Roots versus Screw

Discussion in 'PSI Superchargers Tech Questions' started by bandit496, Sep 10, 2013.

  1. bandit496

    bandit496 Member

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    I don't know the answer, so I am asking as you guys are very knowledgable: Given the same engine specifications (block, heads, cam, fuel, etc), what is the difference in performance of a screw blower and a rootes type blower? Is it more horsepower, less maintenance, cost, etc. ? Why should a person choose one system over another? JW
     
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  2. underby6

    underby6 Active Member

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    more horsepower
    less maintenance
    cheaper

    You can get a good used one for $6k and never have to strip it.

    Brandon Booher
    NHRA TAD #323
    Torque MGMT. - Owner
     
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  3. jody stroud

    jody stroud ZOMBIE Top Dragster

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    Took 481 up to turn my roots at 40 over at 8000 Rpms a blower dyno a screw will use a lot less hp to turn at same boost and Rpms
     
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  4. Mike Canter

    Mike Canter Top Dragster
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    Screw is way more efficient than a roots blower so requires a different fuel curve. Screw has no stripes to wear out so boost remains constant. Belt life on a screw can be very short depending on overdrive ratio and I mean very short. So now that belts are $300+ each you need to take that into consideration. Also a lot of races do not allow screw blowers. Transmission ratios for a screw are very different than a roots.
     
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  5. Critical Mass

    Critical Mass Member

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    Roots versus Screw

    Everybody would love to have a screw blower, it looks cool. If your boost requirements are below 35 psi, why would anyone want to go to the expense unless a very good deal comes your way. Just being practical. Joe
     
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  6. Jason Bunker

    Jason Bunker Member

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    As stated, you free up a ton of HP with a screw. It does require a handful of setup changes as Mike eluded to, and if you dont have rules against it, you can run as fast or slow as you want with it. Low maintanence, smooth power curve, much more linear to engine rpm for fuel system changes, etc...
     
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  7. KZ5 Blown SBC

    KZ5 Blown SBC Member

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    what kind of overdrive difference is there between the two too achieve the same boost. both being good quality equipment.
     
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  8. Dave Germain

    Dave Germain New Member

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    Roots vs screw blower

    This question depends on what sort of racing you are doing? NHRA Top Alcohol classes require recerting blower every three years. I dont think there are any cert requirements on roots blowers. Some classes don't allow screw blowers. But roots blowers require restripping every 5-10 runs if you want it to run at it's best. No maintenance on screw blowers. Both blowers have particular setups as for transmission ratios and fuel systems. Some screw blowers can be tough on belts but not all of them. It depends a lot on your tuneup. Screw blowers require much less hp to turn them so they are much more efficient than roots blowers. I have ran both and hated the restripping process. One thing nobody has mentioned is that if you backfire a screw blower it doesn't hurt it but backfiring a roots blower can hurt it badly requiring new rotors. Dave Germain
     
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  9. skauto

    skauto Member

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    What differences are there in transmission ratios between a roots and a screw? and why, i ask only because we are making the change to a screw this off season we run a b&j 3 spd with a quick drive 1.68 1st, 1.31 2nd with a roots.
     
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  10. MUD SLUT

    MUD SLUT New Member

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    x2 and for the same reason...
     
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  11. PROMOD63

    PROMOD63 Member

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    x3 have a whipple but never changed gears when i converted from roots
     
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  12. skauto

    skauto Member

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    I guess this is top secret info?;)
     
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  13. altered8

    altered8 Member

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    we have seen some interesting things over the past few years in regard to ratios,the psi certainly loves a big run home.
     
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  14. craig moss

    craig moss Member

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    When we ran a roots we were running it @ 150 od on the worn out psi d screw we run it at 206 same boost way more power. This is on a bbc in a boat only turns 7800. Our big problem was getting a big enough bottom pulley on it std cam height. we had a custom 93 semi center flange made & had to cut the fuel pump drive tube out at the bottom. The pulley almost hit's the hex drive for the fuel pump. Hope this helps.
     
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  15. Mike Canter

    Mike Canter Top Dragster
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    Talking about different gear ratios at a high level. Well that depends on if it is eighth mile or quarter mile or weight of car or many other factors. Let's talk about TAFC the reason for a ratio change is that the launch rpm is raised up so the screw blower can make boost faster so when you launch at that high of an rpm it would be too violent with roots blower ratios so you have to calm the car down with a first gear ratio change. On ProXtreme eighth mile car everything is light, you have a converter plus it is the ratio in high gear that you want which is normally around 5.00. Because of this rear gear you change first gear ratio to calm the car down on launch.
     
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  16. skauto

    skauto Member

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    We run a 1/4 mile 2650lb converter car. can you not control the launch through the timing control with the screw as we do on a roots? without changing ratios? my understanding is the timing control on a converter car would be the same as clutch application and ratio change on a clutch? I know the higher the trans ratio helps(1.68 first in our case) as we don't take as much timing out on the launch but is there a happy medium between timing control and gear ratios?
     
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  17. Mike Canter

    Mike Canter Top Dragster
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    That is the trick to tuning them. Taking out too much timing requires too much recovery time, changing ratios also depends on slip of converter. You may not feel the change of the gear ratio if the converter is too loose. There are lots of different combinations.
     
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  18. skauto

    skauto Member

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    i see, i guess it is all relative if we find a set up that works on the roots with timing and ratio a matching timing and ratio change would make sense to keep all things the same as much as possible. Thanks for the input
     
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