<font color="red"> I found a small GM Supercharger gathering dust in a dragracers shed about a year or so ago and have been trying to get it for the modified ever since. It was rebuilt and never used. Now he has said that I can have it but we don't know what size it is. How can I tell if it is a 371 or a 471? </font>
Alfster - 3-71 has two ribs on side, 4-71 has three. 3-71 has 7.482 rotor length, 4-71 has 9.980 rotor length. Mutt
Any idea what the numbers on the GM blowers stand for? 3-71, 4-71, 6-71, 8-71, 14-71. Do they relate to something or did they just wake up one morning and say, I think I'll call this gizmo a 3-71.
Who was dumb enough to let you wander around their shed ?? You up on sunday for the Blowout ??? jsut debating if I will go over at night for Drinkies too, could always crash at Fish's if I needed I suppose
Smokin, I think the last Number was the displacement ( per cylinder ), The first Number was how many cylinders.
<font color="red"> Hey Olds, Do you think I am going to tell you where I found this? This guys shed has more hard core racing stuff than any speed shop. His son has been working in America for a few years and is about to go Doorslammer racing. The mind boggles at the amount of stuff he has. Last time I was there he was using a Hilborn Injection for a door stop. The blower was going to go on the 55 Caddy they have that they were going to use as a tow car for the wildbuncher but they have since brought a dually Chev. So the Caddy is still just sitting, waiting. Heading to Auckland for the weekend. See ya at the Blowout. We got invited back. </font>
I always figured the first number for # of cylinders too but, what has 3 or 14 cyls? and everything can't be 71
The 71 did mean 71 cu.in per cyl. Detroit Diesel also had a series with 53 cu. in per also. Thay were 2 cycle diesels, super cheap and super easy to rebuild. They had a 12V71 that was call "A Hummin Dozen". No tourqe, alot of revs, and oil leaks every where.
There are three series - 53, 71, and 92. The -53 series blowers are smaller, and the B&M and Weiand were patterned after them. The -53 and -71 series came on inline engines, and the V series (6V53,6V71, etc) came on V type engines. There are no manifolds to mount the V series because they have a unique mounting flange (Dyer used to make them years ago and they are rare). The -53 series had straight cut two lobe rotors, and the -71 has helical, or twisted three lobe rotors. There are two sizes of -71 series blowers, the newer ones having a smaller diameter rotor. These are sold as "street superchargers" because they put out less boost than their larger brothers at the same drive ratio. Boost is attained by drive ratio, with large blowers making the same boost in an underdrive (spinning slower) configuration as a small blower that's overdriven (spinning faster). The faster you spin the rotors, the more heat you create, and the more horsepower is consumed to drive the blower, making less horsepower output. The "small" 6-71 blower has a displacement of 339ci/rev compared to a "large" blower's 411ci/rev. The large rotors will not fit in the small "street" case. You have to be careful when buying a used blower, and research before buying a swapmeet bargain. Street Supercharging, by Pat Ganahl gives the information you need before buying a used blower, and would be a good investment before making a purchase. It's an expensive investment to do it right, but the rewards can be very satisfying when done properly. Hope this helps... Mutt
Good info, Mutt. I know a bit about blowers and drive stuff, but I just learned a few things. Thanks for posting.
<font color="red"> Thanks for aal the info., This one has been rebuilt by the top blower guy in N.Z.(Als' Blowers)and never used. It has been sitting for many years and has siezed but Al knows and has seen the blower and says he can pull it down and free it up easily. </font>
on outside appearance, how do you tell the small -71 from the big -71 blowers? just the general size of it, or are there discrete differences? did GMC build two different size blowers or was this something that the aftermarket came up with? david
Rule of thumb is that the 8-71 is an inch longer than the 6-71, the 10-71 an inch longer than the 8-71, the 12-71 an inch longer than the 10-71, etc. My Littlefield 6 is at a friend's place right now, or I'd measure it's length for you. Oh, and measure at the case itself, as the end plates sometimes have different thicknesses.
[ QUOTE ] on outside appearance, how do you tell the small -71 from the big -71 blowers? just the general size of it, or are there discrete differences? did GMC build two different size blowers or was this something that the aftermarket came up with? david [/ QUOTE ] The exterior of the cases, end plates, gears, ect. are the same. The small rotor series was introduced in 1978 by GM, in an effort to reduce horsepower required to drive the blower to reduce fuel consumption. The difference is inside - the bore of the blower and the rotor size. The difference in the rotor diameter is 5.505 for the small rotor, and 5.778 for the large rotor. The larger rotor will not fit the small case, and while the small rotor will fit in the large case, the clearances would not give much boost. I have one of each sitting on my workbench - a street blower from BDS, and a large rotor Littlefield - they are identical outside, except the Littlefield is polished. The BDS is marked by code on the bottom flange as a small rotor blower. A small rotor blower is fine for a street engine that only runs 3-5 lbs boost. If you plan on competition, I would recommend a large rotor blower so that you can get more boost at slower rotor RPM (drive speed). Blower boost is tied to displacement of the motor it goes on - the smaller the motor, the more boost at a given drive speed. So if you have a 283, 0r 327 for instance, a street blower will give you the boost you need with underdrive pullys. To get the same boost on a 400ci you might need to overdrive it. Most street engines will run at underdrive percentages for the low boost needed. There are charts at - http://www.dyersblowers.com/ and http://www.goodvibesracing.com/BDS%20Technical.htm - that show the boost/displacement/drive speed ratios, as well as engine recommendations. As I said, running a blower requires some study to be successful, but it ain't rocket science. Just figure your needs, and use the parts that give the best performance at the least wear and tear. All a blower is doing, in effect, is making your motor think it's bigger than it is, with the resulting performance gain. Mutt
Looks good Alfster. According to my book, it's Half a 6-71, and you should be able to figure out boost by cutting the 6-71 figures in the charts in half. The rotors are the large ones, and put out 205ci/rev. It looks like you could adapt it to a 4bbl manifold pretty easily, with the only problem being getting the drive snout to line up with your pullys - depending on what motor you put it on. Price was certainly right Mutt
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