18-71s vs Screw blowers August 21, 2017 12:23AM
Which one should theoretically make the most hp? It would be interesting to see what a dyno would say.
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Re: 18-71s vs Screw blowers August 21, 2017 12:35AM
I think the screw is the winner on a dyno, but i don't think they are as controllable. I think on some pro mod cars, the screw supercharger is illegal. Only problem with either of them is that they are only good for 2 classes, and i don't see the 14-71 classes allowing either one.
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Re: 18-71s vs Screw blowers August 21, 2017 12:54AM
In NHRA, screw blowers are used in the alcohol dragster and funny car. I think the nitro cars are required to use roots blowers. Pro mods have changed rules a lot and there are other orgs besides NHRA that have different rules, but I believe screw blowers are legal in NHRA's Pro Nod class, which at the moment is probably their best professional class.
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Re: 18-71s vs Screw blowers August 21, 2017 01:32AM
I would have said the same thing at this time last year but in the mod meetings at the Enderle the committee recommend allowing screws in the mod clas. I was very surprised by that. The full board did not allow it to got through. I have heard that it may be approved this year.

S'no Farmer
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Re: 18-71s vs Screw blowers August 21, 2017 02:20AM
Funny quote from Yellow Bullet, "The 1871 is designed to take advantage of the rulebook. The c rotor is why you need a rulebook in the first place." I think D rotors are legal in NHRA and it may involve a weight penalty. Mike Janis on Dragzine “A screw blower takes about 150 horsepower for the engine to turn the rotors, while a roots blower takes upwards of 500-600 horsepower to do the same. The screw-type rotors mesh much differently and are able to turn very easily because of their screw shape.” Looks like a D rotor is 10.8L displacement and a C is 11.2L. S'no Farmer, do you know if they were going to allow both C and D screws, or just the smaller D?
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Re: 18-71s vs Screw blowers August 21, 2017 09:05AM
No one knows what they will do but I've not heard any discussions about C rotor vs D rotor. I'm not sure what the guys that are running the screw blowers have at this point. Last year we had proposals to run screw blowers in the mod class that didn't pass the full board. At that time no one talked about C rotors,D rotors nor was there any mention of overdrive speeds. These are all things that need to be talked about in the meetings. Any mod pullers that have strong opinions one way or the other need to be at the meetings on Enderle weekend to voice their thoughts.

S'no Farmer
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