Why do larger roots blowers use 2 carbs?
10-07-2014 | 06:48 PM
#21
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From: On A Dirt Floor
And that's why I'm thinking clearly ! LOL.
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Extremely difficult to have more atomization that that from a carbs booster. Especially an annular one.
However, what happens 'up there' is one thing. Now it has to travel how far ? with how many sq inch of surfaces near by ? with how many turns ? with how much change of direction (think how many cylinders at one time drawing air - and then the blower rotors not only go down but they must go back up to go back down...lol) vs what we really care about is how much fuel actually makes it's way into each cylinder.
I'm willing to bet - which I have to because I've never sat in a blower case while it's spinning - that a bunch of fuel not only klings and spatters on the rotors, but also get's 'wrapped' in the air column just near it's surfaces.
Think of the oil wrapped around a crank...better yet.....think of the chocolate chip cookie dough wrapped around your blenders thing a ma bobs when spinning. LOL.
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Extremely difficult to have more atomization that that from a carbs booster. Especially an annular one.
However, what happens 'up there' is one thing. Now it has to travel how far ? with how many sq inch of surfaces near by ? with how many turns ? with how much change of direction (think how many cylinders at one time drawing air - and then the blower rotors not only go down but they must go back up to go back down...lol) vs what we really care about is how much fuel actually makes it's way into each cylinder.
I'm willing to bet - which I have to because I've never sat in a blower case while it's spinning - that a bunch of fuel not only klings and spatters on the rotors, but also get's 'wrapped' in the air column just near it's surfaces.
Think of the oil wrapped around a crank...better yet.....think of the chocolate chip cookie dough wrapped around your blenders thing a ma bobs when spinning. LOL.
10-07-2014 | 06:58 PM
#22
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From: chicago
Heres a cool look at the boosters on a dyno pull at the 1:00 mark. https://www.youtube.com/watch?v=a3tpL3z4fbE
10-07-2014 | 09:05 PM
#23
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From: Varna, IL
You would think so. But when running a single 1050 carb, on my 250 blower, the rear cylinders were rich as heck, fronts lean as heck. Later they came out with a carb adapter that moved the carb a little closer to the snout, not sure if that helped much.
Those most HP Ive seen made, with a single dominator on a pump gas roots blower, was right around 700hp range. Roots blowers arent really compressors, they are more or less "air movers". If theres any restriction on the top side, it hurts their efficiency. For example, lets say you got that 671. You want to make say 7psi on a 454. You may bolt the 1050 carb on, and have to drive the blower at say 10% over, to make 7psi in the manifold. Now, you take the single carb off, and bolt on a pair of 750s. All of a sudden, now you are making 8psi, or 9psi at 10% over. To get back to 7psi, you can slow the blower down, and see some cooler intake temps as well. Of course thats just throwing numbers out there to give an example. Although, I know of several roots blown combos, that have went from smaller carbs, to larger carbs, and picked up a bit of boost, with no other changes.
Now a Blow thru setup, heck, a single dominator will support tons of power, being blown thru.
Those most HP Ive seen made, with a single dominator on a pump gas roots blower, was right around 700hp range. Roots blowers arent really compressors, they are more or less "air movers". If theres any restriction on the top side, it hurts their efficiency. For example, lets say you got that 671. You want to make say 7psi on a 454. You may bolt the 1050 carb on, and have to drive the blower at say 10% over, to make 7psi in the manifold. Now, you take the single carb off, and bolt on a pair of 750s. All of a sudden, now you are making 8psi, or 9psi at 10% over. To get back to 7psi, you can slow the blower down, and see some cooler intake temps as well. Of course thats just throwing numbers out there to give an example. Although, I know of several roots blown combos, that have went from smaller carbs, to larger carbs, and picked up a bit of boost, with no other changes.
Now a Blow thru setup, heck, a single dominator will support tons of power, being blown thru.
07-17-2018 | 06:21 PM
#28
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Bringing this back from the dead, in a short housing 6v-71 (about 355ci), would two 750's be sufficient to feed it without restriction?
Obviously a Dominator 1050 single would be to small?
Obviously a Dominator 1050 single would be to small?
Last edited by Mohavvalley; 07-18-2018 at 03:00 PM.
07-17-2018 | 06:54 PM
#29
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From: Murrayville Georgia
when talking roots style blowers you need to understand how they work and what they are designed to do (as was said above they are air movers). the blower comes from the old detroit V series diesels. those motors are two stroke. the only reason for the blower was to move air into the cylinders as the two stroke setup had no intake vacuum in the intake and without the blower it wont move enough air on its own to even start. later with the V92 series they added a turbo to build boost and the last version had a bypass so the boosted air would bypass the blower as it then became a restriction. they then got adapted for hot rod use and other than helix rotors are basically the same. the air moves around the outside of the case and meets back at the middle so they are not really compressing any air, just moving way more than the motor needs so it makes boost. as such they were never designed to have fuel stuffed in there at the same time as the air so it does not control it well, again as was stated above. the more evenly you can distribute the fuel the less the blower screws up that delivery. the issue of boost is one of the things that always bothers me when people say " I want to run 10 psi" or whatever. boost is a reference only. a motor with small intake ports will make lots of boost and no power while a motor with big ports and low boost will make lots of power with the same blower and pulley setup. this is why it is so important to build the whole system together as a opposed to just throwing a blower on in hopes of making big power. just my two cents tho.
07-17-2018 | 06:59 PM
#30
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From: Grand Rapids, MI
I know of a single carb on 8-71 454's. The customer did not want all of the potential power that he could make using dual carbs. He limited the power using the single carb. He had a blower destroy itself and the engine. So he upgraded blowers to 8-71's in case he went bigger. Been running them 3 or 4 yrs now. I believe they dyno'd around 650HP at low boost.
Last edited by Rookie; 07-17-2018 at 07:08 PM.
