View Thread: Turbocharging, Supercharging and etc.

The advantage of turbocharging is obvious - instead of wasting thermal energy through exhaust, we can make use of such energy to increase engine power. By directing exhaust gas to rotate a turbine, which drives another turbine to pump fresh air into the combustion chambers at a pressure higher than normal atmosphere, a small capacity engine can deliver power comparable with much bigger opponents. For example, if a 2.0-litre turbocharged engine works at 1.5 bar boost pressure, it actually equals to a 3.0-litre naturally aspirated engine. As a result, engine size and weight can be much reduced, thus leads to better acceleration, handling and braking, though fuel consumption is not necessarily better.

Solution to Turbo Lag
The first “practical” turbocharged road car eventually appeared in 1975, that’s the Porsche 911 Turbo 3.0. To reduce turbo lag, Porsche engineers designed a mechanism allowing the turbine to "pre-spin" before boosting. The secret was a recirculating pipe and valve: before the exhaust gas attains enough pressure for driving the turbine, a recirculating path is established between the fresh-air-charging turbine's inlet and outlet, thus the turbine can spin freely without slow down by boost pressure. When the exhaust gas becomes sufficient to turbocharge, a valve will close the recirculating path, then the already-spinning turbine will be able to charge fresh air into the engine quickly. Therefore turbo lag is greatly reduced while power transition becomes smoother.

The 3.3-litre version 911 Turbo superseded the Turbo 3.0 in 1978. It introduced an intercooler at between the compressor and the engine. It reduced the air temperature for 50-60°C, thus not only improved the volumetric efficiency (in other words, the intake air became of higher density) but also allowed the compression ratio to be raised without worrying over heat to cylinder head. Of course, higher compression led to improved low-speed output.

Twin-Turbo: Parallel or Sequential ?

The use of twin-turbocharger is a question of both efficiency and packaging. For larger engines, say, 2500 c.c. or above, it is better to use 2 smaller turbochargers instead of a big one, as small turbines reduce turbo lag. Today, performance cars no longer employ a large single turbo like the early 911 Turbo.
For V-shape and boxer engines, it is also recommended to use twin-turbo, because one turbo serves each bank shorten the turbo pipes and save a lot of space. Moreover, the shorter the pipes, the less turbo lag generates.

Some twin-turbo engines have the turbos arranged such that exhaust flow from one bank of cylinders drives a turbo which boost the intake of another bank. This is actually the concept of "feedback loop", which helps reaching power balance between two banks.

Most twin-turbo engines have the turbochargers arranged to operate independently, each serves one bank of cylinders. This is so-called "Parallel Twin-Turbo". An alternative arrangement, "Sequential Twin-Turbo", was designed to improve response and further reduce turbo lag. The turbos operate sequentially, that is, at low speed, all the limited amount of exhaust gas is directed to drive one of the small turbines, leaving another idle. Therefore the first turbine will accelerate quickly. When the exhaust flow reaches sufficient amount to drive both turbos, the second turbo intervenes and helps reaching the maximum boost pressure. Unfortunately, sequential twin-turbo requires very complicated connection of pipes (exhaust from both banks should reach both turbos; so do the intake pipes from both banks), thus is now losing interest from car makers. Porsche 959, Mazda 3rd generation RX7, Toyota Supra and Subaru Legacy are the only applicants as I know.

the compressor is driven directly by the engine crankshaft, it has the advantage of instant response (no lag). But the charger itself is rather heavy and energy inefficient, thus cannot produce as much power as turbocharger. Especially at high rev, it generates a lot of friction thus energy loss and prevent the engine from revving high.
A typical supercharger transforms the engine very much - very torquey at low and mid range rpm, but red line and peak power appear much earlier. That means the engine becomes lazy to rev (and to thrill you), but at any time you have a lot of torque to access, without needing to change gears frequently. For these reasons, supercharging is quite well suited to nowadays heavy sedans, espeically those mated with automatic transmission. On the other hand, sports cars rarely use it.

The introduction of light-pressure turbochargers also threathen the survival of supercharger. Volkswagen group, for example, dropped its long-standing G-supercharger and chose light-pressure turbo. Now supercharger is completely disappeared in budget cars, leaving just a few GT or sports sedans which pursue high torque without much additional to employ it. General Motors is perhaps the only real supporter to supercharger. It offers a 3.8-litre supercharged V6 for most of its budget mid to full-size sedans.

Ram Air
Ram air device can also provide forced induction. When the car is travelling in speed, air will be forced into the engine manifold through the ram air inlet which usually locates on the top of bonnet. That create a slightly higher pressure than normal aspiration.
In fact, you can see ram air devices whenever you watch motor racing. The air box in every formula 1 race cars and the roof air inlet of GT race cars are all ram air devices. A Formula 1 engineer said a typical air box can gain 20 horse power when the car is running at 200 kph.

Advantage: Little additional cost
Disadvantage: Also little additional power, available in high speed only.
Who use it ? Ferrari 550 Maranello
Lamborghini Diablo SV and GT
McLaren F1
GM Pontiac Firebird WS6 and Chevrolet Camaro SS

The grand am GT also uses ram air :fyi:

Anyway, in simpler terms, what is the difference between turbo and supercharging?

GREAT read there dude :cheers:

Originally posted by ROD
The grand am GT also uses ram air :fyi:

Anyway, in simpler terms, what is the difference between turbo and supercharging?

GREAT read there dude :cheers:


It seems to be that turbocharging is excess gas that rotates the turbine in order to gain excess power while supercharging has the compressor driven directly by the crankshaft which increases power . Supercharging wont give you the lag because it kicks in quickly but also gives out at a low range while turbocharging will last throughout the whole range. Turbos seem to be more beneficial for sports cars and s/c's are better for large sedans.

Those were just some examples of the cars that use ram air, btw. The Viper GTS uses it as well.

Sia Bani
Great read definitely....:D this would have been better in the Garage right?

Superchargers give monster torque, but I wouldn't say they're only for low-rpm boost. It all depends on the pulleys, just look at some Comptech Supercharged Hondas/Acuras for that. S/C'ed engines that still give'r to 7K rpm.

Turbocharging doesn't necessarily cause low torque either. Check the 1.8T for that.

And ram air is just a cheap, easy way to give almost no more power but have a gimmick to sell on. If I removed my front bumper I'd have a "ram air" system.

Ram Air supposedly works once you hit 200 mph but who hits that high anyway besides race car drivers?

Originally posted by lexus1581
. Turbos seem to be more beneficial for sports cars and s/c's are better for large sedans.

Turbo reliability has historically been generally lower than supercharger reliability, which explains why big manufacturers sometimes opt to supercharge instead, even in "sporty" cars. Turbo reliability has increased, but...
Also, supercharged sedans like the 2004 Pontiac Grand Prix can run on regular gasoline --- the turbo's I've driven have all required premium.

I wasnt talking reliability but you are correct in your statements.

What i referring to was how s/c's tend to increase power and are used more in large sedans while turbos are for the sporty compact cars/coupes where they tend to increase power at a pretty good rate.

Originally posted by lexus1581
What i referring to was how s/c's tend to increase power and are used more in large sedans while turbos are for the sporty compact cars/coupes where they tend to increase power at a pretty good rate.


Maybe someone can explain why GM chose to supercharge the Saturn ION Redline, which uses the same 2.0L Ecotec in my sig and in Saabs --- turbocharged in those cases. You'd think reliability wouldn't be an issue if Saab and Opel use them regularly.

So maybe cost is an issue, too.

I'm not aware of any supercharged 2.0L's used in the Ecotec setups in Europe. Highly unusual.


They both give the same amount of torque at X CFM, the turbo more actually, theres none lost through a belt. Reason you usually see lower TQ turbo engines is most large displacement engines don't run them, fortunatly thats changing now, there's single turbo kits running on stock LS1s that with just a cam are putting out ~600 ft lb, and only limited by the stock compression and rotating assy.

They SC'd the ion because it provides a better powerband then a turbo would on that little engine.