Projects Supercharger question, please don't ridicule

What would stop a person from mounting a conventional roots style blower on top of the carb(s) as opposed to underneath it/them?

I've noticed the paxton style blowers use a box that encapsulates the carb and was wondering.......why not just force all the air directly down throgh the carb instead of all around it?

Do the carbs need to be pressurized both inside & out?


I've got a blower from a 90's model 3.8(3800) Buick V6 and want to experiment with it after learning a few things. I don't think they put out that much boost......?

 

the availability of a manifold would be the 1st thing to stop most.

skull

 

this is just a guess as i havent played with superchargers, but forcing twice as much air threw a carb, with set amount of fuel = lean motor? or you'd have to run the carb real rich. just my 2 cents.

 

I think the issue with simply blowing down through the carb would be that the additional pressure would blow the fuel back into the float bowl, not down through the carb. especially when the throttle is closed quickly. Where's all that additional pressure going to go since the throttle blades are closed? Encasing the carb completely means that the pressure is the same everywhere around the carb so the fuel is less likely to seek the path of least resistance. Just my .02.

 

The carbs would either need to be pressurized outside (with a box) or you could just pressurize the float bowls, it would do the same thing...but be a bit more dangerous.

Running a roots blower under the carb is usually easier to set up, and it works fine. I think that's why it's done that way.

 

I was wondering about that myself

 

i've also wondered why (picture the traditional 6-71 with carb(s) on top setup) the exact same supercharger could not be powered by turbocharger(s) instead of by a belt.

In other words where the pulley is for the supercharger instead of having this pulley and a toothed belt, instead there would be a turbocharger with it's output shaft connected to the supercharger and then in this case the car would run fine and thus ending the notion/belief that turbochargers just can't work well with carburation?


Actually to make it simpler, instead of the the pulley and toothed belt, this 6-71 is powered by exhaust gases. But everything else is exactly the same.


Please comment.

 

The whole idea isn't that odd, since that's exactly what turbochargers are doing. With the size of a roots, it would almost be more of a pain to troubleshoot or do anything w/ the carb since most of it would have to be hidden by the blower.

 

In order for the carb to meter fuel it requires the presseure differential on the fuel in the bowl verses the venturi. also if the pressure is to great it will crush a brass float.

 

it takes alot more power to turn a 6-71 than a turbo, and you'd have lag if it would turn it(no way though)


skull

 

Early days of drag racing it wasn't uncommon to see a roots blower mounted down low, in front of the engine. "potvin".

Blower doesn't really care where it's at. Everything you see for modern centrifugals in terms of blower hats or carb boxes or popoff valves will work too. You just gotta duct anything pressurized and expect efficiency losses with increased distance. And realize you'll be building all the mounting and connecting hard parts.

good luck

 

I'm wondering how you would mount the blower on top of the carbs. What about the forces on that blower belt. I would think it would want to twist it right off the top of the carbs. Or am I not thinking right? Any way it would look funky.

 

you would need a pop out valve or blow off valve to release the pressure. just like in a turbocharged setup,..when the pressure between the turbo and the throttle body reaches the maximum pre-set level, it will release the pressure. therefor if you do run this setup, you will need the release valve between the blower and carb.

 

Use Fuel injection, probably would be simpler and easyer to tune.

 

Roots blowers need the fuel to cool the rotors. Centrifical do not, since they are more like a turdo.

 

The ultimate lazyman's supercharger, just bolt it over the carb. Why didn't J.C. Whitney think of this? They could have sold a million of them, and most would not have noticed they didn't work as far as adding power, but look cool as all hell!

 

Damn. So my idea won't work?

 

I could only guess at the technical reasons you wouldn't want to do it, and I agree with the more technical view points presented... but to me it would be a pain in the ass to have to pull the blower off everytime I wanted to tune or dick around with the carbs LOL...

Even if I had the choice, i'd still put the carbs on top. Just for simplicity sake. I'd still like to see a blower on top though... just not on my car.

-Chris

 

then how do the eaton, magnacharger, kenne bell(all roots blowers).. . . . and so on stay cool with the injectors below the blower.

 

Not true. I posted a few months ago, because I wanted to run my B&m blower "dry", with direct injection on a flathead. Half the responses said the very same thing.

I contacted some gents in Grand Junction, Co., and was able to get the tolerances opened up a bit to run dry with no problem. You lose about 10%, and have to compensate with a smaller pulley.

 

They are a helix style blower and not a traditional roots style.
I have played with the ones you speak of, but it never occured to me. GMC style need the cooling of the fuel, alcohol blowers are setup tighter due to the extra cooling effects of the alcohol.

 

Mounting the blower on top of the carbs?

No, I dont think it will.

Because of the strain that the blower would put on the castings.

But I dont see why you couldnt mount it of to the side, plumb the blower press side into the tops of the carbs ( with a box or a bonnet, they both work fine )

And I believe the Buick 3.8 blower is a Eaton, which runs dry ( no mixture ) in its original application.

 

We used to run turbos thru side draft webers and holleys. The holleys need solid power valves. The webers needed to be sealed with viton o rings and only foam floats could be used with higher boost 'cause brass ones would crush. The bowls got pressurized too and we ran boost sensing fuel regulators that raised the pressure a pound for every pound of boost.

I dont think it would be an easy task to mount a blower to the air cleaner studs on a couple 4 barrels, too much belt tension.

 

Where did those blowers come from? Uniflow 2-stroke diesels. No cooling fuel there (but IIRC they've got some additional lubrication gubbins that aren't used on non-diesel applications).

 

That's one of the cool things about DCOEs. All the air feeds are through the air cleaner flange. I know of successful commercially available turbo conversions for Alfa Romeos that work on the principle you describe.

 

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. This might work best on blown engines because of the "lost" expansion ratio vs. compression ratio (though you might say that misses the point of supercharging; you've still got a much more favourable combustion-chamber-shape scenario to work with.) I believe some '50s aircraft piston engines worked on this principle, with remarkable success.

 

Yes I was thinking about bolting the blower-adapter-plate to the top of the carb, but also have that plate supported directly to the front & back of the intake as well.
This is a really small blower that uses an average sized serpentine belt.



After some research I've discovered this thing has a vacuum operated butterfly-valve that allows the air (on the stock engine it came on) to bypass the blower & go directly into the intake, dropping the boost level down during low rpm's.....I think.
Anyways, I'm thinking I could connect that valve to the throttle linkage to open up and dump the pressurized air out behind the carb at idle & close whenever the throttle is opend up

I appreciate you guys helping me get my thinking cap on. I know I can do it, I just don't know what the hell I'm doing.

 

71 series blowers run dry at low RPM and almost zero pressure on the diesels. On as gas motor it is spun at 3 times that speed and at much greater pressure. The result is the rotors get bigger and eat the case. More clearance is needed so the parts don't touch. And the best way to seal up the blower is to dump fuel in it with the carb or injector on top.

The Eaton blower is designed to run dry, so you can do whatever you want with it. Blow-through carb setups always have problems though.

Turbo compound engines are pretty cool, but complex as hell and generally only work well at the design speed with a steady state load. Driving a root blower with a exhaust powered turbine would have the same problems, namely a large inefficient gearbox to reduce the speed from the 100,000 rpm down to 8,000 to drive the blower. And there really isn't much point, as a roots blower is less efficient than a centrifugal supercharger.<o></o>

 

You're right, but the weirdness factor would be extremely cool on a hot rod!

I'm starting to wonder about absolute efficiency, though; the sort of efficiency that engineers deal with; what one might call "geek-type" efficiency. It's something very much different to what economists would mean by efficiency, and I'm beginning to wonder if it's any better as a concept. For one thing it ceases to make any sense the minute one considers systems in their entirety, because one has no final input or output to consider. For another it very often misses accessibility or usability or any sense of contextuality. I don't think I'm arguing for inefficiency per se, but I think the concept of efficiency needs to be offset with a concept of appropriateness to a fit into a broader context - which makes possible the idea that the right level of efficiency in any given situation isn't necessarily the highest.

All this because I am increasingly convinced that ecological theorists who call for greater efficiency are digging a deeper hole for us through their failure to understand (or readiness to discount) broader systems. But I think that's another conversation!

 

Good luck,