Screw Versus Roots Superchargers

Why is it that NHRA embraces screw chargers, while IHRA prohibits their use?........

 

Inquiring minds want to know.

 

Inquiring minds want to know.

 

After the intial costs of the screw blower they're
cheaper and faster. (no restripping, etc.) But,
you have to commend the IHRA on giving the class a set of rules and sticking with them. Apples racing Apples.

 

IHRA outlawed them when they first came into use because of some questions about them coming apart I think it was. But anyway they have stuck to that decision and kept their AFC class the way it is. People will argue both ways about which is better. From a performance aspect yes the screw is better, it makes more boost with less effort and doesnt take any power to turn. However I am pretty sure there are a bunch of guys out there that will tell you if your off on your tune up just a little with a screw it is going to hurt alot of parts. I think the roots it a little more forgiving in this department because it doesnt make as much boost. Just my thoughts.

 

actually nick the screw blowers don't make as much boost. i was suprised myself, but at 92% overdrive it makes around 5 pounds less than some of the roots blowers i used to own. the horsepower gain comes from the fact it only takes 20 horsepower to turn the screw blower. a fresh tight roots takes 500 to 750 horsepower to turn. also the air coming out of the screw is cool compared to the heat generated by the roots.the biggest strain on a screw blower car is you have to zing the rpms so high to make the boost and that is what kills parts. i still think a set revlimiter or a pop off valve like indy cars run would cut back on parts breakage. just my 2 cents.

 

Our best high helix roots (56 over) back in 1994 made 5 pound more boost than our new PSI (1.92 over) at the same RPM. I would never want to go through the agony of a roots again.

 

cheaper and faster huh??!!!! right and all politicians tell the truth, its at least double the cost of running competitive roots car.

 

man this seems like an old argument...

so if you are currently running a roots... why do you think it is cheaper than a screw? initial purchase? lower rpm's... why is it cheaper?

and to the screw guys... how do you 'save money' by running the screw?

i'm just curious (and have absolutely no opinion).... because i run an outlaw altered with an old standard (and wore out btw) 14-71. just curious if there is something i'm overlooking? thanks... sean

 

M Tigges, just curious. Where and when have you run both a roots and screw to draw your conclusions from since you have such a strong opinion?

 

Gotta agree with Randy- no comparison- sombody gave you a load of misinformation if you think a PSI is double???

 

Randy the Tigges family raced both the screw and the roots about 2 years ago (Thats right isnt it Mark?) and well Mark can tell you the rest.

 

have you priced a latest & greatest roots blower lately,5-7 thousand dollars for such a good blower! a lot of good used psi blowers out there for sale with all of these teams changing over to a/fd.if you already have a roots setup,it is not cheap to change over to a psi,fuel system-gear ratios-compression changes.but if you are buying first time,it is the way to go.I have done the change over to the psi from a roots setup and will never go back! it just free's up horsepower that is already there.low maintence,smooth power all the way thru power band.it may not be for everybody,and their are people that will blame the psi for there motor damage.but the roots blowers blow up too!! just look at some of the ihra funny cars engine damage they have had when they run them hard!!I don't have the answer to the roots vs psi blower question,but most people that change to the psi setup,and do it right-never go back.that's my 2 cents worth!!

 

rear gears trans parts clutch parts is double,forget the motor,its the rest that costs. we can hammer the motor with the roots and the crank lasts all year, Randy you guys are running great,but look at the damage, dont get me wrong i enjoy disscussing the difference,im not trying to sound arrogant,thats just what we found. where close with Bob,and know GILL AND EVERYONE else up here well,there driving over some serious stuff!

 

Our problem isn't screw blower related. We actually had all the bells and whistles shut off at Sears Point and it still ran pretty good, but had another issue that made Marc and I mutually agree to park it in the semi's even though I had a trailer full of parts to fix it. 'Nuff said.

I will say this, though. When Pete Swayne was with me in 1999, we ran a ton of races, won the Div 7 championship, were number 7 nationally, and ran 5.60's with the PSI at 125% overdrive. The damage report for the entire year excluding normal maintenance: One cracked main cap and 1 broken push rod. We broke no other parts all year.

With the blower turned down to 92%, the story has changed. It's a lot harder on parts and on the wallet. People say we need a rev limiter to control costs...we had one. It was called 125% overdrive and supersonic air flow issues over 9,500 RPM. Want to lower costs? Give me back the overdrive. Unfortunatley, those who know the least convinced the powers at NHRA that 92% would be a good thing. Heck, under the 125% overdrive (5 years ago) we ran a 5.64 at Mission and the engine never went over 8,600 RPM on the whole run.

But life goes on and here we are.

I still wouldn't switch back to a roots, though.

 

Randy..Randy..
It's a gallant fight..but you won't change their minds..the PSI is a "must have" part if you want to have even the slightest chance of being competitive in NHRAville anyway and the roots is the only game in IHRA. Why spend the money to buy the best chassis, clutch, rods, carbon fiber body,motor, etc...and then not go all the way and put a PSI on it..and with the "NEW" lockup clutches being developed, "we're" only going to go quicker and faster...by the way our rear end gears last longer now than ever before..

Hey Todd Veney...Where you at?

 

Jerry: I'm with you on the PSI. Why go all the way with the stuff you mentioned and then slow the blower overdrive down. We have a 5.50 combination so you'd think I'd keep my yap shut about the OD deal. But not so.

See you at Indy.