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Thread: 6-71 supercharged 302 help needed

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  1. #46
    IC2 is offline CHR Member Visit my Photo Gallery
    Join Date
    Sep 2007
    UPSTATE New York

    Quote Originally Posted by shawnlee28
    Do not be scared of a repaired or sleeved block in one of these aftermarkett blocks ,people get scared when they see sleeve and the price is usually pretty low,if the sleeve was installed correctly it is just as good as new.

    Even if it needs machine work and repair,at around 600 to 1000 dollars these make good deals,especially since the power exspectations are not the main concern,you could do 500 or soo in a repaired block and not even stress it at all.
    Racing junk has some used stuff on there .......
    Back in the days of Y-Block Fords (yeah - I'm THAT old), I used a couple of 312cid blocks that had sleeves - and never had a bit of trouble. The big ache with those engines was the bottom end - but when you have a bunch of parts, you do with what you have. If I had used the 292"........

    A good sleeve with the proper installation is absolutely no problem. As a matter of fact, one version of the Ford flathead was OEM sleeved, the '40 - '41s, if memory serves me.
    Dave W
    I am now gone from this forum for now - finally have pulled the plug

  2. #47
    Fastnuf is offline CHR Member Visit my Photo Gallery
    Join Date
    Feb 2008
    San Diego

    I have built numerous roots type supercharged motors. We actually did some R&D for B&M a long time ago when they first came out with their mini roots type superchargers. One of my motors is in their supercharger handbook and was used in some of their advertisements.
    First, a 6-71 is not too big for a 302. A bigger supercharger can be spun slower creating less heat (roots type superchargers are notorious for creating excessive amounts of heat), being more reliable and easier on the crank snout.
    There are actually two 6-71's. A standard size rotor and a big rotor. They are identical on the outside. The big rotor 6-71 uses the same diameter rotors used in 8-71's, 10-71's 12-71 and 14-71 jimmys. (They just get longer as the blower gets bigger) I can't remember the displacement of the small rotor 6-71 right this second but can look it up tonight after work. The big rotor 6-71's are getting hard to find, so you will probably end up with a small rotor 6-71 which is no big deal considering it's going on a 302.
    You will need a good steel balancer (a stock balancer WILL split) and you should consider double keying the crank. As long as you don't overdrive the bejesus out of it you won't need a crank hub.
    As for a cam, try a hyd. 234/244 @ .050 with about .488/.510 lift. Compression should be around 7.5:1 since a roots blower produces ALOT more heat than the efficient screw or centrifugal superchargers and should accommodate 91 octane pump gas with approx 7-8 PSI of boost. If you have any pinging, a MSD boost retard will cure that.
    As for carburetion, two 600 Holleys should work just fine, but I prefer 2 750 D/P Holleys.
    Hope this helps.

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