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3-71 blower on a sbc,advice needed please.

Discussion in 'The Hokey Ass Message Board' started by Moon Rocket, Feb 19, 2013.

  1. Moon Rocket
    Joined: Dec 26, 2012
    Posts: 540

    Moon Rocket
    BANNED
    from GA

    I may have an opportunity to pick up a 371 blower set up for a sbc at a reasonable price.

    My engine currently is a 355 sbc, 9.9/1 forged piston, .488 int, 308 duration and .510 extt, 318 duration cam. 1.94 x 1.50 valves, roller rockers. 650 cfm Holley, 4777 carb. Just a solid old 375hp hot rod motor. 4 speed trans, 3:73 rear.

    My question is, would it be a reasonable application for this blower on this motor? I’m not as concerned with all out hp numbers as I am with drivability. But I would be disappointed if it didn’t perform at least as strong as it does now. I love the look of a blower, but I don’t like the up and down idle a lot of the big blower motors seem to have. So I would want it to have a constant idle rpm instead of the veroom…… veroom…….. veroom.

    I have very limited knowledge regarding blowers, other than to know they look cool as hell!

    My basic concern is, if the blower would push enough cfm for the engine without over spinning it?

    All applicable, knowledgeable feedback is appreciated!
     
    Last edited: Feb 19, 2013
  2. Dan Timberlake
    Joined: Apr 28, 2010
    Posts: 1,331

    Dan Timberlake
    Member

    http://www.mini-blowers.com/gmc-blowers/gmc-3-71-blower.php

    Looks like it is a mere 3X71 = 213 cubic inches/rev. Being a positive displacement supercharger I don't think you can pull more than that through it ( minus some efficiency losses) .
    A 100% volumetric efficiency 350 Chevy needs 175 Cubic inches per rev, so at 1-1 ratio there might be >some< slight supercharging going on, unless the density lost to heating of the air cancels it out.

    Time for someone who actually knows what they are talking about to respond.
     
  3. I'd think a 3-71 blower would be too small to do much good on a 355 Chevy.
    Same train of thought as Dan.
    Your 9.9:1 compression wouldn't take or need much boost though and you can always cool it with alcohol/ water injection. Good question
    If its cheap enough though it would make great horse trading material.
     
  4. Russco
    Joined: Nov 27, 2005
    Posts: 4,194

    Russco
    Member
    from Central IL

    Does it come with an intake? I don't know that I've ever seen a 371 set up for an SBC before. You probably could get some boost out of it but you have to overdrive the hell out of it probably. Are you really at 9.9 compression or is that just what the piston manufacturers label said.
     

  5. Moon Rocket
    Joined: Dec 26, 2012
    Posts: 540

    Moon Rocket
    BANNED
    from GA

    If anything I may be a tad higher than 9.9/1. The heads are decked enough to clean them up, but I didn't cc them.

    The intake is a double plane, four barrel with a fabed adapter plate to mount the blower housing on. It actually looks pretty cool, (interesting).

    It's the overdriving it part I'm worried about. If I'm red lining the engine at 6300 rpm that would be spinning that little blower 7000 with a 10% overdrive.

    I'm mostly looking for a little old school wow factor for a otherwise simple sbc. I'm not a multie carb fan at all.
     
  6. The problem with over driving them is the heat build up in the charge. It reaches a level of diminished returns. the oxygen molecules are so far apart due to being heated that you can't get enough of them packed in. If you cool the charge , most of that is eliminated. Compressing the air heats it up all by itself.
     
  7. Moon Rocket
    Joined: Dec 26, 2012
    Posts: 540

    Moon Rocket
    BANNED
    from GA

    I'm already getting the impression I better leave well enough alone.

    I drive my car alot, don't have any over heating problems and it runs pretty good for what it is. So I don't what to create problems where I don't have any.

    It's not like I'm trying to "fix" anything. It's just a little homely looking under the hood.But I simply refuse to put a crome thermastate housing on it!
     
  8. captmullette
    Joined: Oct 15, 2009
    Posts: 1,929

    captmullette
    Member

    go with a tunnel ram, looks cool also
     
  9. Russco
    Joined: Nov 27, 2005
    Posts: 4,194

    Russco
    Member
    from Central IL

    I asked that because I am running a 471 on a .030 over 327 with forged flat tops and its actually only 9.0/1 with 64 cc heads. I get 6-7 pounds of boost and run a single 750 carb and pump gas. I think the compression numbers the piston manufacturers list are at Zero deck and maybe without much allowance for gasket thickness.
     
  10. BLAINE 816
    Joined: Jan 6, 2007
    Posts: 243

    BLAINE 816
    Member

    FYI just mounting a blower on a NA engine may lead to pressure indications that are misleading. A well tuned blower engine will have had a lot of thought envolved
    in its set up.Primary to its construction would be manifold, rotating assy. cam choice[very important] ignition source, exhaust just to name a few.I run a 471 on my 32
    3/W and would not want it any other way.
     

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