Introduction:

There has been a long debate over superchargers vs turbochargers. They both have advantges and disadvantages. First lets get the basics down. Superchargers and turbochargers are known as force induction systems. They both feed more air into your engine which in turn gets you more ponies. But the difference lies in how these systems are powered. The Turbocharger is driven by the exhaust system, the exhaust spins a little turbine which spins another little turbine and that turbine puts more air into your engine. The supercharger is driven by the engine itself, usualy by a belt or a crankshaft.

Different Types:

This is where things can get a little confusing, so pay attention!!! Although there is only one type of turbocharger, there are different types of superchargers. First there is the twin screw supercharger, these systems are driven by a belt and compressed air is forced in by two screws spinning againt each other. Think of it as two drill bits side by side spinning. Next we have the Centrifugal charger, which is essentialy a turbocharger that is driven by the engine instead of the exhaust. The next one is called the roots blower, this is called a blower cause thats what it does. Unlike the other systems which compresses the air into the engine, this system simply moves the air more quickly, it blows! You dont see a lot of roots (at least i havent), because the twin screw type does the same job with less heat. Heat = horsepower loss.

Advantages/Disadvantages:

These systems obviously have advantages as well as disadvantages. The Turbocharger will give you more power than a supercharger. This is mainly due to the fact that the supercharger uses the engines own power to make power, so it takes horsepower away to make more. The Turbocharger uses the exhaust which is potential energy, because it would just be thrown out unless a turbocharger was there to use it. Of course the turbocharger does make your engine loose some horsepower because your putting a thing in the way of the exhaust system, the gases are harder to expell. However The supercharger will make your engine loose more horses than a turbo will. But because the turbo is driven by the exhaust, the turbo has what is called turbo lag. This is the time it takes the exhaust to spool up the turbocharger so it can create boost. Boost is usually reached at around 3000rpm. The Centrifugal supercharger also suffers from turbo lag, because its driven by gears. However the twin screw and the roots both give boost as soon as you hit the gas pedal and the boost gradually rises as RPM increases.

If your racing you can eliminate turbo lag by reving your engine so you get some boost going. And then launching. If your running a force inducion system I strongly reccomend a high-flow exhaust system and an intercooler to cool the incoming air. Cooler air = more horses.

A supercharger is good where boost at low rpm is needed, such as off-roading or towing. A turbo is great if you have an awsome street machine.

So there you have it. Hope this clears some things up.

Saying there is only "one type of turbocharger" but many types of superchargers is ignorant. You can seriously change the characteristics of a turbo by changing the a/r housing size, the compressor wheels, exhaust turbine, etc. This all can effect airflow rate, power output, turbo lag, if it's there, and if so how much, etc. Furthermore, ball-bearig versus standard turbo...way different. Ball-bearing turbos will spool up 800-1000 rpm faster than the equivlent standard. The parastic loss on a turbo is pretty much non-existant also, it doesn't take much to spin the exhuast turbine. A supercharger, being belt driven, has noticable parasitic loss, like any belt driven assessory, like a/c, etc.

Now, not all turbos have turbo lag. This commen misconception really irritates me. Bigger turbos will have more lag, smaller less in general right? Yes, but there are ways to further reduce and or elimiate lag.

First, get a ball-bearing turbo. They cost a lot more, but are worth it. They spool 800-1000 rpm sooner than the equivelent standard turbo. Right there is less lag. From there, decide how much power you want as a goal. You can there figure of the flow rate of air you'll require to achive this, in cfms. Then you can pick a turbo where this number falls into the 70% effiecency island on the compersor map. If you in the end are only running 8-10psi of boost for a moderate gain, say 225hp as a target goal, you can virtually elimate lag by choosing the right sized turbo and making sure it's ball bearing. Tubro sizing is very important in making sure you have the optimum balance between power about and minimal lag. Also, some of the new turbines and compressor wheels seriously reduce lag even further. There's a lot more to a turbo than choosing a T3, T3/4, GT28, etc and slapping it on. The choices you make can either help reduce or eliminate lag or make it worse, depending on the size or the turbo and a/r housing, the turbine wheel, comprssor, ball bearing or not, etc. Not all turbos are the same, there is a lot more than one type of turbo, don't kid yourself by thinking otherwise.

An intercooler is always a good idea, turbo or supercharger. Why? for even 11.1 degrees you lower the intake temp you get a 1% gain in hp. The air gets hot in a turbo and supercharger when it's compressed. A good intercooler can lower the intake temp by 100 degrees. This is a 9% gain in HP, so if your motor was 185hp before, that's a 16.2hp gain, or 201 total hp approx for the motor. This of course is an example, but you can see how it works. A more effecient intercooler will yeild cooler air, meaning more power. Cooler air = more power because cooler air is more dense, meaning there are more air molecules packed in per sq. cm.

An intercooler also helps reduce detonation and knock by cooling the intake air. Heat can create detonation, and without an intercooler, there is a limit to the amount of boost you can safly run, even on a built motor. This is true for both super and turbo chargers. If your running the Jackson Racing or Vortec Supercharger, your limited in the amount of boost you can run without using their aftercooler (water-air like Vortec offers as an option) or an intercooler.

Now, the Vortec Supercharger is a cyntifigal supercharger. This type of supercharger tends to have no low end and create all it's power on the high end. This basically has the same result as "turbo lag." No real added power down low, then the power hits up higher in the rpm band. Even with supercharger, the amount of "down low" power came be changed. A cyntrifigal supercharger doesn't provide good power down low, it tends to make all it's power high in the rpm band, as I said above. This type of supercharger would have the same effect as a big turbo, basically creating "turbo lag."

With both Superchargers and turbocharger, you can effect the amount of lag depending on the type of supercharger, whether the turbo is ball bearing or not, the size of the turbo, the turbines, etc.

Wow!!!!

this thread shoudl be deleted

this thread shoudl be deleted

Hey, he stated some incorrect things, so I corrected him. What the heck is the purpose of your post saying that. We can all see tThe sticky thread on it at the top. However, it was clear this guy didn't understand some concepts. Therefor I posted to help clear them up a bit. Why should it be delated? Who are we to decide to delate it. It didn't brake any rules, it's not a flame fest. Maybe he did post something repetitive that gets covered a lot, and that theres a sticky on to boot. But that doesn't mean delate it. The poor guy didn't understand some basic concepts, so I corrected him and helped him understand. I'd rather help correct them and help him understand than have a misinformed "tuner" running around.

That doesn't mean it should be delated. Comments like this only serve to up your post count. There's no need to post comments like that.

It serves good information. Pretty interesting, although I already knew most of it, its still a pretty informative/easy to understand post if you dont know shit.

should be added to the turbo 101 thread. well at least the info that wasnt stated in that thread. good info

Thought I would put something in.

Although there is only one type of turbocharger,
Ok, I definately agree that all garrett type turbos are more or less the same, they're use the same design of parts and such. The engineering between different A/R scrolls and center sections isn't terribly different. But there ARE several vastly different turbos, such as the VATN, which stands for Variable Area Turbine Nozzle... basicly it has variable A/R on the exhaust side. Provides a very wide powerband(fast spool, great efficiency) and cool boost temps, plus reduced exhaust backpressure for further volumetric efficiency gains. However, considering your statement against your descriptions of different types of superchargers, I think your general idea is correct. All turbos that I know of use centrifugal compressors and are powered by exhaust heat and pressure through a turbine. Although the VATN is different enough that I would consider it a different type of turbo.

The next one is called the roots blower, this is called a blower cause thats what it does. Unlike the other systems which compresses the air into the engine, this system simply moves the air more quickly, it blows! You dont see a lot of roots (at least i havent), because the twin screw type does the same job with less heat. Heat = horsepower loss.

It seems I've been talking about roots blowers and awful lot lately. Roots blowers were originally used on tractor trailer 2 stroke diesel motors. These motors had low rpm ranges and poor volumetric efficiency due to the 2 stroke setup. Its difficult to get all the exhaust out of the motor with a 2 stroke setup(if you don't know how a 2stroke works, www.howstuffworks.com and read...), so the roots blower was born. The nice thing about a roots blower is its a positive displacement device - every time it turns once, it displaces(moves) the same ammount of air. The original idea behind it was to have the blower displace about the same ammount of air that the big 2stroke diesel should theoretically displace in one engine rotation. Essentially this would 'blow' the exhaust out of the motor, giving the engine a nice fresh charge instead of one contaminated by exhaust. Hence the term, 'blower'. Hot rodders back in the day(40s/50s?) took these blowers that were meant for large displacement 2 stroke engines(which take in twice the air as a same displacement 4 stroke per revolution) and put them on big gasoline 4 stroke v8s. Since the blowers displaced more air than the engine could take in, it created pressure.
Its true that roots blowers generally aren't as efficient as screw type, but screw type is just coming into the mainstream. Roots type have had a HUGE jump on screw type, I mean if you go to any hot rod show or drag race and I guarentee you'll see many more roots blowers, and this is 50 years after roots blowers started to be used on gas 4 strokes. For newer cars, positive displacement blowers aren't used very often. With all the new(within 20 years) engine management systems, smog systems, body designs, overhead cams, etc, engine bay space is at a premium. I mean, a 460 cubic inch big block Ford is probably skinnier than a 4.6(281 cubic inch) OHC motor. You're not going to see many roots blowers on newer cars, certainly not on anything but a v8 or v6. Roots are on their way out, screw is on the say in. I doubt any company is really interested in figuring out how to stick a big GM 8-71 blower on a Honda or any new motor for that matter. Its just very old technology that isn't worth investing in any more. Onwards and upwards...


The Centrifugal supercharger also suffers from turbo lag, because its driven by gears.

Not quite. You're right that the centrifugal suffers from lag of sorts(not really turbo lag since it only hits peak boost once...), but not because its driven by gears(well not mainly). Its right in the name... centrifugal. Means center-fleeing, which is what any mass will do when you spin it in a circle. Inertia makes it want to move in a straight line, which on the path of a circle always leads outwards, away from the center. So basically this design takes air molecules, and 'throws' them with the compressor wheel, they smack into the walls of the supercharger's scroll, into each other, etc. This results in compressed air. Obviously, the faster the turbine spins, the more violently the air molecules will the thrown outwards. The more violence, the more pressure it produces. The problem this implies is, the slower is spins, the less pressure. So no matter what you do, you'll only hit peak boost once. However, since boost rises with RPMs, you might be able to run more peak boost than a roots/screw type or turbo. With RPMs, based on fuel and air and fluid thermodynamics which are far above my head and probably most people reading this, engines become more detonation resistant. So while you may not be able to run 10psi at 3000rpm, you may well be able to at 6000rpm. With a centrifugal type, you may have say 6psi at 3000rpm(which our theoretical engine can take), and also full 10psi at 6000rpm. I think its safe to say we'd have more power with this than with running 6psi on a turbo or roots type throughout the powerband.


If your racing you can eliminate turbo lag by reving your engine so you get some boost going. And then launching.

For a turbo, this only works with either an auto with a decent stall(2500-3500rpm) or a very small exhaust turbine, which will kill mid to top end power and generally make your motor inefficient and nothing to be dubbed 'performance'. A performance turbocharged car WILL have lag. I know some stock cars(specifically turbo mopars) have very little if any turbo lag, and thats simply because these are cars that aren't turbocharged to be a performance car. Mopar simply could not get a sufficient power level N/A, so they put a small turbo on it to give it some extra oomph. Go drive an Audi TT or a turbo Porsche or turbo supra or any real turbocharged sports car, ease off the clutch so you're just at a roll, and put your foot to the floor. You won't move anywhere very fast for a few seconds as the RPMs creep up to the boost threshold... then hang on. However, with a performance car you'll get performance gearing, so with first gear you might get to 20 or 30mph, but not much more than that. The audi tops out at like 25mph in first. It'd be a better experiment to gun it while in third at 1500-2000rpm.


If your running a force inducion system I strongly reccomend a high-flow exhaust system and an intercooler to cool the incoming air. Cooler air = more horses.

Amen. For a turbocharged or positive displacement supercharged(roots, screw/lysholm, vane, rotary, etc, etc etc) engine, the least exhaust is the best exhaust(after the turbo). With a positive displacement blower, you're not worried about exhaust scavenging, the blower takes care of that at any RPM. With a centrifugal, at low rpms where no boost is created, then you need headers/scavenging. However, if its an all out drag/race motor, then you don't really need it.. If you're a decent driver, you'll never fall out of boost. Then again a centrifugal doesn't belong on a race car IMHO.


A supercharger is good where boost at low rpm is needed, such as off-roading or towing. A turbo is great if you have an awsome street machine.

Most sactioning bodies in a lot of racing(esp. drag) forbid turbos. Why? Just like anything thats outlawed in racing, its an unfair advantage. For drag you pretty much have to be running in an Unlimited class to use turbos, and then you're up against a lot of big dollar car with big pony motors. Kinda sucks for the drag racer. Your best bet for competitive drag racing is a positive displacement blower, nitrous, or N/A. either that or bracket race with a turbo. But a turbo may just complicate launching, so just run N/A in that case. Its sad really, especially since I'm a drag race and turbo guy.

Okay, on to the next post!(sorry this is getting rediculously long...)


Now, not all turbos have turbo lag. This commen misconception really irritates me. Bigger turbos will have more lag, smaller less in general right? Yes, but there are ways to further reduce and or elimiate lag.

First, get a ball-bearing turbo. They cost a lot more, but are worth it. They spool 800-1000 rpm sooner than the equivelent standard turbo. Right there is less lag.

Right, let me elaborate. He's correct on this, but there are other ways. One is to retard your timing and inject more fuel. Both of these things(rich condition and retarded timing) will create a lot of exhaust heat - turbos are driven off of exhaust heat and pressure. This supposedly creates a near instantaneous spool. I have never tried it, I plan on trying it when my next motor is together, but for now, I'm only speaking someone else's words. I haven't heard this very often, but the concept makes sense, and I think it would definately help. However, its not the best thing for your motor, I wouldn't recommend using it very often. When you go to the drag strip, fine. Or when you shift too early and are out of your boost range, sure. Another is to inject nitrous. Nitrous creates more exhaust heat too. Simple enough. You can run staged turbos, where you have multiple turbos, one small one and one larger, so you spool quickly with the small and have decent compressor efficiency at the top end and normal exhaust backpressure. Another way is to run a turbo and a positive displacement supercharger at the same time. Also a popular thing on big rigs. The turbos feed into the supercharger which feeds the engine.

An intercooler is always a good idea, turbo or supercharger

The advantage(lower temp) and disadvantage(pressure loss) get too close at low boost levels, most say under 10psi, I'd say under 8psi to be safe. The overall benefits vs cost isn't very favorable, you'll probably end up paying $300 for an intercooler that gives you 5 or 10hp. A windage tray will get you that much for a tenth of the price. You can see why this happens at low boost pretty easily. Intercoolers have efficiencies, as I'm sure you're aware, and the ideal gas law also has a say in the matter. Generally if you're running low boost and an average efficiency turbo, at 6psi you wont have terribly high compressor outlet temperatures. So say on a 80* day on 6psi your inlet temperatures are, oh, 140*. You have a 50% efficient intercooler, so you drop 30*. According to your formula(where'd you find that?), you just gained 3%. 3% of a 225hp engine is a hair under 7hp. For me, 7hp isn't worth an intercooler. I'd rather run without.

I think that about covers it. I'm not sure if there are still debates among professional racers about what makes more power, turbo or supercharger, since turbo is clearly superior in that field. In ease of installation, a centrifugal type supercharger wins. However, they're also the worst performing type of FI. For low end grunt, a positive displacement is the best. All out balls to the wall racing, turbo all the way.

Hope I helped. If I got anything wrong, let me know...

posted by duplox:

For me, 7hp isn't worth an intercooler. I'd rather run without.

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Wow, running turbo w/o intercooler? is the engine not gonna get overheated?? Loosing 7hp (after gaining 50 or more horses) compare to having hard time plumbing the intercooler is such a great deal ( since i thought we have to have intercooler to run turbo )

Roots are on their way out, screw is on the say in. I doubt any company is really interested in figuring out how to stick a big GM 8-71 blower on a Honda or any new motor for that matter. Its just very old technology that isn't worth investing in any more.


Actually, there ARE some companies that make roots s/c for Hondas, check up, Jackson Racing. Even toyota makes their own roots for their cars. I also heard mercedes, and some other german makes have signed a contract stating they will ONLY use Eaton superchargers.

Actually, there ARE some companies that make roots s/c for Hondas, check up, Jackson Racing. Even toyota makes their own roots for their cars. I also heard mercedes, and some other german makes have signed a contract stating they will ONLY use Eaton superchargers.

Let me elaborate on this comment and the comment you quoted.

Jackson Racing DOES use Eaton based Roots s/c, very true. So do many OEMs still, like the ION redline and Mercedes s/c cars. However, even the most effiecent roots blowers have an adiabatic effiecency of around 60%. While this is much imporved over the older roots blowers, it's still not up to par with the most efficent turbos.

It realy all comes down to goals. As the designer or driver, what are the goals you have, why are you looking for added power, and where is it important to achive this power in the power band. Is it important to have the extra power down low, do you need a more linear power curve, is 1/4 mile trap speed important or is it only peak hp you are after? This all plays into which s/c type is the benifital type to use for any given application.

The major benifit of the roots blower is the immediate and proportional response to the throttle: the blower is almost always pumping near the same volume of air. It has a very linear power curve, espically when compared to other turbo types like a centrifugal s/c.

However, roots blowers typically can't pump up the ps too much. A Jackson Racing s/c really isn't any good above 10psi, thats considered the limit for the amount of bots you can run with it, and this is assuming you've upgraded the nessasery things to achive this type of boost safely.

Now the Centrifugal s/c, as I said, has no low end whatsoever. It is more like a shaft driven turbo, with a shaft attached to a step-up gearbox (or belt drive) replacing the exhaust side housing, and this in turn spinning a turbo-esque compressor. This type of s/c makes great peak power, but the low end is non-existent. These type of s/c's, even though they may be considered "more efficent" than a roots blower, tend to be "laggy" and ess responsive. Much like a gaint turbo, they basically suffer from "turbo lag," but without the power potentail output and boost levels of a comparable turbo. Like big a turbo, these s/c build boost slowly in proportion to engine speed and rpm. The closer to redline you get, the more boost and power. The power typically peaks at redline. These characteristics, though present in all turbos to a certian extent, are typically found more in the big turbos, when the greater lag is noticed and the turbo peaks at near redline (versus the smaller turbos where the lag is much less and it peaks sooner).

A centfigul s/c is basically a shaft driven turbo in a sense. The nature of this s/c means it operates with different characterisitcs than a rots blower. If you are looking into an s/c an low end grunt and a predictable linear power curve are desired, then a roots blower may be more up the ally than a centrifugal one, despite the fact it is "less efficent."

Now I personally perfer turbos regardless, as I sort of explained n my first post. However, if you are set on going the supercharger route, which style is best really depends on your end goals. If you care more about high end output and speed, and want a fairly streetable low end (which will help traction), then the centrifugal design, where power is proportional to engine rpm, may be up your alley. The "lack of" a low end will help keep traction of the line, etc, and in daily driving, despite the high peak HP numbers this s/c can attain. However, even though the peak numbers are lower, if you are looking for only increased low end grunt and a predicatable linear power curve (say for autocrossing), then the roots blower may be up your alley. It may not have the tuning possiblities of a turbo, or the high end of a centrifugal s/c, but if these are your goals, then it doesn't matter. In this since "old design" or not, changes are this type of blower will always have a place somewhere (like lots of school buses use roots blowers for these reasons, low end power and linear predicatable power curve, peak power isn't important in this case).

I see, but why is there a limit for a roots s/c?

The reason why I like s/c's are because of simplicity, doesn't require a professional to install it, costs cheaper than turbos, and you need to buy accesories that are like strings attached which costs you more money, I also prefer throttle response (roots) over pure power anytime.

I see, but why is there a limit for a roots s/c?

The reason why I like s/c's are because of simplicity, doesn't require a professional to install it, costs cheaper than turbos, and you need to buy accesories that are like strings attached which costs you more money, I also prefer throttle response (roots) over pure power anytime.

Well, one reason is with a Roots blower, the supercharger assembly is usually cast into a special intake manifold, which is of course part of the engine. This makes it rather difficult to package an intercooler into the design with it. Furthermore, it's hard to plumb an intercooler into a roots blowers long trianglar discharge vent.

This lack of parcitcality in terms of an intercooler means it is usually not an option with a roots blower (if you do manage it, it can be quite spendy). This limits the amount of bost you can really throw at it, as higher boost levels result in more heat, and without an intercooler, this will result in engine damaging knock and detonation.

Now, as I said earlier, there are other ways to get low rpm hp besides roots blowers. The newer low-interia, low friction small turbos can spool up faster (good throttle response), resulting in more boost at a lower rpm than even a roots blower. With turbos, it's all about choosing the right sized turbo for your appilcation. Different sized turbos are ideal for different appications. If you take the time to learn, you can find the right sized/engineered turbo for your application, even if the application is low rpm boost.