Roots Blower Info

[polcat]

I am looking in buying a roots style blower. Possibly a 671 style blower. I see alot of them on ebay that are in good shape and for alot less than if u go with a name brand. Other than possibly needing a high speed bearing and installing a drive to make it work on a gas engine. What is the basic difference? I have worked on diesel engines for years and gas engines. And have rebuilt a few 671 and 871 blowers for the detroit engines. But have never set hands on a BDS or Wiend roots blower so I really don't know if their is a difference or not? Just looking for some information. Another question is, is were do you tap into to check your boost? I am planning on running no more than about 10lbs of boost so I figure a 671 will work for my application.

[Freightrain]

I run a box stock, NOS 671 blower on my 390(right outta the DD box). I did replace the back bearing plate with BDS version(instead of making my own cover plate). Can't recall what for bearings I used? Maybe originals? been 8 yrs now.

I shortened the original shafts(removed extra gears) and installed BDS drive. Basic, simple job. 8yrs, alot of miles and not had any issues. Just a side note: Car sits in storage all winter(6+ mos) and I went in and pushed on relief valve in front gear cover and it still have "pressure". Seals must be good!!

Not sure what the blower guys do with their set ups? Clearances? bearings? If they are tighter or looser then a stock DD blower? I run 6# of boost in mine. I know my rotors are NOT double pinned and I know I've read that that is a good thing to do as you don't want the rotors spinning on the spline shafts(things tend to touch inside!). I"ve read that the "teflon tipped" versions are not good for street use as they will get torn up with all the dirt it will eat with years on the street.

My friend is rebuilding a blower motor he bought and he called Don Hampton and spoke with him about the set up. Super nice guy and I'd recommend maybe calling him if you want some specifics. From the story I got, he's a one man band that still does all his own work, even after all these years.

Mount your vacuum gauge BELOW the blower so you get BOOST readings(and vacuum). If you put in up at carbs, you'll only get vacuum. Ya, I hooked it up that way first, then realized you'll never read boost up there! DOH!! I then machined hole in rear of spacer below blower for fitting. I run a BT intake with 3" spacer to raise blower to run stock dizzy.