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Old 01-13-2007, 01:46 PM   #1 (permalink)
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roots blower?

I know older 2-stroke diesels used blowers to get the air going, but could a blower be used instead of a turbo? I know the answer is yes, but what I really want to know is... would it be a suitable match for a performance diesel? I am unsure about how screw-type blowers would affect intake temps and what their practical pressure limit is.
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Old 01-13-2007, 05:45 PM   #2 (permalink)
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Re: roots blower?

Most of those old 2 stoke diesels used a blower to feed a turbo charger. Better make sure your engine is built for more boost than stock. You will need a large blower to feed our engines like a 10-71 or even a 14-71, I don't think 6-71 or 8-71 can produce enough air flow. How you gonna spin this thing? Look into teh older hot rod sceen, they used a direct crank drive, and put the blower in front of the engine, and plumed the compressed air to the turbo charger. Of course you could use a centrifical, plumbing would be easier. Drivers right off the serpentine belt... Need something like a Novi 2000 or larger. I guess the question what are the numbers for air flow required by the 7.3 at WOT. Once you have these numbers, then you can find a blower that can feed the turbo. Of course you will need to change the compressor wheel, perhaps the entire turbo.
I think toyota had an article out that used an electronicly controled selenoid(sp) to allow the blower to feed the engine until enough boost was created by turbo, then switch the input to the turbo, thus no turbo lag. What are you trying to acomplish?

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Old 01-13-2007, 06:41 PM   #3 (permalink)
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Re: roots blower?

never gunna work, the older 2strokes NEEDED a blower to....blow the exhasut air out and blow fresh air in all in the same piston stroke, totaly differnt then a turbo charger or even a Paxton supercharger that was mentioned.

Blowers buy definition DO NOT raise the intake air presure above amoshperic presure, a turbo or supercharger onthe other hand will.

the term "blown" chevy, or ford or whatever does use a "blower" derived from an old 2-stroke Detroit blower, hence a 6-71, 8-71 and such they come off that motor and were fitted onto a chevy, but since the chevy had a smaller CID then the detroit the blower would pressurise the intake air above atmoshperic pressure and the original use/term "blower" was lost.

Detroit used a turbo on top of a blower setup on the silver 6-92 engines, worked rather well the turbo would take away the blower lag and once the charger was spinning the blower would somehow be bypassed. how you could use a blower to feed a turbo is beyond me..... and a blower will never put out as much psi as a turbo, a bone stock PSD will do 12, modded will be over 30 psi, no blower will ever put out that much.

ok off my soap box, sorry....

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Old 01-13-2007, 08:56 PM   #4 (permalink)
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Re: roots blower?

The blower takes the place of the intake and exhaust strokes when it is used on a 2 cycle engine. When turbocharged they worked the other way, the turbo fed the blower not the blower feeding the turbo. Then they could add a check valve to bypass the blower when the turbo boost came up but this was for additional performance, a regular turbo/blower setup also gave good results.

Anyway a blower is inferior to a turbo on diesel engines because all the power to turn a blower is taken from the engine crank shaft that could otherwise go to drive the wheels. A turbo recovers some of the lost energy that would otherwise go out the exhaust. However some of the power to drive a turbo comes from the engine in the form of increased back pressure but not a whole lot. It's not all free power but a lot of it is free power.

Also a blower would cause seriously bad fuel economy because it would be making the same boost at a given RPM no matter what the engine actually needed. A turbocharger by its nature varies boost in proportion to what the engine needs.

Years ago there were Cummins engines with a blower forcing air in but that was when diesel was cheap and turbo technology was not as good. They were called an "iron lung". However turbochargers have been pretty much standard equipment since the mid 1960s so that should tell you something.

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Old 01-14-2007, 12:13 AM   #5 (permalink)
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Re: roots blower?

I knew there was a reason no one did it. I know that turbos are better, but I just wondered if you could get decent boost from a roots blower... enough to supply a diesel anyway.
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Old 01-14-2007, 12:16 AM   #6 (permalink)
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Re: roots blower?

[ QUOTE ]

Blowers buy definition DO NOT raise the intake air presure above amoshperic presure, a turbo or supercharger onthe other hand will.


[/ QUOTE ]

I disagree with this. blowers make measureable inlet pressure. I just tweaked a Pontiac 455 with a smaller pulley and it took it from 5 psi to 8. Absolutely there is pressure from a blower.
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Old 01-14-2007, 01:33 AM   #7 (permalink)
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Re: roots blower?

Ok, here we go again.
Different words are used to describe the same parts depending on what function they serve.
A blower is used to "blow" out exhaust, and fresh air in. Not intended to raise manifold pressure, but a slight increase is inevitable. Two cycle Detroits are a good example of this. They need a blower to run, as there is no exhaust stroke.
Now this is where my memory gets hazy.
What is commonly referred to as superchargers are meant to raise manifold pressure. There are many different types. Screw types that are driven off the crankshaft via gears or belts, and take significant hp to run, and always produce a given amount of psi for whatever rpm they are turning. Centrifugal (like a turbo) that are also driven off the crankshaft. Then the traditional turbo, which I believe is actually a turbosupercharger. It is driven off exhaust gas, and amount of boost is directly related to engine load. More fuel going into the engine, bigger bang, more exhaust coming out, makes turbo spin faster, which crams more air into the engine.
Never heard of a blower feeding a turbo.....just doesn't make sense. I know a lot of old Detroits used turbos to feed the blower. I beleive, as was said, when engine speed and load was great enough to create enough "boost" from the turbo, the blower was bypassed, which reduced parasitic load on the engine, which put more power to the ground.
It's all a little fuzzy to me, but thats the way I understand it.
Back to the initial post, yes you could do it, but I don't believe you would get the desired result. If it was worth doing, someone would have done it already.
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Old 01-14-2007, 01:35 AM   #8 (permalink)
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Re: roots blower?

Most comments are correct however there is an increase in pressue. Just read a few operating manuals on the 2 cycle DDA engines and there it is in black and white. There were a few problems with this idea, first of all it takes about 35 HP to drive the blower on those engines. This is why the bypass was added to allow the turbo to actually bypass the rotors. Second mentioned was the increase in pressure. Yes, there was an increase of about 5 to 7 lbs. Now if you used 35 Hp to drive the blower you need a smaller CID engine to compensate for the HP loss. Now back to more air, more fuel. And the added bonus of alternate fuel also. [img]/ubbthreads/images/graemlins/grin.gif[/img]
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Old 01-14-2007, 12:40 PM   #9 (permalink)
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Re: roots blower?

[ QUOTE ]
[ QUOTE ]

Blowers buy definition DO NOT raise the intake air presure above amoshperic presure, a turbo or supercharger onthe other hand will.


[/ QUOTE ]

I disagree with this. blowers make measureable inlet pressure. I just tweaked a Pontiac 455 with a smaller pulley and it took it from 5 psi to 8. Absolutely there is pressure from a blower.

[/ QUOTE ]

yes, I agree that you can use a blower to increase manifold pressure, but you are using a "blower" in an aplication that they were never intended to be used.

The term Blower is getting vage. in the diesel world you say blower and everyone thinks of a 2-stroke detroit, in the racer world you say blower and everyone things of excatly what you have on that 455 pontiac. it is a blower, but not being used for what it was intended for, a 2-stroke detroit. it is being used to increase manifold pressure on a gas engine, to me that is a supercharger, but a supercharger to the race world is a Paxton belt driver turbo charger so the words are all so cross refercenced and used diferently it gets rather confusing.

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Old 01-14-2007, 12:55 PM   #10 (permalink)
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Re: roots blower?

[ QUOTE ]
[ QUOTE ]
[ QUOTE ]

Blowers buy definition DO NOT raise the intake air presure above amoshperic presure, a turbo or supercharger onthe other hand will.


[/ QUOTE ]

I disagree with this. blowers make measureable inlet pressure. I just tweaked a Pontiac 455 with a smaller pulley and it took it from 5 psi to 8. Absolutely there is pressure from a blower.

[/ QUOTE ]

yes, I agree that you can use a blower to increase manifold pressure, but you are using a "blower" in an aplication that they were never intended to be used.

The term Blower is getting vague.

[/ QUOTE ]

I typically divide them this way: A blower does not compress the air internally, it acts as a positive displacement pump. Other forms of superchargers which do compress the air internally (centrifugal, lysholm, etc.) are not blowers. Roots blowers were originally designed to move air through mine shafts and into furnaces, not to compress the air.
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Old 01-14-2007, 01:12 PM   #11 (permalink)
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Re: roots blower?

"positive displacement pump" very good way to put it, and when the PDP displaces more air then the engine it is forcing it into, then you get a raise in manifold pressure.....

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Old 01-14-2007, 02:06 PM   #12 (permalink)
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Re: roots blower?

Ok, cool... we're all talking about the same thing, just different ways they act in different applications.
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Old 01-14-2007, 09:30 PM   #13 (permalink)
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Re: roots blower?

Yes for a blower to provide any increase in power or in the case of the old 2 stroke DDA's the blower had to "pump" more air than the engine displaces to completely "push out" empty the exhaust from the cylinders. The blower displacement and drive ration determine the amount of boost a root type blower is capable of. In the case of the mid 90's Thunderbird SC where Ford mounted a root blower onto a 3.8L V-6. In stock form 12# of boost was about the maximum. If the root blower pulley was changed to a smaller diameter then the blower turned faster in relation to the engine spped, with a 10% smaller blower pulley you could see close to 20# of boost. Ford also used bypass system on the blower to minimize the mechanical load when boost was not required.
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