Roots versus Screw

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

 

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

 

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

 

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

 

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...

 

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

 

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

 

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.

 

x2 and for the same reason...

 

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

 

I guess this is top secret info?

 

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

 

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.

 

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?

 

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