Projects Supercharger question, please don't ridicule

If you mount the blower up front and crank drive it and put the carb in a pressure box it will work but it is sort of like using bag pipes to power a pump organ. WHY is the big question when the other way works so well. As for a manifold and conventional mounting carb over blower, , mill the stock four barrel manifold flat (so the bllower will mount flat at exactly 90 degress to the belt and the belt will stay on) and bolt a plate to the carb flange then bolt the blower to the plate. 3/4 in aluinum would be fine I believe.
I built a set up for a Dodge Colt 1600 using a magnuson blower in the seventies, long before magnuson thought of selling blowers for hi perf use. I have pics of it. It worked pretty good too.

 

On WWII aircraft it was not uncommon to have a turbocharger blowing into a supercharger...

 

Some of this reminds me of the 1980's Pro Street craze where the turbo-charged NOS-equipped supercharged engines could barely run and only stumbled up and down the trailer ramps. But they all had 1300+ horsepower! ;o)

 

Like the Lancia Delta S4: http://en.wikipedia.org/wiki/Lancia_Delta_S4

Or indeed the turbo versions of Detroit Diesel 2-strokes.

 

Or, in alot of semi's, motorhomes, and tractors.
I.E. Detriot Diesel turbo straight into a "GMC" type geat driven blower.
I've seen twin turbo setups and even twin turbo-twin engine setups
in full race semis. Almost everything that can be thought of has been done.


A few years back I got an old turbo with a bad exhaust side, and made
a new shaft and mounting plate to turn it into a Paxton type belt driven
blower. I never mounted it on anything but still have it in my tool box.

Good Luck
Jeff

 

any time you do a "blow threw" set up the fuel pressure has to be raised under boost or the pressure will push the fuel out of the float bowl. But you can't just set a high fuel pressure , it must raise under boost and lessen at idle.

 

The prewar Mercedes Benz system is a roots blower going through the carb. It is SUPER complex because of the fuel pressure issues.

 

Most aftermarket fuel pressure regulators have a vacuum port that will run whatever pressure you want at idle and raise the pressure under boost.


Quote:"I've had the opposite idea: plumb the turbine side of a turbo into the exhaust and gear it to the flywheel via a reduction gear drive and sprag. You're recovering exhaust energy directly as mechanical torque.":Quote

With the turbine normally spinning at 100,000+rpm's I'd think you just have a big exhaust restriction trying to spin it slower. Not sure it would put out enough torque to make a difference.

 

So the whole reason for wanting to top mount it is that bypass valve?? Plug the valve, people run bigger roots blowers without bypass valves all the time.

Those 3.8 eatons have some screwy inlet and outlet mounting, I'd mount the thing like an accessory and build a duct. Those are widely adapted to other engine forms and if you start googling thru late model forums you'll see em on everything from imports to motorcycles.

Realistically there is only one reason to try and top mount, and that's shock value. And with the size of those little eatons, there's not much shock behind the extra 40 hp it's gonna produce.

good luck

 

Alot of obstacles to overcome...thats rodding ain't it? engineering-how to achieve anything
The pressure won't blow the fuel out of the float bowl via the vent. It might aerate the fuel supply by blowing back past the needle valve into the supply line and pump... unless you run a fuel pressure regulator and have a strong enough pump to push against the boost.
The fuel bowl is vented to the air horn so the % balance of pressures throughout the carb will still be balanced.
If you compare the float bowl, upper and lower side of the venturi's and fuel/air passageways; The venturis will still exhibit pressure drop across the fuel ports to draw and atomize fuel. The air pressure relationships will still have similar personalities but at an increased volume.
Air being greatly compressible isn't going to require a change of air jets/passages to keep airflow differentials tuned.
Gas,liquids,and solids are hydrodynamic. These are the mechanical stresses or properties we are dealing with but even electricity exhibits the same properties.

Some "rules of thumb"
All stresses conduct primarily along a surface.
Boundaries between substances are a surface.
At this level gas,liquid,solids,energy all have the same physics but they exhibit this same physics in different ratios.
Different representations and equations are used to represent the different physical properties of each classification.

Gas(Air) density and speed, changes easily but net flow across a restriction is minimal.

Liquid(petrol) density and speed changes less easily and is going to meet restriction with a marked change in net flow.

Your boost is your new atmospheric pressure

Even though air pressure differentials remain balanced throughout the carb under the increased pressure of boost or when the exhaust back pressure is freed up by installing headers and better pipes; The fuel pressure differentials will not and that's why we change jets.

The only places I see the boost creating a problem is your jetting, fuel pressure and the danger of carb gaskets leaking fuel out or fuel/air mixture leaking out past the throttle shafts.
There's also your vacuum advance.
It ports manifold vacuum against atmospheric.
You'll have to port blower boost to the atmospheric side of the advance diaphragm but manifold(actually off idle vacuum port) vacuum to the normal port remains just like stock.
Remember, no matter how much boost your putting into the engine there will be a pressure drop across the carb.

From Wiki " A column of air one square inch in cross-section, measured from sea level to the top of the atmosphere, would weigh approximately 65.5 newtons (14.7 lb_f)."

At sea level your normally aspirated engine is operating with 14lb/sq" boost.
The exhaust pipe is also under 14lb/sq" back pressure but only the high pressure pulses have to overcome this.
Back pressure is blocked off from the cylinder by the valves.
The exhaust stroke from bdc to tdc pumps the cylinder out and you still have 14lb/sq" in the combustion chamber.
If the valves remained closed on the intake stroke it would pump the atmospheric pressure of the combustion chamber down to a lower than atmospheric pressure at bdc an inverse of the compression ratio.

Nominally that should be a drop to 1/10th of atmospheric pressure in an engine of 10:1 compression ratio.

Actually there are inefficiencies and variances and the intake valve being open is a great big leak to let in freash air and fuel to burn. The If anyone ever acts like car hobbyists are dummies or hotrodders are fools remind them that I didn't come to know this by experimentation and discovery. I learned all of this and most of what I know about physics and math not from a university but from 40 years of reading Hot Rod and anything else I could get my mind wrapped around.
American Hot Rodders I believe have been a great part of driving our scientific achievement.
The achievements of Hot Rodders and our individual and corporate freedoms to express our passions and talents are capitol to our place among nations.amount of pressure drop in the cylinder from atmospheric also affects the incoming speed of the air/fuel mix.
The momentum of the speeding air/fuel mass into the cylinder can ram the cylinder with pressure above atmospheric and this pressure wave travels from the atmosphere, through the carb and intake to the piston top and back to atmosphere at the speed of sound.
Ram tuning the engine captures this pressure wave on it's 1st rebound (second pressure spike).
That's the core of how it all works, getting the air into and out of the engine.

If anyone ever acts like car hobbyists are dummies or hotrodders are fools remind them that I didn't come to know this by experimentation and discovery. I learned all of this and most of what I know about physics and math not from a university but from 40 years of reading Hot Rod and anything else I could get my mind wrapped around.
American Hot Rodders I believe have been a great part of driving our scientific achievement.
The achievements of Hot Rodders and our individual and corporate freedoms to express our passions and talents are capitol to our place among nations.

 

The proper answer to why not blow through any Rootes type blower including Eatons, Whipple's etc. Is that they are all positive displacement. You can't build a box strong enough to hold the boost, because it keeps on building as long as the engine is turning.Centrifical's and turbos do not.
GeminiEFI

 

One thing about having the carbs on top of the blower, that no one seems to have mentioned, is that the blower doesn't have to do any work most of the time...because most of the time, the throttle is nearly closed, there is not much air density in the blower, and it is NOT making boost.

The stock setup for your little blower has the throttle body BEFORE the blower, doesn't it? so there is no boost most of the time. I think the bypass valve is used to reduce losses just a bit more...but a normal roots blower without the bypass valve is not doing anything at light throttle conditions anyways.

 

The stock 6-71's has to be set up loose because they only pump air, and have nothing to cool it, if you run fuel through it to keep cool you can tighten up the clearances to make them seal better thus being more efficient (builds boost sooner, at lower speeds, plus the fuel also helps it seal even better). With a blown injected alcohol, or nitro engine the majority of the fuel goes into the blower the rest goes in at the intake ports with jets so you can lean or richen each individual cylinder to balance out the fuel distribution.

 

The butterfly on top of the blower also has a mechanical lever on it so you can shut the air off to the engine, if you don't have the injection system set properly the engine will run away, and the only way to stop it is to trip butterfly shut to kill the engine.

 

Whew, I was wondering if anyone was going to get around to that... Any sort of Roots type supercharger is always going to be making pressure. There is no room for "bypass" air inside the case as there is with a centrifugal.

If you try to blow through with a roots, it will over-pressurize the carbs and try to keep feeding the engine air when the throttle is closed!

Imagine trying to shut off a high pressure washer by kinking the hose... Which would be easier, blocking the garden hose that is feeding it, or trying to block the high pressure side? Same problem with using the carb butterflies to cut off the air coming out of the blower.

Oh, and they weren't used to "supercharge" the Detroit Diesels. The blower was sized and geared to provide exactly the amount of air needed to clean out and re-charge the cylinders on the particular engine it was used on. That's where the "6-71" designation comes from- 6) 71 cubic inch cylinders.

 

Excellent point squirrel, I never thought of that!

I found the theory explaining the venturi effect:
The Bernoulli Equation can be considered to be a statement of the conservation of energyenergy density. In the high velocity flow through the constriction, kinetic energy must increase at the expense of pressure energy. principle appropriate for flowing fluids. The qualitative behavior that is usually labeled with the term "Bernoulli effect" is the lowering of fluid pressure in regions where the flow velocity is increased. This lowering of pressure in a constriction of a flow path may seem counterintuitive, but seems less so when you consider pressure to be energy density. In the high velocity flow through the constriction, kinetic energy must increase at the expense of pressure energy.

Gemini, Actually a roots type blower effectively creates a linear boost or expressed a different way a pressure increase that is a linear function of speed and displacement. The pressure or volume movement graphed out against (engine or blower) speed will increase along a straight line.
A centrifugal blower or turbo because of it's high speed and the imparting of momentum to the air by the fins aligned with the flow creates a pressure increase that is effectively exponential not linear.
The pressure or volume movement graphed out against (engine, not blower) speed will increase in a curve.
It's the same physics involved in there being significantly more wind resistance between 60 and 70 mph than there is between 40 and 50 mph.

Boyle’s law states that, at a constant temperature, the volume of a given mass of gas varies inversely with pressure.
Charles’s law states at a constant pressure, the volume of a given mass of gas is directly proportional to its (absolute) temperature.

The equation of ideal gas law is one of the most fundamental relationships linking the three variables temperature, pressure and density that describe the thermodynamic state of the atmosphere.

When mass and pressure are held constant, the gas law collapses to Charles’s law. When mass and temperature are held constant, it is equivalent to Boyle’s law. Thus, the gas law combines the two laws.

The Ideal gas law represents what's going on in the blower

Somehow the ideal gas law is involved with maybe moles law? in how pressure increases exponentially as volume increases in a closed space.
I can't find exactly what I'm looking for. It's been so long but I'll take a shot at describing it.
Moles law involves the pressure of a gas. The electrostatic and nuclear pressure of it's molecules against each other. Each gas has a different mole value (pressure) at the same temperature and volume. Since E=MC^2 energy and mass are interchangeable.
At any chosen temperature and volume applied to any gas, an increase in mass equates to an increase in pressure. It is a measure of the compressibility of a gas. reduce the temperature down to absolute zero and on the way down the molecules slow down then cease to bounce off each other and the gas becomes first a liquid then a solid.

When compressing a gas into a closed space like the tank of an air compressor at first it follows the Ideal Gas Law then as pressure increses it begins to follow another law(which I cannot find).
When the volume of the air is increased in a finite space and heat is created by this increase in density as per moles laws the system is no longer represented by the Ideal Gas Law.

For compressing air, the pressure increases roughly by the square of the change in volume.

The size of your car does not change but the faster it goes, the more volume it displaces. At increasing vehicle speeds there is less time for the air pressure to bleed of of the leading surfaces of the vehicle resulting in a change from an open system to a closed system with a build-up of pressure in the area it cannot get out of. This occurs between 60 and 65 mph for most cars produced up into the early 80's and is why fuel mileage decreases dramatically above these speeds. More aerodynamic cars will experience this at higher speeds resulting in better high speed economy.
Same thing happens on the inside of the engine. The roots blower spinning displaces a set amount of air in relation to what the engine displaces both are turning at the same speed and there is no change in the displacement ratio.
A centrifugal compressor mechanically driven off the engine also has no change in the space displaced by it's vanes compared to engine speed. There is a big but...
But since pressures and inertia of the compressed air in the centrifugal compressor greatly exceed that of the air in the blower, as per moles law the centrifugal compressor has a non-linear increase in efficiency. it gets more efficient the faster the engine turns.
The blower is grabbing each parcel of air and pushing it through with linear force. The air in a centrifugal compressor is accelerated outward by centripetal acceleration.
The turbo compounds these forces multiplying the acceleration of the exhaust against the centrifugal impeller to drive the centrifugal compressor.

In actuality the difference between a roots and centrifugal compressor are only operating speed and efficiency. Both are engine driven but the centrifugal is more efficient. if you could run the roots blower at the same high speed it would (except for the centrifugal effect) increase the air pressure exponentially more like the centrifugal just like you said so your not really wrong after all but I think your mistaken in which one is more efficient.
The turbo will start out with no boost then increase boost much more rapidly as EXHAUST speed increases.
So much so that they have to install a wastegate to bleed off exhaust pressure at a set pressure to keep from from overdriving the turbo and making too much boost. Does the same thing as a blowoff valve but from the other end

 

Have you ever seen a street roots that made boost at idle? I haven't.

Even with blow thru, the engine will shut off. If it didn't you'd have a perpetual motion machine.

Personally, I think the blow thru eliminates one of the biggest advantages of a roots. The way they turbulate the air is great for fuel mixing and regardless of huge cam they deliver great vacuum to the base of the carburetor. Which solves a couple huge driveability issues with radical engines on the street.

 

That's only because you've never seen a street roots with an open hole on top, blowing into carbs

 

Yeah, you could get some really high pressures when coasting the engine ( high RPM, throttles closed )

But since the blower would be pumping dry air, you should be able to fix that with a Blow Off Valve.

 

Heres a web link to a buick GN sie with how to calculate for turbo math
http://www.gnttype.org/techarea/turbo/turboflow.html

 

On the newer style blowers, oil flow channelled through hoses from the (i believe the new kits come from the oil pan, may be wrong) is used to cool the blower, so the technology of turbo chargers have kind of passed on to the new style superchargers.

 

I've never heard so many people talk about blower "cooling" and I'm pretty sure those blowers that use pressurized oil is used for lubrication. Maybe I'm crazy but the last time I looked at a blower with oil lines they just ran to the bearings. I didn't see any coolant passages anywhere.

 

ALL Rootes are positive displacement. That means they MUST be run as draw throughs. Carburetor butterflies won't hold back the boost. There is no need to modify Eaton superchargers to run wet or dry. An Eaton M-90 can be pulleyed to make 20+ lbs. boost on a 3.8
GeminiEFI

 

Anytime you have oil "Flowing" the cooling is inherent in the flow. The oil comes in at one temperature and absorbs or loses heat from the surfaces it comes into contact with. So if the oil entering is at a lesser temperature than the blower bearings it will cool the bearing at the same time it is lubracating them.

 

if you can run an 8-71 at 150% overdrive to 7000 rpm with out pressurized oiling than I wouldn't think the addition of oil lines was not intended for cooling. The fins on the side of the case have a cooling effect but thats not why they are there. Oil is not a very good conductor of heat compared to water or glycol. If you really wanted to cool a blower you would be better off using some kind of "coolant". go figure.

 

People have successfully used blow thru turbos, so it could be done. As everyone has said, pressure on all parts of the carb need to be equalized, (air box) foam filled floats so they don't collapse under boost, the hardest is fuel pressure must always be higher than boost, but not so high that if floods at low boost (idle).

 

A flooded engine then a backfire would be interesting with the blower above the carbs. Lippy

 

Was it something I said? LOL. Lippy

 

It's not the same, it's NOT the same, it's NOT THE SAME.............. Please re-read Gemini's last post.

 

It is very possible just not as easy. It would be best to enclose the carbs in a box for simplicity sake, and so you don't need carbs made for a blow through application. As long as you are making around 5 to 10 psi you shouldn't need to worry about pressure crushing the floats. Set up the rest of fuel delivery as if you have a blow through carb with a centrifugal. You will need more fuel pressure, and probably a boost referenced regulator. I'm sure this has been done before. As far as the fitting of a roots over carbs, mAke a box that goes around the carbs and that bolts to the manifold and that the blower can bolt to.