Thread: Which to choose 390FE or 460

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The 8:71 is just like a 6:71 except aprox 3/4 inch longer---hardly any difference unless you are running it at 45-50 % over---
a large bore must mean that they have over bored a 6:71 case and come up with some sort of roter to fit it---however there is a standard distance between the rotors so the gears mesh properly so they must have a completely different blower and are just calling it an big bore 6:71--this would take different endplates, gears, cases, rotors---everything but maybe they use the 6:71 manifold bolt pattern---i would like to hear more about what they have done

Originally Posted by jerry clayton

The 8:71 is just like a 6:71 except aprox 3/4 inch longer---hardly any difference unless you are running it at 45-50 % over---
a large bore must mean that they have over bored a 6:71 case and come up with some sort of roter to fit it---however there is a standard distance between the rotors so the gears mesh properly so they must have a completely different blower and are just calling it an big bore 6:71--this would take different endplates, gears, cases, rotors---everything but maybe they use the 6:71 manifold bolt pattern---i would like to hear more about what they have done

Jerry, I was as surprised as you appear to be when, a couple of years ago, I discovered that there are large bore and small bore 6-71's. I found this out competely by accident when reading through specs on Blower Drive Service's site. Begin reading here...
BDS Street Blower Boost Charts
on this page...
http://www.blowerdriveservice.com/techcharts.php

Just shows to go ya, we're never too old to learn something new.

Found this on their site thanks Jerry:

There are two different 671 blowers commonly used. They are the larger diameter blower and the small diameter blower. The large bore blower (case thickness 1/2"-) is approximately 11 percent larger in volume than the small bore. The small bore blower (case thickness 3/4"+) is recommended for 370 CID engines or less for street applications. The larger bore blower is recommended for 371-500 CID engines in high performance, racing applications.