Blower trivia
 

Most roots type blower makers use numbers to describe their blowers (ie Holley 420, Littlefield 10/71, B&M 250, etc.)

These are not just model #s. What do the numbers mean? (Long answers accepted, so weigh in mcollinstn!)

Well, I know one part of it. The GM blowers are from Diesels. 2-71 is a from a 2 cylinder 71 cu/in per cylinder engine. 6-71 from 6 cylinder 71 cu/in per cylinder and so forth. There are 110 cu/in per cylinder engines-very old, 53 cu/in per cyinder engines-newer and the 71's.

Ok, next trivia question...of the popular blower sizes available today...which were never available as a GM diesel?

BTW-I believe all the numbers are relating to their displacement, not just the GM engine series.

I'm withcord on the 144, 174, 177, 250, and 420's.
Gary

Meaning what?
:confused:

i would think that the only blowers used on automotive type engne were the 6-71 and the 8-71. beyound that the 10-12-14-71's were aftermarket blowers the used the standard means of measurement i dont think the smaller blower 171 and 144 are a diesel direvetive.
later

Oops, kind of short on that answer/guess.
That series is numbered by displacement. cu inches of air in 1 revolution?
Gary

All pretty much right so far. Back in the old days we did fit a 2-71 blower to a motorcycle engine.

alright,reading an encyclopedia one day,helping my kid do his homework I came across this,in what application did they use transmisions to actually switch the speed of the superchargers while underway and why? and wouldnt that be kick butt in a boat!

I know the WWII Merlin engines had two speed superchargers (the P-38 Lightning had turbos in place of the centrifugal superchargers). The big bombers with radial engines had mulitple settings for their turbochargers. Some bombers, like the B-29, had both turbos and superchargers.

One reason for multiple blower speeds, for aircraft, is to have the same power at high altitudes as well as at sea level. The higher the altitude, the lesser air density, more boost is needed to maintain power level.

Recap:

GM two-stroke diesel scavenging blowers were indeed rated from what # of cylinders and displacement of the cylinders from the motor the blower came from.

Current aftermarket blowers are rated at the cubic inches of air at atmospheric pressure that the blower displaces in one revolution.

Multi-speed blowers have been used in aircraft to normalize air density at altitudes (running them at high speed caused fuel mix and detonation issues, not to mention that the high-powered fighter and interceptor planes had enough prop torque on takeoff to make it really tough to keep from torquing the plane into a "donut" going down the runway and destroying it - more boost would make it even worse). Two speed blowers were used on some Mercedes road cars of the 1930's as well...
(kick in a boat? not really, since we all run our single speed blowers at the edge of detonation anyhow - another speed would turn pistons into objects of art)

Okay, now, who can tell us off the top of their head whether the rotors in a roots blower rotate "out" or "in" on a typical installation? And who can tell us WHY? (yes, I know the answer).

Rotates out. Because the air is trapped in the groove between the rotor and the case.

On a "Roots" type the rotors rotate out.
The air is drawn in from the top and passes along the outer casing before discharging in the bottom center. The incoming air will also help keep the casing cool.
The rotors have low pitch spiral in them so there is constant contact (mesh) between the two rotors as they meet in the center and to help even out the discharge pulses.
A "screw" type (Whipple) is like having two large diameter screws with opposite threads in constant mesh. The long pitch of the rotors delivers a more constant flow of air with little pulsation.

so now you guys know how hard it was getting my boy back to doing his homework!

It wasn't uncommon to see the pilots of The Merlin-equipped Mustangs pulling 63-67 inches of manifold pressure on take-off, but the power was applied in stages to help deal with the P-factor, the highest power settings being applied after the tail was off the ground andf positive rudder authority was gained. These engines could be run (and often were!) at power seetings as high as 71 inches mainfold pressure, what the pilot's operating handbook called "wartime emergency" power setting.
And yes, aircraft use superchargers and turbo-superchargers to allow them to make rated power at high altitudes, but not to make more than that.

Taken from engine builder at Reno Air Races

"Before we came to Reno we'd never had the engine over 60 inches. We ran it at 3050 rpm and 80 inches of boost there, still in low blower, the difference between a Merlin and a Griffon, a Merlin in high blower at low altitude, like Reno, all it does is make heat, it doesn't make any more boost at all and that's why nobody uses it, but a Griffon's boost is geared different in the blowers. At Reno altitude, in high blower, I think we could run at 90-95 inches of manifold pressure, which would have given us about 300 more horsepower.."

How does inches compare to psi?

At sea level, standard day, pressure is 29.92 in. hg. which is 14.7 psi.

So 65" of boost is equal to 32 pounds of boost. Pretty good for a gasoline engine.

You have to remember that those Rolls Merlin engines were over 1700 ci in displacement.
It's not like you're trying to stuff 32 lbs of boost into a 454.
1700 ci divided by 12 cylinders = 141.67 ci/cyl.

Actually, since it is measured in terms of pressure, and not volume, wouldn't it be even MORE of a feat. That is like putting in 4 times more air than a 454... no make that 16 times... well, it is more of a feat than doing it with a 454. Ask mcollinstn how many times more air, but it is a bunch.:D :D :D But 32 psi is 32 psi whether it is in a 56 ci cylinder, a 141.67 ci cylinder, or a scuba tank of compressed air.

Yeah, boost is boost.

2 atmospheres (29psi, 60inches, etc) is going to be the same PERCENTAGE increase on any size engine.

Volume-Pressure relationship is affected also by temperature. The math for figuring this relationship is shown in the "ideal gas equation": PV=nRT (where Pressure x Volume = molecular quantity x gas constant x Temperature). Ignore the R since they wash out when comparing the same gas (in this case it is essentially regular air with some fuel suspended in it). This illustrates that PV~nT.

If we reverse the equation to solve for n, then it becomes: n~PV/T

It becomes evident here that the discharge temp of the blower or aftercooler will dramatically affect the "n" (the actual number of molecules of air) that are crammed into the cylinders. This, in turn, is what will create more power, assuming that it can be lit off without detonating. Looking at the equation, a "doubling" of the discharge temp (in degrees on the K scale) will HALVE the molecular count of the charge, if introduced at the same pressure. We know, though, that a blower will introduce a higher pressure at a higher temperature. As long as the temperature (adiabatic efficiency) curve of the blower is in its design zone this temp increase is expected and is simply part of running a higher boost. As the blower reaches the upper limit of its design range, it will begin to raise the TEMPERATURE far more for each unit increase in boost pressure. This is where the equation will show that you are no longer actually feeding the motor any more effective intake charge - only more heat and pressure which invites detonation...

The comparison chart for a 454 vs a Merlin would be incomplete without comprehensive temperature/pressure curves for each supercharger and aftercooler...

m

I've got one for you. What American car manufacturer used what centrifugal blower on one of their models in the 1950s? That's the easy part. What did they do to increase low RPM power?

weren't the 58 vettes charged

No, I believe that it was the old studebakers. They had a early Paxton on them.

The Studebaker Hawk came in a supercharged version as well as the Ford Thunderbird.
The Studebaker Avanti of the early 60's had a Paxton supercharged version too.
Shelby built a couple of turbocharged examples of the 427 Cobra (Bill Cosby had one) and paxton supercharged versions of the GT-350 Mustang. And Chevrolet built the Corvair Spyder which was turbocharged.

There were a couple of cars built in the 30's that had blowers mounted in front of the engine and connected directly to the crankshaft. Just don't remember which ones.

mcollinstn
You been watching the discovery channel? :D

Don't have much time for TV - 'cept for reruns of Dark Angel and any show with Britney Spears on it...

1950's cars with centrifugal blowers? Stude Hawk and TBird both had Paxtons. The Studebaker version was actually marketed as a "Paxton by McCulloch" supercharger and had a variable-speed drive based off of a ball-ramp type system that was controlled by a boost-sensing diaphragm that worked against spring pressure to reduce the overdrive ratio once the blower showed good boost pressure. This setup never supported BIG boost pressure, as the ball drive would slip - this is why we don't see that style of variable speed drive anymore.

Yeah. What he said.:drool:

Hey m:

Can't get nothing by you! OK, who was the first racer to use a 6-71 blower and where was it mounted?

I have always wanted a selectable supercharger like Mad Max had.

Yes I know it was just a movie and it could not work. But it would be cool to be able to switch on the supercharger when needed.

Ron

NOS would work! If you want toggle switch on off control. :D

rj,

CAN DO - WILL work.

Electromagnetic clutches are used today on every Mercedes that has a blower. Computer controls when it is on and when it is off - Motor starts with it on, and it engages whenever the motor accelerates beyond a certain rate (rate of acceleration that is).

Larger A/C clutches will transmit a big chunk of horsepower (think bus A/Cs).

The Mad Max "big red button on the side of the Hurst shifter" can be done. Go for it.

*********************

Now,
I can't say who ran the first 6-71 blower, but in 1952 Ernie Hashim ran a 4-71 blower on a Ford flathead V8, and in 1955, he mounted another 4-71 blower to the FRONT of a Chrysler Hemi and ran a snake of intake hoses to a methanol injection setup. Ernie and Ed Iskendarian ran a side operation, also in the mid 50s, converting 6-71 blowers from WW2 surplus for automotive use.

That's as close as I can get to Tomcat's quiz of the night.

You are correct sir! I knew about the front mount with pipes, not the flathead. I think the Hemi is in Big Daddy's museum.

OK guys how can it work? I thought a roots type blower is a positive displacement pump so that if it wasnt turning it would not let any air through at all.

If you have a roots blower on an engine and you take the blower belt off will the engine run?

Ron

Rj,

The Mad Max car was fictional. The blower has to spin for the motor to run, unless there is a vacuum bypass in the blower (there are some OEM Eatons with a vacuum bypass, but not a regular 6-71). You CAN, though switch a clutch to DRIVE the blower or let it freewheel. You just won't get the cool look of the movie by going from STATIONARY pulley to SPINNING pulley unless you clutch both ends of the belt (I reckon that would provide the proper look).

The blower will freewheel, engine vacuum causes it to spin. Yes, an engine will run with no blower belt - if you watch drags, you'll see lots of cars finish a run with no blower belt (they don't usually WIN that way, though).

***************

Tomcat

Garlits museum ROCKS.

Even the incredibly NON MOTORHEAD wife got a charge out of it.

Last time we went (a good while back), my kids were 6 and 8. My 6 yr old ended up leaving with a HEMI connecting rod necklace around her tiny neck (I had to tie a knot in the chain).

Ron,
Lost a belt on my 525SCs, still pulls enough vacuum to turn the rotors and run. Happens all the time in blown dragsters.
But for it to be efficient, you would have to bypass the blower. You would simply need to close the bypass when the blower is engaged.
Gary

FYI:
In Mad Max the blower was just an empty casing with a carb inside.

I found this at MadMaxMovies.com
There's some interesting info on the original move there.

The Blower

The supercharger is made by Weiand (pronounced "why and"). They make twisted-vane, roots-style superchargers for many after market applications. The system uses a GM 6-71 case as the base, and a Scott injector hat at the top.

On the movie car, this was all faked. The supercharger was empty and the carburettor sat inside. A small water pump was attached to the front of the supercharger to hold the drive wheel, this also moved the supercharger belt forward to clear the standard 351 water pump assembly, and the distributor has a 90 degree elbow to allow it to clear the supercharger. The supercharger belt is driven by an electric motor which is hidden by a yellow bucket in the garage scene in MM1. Weiand never had a supercharger that could be activated and deactivated. Even with huge compression it would be tough to generate 600bhp on a 351 in 1974 without rebuilding it once every couple of hundred miles.

Of course, most people building replicas have not duplicated the above convoluted setup, and have opted for a variety of different setups to duplicate the same basic effect. As long as the blower sits at the right height out of the bonnet, and the pulley spins, it doesn't matter too much what method you use to hook it all up

Iggy,
So you're saying everything/everyone in Hollywood is phony. Who wouuld have guessed?:D
Gary