture) through an engine’s intake valves at higher than atmospheric pressure is called supercharging. A supercharger, therefore, is a mechanical air compressor that pressurizes the air going into the engine’s intake manifold. There are several types of compressor used for car and truck engines, the most common being Roots-type, centrifugal, and Lysholm-type compressors; each has pros and cons, but they have the same basic purpose.

Q: So, what’s a turbocharger, then?
A: As we said, a supercharger is an air compressor and it requires a source of power to operate the compressor mechanism. Most automotive superchargers are run by a drive belt (or occasionally a train of gears) operated by the engine, much like a power steering pump or air conditioning compressor. An alternative is to run the supercharger with a turbine wheel placed in the engine’s exhaust manifold, turned by the flow of burned exhaust gases rushing of the engine. An exhaust-driven supercharger is called a turbocharger. (Years ago, they were often called turbo-superchargers, but that term has fallen out of common use, although it is occasionally applied to combinations of engine-driven and exhaust-driven superchargers.)

Q: What’s the advantage of supercharging (or turbocharging)?
A: More power! The more you increase the pressure of the intake air above the local atmospheric pressure (boost), the more power the engine produces. Automotive superchargers for street use typically produce a maximum boost pressures between 5 and 15 psi (0.33 to 1.0 bars), providing a proportionate increase in power. This is particularly useful at high altitudes: A supercharger can pressurize the intake charge to something close to sea level pressure, compensating for the power lost to reduced air density at high altitude. (Superchargers are popular for high-altitude aircraft piston engines for precisely that reason.)

Q: Does adding a supercharger or turbocharger burn a lot of fuel?
A: All else being equal, yes. Engines burn air and gasoline at an ideal (stoichiometric) ratio of about 14.7:1 (depending on fuel blend and octane), which means that if you burn more air, you must also burn more fuel. Even when the supercharger isn’t producing much — or any — boost, a supercharged engine is somewhat less fuel efficient than a non-turbocharged (normally aspirated) engine of the same displacement and configuration. On the other hand, a supercharged engine tends to consume less fuel in day-to-day driving than a larger displacement, normally aspirated engine of similar power. For example, a 2.0-liter (122 cu. in.) turbocharged four-cylinder engine with 240 hp (179 kW) will generally be somewhat less thirsty than a 3.5-liter (214 cu. in.) normally aspirated V6 engine of the same output, at least in relaxed normal driving. As any owner of any powerful turbocharged car will tell you, however, if you use the boost a lot, you’ll pay the price at the pump. In other words, your actual fuel consumption will be roughly proportionate to the engine power you use (what engineers call specific fuel consumption) more than the size or configuration of the engine.

Q: Why use a supercharger instead of just using a bigger engine? Wouldn’t that be easier?
A: To some extent, it would be. A supercharger significantly increases an engine’s specific output — the amount of power generated per unit of engine displacement (usually quoted in terms of horsepower per cubic inch or horsepower per liter), but, as the old adage says, there’s no substitute for cubic inches (or, more pithily, no replacement for displacement). Increased displacement provides more power without the added cost, complexity, and sometimes nonlinear behavior of superchargers. Still, a large-displacement engine usually ends up being bigger and heavier than one of small displacement, which makes it harder to fit under the hood,and does unfavorable things to weight distribution. A smaller, supercharged engine can provide similar power with less bulk and somewhat lower average fuel consumption and carbon dioxide emissions. In addition, some countries levy prohibitive tax and licensing surcharges on cars with large-displacement engines, making a smaller displacement, supercharged engine much cheaper to buy and operate.

Furthermore, any existing engine design can only have its displacement increased so much without a major redesign, so the addition of a supercharger or turbocharger can be a useful way to pep up an existing engine that has reached the limits of its growth potential. It’s a relatively easy “bolt-on” power increase that doesn’t require a vast amount of engineering work.

Q: Why don’t superchargers produce maximum boost all the time? What’s “turbo lag?”
A: The amount of boost any supercharger produces is dependent on the size and rotational speed of its impeller(s) as well as the type of compressor it uses. (For example, centrifugal superchargers, whose output increases proportionally to the square of the rotation speed, are most efficient at high speeds, while Roots-type superchargers are most efficient at lower speeds.) The peak operating speed of a typical automotive supercharger is more than 30,000 rpm — for some turbochargers, more than 100,000 rpm. The compressor does not produce its full boost until the impeller has reached that speed.

Let’s look at a specific real-world example: the belt-driven Paxton Model SN supercharger used on Studebaker’s R2 engine and offered as an option on some GT-350 Mustangs. Described in some detail in the July 1966 issue of Car Life, the Model SN was a centrifugal supercharger with an impeller 5.8 inches (147 mm) in diameter, geared to rotated at approximately six times the speed of the engine crankshaft. It produced its maximum boost, 5.0 psi (0.35 bars), at an impeller speed of just under 30,000 rpm, corresponding to an engine speed of 5,000 rpm.

What about at lower rpm? As we mentioned above, in a centrifugal supercharger, the boost is proportional to the square of the rotation speed. If the supercharger produces 5 psi (0.35 bars) of boost at 5,000 rpm, reducing engine speed by half would reduce boost by a factor of four, which in this case would be about 1.25 psi (0.09 bars). Halving engine speed to 1,250 rpm — just off idle — would yield only about 0.31 psi (0.02 bars) of boost.

What did that mean in practical terms? When the supercharger was making full boost, it provided a significant amount of extra power, on the order of 20-30%. At very low speeds, however, boost was negligible, probably not enough to make up for the power used to run the compressor. This was borne out by contemporary road tests of the supercharged GT-350, which found the supercharged car no faster than its normally aspirated counterpart under about 40 mph (65 km/h), but noticeably quicker to 60 mph (97 km/h), with significantly higher trap speeds in the standing quarter mile (0-402 meters).

Turbochargers, which usually use centrifugal compressors, have the same limitations as other types of supercharger, further complicated both by the turbo’s higher peak speeds and the fact that the speed of the impeller is dependent on the speed of the exhaust stream rather than engine speed. Unlike an engine-driven supercharger, the turbine speed isn’t fixed; it varies with throttle position (among other things).

At steady cruising speeds, the turbine is often spinning well below its boost threshold — that is, turning too slowly to provide any boost. When you press the gas pedal the speed of the exhaust gases increases and the turbine begins to accelerate, but there’s a delay while the turbine overcomes its own inertia and accelerates (spools up) to peak speed. Since that peak speed is usually quite high, this produces a brief but annoying delay, known as turbo lag or boost lag, where not only does the turbocharger not produce any extra power, it actually reduces output slightly because of the increased back pressure the turbine creates in the exhaust stream.

The severity of turbo lag often depends on how much boost the turbocharger produces. More boost requires either a bigger compressor — which has more inertia — or a higher operating speed, either of which take longer to spool up. Engineers have developed various tricks to reduce turbo lag, including reducing the mass of the turbine blades, changing their shape to improve their acceleration, and even adding movable nozzles that change the direction at which the exhaust stream hits the turbine blades, depending on their speed. (Porsche recently introduced a “variable geometry” turbo system, claiming it to be a first, but Chrysler and Honda had conceptually similar — albeit short-lived — systems back in 1989–1990.) Some sports cars have also used two or more sequential turbochargers of different sizes, a smaller turbo offering good low-speed response and a bigger one that takes over to provide maximum boost at higher speeds. The limited-production Porsche 959 used sequential twin turbos, as did the third-generation Mazda RX-7 and fourth-generation Toyota Supra Turbo.

Reducing turbo lag is easier with turbochargers whose maximum boost is relatively low; the “light-pressure turbochargers” used by some Saab and Volvo engines, for instance, don’t produce a great deal of boost, but they have little lag and a fairly linear power curve.

A more complex alternative is a two-stage turbo-supercharger, which uses both an engine-driven supercharger and a turbocharger in sequence. The supercharger is designed to produce its maximum boost at low speeds; at higher speeds, a clutch disengages the supercharger and the turbocharger provides the boost. This was not uncommon on aircraft engines in the 1940s and Volkswagen recently reintroduced the concept with its “twincharger” engines, used on some European Polo and Golf models.

Q: Are there other disadvantages of superchargers and turbochargers?
A: Definitely. The most obvious are cost and complexity. Aside from adding a bunch of extra parts to the engine (which means more to break), the moving parts have to be precisely machined and quite strong. Turbochargers require fairly exotic materials to withstand both the high temperatures of the exhaust system and their very high operating speeds. Forced-induction engines need to be well lubricated as well, and they tend to put a big strain on the engine’s oil system, requiring good-quality oil and frequent oil changes to avoid a build-up of sludge.

Another potential problem is detonation. If you increase the pressure of the intake air, you also increase its temperature. When the mixture enters the cylinders it is compressed before it burns, raising its temperature even further. If the mixture is too hot, it may be prematurely ignited by hot spots within the combustion chamber (this is called detonation, preignition, or knock). Detonation can cause severe internal engine damage. To reduce the risk of detonation, forced-induction engines often have their compression ratios reduced so that the pistons do not compress the mixture as much prior to burning. This avoids detonation, but it means that the engine’s power output is reduced, particularly when the supercharger is not producing much boost. Many forced-induction gasoline engines require higher-octane fuel, which is less susceptible to knock, but costs significantly more.

As we’ve mentioned above, superchargers consume a certain amount of engine power even when they aren’t producing useful boost. Turbochargers increase back pressure in the exhaust, which also costs power. The compressor can also create a certain amount of internal drag at low speeds. At maximum boost, the increased power provided by the compressor far outweighs these parasitic losses, but they make the engine less efficient off-boost.

Superchargers and turbochargers also take up a little more space in the engine compartment and add a certain amount of weight. These penalties are modest compared to the benefits (bolt-on superchargers typically weigh less than 50 pounds and fit fairly easily under the hood), but they’re not negligible.

Moral of the story: there is no free lunch.

Q: What’s an intercooler?
A: As we said, increasing the pressure of the intake air raises its temperature, which is really not desirable. Not only does it increase the risk of detonation, it lowers the density of the intake charge, which starts to defeat the whole purpose of supercharging. There are several tricks that can reduce that temperature. One is to inject a little bit of liquid (such as water or alcohol) into the intake manifold; some of the thermal energy of the compressed air then goes to vaporizing the liquid, reducing the air’s temperature. Another method is to add an intercooler, which is a heat exchanger — basically a small radiator — that removes some of the heat from the pressurized air before it enters the engine’s intake manifold. A properly designed intercooler dramatically reduces the intake air temperature, avoiding detonation and, as a bonus, increasing the density of the intake charge. Intercoolers aren’t generally necessary for low levels of boost (less than about 5-6 psi/0.3-0.4 bar), but they’re virtually mandatory at very high boost pressures.

Of course, adding an intercooler further increases cost, complexity, mass, and bulk. The heat the intercooler extracts also needs somewhere to go. If it’s an air-to-air intercooler, it needs a good flow of cooling air; if it’s an air-to-water intercooler, the engine needs a bigger radiator to cope with the extra heat added to the engine’s cooling system.

Q: How long have superchargers and turbochargers been around? Did Saab invent the turbocharger?
A: The Roots-type compressor has been around a lot longer than the automobile — that type of blower was patented back in the 1860s for mine shaft ventilation and the first patent for an automotive version was filed by Gottlieb Daimler (of Daimler-Benz fame) in 1900. Rudolf Diesel patented the supercharged diesel engine in 1896 while the centrifugal supercharger was patented by Louis Renault in 1902. The turbocharger, meanwhile, was invented by Alfred Buchi and patented in 1905. Turbochargers were used on diesel engines starting in the 1920s, but the difficulty of manufacturing turbines able to reliably endure the higher exhaust temperatures of gasoline engines kept turbochargers from wide use on petrol engines until the mid-1930s. Turbochargers became common on aircraft engines shortly before and during World War II.

Every so often you’ll find someone on the web claiming that Saab offered the first production turbocharged gasoline engine, which is simply not true. Turbocharged race cars began to appear in the early 1950s, but the world’s first production car with a turbocharged gasoline engine was the 1962 Oldsmobile F-85 Jetfire, followed a few weeks later by the Chevrolet Corvair Monza Spyder. The Jetfire turbo lasted only two years, the Corvair turbo for four, but both beat Saab by more than a decade.

Turbochargers are nearly universal on modern diesel engines, but forced induction for petrol engines has fallen in and out of favor over the years. With increased political pressure for better fuel economy and reduced carbon dioxide emissions, however, turbos are again becoming common. In fact, some engineers think that light-pressure turbochargers will eventually become standard on gasoline engines, just as fuel injection has. Predicting the future of this industry is always a dicey proposition, but at least for the present, forced induction is an increasingly popular solution to the always-tricky problem of extracting big-engine power from smaller, less-thirsty engines.



Add a Comment
  1. Is there an aftermarket turbo for the Chrysler 3.5 L engine?

    1. As far as I know, there is not, but I’d suggest asking the folks in the Allpar forums (at

      They would probably be able to tell you.

  2. Would you happen to know if there is an aftermarket turbo or supercharger for the 3.0L V6 found in a 2003 Mitsubishi GTZ? Or who I could ask? Or someplace to find a suitable super or turbo for the engine? Thanks

    1. I don’t know — sorry!

  3. Long time reader, first time responder. Thanks for all the well-researched articles and sharing your wealth of knowledge. One minor correction, though. The twin turbos in the VG30DETT-powered second-generation Nissan 300ZX are not sequential, they’re T25/T2 hybrids in parallel, each feeding the opposite cylinder bank’s intake. I tried to find a source more authoritative than “I’ve driven mine for 19 years and 288K miles”, but the best I came up with is [the Technical School forced induction page].

    1. Thanks for the correction — I’ve amended the text.

  4. can I twin turbo a 1.8? It’s currently in a 1998 Audi A4 and already has a turbo aswell. I only ask because I want to make one of the Quattros a little rally kinda sleeper. Thank you!

    1. I’m afraid I’m not qualified to give technical advice — sorry!

  5. Hello Aaron Severson,

    My name is sricharan, i am from India. I would like to get some suggestion about the centrifugal supercharging on small engine car, i am talking about a 800CC normally aspirated petrol engine, what parameters should i consider before selecting a supercharger which would be safe to run on such a small engine. can you suggest me some thing, if not it would be very great if you could advice a book or a website where i could find this technical information. Thank you sir

    1. Hi Sricharan,

      I’m really not qualified to offer any kind of technical advice. I understand the basic principles of supercharging, but I’m not an engineer or a mechanic and I don’t have the kind of information you would need for that. Sorry!

  6. Hey
    It would be great if u could comment about the changes that has to be made in the ignition timing for a naturally aspirated si engine which is to be supercharged… I’m well aware that it depends on individual engines.. I just need to know to what extent the ignition should be advanced or retarded(I strongly believe it shld be advanced since more fuel air mixture gets into the cylinder.. ) I’m talking about an engine that is carburated doesn’t have an onboard ecu or electronic

    1. I’m afraid that would end up sounding perilously like technical advice, which I’m not qualified to offer. It’s not a simple question, since it depends on the compression ratio, the turbocharger A/R ratio, how much boost you’re using, how aggressive the timing curve is to start with, and whether you’re using any other tricks like water injection (see 1962-1963 Oldsmobile F-85 Jetfire). Short of some complex mathematical modeling that’s certainly beyond me, about the best you can do short of trial and error is find people you trust who’ve built turbos or superchargers for similar applications and see what they recommend.

      As for advancing versus retarding, all I will say is that you might want to keep in mind that electronically controlled engines with knock sensors manage detonation (which can be a real problem with forced induction) by retarding the ignition timing as soon as the sensors detect spark knock. So…

  7. excellent Article !

  8. I am getting ready to buy a new 4Runner Limited (AWD/4Wd, 2015/2016 ?), I have the opportunity with the purchase (after purchase, but part of the after purchase package) to add a supercharger, years ago I had a turbo on a Subaru… it was fun, but I found myself being too lead footed as I liked the sound of the spooling up…. it ended up being terrible on fuel, so I am focusing on the supercharger…. I live in Phoenix which is 900 feet+ in elevation and it HOT during the summer…. aside from the obvious power increase, my in interest is better economy and power on demand…. I have noticed in the greater Phoenix area during the summer time… my various cars are kind of doggish in operation…. hot air and higher altitude, what I am trying to do is offset that by jamming more air in and end up with something that resembles reasonable fuel economy with normal driving… I have had my hot rods, now it’s time for a sleeper with some extra bells and whistles. TRD offers a nice roots blower that I am interested in….
    Thanks for your thoughts on this matter.


  9. Pls sir,what is the amount of fuel and air that goes into the chamber for combustion?

  10. Aaron,

    While the term inter cooler is loosely throw about in the vernacular an inter cooler is technically placed between super chargers. Two stage superchargers where used in some WWII aircraft engines to give added boost at high altitudes and the charge from the first stage was cooled before it entered the second stage. What most of us have, whether roots type or centrifugal as in a turbo are charge air coolers. My EcoBoost 3.5 has an air to air charge air cooler, as it is referred to by Ford. Tomtomz roots type if he indeed opted for it has an air to water charge air cooler mounted under the what in the ’50’sand ’60’s at least was commonly called a blower. Toyota’s charge air cooler for the 4.0 V-6 uses a system separate from the engine cooling system.

    Newer designs have virtually eliminated any perceptible turbo lag. Going back in time to in head exhaust manifolds has allowed turbos to be mounted directly to the head which I assume helps them spin up with less lag as they are closer to the exhaust valve, offers a shortened heat path and more receptive media for that heat ( Al vs air) for the exhaust turbine and increases exhaust velocity. Computer control of throttle valves has also played a big part as well as computer controlled blow off valves to eliminate over run where boost pressures don’t drop in direct response to throttle closure. These and other refinements of turbocharging have the motorcycle industry where turbo lag and overrun doomed the turbo bikes of the 1980’s looking at turbos again.

    1. I’m as willing to be pedantic about terminology as anyone, but in this case, I don’t think the use of the word intercooler is wrong; the definition has simply evolved since World War II. Of course, an intercooler in the modern automotive sense is certainly a charge air cooler, but I would consider that more a definition or description than a more technically correct term. It’s comparable to the word turbocharger as an alternative to “exhaust-driven supercharger.”

      Turbocharger and supercharger applications have certainly come a long way. Aside from the factors you mention, another consideration is that knock sensors, precise electronic ignition control, and particularly the adoption of direct fuel injection for gasoline engines have greatly reduced the need to sacrifice off-boost power for on-boost survival. It’s not like 35 years ago, when turbocharged engines had to use lower compression ratios and sacrifice a bunch of spark advance so they wouldn’t blow up under boost. Modern OEM turbochargers benefit greatly from being carefully integrated with the rest of the engine management system; we’re not to the point that engineers at Saab (among others) once predicted, where turbochargers are simply taken for granted on all engines, but it’s getting there.

  11. On a small block Chevy is it capable to install a supercharger and still have powersterring and altinator I’m talking like a 6-71 supercharger with the big belts. If so is there a kit for them or something thanks

    1. I can’t help with parts or modifications, sorry.

  12. You can actually research everything you are wanting to know on the internet as I did and found that even though I have a naturally aspirated 7.3 diesel that if I add a turbo that does 10 lbs of boost or more that it would lift the heads on my engine and break the head bolts and to be honest there truly are more certified people to answer questions that this redundant person can’t answer anything

    1. This is not a forum for modification or repair advice and I have never represented it as such. Indeed, given the number of times I’ve clearly said that I can’t help with that kind of stuff, I’m puzzled that people keep asking. Even if I were qualified to advise people on repairs or modifications, which I am not, I’d shy away for legal liability reasons.

  13. Any redundant person knows how a supercharger or turbocharger works and to be highly educated on them and to have a forum for them you should actually learn a few things about them like take a 1988 f250 truck with a non turbo diesel (or naturally aspirated 7.3 v8 diesel engine) I do know that if you add a turbo without doing a bunch of internal work then it can’t even produce 10 lbs of boost without lifting the heads and breaking the head bolts so please learn something more than just how they work and no I don’t need a response as I myself am not a certified mechanic but I do know how to research what I am looking for but I do have knowledge of mechanic work as to the fact that I have several race cars that I rebuild every year and I did stumble across this forum trying to find out if it is even remotely possible to add a supercharger to my diesel truck

  14. People…..REALLY? It seems that most of the people posting questions here are on the WRONG FORUM! General informational questions from people who have already done their application-specific homework and have an understanding of what they are trying to accomplish belong here. If you had a thought 10 minutes ago starting with ” I wonder…” GO DO YOUR HOMEWORK IN A VEHICLE-SPECIFIC FORUM!!!! Any additional questions may be answered here for general direction once you’ve figured out what direction you are going and what the specific limitations of your vehicle’s engine are. I have been working on a NeonSRT4 since 2004 and found the information here enlightening, but this isn’t the place for me to look for specifics on my project. Just general guidelines to make sure I’m still headed in the right direction. Please keep this in mind, and the best of luck with your current project! :-)

  15. a vsl which one is design kort nozzel system vls l 41m. b. 9m. d .4.5m.
    gearbox ratio 5.65:1 but the dockyard adviser remove the kort nozzel system fitted open propeller didnot modify neither gear ratio nor mian engine(1360BHP) like this vsl being prepared finally went to sea but failed to reach the rated rpm when the vsl in trawling mode(mid water system) engine cannot reach is rated rpm because the propeller overpeached and getting the all enigne parameters above the maxm.
    say exhaust temp mix. 500 but engine getting more than recommended 600
    rest of the other parameters like this
    So im thinking to add intake manifold centifugal blower snd check the propeller pitch wheather it is over pitched or not if like this canot perform csn i suggest to chnge the gearbox ratio 7;1 because the propeller orginally kort nozzel design thats why for open propeller 7;1 gb rstio will be up to the mark pls give me a suggestion

    1. I’m sorry, I’m really not qualified to give any kind of technical advice.

  16. plz tell me which one run first supercharger or engine…

    1. Most superchargers rely on the engine for motive power — a belt- or gear-driven mechanical supercharger is driven by the engine in the same manner as a power steering pump or air conditioning compressor while a turbocharger is driven by exhaust gases. An electric supercharger (that is, one where the compressor turbine is run by an electric motor) isn’t as directly operated by the engine, but since power for the motor still ultimately has to be supplied by the engine (if only in the sense of recharging the battery), that’s sort of hair-splitting. So, broadly speaking, the answer would be “the engine.”

  17. can i use supercharger in toyota 5a engine , which model of supercharger should be better and what other parts should be added in my car (ae91) ,,, how much horsepower can i get from it , and is it cost much fuel, can i run it in natural gas

    1. As I’ve told other posters repeatedly on this thread, I can’t advise anyone on modifications or repairs. There was a factory supercharger for the 4A-GE engine, but how well it would work for a 5A I don’t know.

  18. Can a turbo be mounted further down the exhust system to reduce heat?

    1. I suppose, but you’d also lose exhaust gas velocity that way, so it would be less efficient.

  19. An engine is a vacuum pump, hence nearly all the factors that contribute to volumetric efficiency also apply to forced air induction. The CFM, PSI induction pressures, displacement, air flow friction, both intake and exhaust, exhaust pressure, cam height and duration, cam timing, low internal engine masses and weight, low internal engine friction, and throttle opening, all effect power and torque. The engine itself in design is limited by angular momentum of the crank, inertial mass of rods and pistons,and cam and factored and calculated by the metallurgy of materials used in the engine. Once an engineer calculates the destruction point based on tensile strength of the engine( Red Line RPM) a program is calculated in conjunction with the turbo chargers or superchargers to regulate internal pressures. The air and CFM going into the intake ports is regulated by Air Flow Meters going through the induction system from the outside. Internal turbo pressure is regulated by waste gates, and relief valves. Theoretically a turbo will continue producing power to the limit of the angular momentum of the turbine and compressor where a supercharged device will fall off considerably past a certain RPM, due to Crankshaft friction loss and the much larger veins of the compressor within the supercharger itself. Everything is regulated by the CPU of modern day engines, depending on the demands of the engine at the time, air flow , temperature, Vacuum, exhaust gas recirculation, load etc. So generally what is being discussed is generally true, but the chip and other engine management controls must match the size of the blower, which ever one you use so the blower can also match the demands of the engine at the time for maximum efficiency and emissions , along with durability concerns. It is very possible to produce 100 percent more power and torque of an engine, but even with better oils today, the extra top end pressures of the engine can reduce the engines ability to produce the same efficiency of power and durability over a sustained period of time.

  20. I think the effectiveness of turbocharging or supercharging relates directly to “no replacement for displacement,” except that we need to rethink exactly what displacement means. The old notion of static displacement, area-of-piston cross-section X stroke X number of cylinders, specifically at atmospheric pressure, was never fully accurate in the first place. Instead, think of displacement as the actual amount of fuel/air mixture in the cylinder when the intake valve closes during dynamic operation. Also, realize that pretty much no engine always operates at 100% efficiency. At the least, friction and constriction reduce intake flow to the cylinder to work against filling to full displacement.
    In this context, the displacement of a naturally-aspirated engine with a big cam changes with RPM. At low RPM, with both intake and exhaust valves both open during lift overlap, the flow momentum of the exhaust gas can pull some of the initial charge mixture out of the cylinder before the exhaust valve closes, and any cam timing that keeps the intake open after bottom dead center may push some charge back into the intake. However, there is still close to a full “fill” of the cylinder reflecting a volume close to the calculated static displacement. At high RPM, this same cam tends to assure full scavenging of exhaust, but when the intake valve remains open after bottom dead center, there tends to be a “cramming in” of more air/fuel mixture due to the force and inertia of the incoming air, so even while the piston starts up in the bore more charge is entering the cylinder. Effectively, this results in more fuel/air mixture entering the cylinder than calculations would indicate is the actual displacement.
    Extending this thinking to turbocharging or supercharging readily explains the additional power. At idle, the air/fuel mixture is very similar to a normally-aspirated engine, as the power-adder is not yet producing additional flow or pressure. To simplify, think of the turbo or supercharger, with the appropriate blow-off valve, spooling up to produce one and one-half times normal atmospheric pressure. The pressure is what forces the air through the passages into the cylinder: more pressure forces more flow. To illustrate, imagine inserting an air nozzle on a hose from your compressor into a balloon: almost instant inflation. Remove the nozzle from the hose, insert in mouth, and blow into the balloon: still inflated, but much more slowly. Similarly, charge air under pressure enters a cylinder more quickly and results in more being forced into the cylinder before the intake valve closes. The higher the pressure, the more quickly charge is “stuffed” into the cylinder, helped further by a blower cam with little overlap. Assuming (admittedly not scientifically accurate) that 1-1/2 X atmospheric pressure out of the charger results in 1-1/2 X the amount of charge mixture “pressed” into the cylinder. the effective, “dynamic” displacement of the engine is now 1-1/2 X the calculated static displacement. This also raises compression compared to traditional static calculations, greatly increasing torque output.
    I am certain there are physicists and automotive engineers who will pick apart the details of this representation, but this is simply meant to illustrate the concept, not be an engineering paper for the SAE. Plus, they didn’t write first and have the luxury of second guessing. I hope this helps a little with some insight into what happens.
    There may still be no replacement for displacement, but it may not necessarily come from increased bore or stroke.

    1. I’m not an engineer either, and I know there’s a lot more to be said about the mechanics from an engineering perspective (including some other factors like expansion ratio, which gets into a tangential discussion about Miller-cycle and Atkinson-cycle engines). However, I think the idea that forced induction makes an engine act like it has more displacement sometimes — but not always — does sum up the essential rationale. That’s also more or less the basis of the various FISA formulas for calculating the equivalent displacement of a turbocharged engine for classification purposes. (I realize I don’t actually know what the current factor is. It was 1.4:1 for a while, then 1.7:1, but since I don’t follow racing, I don’t know the formula used today.)

      On the other hand, displacement — in the basic geometric sense — is harder to replace in other ways. A big normally aspirated engine can back off on the valve lift and overlap, providing more torque in the off-idle and part-throttle regimes where forced-induction engines are traditionally at their weakest. (That’s changing as engine technology improves, but that’s been a fairly recent thing.) A normally aspirated engine also avoids a lot of the trade-offs of power consumption from the supercharger itself, added heat (both adiabatic heating of the intake charge and just waste heat), and so forth.

  21. the temp at the track next week is going to be 50 degrees, how does that affect a FI car versus a NA car. do they both get the same amount of benefit?

    1. Cooler air is denser, which helps in general, but is probably more helpful to forced induction engines. Supercharging raises the charge temperature, so it’s beneficial if the intake air starts at a lower temperature. Also, if the forced induction engine is intercooled, cooler outside air may provide additional benefits due to greater intercooler effectiveness.

  22. I just bought a 2003 old Nissan Frontier with supercharger and only 35,000miles. The previous owner used regular gas the whole time. It doesn’t feel like it has a supercharger. Do you think she might of cause some engine damage. CanI just start using premium gas and the knock sensor will start to regulate the premium gas and the supercharger will start to work the way it’s supposed to.

    1. I’m not a mechanic and can’t advise you on repairs or modifications. However, it looks like Nissan did list premium fuel as required for the supercharged engine.

  23. I’m looking into supercharging or at least putting a turbo into my 1996 Thunderbird LX (v6) i’m not sure if it is a great idea but i am trying to put a little more power into it’s step. Any suggestions? I’m leaning towards putting in a turbo but i’m not sure still.

    1. I wish people would read some of the other comments on this thread where I keep saying I cannot advise anyone on modifying their cars. I can’t help with that! Really!

  24. can I change a 3.1 Isuzu trooper turbo diesel engine to non turbo

    1. Martin,

      At the risk of sounding snippy, I must say again — as I’ve now said quite a few times in response to similar comments on this article — that I cannot advise people on modifying or repairing their engines!

  25. I have wondered about electric superchargers. II assume the issue is with the excessive weight required to generate significant booste, not just the electric motor, but probably batteries and alternator. But with the modern advancements in electric motors I would expect an electric blower to become feasible at some point. I was also considering the idea that it would likely beneficial for the blower speed to be independent of the engine speed allowing for boost to be produced proportionally to the desired power at a given moment and the blower to essentially be I. Neutral when the engine is at idle. With very little time being spent with engine output at far less than the boosted max. I was wondering if anyone has any further knowledge or comment on that subject.

    1. Electric superchargers already exist and are already in production for a few cars, including some recent Audi models. Audi uses the Valeo electric supercharger and BorgWarner recently launched its rival eBooster line. I believe Honeywell has one as well.

      The Valeo and BorgWarner units are designed to supplement a conventional turbocharger, more or less eliminating turbo lag by providing instant-on boost while the turbocharger turbine spools. They draw a great deal of juice (both are 48-volt systems, although Valeo says they also offer 12V and 24V versions at some cost in efficiency), which imposes some practical limits on how much boost they can provide and for how long. If you do a web search for “Valeo electric supercharger” or “BorgWarner eBooster,” there are a fair number of articles talking about how these systems work.

  26. twin chargers , i have a 2015 tundra supercharged , i would like a little more out of it power wise, is twin charging a good way to go or what do you suggest

    1. I can’t advise people on modifications or repairs, sorry!

  27. Thanks for the great article. How much increase in air temperature after the turbo is due to the temperature of the hot turbine wheel vs the physical property of compressing the air? Do superchargers need less intercooling (or, charge cooling!) than turbo chargers for this reason?



    1. I’m no engineer, so a thermodynamic analysis of supercharger systems is really well beyond my abilities. For obvious reasons, friction associated with the spinning of the turbine wheel on its bearings will itself generate a lot of heat, some of which will be absorbed by the charge. However, as I understand it, the compression of the charge itself is the source of most of the added heat, which is proportional to how much the air is compressed, so in high-boost applications, I would assume that accounts for the lion’s share of the heat increase. In that regard, the need for charge cooling would depend mostly on the amount of boost rather than how the compressor turbine is powered. It’s true that mechanical supercharger applications often forego charge cooling, but I think that’s mostly because those applications have fairly modest maximum boost, on the order of 5–6 psi, at which point the benefits of charge cooling aren’t necessarily worth the extra hassle.

      At least in single-stage supercharging applications, mechanical superchargers are less efficient than exhaust-driven turbochargers and some of that inefficiency shows up in the form of extra heat, but I don’t think that necessarily shows up in the charge temperature. Quantifying it more precisely than that is beyond my skill, although it sounds like it would make a decent paper for an engineering journal!

  28. The Mercedes “Split Turbos” in their Formula 1 cars, where the turbine wheel is separated from the compressor wheel by a long axle, apparently allowed the cars to have smaller, more aerodynamic intercoolers, which probably played a role in their winning races. It also suggests that the temperature of the compressor wheel plays a role in the magnitude of the increase in temperature of the charge air.

    1. I’m not familiar enough with F1 stuff to comment on the mechanics of that application, although I would assume that separating the turbine and compressor with a shaft would entail other compromises (such as rotational inertia and deflection). As I said the other day, I don’t doubt that the friction heat of the spinning turbine is significant, but not being an engineer, breaking down what component of charge heat is due to that rather than adiabatic heating from compression is beyond my capacity. I’m sure someone could (and did!) estimate the impact of each of these issues, but quantifying that is beyond my skillset!

  29. What is the best supercharger for the lexus 1uz v8?

    1. I can’t advise you on modifying engines, sorry!

  30. There’s a lot of discussion and documentation on the pros and cons of turbochargers and superchargers and increase in WHP and torque for various engines. I happen to have a BRZ with the FA20 engine with a compression ratio of 12:1 and am considering adding a supercharger. Reports indicate this would raise the WHP from the mid 160’s to around 250 or so.

    however, with an already high compression ratio, would more power/torque gains be able if the compression ratio were lowered to say 10:1? Understanding the pistons, rods and possibly the injectors would need to be changed which adds cost but that aside, would higher gains be expected? Similarly, is there any way to determine the optimum compression ratio for boosted applications?

    1. I’m not a mechanic or engineer, so I’m not comfortable advising people on how to modify their cars or engines — that’s way beyond my technical competency.

      In general terms, it’s important to understand that the primary limitation with high compression ratios and forced induction is that the combination tends to produce very high combustion temperatures, increasing the risk of detonation and the production of oxides of nitrogen in the exhaust. Direct injection (the FA20 uses both direct and port injection) mitigates that effect somewhat because the vaporization of fuel absorbs some of the adiabatic heat of compression. Beyond that, it comes down to the knock sensors recognizing preignition and signaling the engine computer to back off on the ignition timing to stop it. So, to optimize the balance of boost and compression, one would need to model the combustion chamber temperature curve, taking into account the vaporization effects, and also the behavior of the knock sensors to find the most power you could achieve from a particular combination of parameters before the knock sensors cause power to drop off.

  31. Not a Engineer?? Could have fooled me. Modeling compression chamber temp curves and those parameters sounds like CFD’s which is way beyond this Architects capabilities and most of the Engineers I know except for a few. I appreciate the response. I’ll keep researching.

    1. You might want to look into Nissan’s MR20DDT variable-compression turbocharged engine, which supposedly can vary its compression ratio from 8.0 to 14.0:1. I don’t know too much about the VC-T engine, but its strategies might be helpful to you — if this is an area you’re serious about, it might be worth seeing if there are any technical papers on it from the SAE or the like.

  32. Thanks for the tip Aaron. I’ll look into it and post what I find.

  33. Can coolant get in your engines oil when you change manifold gaskets on a 2004 Pontiac Grand Prix gtp?
    Does your engines oil need changed after replacement?

    1. I’m not a mechanic, so I’m not able to provide repair advice. Sorry!

Leave a Reply

Your email address will not be published. Required fields are marked *

Comments may be moderated. Submitting a comment signifies your acceptance of our Comment Policy — please read it first! You must be at least 18 to comment. PLEASE DON'T SUBMIT COPYRIGHTED CONTENT YOU AREN'T AUTHORIZED TO USE!