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Old 01-22-2005, 12:00 AM   #1
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formula for figurein boost and good info on super chargers

SUPERCHARGERS


Supercharger Overview
Boost -vs- Compression

.

PAXTON
VORTECH
Jackson Racing

Supercharger Overview

Superchargers, also called Blowers, are essentially Air Pumps turned by a belt driven off of your crank. They come in two main types: Positive Displacement and everything else. I realize that sounds like an overly simplified classification, but it really is that simple. Positive Displacement Blowers, such as Roots Style, move a certain amount of Air with each revolution. They are classified as "external" compression superchargers as all of the "boost" is made in the manifold and not in the blower itself. This style of blower raises your effective compression all the time. This is why they are mainly used only on Race cars and Show cars, not on your daily driver. Most street driven cars with these blowers run low boost and low motor compression. In these cases the blower is more for looks than performance, or is an attempt to make a low performance motor into a higher performance motor. For this reason I don't recommend this style of Supercharger, and wont go into it any further.

Most modern Superchargers are centrifugal style. These are classified as "internal" compression as they produce much of their "boost" in the blower before sending it on to the manifold. This design was heavily used way back in World War II in military planes. It was used to overcome the thin air at the high altitudes that the planes were forced to fly at. It wasn't until recently that this design really took off. While Paxton has been making this style blower since day one, it took a competition with Vortech to really bring the blower to popularity. Paxton superchargers have actually been used on some special edition cars the factories used to turn out. Today, things are a little different. Paxton's design problem lead Vortech to do a slight change that made a huge difference in both performance and reliability.

Paxton has always used huge ball bearings as a form of planetary gear to step up the speed of the impeller. The impeller is what spins to create the boost. The problem with this design is that the bearing must fit very tightly so as not to slip. This means it takes lots of force to turn the blower and the tightly packed bearings are going to get very hot. As a test, I used a torque wrench to measure how much force it takes to turn a paxton - 42 ft lbs. That means your motor has to really work to get its extra power. If it takes 60 horsepower to get 120, is it really worth it. The problem with all the heat is that the ball bearings begin to slip and you loose boost. This usually happens when you reach normal opperating temperature. Paxton has tried to fix this with special fluid coolers and bearing retainers, but this is a patch at best. To creat a new Super Blower, the Novi 2000, Paxton used a gear drive like the one Vortech has used since it's day one. The problem with the Novi 2000 is its cost. While I will admit it is a really great blower, it's just not cost efficient.

If it sounds like I am biased towards Vortech, your right! I have had a Vortech A-Trim since 1992 and that same unit has worked flawlessly for about 50,000 miles. I have used a pulley configuration that Vortech does not recommend, to gain boost levels they claim are not possible, and it just keeps working perfectly. For these reasons I can't recommend any other blower more than Vortech.

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Compression -vs- Boost
Almost as fast as a supercharger can be bolted on, the question of how much boost can be run is instantly a concern. When building up a motor to be supercharged, you've also got the question of just how much compression to run. Both of these questions relate to essentially the same set of equations. Assuming that all of the other requirements of the motor are satisfied, the compression -vs- boost aspect is not all that difficult.

The only way to make more power is to increase cylinder pressure and burn more fuel. The main purpose of the supercharger is to supply the motor with a more dense air charge, which allows for the ability to burn the additional fuel. By adding a supercharger, additional air should no longer be a problem. Ensuring that there will be enough additional fuel to maintain the proper air to fuel ratio will be the key to using the maximum effective compression.

All motors have a static compression ratio. This is the amount that the air inside the cylinder is compressed. It is a ratio of the cylinder volume at BDC to the volume at TDC. When a supercharger is added, additional air is forced into the cylinder effectively raising the compression ratio. The result of this is called effective compression. The formula for finding the effective compression is very easy:

((boost psi / 14.7) + 1) x motor compression = effective compression.

The effective compression allows a supercharged motor to be compared to a normally aspirated motor. For the most part, a supercharged motor with the same effective compression as a (similar) normally aspirated motor with the same static compression should have about the same overall power.

This may bring up the question that if the overall power should be about the same, why go with a supercharger? The main advantage of the supercharger is that it allows for a moderate compression level during normal driving while allowing for very high compression levels when needed. Obviously a high compression motor of about 14:1 makes a lot of power, but it would never survive daily driving. A lower compression motor is great for daily driving, but greatly reduces the potential for power. The supercharger allows for higher compression levels than could be used without a supercharger, while still offering the benifits of a standard compression motor. Many street supercharged systems will go beyond 18:1 effective compression under boost. Under race conditions, many supercharged race motors will go well beyond 22:1 effective compression. Both of these levels are far beyond what could be done reliably or cost effectively without a supercharger.

This brings us back to the question of just how much boost or compression can be run. Obviously there can't be a simple number that could be used for every application. This is why it's so critical to chose the proper components. It's not necessary to build a low compression motor to use a supercharger, but the correct parts are still necessary. The biggest factors will be in things like head bolts (or preferably studs), gaskets, and the strength of the other engine components. It goes without saying that the incredible power that a supercharger can add, can easily start breaking things. It is very important that as the boost levels rise, the need for a stronger crank, rods, pistons, etc... becomes very critical. Many people forget this as the motor itself is relatively mild, while the supercharger pushes it well beyond the practical limits it was intended for.

Now, back to the compression issue. Anyone who has looked into supercharging has heard that you need a low (static) compression motor. This may have been true once upon a time, when roots type (positive displacement) superchargers ruled the land, but it's not so necessary now. The problem with a low compression motor is that it relies heavily on the supercharger for its power. An 8:1 motor is definitely not going to be a power house. Sure, you can throw 18 lbs of boost on it and get some real power, but why? A higher compression motor of 9.5:1 will have much more power without the blower. Then, with less boost you could easily have the same overall power - only it would be much more usable. Both of the motors (8:1 with 18 lbs boost and 9.5:1 with 12 lbs boost) will have almost the same effective compression and about the same overall power. The big difference will be where you see the power, and how much of a demand will be placed on the supercharger. Obviously, the 9.5:1 motor is going to have far greater torque and low end power as the boost is only starting to come in. It is also going to be much easier to find a blower to survive only 12 lbs of boost -vs- one that would have to put out 18 lbs. It is now very easy to see why a higher compression motor with lower boost is becoming so popular.

Please understand that when I say higher compression and lower boost, there are limits to each. Going over about 10:1 will make the amount of boost that is usable drop quickly to the point that the supercharger is somewhat wasted. In my opinion, anything less than 8 lbs of boost is a waste of a supercharger. Going over 10:1 will also make daily driving with pump gas much more difficult. In this same way, compression levels much under 9:1 will require substantial boost levels to make massive power gains. This would require boost levels that are very demanding of a supercharger. This is truly unnecessary. This isn't to say that the lower compression / higher boost set-up doesn't have a slightly higher potential for power, because it does. A lower compression motor has the ability to contain more volume. This can be an advantage, but is such a minor one that it's not necessarily worth the effort - unless it's for an all out race motor. Even then there are limits for the same reasons as the street / strip motor.

Once again, the compression -vs- boost issue. For a car that will see the streets (actually for most applications), the best thing to do is start with a motor compression that is high enough to make the horsepower you want for normal driving. Don't rely on your supercharger to make all your horsepower. With a good motor compression, add as much boost as is safe for your particular application. Decide on a final effective compression, and work your way back through the formula to find your maximum boost level: ((effective compression / motor compression) - 1) x 14.7 = boost. With the proper fuel system and related engine components, an effective compression of 16:1 to 18:1 should be more than workable. For heavily modified cars, effective compressions over 20:1 should be very carefully considered. Remember, even Indy cars only run about 18 Lbs of boost and reasonable static compression levels. Technology has come a long way and modern day supercharging should take full advantage of this.

While these opinions are not exactly the most popular, they are based on facts and real world performance. While there will always be those who continue with tradition and stick with what was done in the past, it is those who reach for something more that are winning races. Often times, some of the best advice can be found from those who have done what you want to do. All too often it is those who know the least that offer the most advice. After having been involved in supercharging for many years, I have heard it all. Most of it was worthless. It was often the least mentioned things and trail and error that have been the most rewarding. Hopefully this information will help to explain some of the often misunderstood aspects of supercharging.

Source: Motor Sports Digest

TOP


http://www.paxtonautomotive.com/

Of all the centrifugal brands out there today, Paxton has been around the longest. Until recently, all of their superchargers have used the same technology. Paxton superchargers use a planetary style step-up system using large ball bearings instead of gears. These bearings are very tightly packed and have a large knuckle gear to keep them in place. A self contained lubrication system helps to keep this step-up system cool. This design is among the most quiet and has been very popular over the years.

Unfortunately for Paxton, this design has many weaknesses. What worked well in the past is having a hard time in today's demanding environment. Once upon a time, people were happy to have a five to six pounds of boost from their supercharger. For these people, the Paxton design worked out just fine. Today engines rev much higher and can take advantage of far more boost, which most people really want. These are requirements that are very hard for the "ball bearing" design to keep up with.

The main problem with the "ball bearing" design is the amount of force needed for the bearings to keep enough grip to make boost. On a Paxton SN93 I measured 45 ft/lbs of force required just to move the input shaft. This large effort is an example of how much of a drag it is on the motor and how much Horsepower it will take just to spin the thing. The Paxton design is not very efficient due to the ball bearing drive it uses. The next problem for the Paxton is heat! As the temperature rises, the grip inside goes down. This means that once the blower gets hot, and it will, the amount of boost it will create will go down - sometimes cut in half. Part of this problem comes from the self contained lubrication system. To help reduce this problem Paxton offers a fluid cooler and special Paxta-Trac fluid. While both really do help, they are a patch for a weak design at best.

The results of this weakness are reduced life span and inconsistent boost. When the bearing slippage begins and the heat level rises, the results can even be worse than the inconsistent boost. It can also lead to the unit destroying itself. Typically these problems only happen when running boost levels above 7-8 lbs boost, or higher than recommended impeller speed. As with all superchargers, maximum impeller speed should not be exceeded without special attention.

The care and feeding of the Paxton ("ball bearing" units) takes a little more attention than most other superchargers mostly because of it's self contained lubrication system. This involves needing to replace the fluid every 3000 miles (every engine oil change). It also helps to monitor the condition of the blower at these intervals to insure the supercharger is not too loose or too tight.

The installation of the Paxton is very simple, partly because of its self contained lubrication system. Everything is very straight forward and the quality of the kits is good. For the most part, the kits are also complete. Typical installation should only take about an afternoon or about 5 to 7 hours on an '89-93 Mustang.

While I would never recommend Paxton superchargers, there is one exception - the Novi 2000. This is definitely one of the better superchargers out there. This is mostly due to Paxton using Vortech's gear design. Using heli-cut gears, the Novi 2000 can create over 27 lbs boost and supply over 1700 cfm of air flow. It can do this all day long with its improved reliability. Care and feeding is easy because it uses engine oil for lubrication, again like a Vortech. While these gears will make more noise than the "ball bearing" units, this can be either a plus or a minus depending on who you talk to. About the only down sides to the Novi 2000 are its relatively high price and its installation. At this time all units are sold as supercharger only - no mounting hardware. Almost all aftermarket install kits mount the unit on the drivers side and are meant for racing only.

The bottom line on Paxton: Unless you want the Novi 2000, look into another brand. If you have the money or are building a Race Car only, the Novi 2000 is an excellent choice!

TOP




http://www.vortecheng.com/index.html

More than any other centrifugal brand, Vortech has made modern day supercharging what it is. When Vortech started into supercharging, there were not a lot of choices. While there are many brands out there now, it was Vortech that made the change that really got things going.

Vortech started with the same design as Paxton, only they took things to the next level . While Paxton had been satisfied making the same design year after year, Vortech made the changes that would match the modern engines they would work with. The biggest change made was in the step-up system. Vortech used a gear driven system that would be both reliable and consistent. The gears step-up the input speed 3.45 times to the impeller. Also very important was the change to engine oil for lubrication for these new gears. It is argued that the Vortech design is the most efficient supercharger available other than the turbocharger. All this makes for a very user-friendly, highly reliable, and incredibly powerful supercharger.

Over the years Vortech has proven itself to be the leader in automotive supercharging. They have put forth a lot of effort into making the most factory quality kits available, and it worked. While their quality is always first rate, it's their performance that has brought in the customers. Vortech superchargers are by far the most popular brand, especially at the track. It only takes one visit to any track to see that Vortech cars are the most consistent performers. Part of all this popularity is the range of kits Vortech offers. They have everything from entry level kits all the way up to the all out race supercharger - the Mondo X-Trim. These superchargers range from 6 to 8 lb kits, all the way up to almost 30 lbs boost. All these different kits ensures that there is a supercharger for everyone.

The care and feeding of the Vortech takes very little effort. With the internal gear drive they are very reliable. There is no need to worry about fluids, that's taken care of with every engine oil change. A small amount of engine oil that runs through the supercharger while the engine is running. Many people claim this as a down side, but they are greatly mistaken. Engine supplied lubrication is by far the best method of lubrication possible. The rumors of the blower damaging the oil are only rumors. Again, the small amount of oil that does go through the supercharger can do no harm . The Vortech supercharger is by far the most worry free design.

The installation of the Vortech is very simple. Everything is very straight forward and the quality of the kits is exceptional. The kits are very complete. Typical installation should only take about an afternoon or about 7 to 9 hours on an '89-93 Mustang. The hardest part of the whole install is the tapping of the oil pan for the oil return line. Everything else is very simple. The final fit and finish are the best of any supercharger kit.

While Vortech has offered many different supercharger "Trims", the line has finally narrowed itself down to a few units to fit anyone's needs. The now defunct A-Trim and B-Trim have been replaced with the S-trim. The S-trim offers greater efficiency and a wider range of boost. Boost ranges from 8 to 20 lbs come in relatively early and are proportional to the needs of both the car and the engine. For those who need a little more, the T-Trim can provide up to 1,200 cfm, or a little over 20 lbs of boost. For engines under four liters of displacement, there is the new V-5 supercharger. This unit offers up to 26 lbs boost at over 650 cfm of air flow. For larger motors and all out racing there is the V-4 "Mondo" X-Trim. This is the Big Daddy of centrifugal superchargers. This unit can supply well over 1600 cfm of air flow at almost 30 lbs boost. Almost all aftermarket install kits for the Mondo, mount the unit on the drivers side and are meant for racing only. Vortech offers S-trim kits for most all popular American cars and trucks. Custom kits can be easily be fabricated for those that Vortech doesn't offer one for.

The bottom line on Vortech: The best, most complete supercharger line available, and there truly is a kit for everyone at a reasonable price.

Source: Motor Sports Digest

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Last edited by blazealm; 01-23-2005 at 02:19 AM.
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Old 01-22-2005, 12:37 AM   #2
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damn thats a lot of reading but interesting very interesting
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Old 01-22-2005, 06:57 AM   #3
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not completely accurate, but for the most part is some good info
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Old 01-22-2005, 07:51 AM   #4
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What part wasent accurate ?

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Old 01-22-2005, 09:05 AM   #5
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Thanks for the post, blazealm! I'm no mechanic by any stretch of the means, but I got A LOT out of that!
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Old 01-22-2005, 10:57 AM   #6
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Great Post! A lot of things on there I didn't know about.
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Old 01-22-2005, 12:25 PM   #7
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This ignores the other positive displacement supercharger that is far superior to all of those listed. The twin screw. Both the Autorotor and Lysholm compressor have incredibly high adiabatic and volumetric efficiencies far surpassing those.

The Lysholm was the choice of Ford for the new GT.

Check these...

http://www.superchargersonline.com/content.asp?ID=76

and

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Old 01-22-2005, 01:08 PM   #8
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yea but if ford would have use a centrifugal supercharger on the gt with an intercooler they could have pulled more hp so all that is basically sayin is that a centrifugal supercharer r the best type of supercharger
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Old 01-22-2005, 02:22 PM   #9
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No it would not get more power, it would get LESS!

I don't mean to offend but the centrifugal supercharger produces no low end boost and very little mid range. Plus it's just not as effecient over all as a twin screw. Low rpms, it's draining power yet producing 0 boost. Mid-range it's still pulling power and producing only a couple of PSI.

They don't start producing boost untill 3000 rpm, yet a twin screw can be set to produce 10 psi at 1500 rpm and hold that 10 psi until you decide.

A simple look at boost curves will show which is the better SC. But you pay a price for them.
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Old 01-22-2005, 11:08 PM   #10
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there is no "better" supercharger in my opinion...they are only different. it all depends on what your application is
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