flrtin1

I came across this info on my B&M mega charger and it is a good read for basic roots info..... a little dated but still very accurate.
B&M sold the blower division to Holley in the late 90's then Holley discontinued the 420 mega charger a few years ago so this info is not available any longer. I edited the assembly instructions out so it is a little cut up

Another good blower basics read is here:
http://www.holley.com/data/TechServi...ech%20Info.pdf

flrtin1

flrtin1

SleeperFromHell

The roots is a waste. The twin screw's cost is easily absorbed after you see how much more power they put out over the roots.

The Roots Supercharger (aka "blower")
The roots supercharger was originally designed as an air moving device for industrial buildings. The roots supercharger features two counter-rotating lobes that trap air from the intake side of the supercharger (normally at the back of the supercharger), move it around the outside casing of the lobes, and out the bottom of the supercharger through an outlet / discharge port. Like the twin screw supercharger, the roots is a "positive displacement" aka "fixed displacement" supercharger, meaning that it moves a fixed volume of air per rotation. Notwithstanding minor amounts of air-leak at low rpms, the roots supercharger cannot flow backwards like a centrifugal supercharger, and is thus nearly as efficient in its ability to pump air at low rpms as it is at high rpms. What this means is that roots superchargers are very capable of making large amounts of boost even when engine rpms are very low. This makes for great low-end and midrange power, and also makes them great for trucks and towing vehicles. The roots is also self lubricated, and is the simplest of the supercharger designs, meaning it is reasonably priced and very reliable. This is why roots superchargers have been the choice of GM, Ford, Mercedes, and Toyota for OE applications.

The only real disadvantage to the roots supercharger is that it creates a lot of heat. There are two reasons for this. First, the roots supercharger does not compress air - it only moves from the intake port to the discharge port (i.e. it is the only supercharger design with no internal compression ratio). All of the compression is done in the intake manifold. Laws of thermodynamics kick in in favor of supercharger designs with an internal compression ratio (centrifugal and twin screw) because they do less work on the incoming air charge. We will leave the mathematics of this phenomenon to a later (much more boring) discussion. Another reason roots superchargers create higher amounts of heat is because they tend to carry some of the compressed air in the intake back into the supercharger because it gets trapped by the rotating lobes that are exposed to the hotter air in the intake manifold.

Shagwell

- if roots don't make any power then ssssssssshhhhhhh don't tell them that. - My dad's 68 Camaro is running a +.100 Gm 427(445ci) - The bottom end is nothing pieces. He's got an old set of Dart 360's, and an 871. - He's running low 5's at over 140 in the 1/8, and we've only made a few passes...we don't even have the bugs worked out. - also, he turns it between 9600-10k in low gear, and the blower is 30% over driven...if it's not building any power, then please don't tell it that...

flrtin1 - thanks for the info.

SleeperFromHell

It's not that the roots don't make any power. The twin screw's just make so much more power at equal psi.

I believe kenne bell has a comparo on his site between a 90cid roots and a 90 cid twin screw. The Twin screw put down 40 more horsepower at the same psi then the roots.

flrtin1

SleeperFromHell...... Not wanting to argue.... you have some good points but I would get some real world experiance before you start making bold statements based on what you have read....another thing to think about is that the whipple has been around for at least 20 yrs yet you don't see people tripping over themselves to get one think there might be a reason for that?

I posted this because it has a lot of good info in it that is hard to find for people wanting to find out about roots blowers and what is needed for the engine

This is a pic I took in the late 80's I am pretty sure that is a Whipple on it
Edit: The more I think about it that might be a Latham it's been long enough I can't remember lol

flrtin1

Wow that is hard to read lol.....I will work on getting it cleaned up tomorrow

SleeperFromHell

Flirtin,

Not trying to argue. Just posting what i have seen.

Best example is what i'm going to post below. Whipple vs eaton, 8 Psi, everything else stock.

flrtin1

Ok I agreed with you that the whipple has some good points
that said there are lots of factors here like the fact that "roots type" blowers for the small block chevy range in size from 144ci to 430ci and as you go up in size the slower you have to turn which in turn lowers the heat loss factor

I went to the whipple site HERE
and noticed two things
One they don't tell you what size the 5.3 blower is
Two the only SB kit they have is for the 99 up 5.3 which I don't think is going to do anyone here any good
The article above is for a 420ci blower so the things you are talking about are like comparing apples to oranges

Also boost is boost for the short block so almost all the info for the short block applies no matter what blower you have

flrtin1

Ok I fixed it........still a little chopped up but thats as good as I can get it sorry

brodyscamaro

I just run nitrous.

EvilCartman

iTrader: (1)

I wanna run roots and nitrous Thanks for the good read

SleeperFromHell

Flirtin, I was doing some research and came up with some startling facts.

The Weiand blower package is a great bang for the buck considering i just saw one on ebay for 900 dollars. The main difference between the weiand blowers and the twin screw superchargers is the CFM they produce.

The weiand 142 blower puts out 142 cfm, The 177 puts out 177cfm, The 671 puts out 411cfm and the 871 puts out 436cfm.

The Whipple superchargers are alittle different. The 72cid Whipple puts out 831cfm, The 87cid whipple puts out 997cfm, and the 139cid whipple puts out 1274cfm

The CFM numbers tell the story. While the weiand kit would be good for near stock apps.. The whipple would be good for ***** to the wall app. I hate to estimate but i bet a the whipple gm tuner kit would put out about 90-100 more horsepower at the same psi then the weiand kit on the same exact engine combo.

High Toned SOB

This is not true. The reason the air gets heated is because it is being compressed. The "real" compression is not in the intake manifold, it's inbetween the rotors when they spin. If it did not compress the air, then why would the air get hot? When the air gets trapped inbetween the rotors, it compresses and then is pushed into the intake at a much higher density ratio.
Laws of thermodynamics? Look at the rotor design then imagine them spinning. They are litteraly "beating" the air into the engine. From this comes a great amount of heat.


QUOTE]Originally posted by SleeperFromHell
Another reason roots superchargers create higher amounts of heat is because they tend to carry some of the compressed air in the intake back into the supercharger because it gets trapped by the rotating lobes that are exposed to the hotter air in the intake manifold[/QUOTE]

If this was true, every time the rotor spun, it would push air back up into the carb., causing it to backfire everytime the rotors turned. It has to have suction when they come back up against the case, otherwise they would be trying to pump air and fuel mix
into the bottom of the carb. It would be trying to make a circle.

just my .02

flrtin1

lol I think you may be a little confused......the 144 to 430 size on the roots is cubic inchs per revolution not CFM That info is on the bottom of pg4 in the Holley link I provided above


The problem with the 140 and 170 series blower is to get higher boost numbers out of them you run into a ceiling because of heat and flow



Do you have any idea what a 6-71, 420 or 8-71 roots blower looks like?
To say that would only be good for a stock setup and leads me to belive you don't.

Post where you got your numbers from so we can see how they got them and then do the math

I will also bring up again they don't make a true bolt on kit for the SBC by the time you pay around 4k for the cheapest whipple supercharger and almost 8k for the biggest then 2-3k for the fuel system then fabricate it and tune it you are into a lot of money.....not counting the cost of building the long block also

AFBCamaro

Damn, my blower only flows 411cfm??

Those whipples are great but they lend themselves better to fuel injected motors or full out injector hats. They must be feed from one end and not the top like roots blowers. They are a better design but they sure cost more than they are worth for anything but the most radical of cars.

I know for a fact that I have waaaaay more power than i can use on the street on this little 411cfm blower :-)

Saying that they are worthless (roots) is like saying a 350 is worthless. Sure to some it might be compared to a 540 Chevy big block. Its all on how you look at it.

I am pushing 13psi of hot, dirty and inneficient boost with a 1968 detroit diesel Roots blower. Saying that turns me on..... ...... No really!

High Toned SOB

I'm not even sure that a screw type would be much better anyways. You'll never be able to move the same amount of air as a twisted rotor or hi-helix could.
Look at the little 3.8 superchargers and the Ford 5.4 lightining charger. They are screw type like a whipple. If they were so much better, they'd be bringing the big money. Just because you can get 6 psi out of one, doesn't mean it is pushing the same volume.

I think you've got your stories mudded up. The screw type is better on a stock application, whereas the older straight and twisted lobe roots blowers are for the big power. A roots isn't ineffiecient, it's just wicked.

Shagwell

notice how Pro Mod/ Top Fuel aren't running screw type? - If you want extreme, you still go roots. For that extreme its hi-helix though... - Anyhow look around at the racing world, you'll find more roots blowers than screw blowers. - To many of these racers, money is nothing. If they made that much more power, you'd see more of them...

edit: I should note that the 1671 and 1871's do have screw type rotors, but not considered a "screw blower". The true screw blowers have more twist in the rotors, and are rear-fed.

AFBCamaro

The roots blowers are actually ineficient (around 45-50% efficient), however since they can displace so much volume top racers dont care. The whipples can aswell. They are not actually being limited by power so if the roots makes 50hp less (everything else being equal) it really doesnt matter, they already have to much useless power anyways.


They also run alcohol or nitromethane which is a very cold fuel and when that happens the difference (especially since they run teflon strips) between the both units close to disapears. So they go with what is easier and faster to replace/fix not with something that is slighly more efficient on the field. (This has nothing to do with money eighter)

On the street this is slightly different, you can definately see the difference between the twin screw and the roots (all else being equal). But if the screw guy has slighly more power than you you just simply go up a tooth on the pulley. He can do the same and you can go back and do it again until the power reaches the sky and chokes the lot of them. BUT you are also on the street sooooooo......

I am rambling.... I always do that......