Basic Principles in SuperCharging: A Go Kart With More Bolt On Power

 

“Ram more air fuel mixture in, get more power out.”

Supercharging gets its name from the Latin word “super” (pronounced soo pear)  meaning “I conquer”  and the English word  “charging” which means the air charge that goes into the engine during intake cycle. The engine is having an additional air charge being (conquered) compressed into the intake stroke.

This translates into more fuel air volume being burned per intake stroke. What this means to you and me is that there is more pressure pushing down on the piston and therefore more power going coming out of the engine.

They’re different methods for ramming more air into the engine and they basically are as follows:

– The turbocharger

– The centrifugal  blower

– The roots blower

– The off set blade blower

– The scroll blower

– The turbine compressor blower
Each one of these different types of superchargers or blowers generates its compression energy from the engine or from some source somehow.

The blower that saps the least amount of energy from the engine is the turbocharger. Basically the turbocharger uses expended exhaust gases and takes advantage of the expanding heat energy from these exhaust gases and turns the turbine. The turbine then turns a compressor turbine which rams air into the intake. The remaining other compressors in the list above use belt drives or electrical drives that come off the engine.

The centrifugal blower for example uses a belt drive that comes off the drive shaft of the engine and turns a blower. This belt drive consumes energy from the engine.

The most cost-effective supercharger method is to use the turbocharger. The reason for this is that it is the most reliable and readily available supercharging method available at low cost. This however does not mean that it does not have its own subtle complexities and design challenges. What I do mean however is that it is the most cost-effective meaning under $200 supercharging method available to a enthusiast. The belt driven superchargers however have higher response rates but have the corresponding cost issues due to the tight tolerances  that are required for manufacturing the supercharger in question.

We’ll briefly go through each designed so that you understand what they do and how they’re made.

The turbocharger uses a high-speed turbine which runs off the exhaust gases. The turbine runs a compressor is on the other side of a shaft. The design challenge is that the turbine shaft must be supplied with oil at all times. The design challenge  is coming up with a system that generates the oil pressure necessary to run the turbine or keep it from seizing up. The other design challenges that you want to develop your own custom manifolds which in most cases is not that difficult.

The final design challenges coming up with the manifold and pressurization system that will work with a small engine.

There are two methods to tackling the pressurization problem:

– Sucking air through the carburetor into the turbocharger and into the engine

– Ramming air into the carburetor and into the engine.

Both systems are viable, however the second method is the most cost-effective. The first method sucking the air through this turbocharger into the engine requires tight sealing and may not start initially when the engine is required to start. Additionally there will be Turbo charger lag due to the extended length of the manifold from the mouth of the turbocharger to the engine block itself. It is however  the safer method in that you do not have to do plumbing to your gas tank and carburetor.

Ramming the air through the carburetor requires that the carburetor itself be pressurized and that the gas tank itself as well be pressurized. Not all carburetors are able to be pressurized and a thorough knowledge of carburetor principles needs to be understood before undertaking pressurization of a carburetor.

The Centrifugal Blower

The centrifugal blower utilizes a belt drive that spins a glorified fan or turbine. A simple centrifugal blower can be developed that can generate 1/2 to 1 psi pressure using every day materials. However to get pressures any higher the tolerances between the impeller and the housing and all the seal of components needs to be tightened up. Additionally lubrication and drive components need to be addressed seriously. The problem with the belt drive system is that the belt itself (especially that of the belt) generates large side loads on the shafting which causes it to heat up and the heat will not dissipate readily in the belt pulley interfaces. A better system to use would be a kind of belt that has cogs on it.   This is know as a cog belt .  The cog belt and the supercharger orientation relative to the engine needs to be very exact otherwise the cogged belt will destroy itself or jump the track. The nice thing about a cogged belt is that it does not exert side loads on the shafting large enough to cause the shaft heat up. And finally the shafting itself in the bearing lubrication needs to be given tight clearances, polished surfaces,  and lubrication otherwise the shafting will heat up and gawl between that shaft and the bearing interface.

The amount of effort that is thrown into developing a mere one (1) psi is certainly not worth the time and cost to use the centrifugal style blower; the better option would be to use a turbocharger with the belt drive on it,  however even that needs to be lubricated.  Additionaly a turbocharger needs to rotate way above and  beyond what the engine connections put out. The turbocharger runs at around 60 – 100,000 RPMs to generate the kind of pressure needed to give good engine performance.

Electrical SuperChargers

There are electrical superchargers available on the Internet, however the pressures that are needed to generate horsepower that is noticeable, especially on a small engine is close to five 2 to 10 psi and a electrical superchargers not going to give you that kind of pressure. Additionally the added weight of having a battery will be needed which will far outweigh what a supercharger is really adding for power to weight ratio benefit, especially on a go kart.

Roots Blower

The roots blower is a supercharger that uses two interfacing cam gears that rotate relative to one another. They really aren’t gears or cams,  and they are expensive in their manufacture. The reason why they are expensive is on a couple levels:  first of all the cam lobes themselves need to be machined or developed using high tech machining processes. Secondly the relationship between the cam lobes to one another is related by a gear set. And finally the whole housing needs to be developed which is closely paired up with the lobes so pressure losses or blow by not allowed. So you can see that the cost of the roots blower is very expensive and not cheap. It however adds a benefit in that the pressure is always there when you want it versus a turbocharger which needs to generate boost or as a turbo lag. That is why most dragsters use roots blowers because the boost is “now” when it’s needed.

There are roots blowers that are sold for racing go carts, however they are expensive upwards to $2000 – $3000 alone.

The Offset Blade Supercharger

They offset blade supercharger uses a rotating drum with blades that come in and out of it. The blades are flung out with centrifugal force up against the walls of the supercharger housing. The rotating drum is offset so that one side has a larger volume than the other. The blades sweep along captivating air and ramming it out the other end. This particular supercharger is used on low-budget blowers in automobile motor industry especially in exhaust recirculation systems. They were available in the late 70s and 80s and progressively became obsoleted when fuel injection became more efficient. However some older exhaust recirculation pumps are available and can be used as superchargers.

The downside to this particular superchargers that it does not have an intake filter and so care must be taken to put a filter into the intake system. The air will have to be rammed through the intake filter versus being sucked through. So the air filter will need to be put in the downline from the offset blade supercharger.
Offset superchargers are by themselves complex in machining and parts development, however because they are the most available on the market they do lend themselves to being a cheap alternative to a turbocharger.

The tolerances between the housing, the veins in the rotor, need to be tight otherwise you have leakage and loss and so one of the downsides to the offset superchargers that may be not able to develop as higher pressure as the turbocharger could. Instead of developing 5 to 10 PSI you may only be able to develop 1 to 3 psi. Additionally a special polling only to be developed that will take the RPMs and crank them up on the supercharger itself.

The Scroll Supercharger

The scroll supercharger uses the involute spiral method to cause a mashing, ramming action. Basically to involute spirals are meshed into one another. The one involute spiral is moved in and in eccentric fashion and causes a rubbing scrubbing the ramming action.

As can be guessed the tolerances between the involute spirals needs to be quite tight as well as the edge of the involute spirals needs to be quite tight relative to the mating surfaces. Otherwise leakage will occur and pressure cannot be developed.

The Turbine  Supercharger

The turbine supercharger is a set of turbine blades that are set up like a compressor section on a jet engine. The turbine itself is turned by a belt  drive or a gear drive.

This particular superchargers is not as readily available due to its complexity. The individual turbine blades need to be machined out. The housing of the supercharger as well needs to have close tolerances so the pressure can be developed.

Multistage Centrifugal Force

Multistage centrifugal blowers utilize centripetal blowers that are stacked on top of one another. Some of your higher suction vacuum cleaners used to stage blowers to this effect. The trouble with vacuum cleaners is the the amount of pressure that can be developed by them is not high enough to actually supercharger engine. The amount of pressure developed by stacking for example is usually only around one (1)  psi at the most. The reason for this is the tolerances on the blades and the leakage that occurs cannot develop the heads necessary for higher pressure. Also the RPMs of the motors can not reach the high RPMs needed for good head pressure.

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One Response to “Basic Principles in SuperCharging: A Go Kart With More Bolt On Power”

  1. if you ever want to supercharge a go kart… an old smog pump works great!

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