Editing Blowers

THIS ARTICLE WILL LOOK A LITTLE GOOFY FOR A WHILE, UNTIL I GET EVERYTHING SORTED OUT.....

I had an article on blowers on another forum that got over 2,500 hits in a little over 2 years. Then, when they did an update on the forum, they lost all the information. I plan to research and do it again here real soon.
techinspector1

I'll be investigating and reporting on these and any others I can find......
http://www.roadsters.com/engines/#Blowers

First of all, why a blower? What good is it?
By increasing the pressure of the intake charge, you push more air into the cylinder. More air, when mixed with more fuel, makes for a stronger combustion burn. The stronger burn pushes harder on the piston, which pushes harder on the crankshaft, which creates more torque/hp. This article will only address mechanically-driven blowers or superchargers. Turbochargers will be covered later in another article, probably by someone else, because although I know they work very well, I just can't get wrapped around the maps used to size them. Maybe later.....

This will get us off to a good start....
http://www.superchargersonline.com/content.asp?id=15................................................
http://www.superchargersonline.com/content.asp?id=16................................................
http://www.superchargersonline.com/content.asp?id=31................................................
http://www.superchargersonline.com/content.asp?ID=76................................................
http://www.superchargersonline.com/content.asp?id=85................................................

There are SEVERAL types of blowers; Roots, Screw and Centrifugal to name the most popular today. In the past there have also been sliding vane (Judson) and axial flow (Latham)units, piston type (like the unit on the top of your air compressor) and probably some other types I've never heard of.  Let's look at each one and list some sites for finding them......

ROOTS TYPE....
These blowers were never designed to compress air, just to move air from one place to another, sort of like your house fan. No internal compression takes place in the blower, but the restriction of the closed intake valves in your motor allow the buildup of pressure in the intake manifold and head ports. The centrifugal and screw type blowers make pressure inside the blower. 
There are Roots designs which have 2 lobes on each rotor and others with 3 lobes on each rotor. There are also variations where the rotors are "twisted" into a helix along their axis to help prevent the "backwash" of air between the rotors and reduce "buffeting".  
http://en.wikipedia.org/wiki/Roots_blower
A neat animation showing a straight-on view of the rotors in a 3-lobe Roots. Air entering is in blue and air exiting is in red....
http://www.mekanizmalar.com/roots3.html
The Roots types we are most familiar with came as original equipment on GMC two-stroke diesel engines. The number of cylinders and the cubic inches per cylinder is the way the engines were designated, so the blowers just naturally were called by the same designation. For instance, a 4-71

The Roots types we are most familiar with came as original equipment on GMC two-stroke diesel engines. The number of cylinders and the cubic inches per cylinder is the way the engines were designated, so the blowers just naturally were called by the same designation. For instance, a 4-71 blower would have come off a 4 cylinder inline motor with 71 cubic inches per cylinder for a total displacement of 284. This blower would be a good choice for a motor of around 300 cubic inches and could be overdriven (by juggling drive and driven pullies) to feed a larger motor or underdriven to feed a smaller motor. Here are some of the GMC motors I could find.....
2-53, 3-53, 4-53, 6V-53(V-configuration rather than inline), 8V-53, 12V-53, 2-71, 3-71, 4-71, 4Twin-71, 6-71, 6Twin-71, 6Quad-71, 8V-71, 12V-71, 12VTwin-71, 16V-71, 16VTwin-71, 6V-92, 8V-92, 12V-92, 16V-92, 6-110, 6Twin-110, 12V-149, 16V-149. Add to those....Turbo.....Turbo Intercooled.....Turbo Aftercooled.....Turbo Intercooled Aftercooled.....those are documented but may be a few others. Not certain if there was a 171, and there were some V71 Twins and Quads.. inline had High and Low blocks. There were also V-53 and 6-71 alloy block versions. 

The most popular for hot rod use today would be the 4-71, 6-71 and 8V-71 (just called 8-71)units. There is some work to be done on a stock (fresh off the diesel)"Jimmy" blower that you maybe find at a swap meet or on ebay. The rear case cover bearing bosses need to be strengthened with steel collars and the rotors must be clearanced to the case interior. These and other mods will be addressed in Pat Ganahl's book. If you're considering a blower, it is well worth the investment to buy and read this book.....http://www.themotorbookstore.com/supercharging.html
I have no commercial arrangements with Pat and don't make a dime off him selling you his book, I just like the way he writes. By the way, speaking of swap meet or ebay, did you know there is a small bore and a large bore 6-71? Click here and let Brother Vern lead you to an explanation of the differences.....http://www.fordflathead.com/blowersize.html

Of course, most of the blowers bought today are purpose-built aftermarket units that have the proper clearancing and strengthening mods built in. Some manufacturers use teflon strips on the rotors to tighten up the rotor/case clearance and increase the efficiency of the unit.