Hi all,
I've been trying to verify this for some time, and keep getting conflicting data. Wrote to ATI and they were saying blower pulleys are 2.81" bolt circle 2" register which they claim is standard Mopar. AFAIK blower pulleys are 2.782" 2" register.
What is the standard bolt circle for roots blower pulleys (I know the center register is 2" vs Mopar 2.25")
What is the standard SBM/BBM crank pulley bolt circle and register?
Trying to see if I can use standard blower pulleys on a harmonic balancer (not looking for the "no need for balancer, get a hub" answer, I have my reasons).
Thanks,
Ran

Thanks Dave,
I saw this too late to call, but I did some calling and more research.
Standard SBM/BBM bolt circle is 2.811" give or take a thousandth
Mopar center register is 2.25"

Industry standard blower pulleys are 2.75", 2.76" or 2.782" bolt circle (depends where you check), with a 2" center register.

There used to be Weiand style pulleys with a 2.25" center register. Supercharger USA show them as an option.
http://www.superchargerusa.com/weiand_pulleys.htm
However, they don't say what the bolt circle is. They (probably more like a "he") are away until May 3rd, so I'll call them then and ask. I also saw some ebay seller that claims he actually makes the pulleys, so he can custom make them. Sent him a question about that.
I called several blower shops, the ones I got a hold of, told me they only deal with the industry standard stuff.
I couldn't get a hold of Littlefield, Mooneyham or BDS yet, so I'll try to see if they can help.
I'll update here when I get an answer. Not that it should matter to anyone building a blower only engine...I just want to use a system that will allow me to use the engine without a blower (when the blower gets migrated to another engine for example).

Ran

Ok, finally got an answer I was happy with.
I did some more calling around, Good Vibe Racing said that you can use the industry standard pulleys on the Mopar balancer since it's only 50 thousands difference.
I wasn't sure about it, and I finally got a hold of Supercharger USA - they offer "Weiand" pattern blower pulleys.

So - here's the deal, "Weiand" pattern is 2.81" bolt circle 2.25" center register (bingo - Mopar pattern)....but here's what they said they do - they just drill an industry standard pattern to 7/16" which allows the use of the 2.81" bolt circle, and they open the center register to 2.25".

I also dug out the parts I have, and the 8 mm bottom pulley that I have is 2" center register, 3 hole BBC bolt pattern - more than enough meat to drill and open up to Mopar pattern.
So - I'd have to get V belt pulleys and spacers drilled out to 7/16" and make sure they have the right center register.
Worse comes to worse, some things will need to be fabricated.

Ran

Thanks Dave, but I never said anywhere that I'm going to use a factory damper. That would be unwise. I want to use a steel aftermarket SFI balancer. It's a street engine, so if/when I move the blower setup to a different engine, I don't have to worry about replacing the hub setup with a damper.

Ran