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Technical pros and cons of a blower motor

Discussion in 'Traditional Hot Rods' started by 46international, Oct 13, 2018 at 2:49 PM.

  1. Many of you have helped with my short lived 4-53 blower on a Y block project, Thanks.
    I have found out that a 4-53 is too small for for a 292, would be better for a 239 flathead but too small for me. (Anyone want to buy a 4-53 cheap?) It is the larger one of the two.
    This brings us to my new project, a 4-71 blower on a Y block. Before I get too far into this, what are the pros and cons?
    Price, I can make most of the parts I will need and a Hamber is getting me a good deal on some stuff.
    Performance, well, I guess that will be a plus.
    Dependability, any thought on this?
    Will affect the idle quality? I have an automatic.
    What about some thoughts on how to set it up, What size carb should I run? would like to use a 4150 Holley.
    How about the power valve? I guess that works the same. What about my vacuum advance? can I still use it?
    Anything else I should consider for a street 292 Y block in a Model A?
     
    Marcosmadness likes this.
  2. big duece
    Joined: Jul 28, 2008
    Posts: 4,865

    big duece
    Member
    from kansas

    Compression ratio plays a large part in setting one up. What is typical CR for Y block, if close to 9:1 it limits you how much boost you can generate. Can you get dished pi$tons for Y block? 4150 carbs will need to be boost reverenced for blower setup.
     
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  3. It's always been the easiest power aid. How far do you wanna compress it is going to determine parts and combination of build.
     
    46international likes this.
  4. Mike VV
    Joined: Sep 28, 2010
    Posts: 1,111

    Mike VV
    Member

    One big misunderstanding/lack of understanding on cam choice...
    A cam with 112 to 114 degree (intake to exhaust) lobe centers is one criteria to have when you pick a cam. If you pick a cam with the more normal 110 or less degrees, will let the blower pressure just go out the tail pipe rather than push the pistons down the bores..!
    A cam for a carbureted engine is different than a cam with a blower (belt driven).

    Mike
     
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  5. chevy57dude
    Joined: Dec 10, 2007
    Posts: 4,351

    chevy57dude
    Member

    Blowers produce heat!
    That's the only drawback I have to list.
    Power all the time is the biggest plus. Boost referenced power valve is a must.
     
    46international likes this.
  6. DDDenny
    Joined: Feb 6, 2015
    Posts: 9,581

    DDDenny
    Member
    from oregon

    Last edited: Oct 13, 2018 at 4:13 PM
  7. dirt t
    Joined: Mar 20, 2007
    Posts: 4,112

    dirt t
    Member
    from Kingman,AZ

    4X71 =284 cubic inches you have 292.
    You can overdrive the blower to make up for the differance. On a street motor for relialibity I would run 3 to 5 pounds of boots. Things like double keyway the harmonic balancer and make sure your blower is parallel to the crank or you will through belts. It's not rocket science but takes a well thought out plan.
    Good luck
    Terry aka dirt t
     
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  8. G-son
    Joined: Dec 19, 2012
    Posts: 359

    G-son
    Member
    from Sweden

    The more parts and systems you put on an engine, the more failure points it has. If you simply want reliable performance there should be plenty of conventional N/A tuning possible. If you want a blower for the sake of having a blower motor, that's going to be a different road to walk, quite possibly with a less reliable engine as a result.
     
    46international likes this.
  9. ^^^^^ Not true. It's the applied right foot pressure that usually is the root cause of "all" failures blown or not blown.
     
  10. 270ci
    Joined: May 17, 2010
    Posts: 327

    270ci
    Member

    Thats somewhat misleading, because that 292 will need two revolutions to use its 292 ingested cubic inches, while that 280 inch displacement blower (4-71) will be pushing in a total 560 cubic inches during two revs, if run at 1:1 ratio and you let it eat (open throttle). No overdrive required, that's how you make boost.
     
    Last edited: Oct 13, 2018 at 4:48 PM
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  11. 270ci
    Joined: May 17, 2010
    Posts: 327

    270ci
    Member

    Do it, the 292 will thank you. And BTW, there are no cons to a blower motor, if you do it right....just like anything else.
     
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  12. DDDenny
    Joined: Feb 6, 2015
    Posts: 9,581

    DDDenny
    Member
    from oregon

    A biggy is forgetting to give a good shot of gas first with that right foot before trying to start a supercharged engine (non EFI).
     
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  13. miker98038
    Joined: Jan 24, 2011
    Posts: 315

    miker98038
    ALLIANCE MEMBER

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  14. 6sally6
    Joined: Feb 16, 2014
    Posts: 119

    6sally6
    Member

    Just wonder'in............why is that? Patting-the-gas a couple of pumps BEFORE spinning over a blower motor?!
    Needs a rich charge?..... Whatz the reason?
    6sally6
     
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  15. big duece
    Joined: Jul 28, 2008
    Posts: 4,865

    big duece
    Member
    from kansas

    Lotta air moving through there, better a bit rich than lean.
     
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  16. 5window
    Joined: Jan 29, 2005
    Posts: 6,238

    5window
    Member

    Bigger blower will affect your sight lines.
     
    46international likes this.
  17. Good blower pistons have a little more meat above the ring land, might be hard to find for a Y block.
     
  18. el Scotto
    Joined: Mar 3, 2004
    Posts: 3,903

    el Scotto
    Member
    from Tracy, CA

    Cragar made a 3-71 and 4-71 kit for the Y block

    It only costs $322 too!

    IMG_5710.JPG
     
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  19. I have two sets of heads, one set that will give me about 9:1 and another one 8.1 :1 or so. The higher compression heads have the larger valves. I would like to be about 4 to 5 lbs of boost if that would not hurt dependability much.
    What would have to be done to "boost reference" the carb?
     
  20. Yes, I have been reading about that. I have a larger rumpity cam in the car now I think it is 108* but would have to check. This may end up the most expensive single item to correct, what would you think about a stock cam? I don't know the the separation angle is on it.
     
  21. The heat thing is a down side, I drive this in the summer and would hate to worry about overheating all the time, how bad is this problem with 4 to 5 lbs of boost?
    Explain about the boost referenced power valve.

    On a side note, I'll see you next saturday up in Gettysburg.
     
    chevy57dude likes this.
  22. Would this bee needed for 4-5 lbs of boost?
     
  23. that would be nice
     
  24. chevy57dude
    Joined: Dec 10, 2007
    Posts: 4,351

    chevy57dude
    Member

    In street mode, I'm producing 6 pounds of boost.(turbo guys laugh now). By 3000 rpm, it's producing over 400hp and rising. Twin fans, big radiator.
    Temps climb at highway speed, sustained 3000+ rpm makes the temp climb toward 200. Not enough to worry about, but it freaks me out to see it rise.
    Ever hear a blown car ''surge''? If the power valves don't "see'' boost they are experiencing constant vacuum and the engine searches for equilibrium. At idle, it will continuously rev then drop, not something I'd want to drive, with a clutch.
     
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  25. Jmountainjr
    Joined: Dec 29, 2006
    Posts: 741

    Jmountainjr
    ALLIANCE MEMBER
    from Maine

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  26. blowby
    Joined: Dec 27, 2012
    Posts: 4,883

    blowby
    Member
    from Nicasio Ca

    My blown flathead Ford takes some fuel to get it started, and I had to play with power valves on the Strombergs a bit. It runs hot but it ran hot before..

    My stock SBC daily got a street blower earlier this year. It fires right up without pumping the gas and never runs hot. I just plopped the Q-jet back on without any changes, no idea what it has for a power valve.

    Both don't see more than 5psi, but that seems enough to make a big difference, although a good running Prius would probably outrun either one. :(
     
    Last edited: Oct 14, 2018 at 9:10 AM
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  27. big duece
    Joined: Jul 28, 2008
    Posts: 4,865

    big duece
    Member
    from kansas

    Here is a chart for compression ratio efficiency. Ideal is 12:1 or under "effective comp ratio" not static. Static CR is on the far left of the column. If you use 8:1 static, and 6 lb boost you would be at 11.3 effective CR. So, using 5-6 lb of boost would be your sweet spot. You will have to ask a carb guy about boost reference, but I know if those huffers cough and back fire it blows powervalves out. I would look into running the heads with larger valves, only if you can find dish pistons to lower CR. Cams; some came with 114 lobe seperation. The old GM 350hp cam "151" was 114, so there are some stock cams but dont know squat about Y blocks. Also, look for a cam with split duration, a bit more duration on the exhaust side. No problem with air being forced into the engine, but longer duration on exhaust will help flow for exhause getting out. Compression-Ratio.jpg
     
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  28. big duece
    Joined: Jul 28, 2008
    Posts: 4,865

    big duece
    Member
    from kansas

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  29. big duece
    Joined: Jul 28, 2008
    Posts: 4,865

    big duece
    Member
    from kansas

    What is the casting # of the two styles of heads you have now? the 5750-471 head is spoke to be the best for supercharged application for combustion size and flow.
     
  30. big duece
    Joined: Jul 28, 2008
    Posts: 4,865

    big duece
    Member
    from kansas

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