Lately I've been getting some PM's and emails about guys wanting to supercharge, and it seems like their is a lot of misinformation, or some simply do not understand the different sizes of these style superchargers. So, I figured I'd make a little list for reference. I will start with the smallest, and go up.

174 CID=B&M 174
177 CID= Weiand 177 (or stock 525sc supercharger)
250 CID= B&M 250, blower shop 250, or on some 575sci merc stock supercharger.
256 CID= Weiand 256. Also used on 575SCI merc.
411 CID= Large case 6-71 GMC style blower.
420 CID= B&M 420 Megablower, also stock supercharger on the merc 600SC, and 800sc engines
436 CID= 8-71 GMC style blower
469 CID= 10-71 GMC style blower
497 CID= 12-71 GMC style blower
522 CID = 14-71 GMC style blower

Now, what you will see here, is the displacement of these "air movers". I call them air movers, because they aren't really compressors. They dont compress the air inside the blower itself. What you are simply doing, is moving more into the engine, than it can handle, which results in a positive pressure, which is seen as 'boost".

Now, there are many guys who run the smaller, 174/177/250/256 style superchargers. Many times guys have asked me, is it worth going from say a 177, to a 250 blower on their engine.

Going from a 177, to a 250, would be like going from an 8-71, to a 14-71. While it is a substantial change, its not as big of a change, as going from say a 177, to even a 6-71 or 420 B&M. Getting away from these small 174/177/250/256 blowers, can provide a substantial increase in power, reliability, and cooler air charge. I'll get into that more later. I'd like to discuss the blower construction first.

I'll start with the 174 B&M. This is a straight, two lobe, teflon tipped supercharger. It's primary introduction, back in the 1980's, was for low RPM, low power smog era 454 Tow engines. This blower worked very well on a low rpm engine, that was simply looking to add a little more grunt down in the idle to 4000RPM range. It worked well in that application. This blower utilized a single carb setup. Was also used on the old Hawk Marine 525 engines. This blower should be limited to about 5lbs of boost on a 454ci marine engine, if it must be used.

Next on the plate is the weiand 177. This also is a straight two lobe, NON teflon tipped blower. Very similar to the 174, as it too is a single carb only. This blower uses oil bath rear bearings, where as the 174 uses sealed bearings. This blower was also introduced to compete with B&M's 174, for the low rpm tow rig and or mild street engine. Also, this blower should be limited to about 5lbs of boost, and 454ci on a marine engine.

The 250 B&M. Also, straight two lobe, teflon tipped blower. This blower was introduced around 1990. It was designed to fill the gap, between, the 174 and the 420 blower. The 420 was too large to fit under most stock hoods, and the 174 was simply too small for a "HOT'" big block. It can be used with a single carb, or a dual carb application. It uses sealed rear bearings, and works well on mild 454/502ci. Key word, "MILD".

Weiand 256. Straight two lobe, NON teflon tipped blower. This blower also has oil bath rear bearings, available in single or dual carb setup. Was designed to compete with the B&M 250 setups. Their application and performance, is right on with the B&M 250 version.

B&M 420 Megablower. This blower was simply introduced, to compete against the company's remanufacturing and modifying, the old GMC 6-71 blowers, in the 1980's. This was a straight, two lobe, teflon tipped, blower. Sealed rear bearings. This blower can only be used with twin carbs. Performance wise, it is right between a 6-71, and a 8-71. I think this blower is well suited, from 454/540ci.

8-71 thru 14-71. These blowers, today, vary so much, from builder to builder, its too hard to put a story together on them. Different style rotors, stripped or not stripped, many many variances, per the application. They can suit a wide range of things from a pump gas 5lb boost deal, to a high boost alky deal. easiest blower to get parts for, and generally, very reliable.

Now, even I mentioned, and its always been known, that blower size is relative to engine size. HOWEVER, I partially agree with that theory.

Now, I mentioned about a 177 on a "mild" 454. As we all know, an engine is an air pump. We also know, that it takes X amount of fuel, to make X amount of power.

A 454 engine, with peanut port heads, a small RV cam, and stock exhaust, with a 177 driven at 115% over, may make 10lbs of boost. Now, take a 454, with some AFR, Brodix, Dart heads, big old high lift camshaft, headers, and so on. You bolt that 115% overdriven blower on this other 454ci, and now, you're only making 3lbs of boost.

I feel the size of the blower, is more related to the horsepower you are making. You cannot expect a 177 blower, to support 1000HP. I dont care if it was on a 600ci, or a 350 small block. The blower is simply, incapable, of moving enough air, to make that kind of power.

One may say, a 1471 is perfect for a 598ci, but entirely too big for a 540ci. I would want to know the details of the build, and the HP goals, before truly giving an idea of what size blower should be utilized. Is this 598ci going to be a mild 800HP deal? Is the 540ci gonna be a max effort 1000+hp deal? Putting a 14-71 on a 598 with crap cylinder heads, and crap camshaft, is not gonna really help anything. Putting an 8-71, on a max effort 540 seeking over 1000HP, may, very well be, a limiting factor.

MT , what gear oil do you like to run in your blowers ? Amsoil Severe Gear ? BDS 871 do you fill to the bottom of the sight glass ? What do you use to get it in there ?

Now, you may ask, well why not bolt a 14-71 on a 454. Well, for two reasons. For starters, you'd be at a very low drive ratio. The negative result of that, can be simply inefficiency, especially at low rpm. The rotors turning too slow, can result in carryback. The other reason, is its simply taking alot of power to turn that large blower, when its not warranted. 20lbs of boost? Ok, now we might be getting close, but for the typical marine 5-8psi, it's just not needed.

Why cant my small blower work just fine?

Well, it can. To a point. What happens when you spin the blower too fast, is it creates heat. Lots of heat. Not only does heating the intake air charge, help invite detonation to the party, it kills power output. Lets say you have a small 174/177 blower just screaming back there. You may have intake manifold temps easily exceeding 200+ degrees. By simply going to a larger blower, say, 8-71, 420, 10-71, you may drop the temperature down 50, 75, or even more degrees. How much of a gain is that worth, well, think about how you're N/A car would run on a blistering 120* degree day, vs how it would run when its 60* at the track. There was an oso member, who converted his 575sci mercury engines that had the 256 superchargers, to 8-71's. With the same amount of boost in the manifold, he picked up around 5mph in his 40' outlaw. I, also personally switched from 250 blowers, to 420 blowers, and gained about the same in my 38 Fountain, again, at the same boost level.