Roots Blower overdrive limit

I realize that roots blowers Loose efficiency the faster you spin them (going from 28% to 38% overdriven picked up quite a bit less than going from 20%-28% overdriven) . What overdrive do they stop making gains at all? Running a TBS 10-71 HH (single strip per rotor) blower and not turned it any faster than 38% over and wondering if it’s even worth trying to spin it harder.

 

you say it only has a single strip, I'm assuming it's the rotor tips that have the material, if this supercharger had teflon strips in the valley, you could slow the OD down from what you are now and it would make more power, boost wise, and efficiency, being that its s high helix, you actually have more leakage between the rotors because of the twist

 

I'm assuming that you purchased this blower for a performance application, can I ask why did you buy a high helix without the teflon in the valley?

 

Thanks Mike, 38 yrs working on superchargers, I've seen s lot of things evolve in this industry

 

A factor that has an affect on the over drive is engine speed. You need to look at RPM x OD for rotor speed. You run a slower engine RPM you can run a higher OD.

 

A lot of things come into to play at where each blower is the most efficient, Inlet open size is very important. Rotor profiles, Outlet shapes and sizes, and so on also come into play. Critchley told me anything past 29 is pointless but it depends on the blower and your setup. With a torque converter dragster using 14-71 HH retros the PSI roots 2" unit was liking 42 od where as the SSI F3 was liking 38 and my current blower likes 25-29. Andy would be a great person to talk to on that or check with guys who run that blower and see what they have found. MPH can help with telling efficiency. Best wishes, Trev

 

i just got 2 new LB22 from Andy, they are a beautiful thing!!!!! There is a lot of technology in them.

 

I think most guys will tell you that there is no difference in shifting an engine at 8500 versus 9500. Some guys think they can cheat a blower by spinning it 33 over and shifting 8500. But you’ll go faster shifting 9800 and spinning or 20 over . It’s a Hemi it’s consuming parts the same amount of parts at this point. But heating a blower up trying to spin the od hard just wears a blower out with the quickness. I’ve seen some shooting Teflon out the pipes on the 2 step.

 

Monitor intake temp. Higher temp = more power loss. When you start getting close to 140 degrees, you're spinning it too fast. Top opening is a big factor...you need to spin a blower with a 11.5" top opening a lot faster than you need to spin a blower with a 10.5" top opening.