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Technical Cadillac flathead what's needed to survive 10psi

Discussion in 'The Hokey Ass Message Board' started by BILLIKENN, May 20, 2021.

  1. BILLIKENN
    Joined: Oct 1, 2009
    Posts: 2

    BILLIKENN
    Member

    Love my 46 cad, but want to do something cool with the motor and get some more umph out of her.
    Still has the 346 flathead V8 but pretty tired. I'm keen to keep the flathead, with rebuild and forced induction.

    Thinking we can squeeze a 4-71 Blower under the hood with some creativity.

    Do you have any suggestions to handle up to 10psi ? what mods to the motor are a must, nice to have, or just plain cool?

    Street motor for cruising and touring.

    Josh 20210221_174612.jpeg

    Sent from my SM-G996U1 using The H.A.M.B. mobile app
     
    kidcampbell71 likes this.
  2. 10 pounds of boost is too much for a happy street flathead build.
    It will require a large sum of money to make it last,,,,,5-6 pounds is more fun .

    Tommy
     
  3. squirrel
    Joined: Sep 23, 2004
    Posts: 48,670

    squirrel
    Member

    just imagine how much it will overheat with a blower on it...ugh....
     
  4. lippy
    Joined: Sep 27, 2006
    Posts: 5,533

    lippy
    Member
    from Ks

    Lots to think about. If the mixture is right your battle is half won. If your going to hammer on it a bit, Squirrel is right the cooling system needs re evaluated. Then.......you get to see how long the rest lasts. JMO Lippy
     
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  5. Pete1
    Joined: Aug 23, 2004
    Posts: 1,969

    Pete1
    Member
    from Wa.

    We got one going over 180 at Bonneville in 2011. Engine did around 600 hp.
    Contact "Bored & Stroked" over on the Fordbarn Early V8 for details.
    Makes good street engine in milder form.
     
  6. F-ONE
    Joined: Mar 27, 2008
    Posts: 2,761

    F-ONE
    Member
    from Alabama

    Sell the car.
     
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  7. miker98038
    Joined: Jan 24, 2011
    Posts: 588

    miker98038
    ALLIANCE MEMBER

    If that doesn’t pan out, you might think about a VS57 McCulloch. Couple guys out there building those to 8lbs or so, and the bonnet and blow thru carb aren’t a big deal or a clearance problem. Period correct for the early 50’s, so not far off.
     
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  8. Bird man
    Joined: Dec 28, 2009
    Posts: 664

    Bird man
    Member
    from Milwaukee

    Love your thinking & the Paxton idea has merit too. Likely the biggest obstacle is the strength of the 3 mains?
    With some porting, relieving & a mild cam, she ought to be fun? I would love to see some dyno numbers for good street builds.
    Keep us in da loop.
     
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  9. Fortunateson
    Joined: Apr 30, 2012
    Posts: 4,024

    Fortunateson
    Member

    I like what Birdman advised bu it wouldn't put a blower on it. Never be shy about changing the rear end gears but then you may not be shy at gas stations either...
     
  10. I"d look for a second 346 to build up.That way if you break something beyond repair at least you can put that nice car back to stock.
     
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  11. I'll be watching as I had a 47 with the 4 speed hydro. 150 H.P. stock but had a lotta torque to haul that heavy body around. 47caddyandscotty.jpg
     
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  12. Flat Roy
    Joined: Nov 23, 2007
    Posts: 454

    Flat Roy
    Member

    Supercharging is not a problem on the street. One way to improve street performance is to use a recirculation valve like all the new factory jobs out there. That way you will only be boosting when you put you foot in it. Check it out. Easy to do. Keep the boost below 6Lbs
     
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  13. Torana68
    Joined: Jan 28, 2008
    Posts: 1,252

    Torana68
    Member
    from Australia

    I wouldnt want it going off boost , got a link to this recirculation valve your speaking of?
     
  14. mgtstumpy
    Joined: Jul 20, 2006
    Posts: 8,760

    mgtstumpy
    Member

    HAMBer 38FLATTIE (www.flatcadracing.org) has a blown flathead Caddie in his 38 Chevy coupe. Lots of work, crank girdle etc etc Buddy hasn't been on the HAMB since March 2019
    upload_2021-5-21_18-16-44.png
     
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  15. Truckedup
    Joined: Jul 25, 2006
    Posts: 4,070

    Truckedup
    Member

    Maybe some guys here running superchargers can explain how intake restrictions affect the boost you see on the gauge and the actual boost in the cylinder...
     
  16. squirrel
    Joined: Sep 23, 2004
    Posts: 48,670

    squirrel
    Member

    A free breathing engine, such as a hemi or rectangular port big block chevy, has very little restriction between the blower and the valves, so the boost you see at the gauge, is the same as what you see in the cylinder. But a flathead with it's small, convoluted ports can build pressure in the intake manifold, that never really makes it to the cylinders at full strength. you might see boost go up at higher rpm, but power doesn't go up proportionally.

    The idea of using a bypass valve such as on a modern production blower, sounds helpful, from the overheating perspective. Although using one with a carb might be challenging...the cars that come with them, have efi, so it's easier to control the fuel mixture.
     
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  17. BILLIKENN
    Joined: Oct 1, 2009
    Posts: 2

    BILLIKENN
    Member

    Thanks for the input everyone. I followed along with the flatcad build years ago and reread a few times over the years. Amazing.
    I want something a tad milder than Bonneville worthy.

    This is not a whim, been dreaming up a postwar Caddy for 25 years. I thought it would be a 49 sedanette, even had a major project for a decade, but my wife persuaded me into the 46 convertible when the opportunity came. Weve had it a couple years now and both love that car.

    My first intention was to put a small turbo on it, because that stock manifold is screaming to me for one.
    I've considered the vintage centripetal blowers, they sure look cool, but it just doesn't seem my flavor.
    Second thought was two judson style blowers, one over each head. I still dig this idea.
    Then a builder got me interested in the 4-71 for the low end torque and period fit. Looks like we can just barely squeek it under the hood without mods. Not my favorite for looks, but it hits the mark for torque.

    I'm not looking to start a museum, but intend to keep nearly eveything on the outside of the motor reversible. The body will remain stock.

    Heat I can deal with.

    I'm somewhat familiar with the volumetric efficiency, been studying different induction systems for a few years off and on. This motor is probably starting around 70%? I'm also somewhat familiar with flow dynamics from my work. I'm not expecting a hellcat, and I'll have poor value $/hp. Oh well, price of period cool.

    I'm hoping I'll have less than 20k in the motor. If it can't be done, I'll have to come up with a new plan.


    Any ideas what it takes to build a falt cad that can reliably withstand 10psi at the manifold? (not necessarily saying I'll run 10)

    Josh

    Sent from my SM-G996U1 using The H.A.M.B. mobile app
     
  18. Pete1
    Joined: Aug 23, 2004
    Posts: 1,969

    Pete1
    Member
    from Wa.

    Like I said, contact Dale over on Fordbarn early V8 forum. He built the Flatcad engine for the 9785 coupe.
    He may still have a street cam I ground for it when it was still in the development stage.
    By the way, that car was a real piece of shit, constructionwise. I was surprised it made it through tech.
    Among other things, it had a pair of vise grips for a door handle. The first time I drove it, the chute did not deploy
    and the brakes failed.
     
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  19. chop&drop
    Joined: Oct 11, 2006
    Posts: 438

    chop&drop
    Member

    My guess is that building a flat cad that will take 10 psi will exceed the value of the car even once that engine is in it. I understand your wish to keep the flatty but why not just keep it all Caddy. A 472 or 500 Cad would triple or quadruple your current power output in stock form at way less cost and you can keep the 346 in case you ever want to put it back to stock. Just food for thought. Good luck with your project.
     
    Last edited: May 21, 2021
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  20. Rusty O'Toole
    Joined: Sep 17, 2006
    Posts: 9,516

    Rusty O'Toole
    Member

    As a general rule any engine will take 4 - 5 pounds of boost no problem. When you get up around 7 you start getting problems with blown head gaskets, overheating, burned exhaust valves. 10 psi is asking for burned pistons, bottom end problems, bent rods, etc.
    Having said that the Cadillac is one tough engine and would probably stand the gaff better than most engines of its time.
    Talk to someone who has been through the mill, see what they say. If it was me I would go for 5 pounds boost and see how it went, if it worked ok maybe go a little higher.
     
    tractorguy likes this.
  21. unless you do a mega drop on your static compression 10 PSI is not a street motor. If you lower your compression to the point that you can run on pump gas @ 10PSI you are really defeating your purpose.

    In stock form and built @ 8:1 it will easily survive in the 3-5 pound range, I think if you are a good tuner you may pull 8 PSI off on pump gas if you stick with premium, you may need to add a little octain boost. All of this is easier with a computer obviously. I am assuming that you want to go old school and no electronics.

    I would prefer to run forged piston if you go much above 3 pounds, and I am a fan of polished rods on about anything. If I wanted to be one of the cool kids a stud mount crank is always a good idea and if you intend to really hammer it a stud girdle is also a good idea.

    A 3 angle valve job is a good idea, and on a blower motor wide flat mating faces is a given. Stronger intake springs than stock are a good idea too. O ringing the block is also a good idea, you can find the proper head gaskets to use with o rings.

    I do no know if anyone makes a blower cam for that motor but if you could find one that would be cool.

    I have missed a lot on this as I usually do but someone will fill it in.

    Good luck on the build. I like your thinking.
     
  22. squirrel
    Joined: Sep 23, 2004
    Posts: 48,670

    squirrel
    Member

    compression ratio on a stock engine is 7.25
     
  23. Bandit Billy
    Joined: Sep 16, 2014
    Posts: 7,647

    Bandit Billy
    ALLIANCE MEMBER

    I cant help on a caddy fladdy, but my 8BA with 7 pounds of boost from a 471 has ran the last couple of years with no overheating ever. It runs pretty hard not just for a flatty but for any power plant. I've owned a lot of SBC camaros and this is faster. I put a lot of money into the build but I still don't abuse it...much.
     
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  24. But Billy,
    How much was it again on your engine build,,,,,,?
    It is awesome though,,,,,,that is paramount !

    Tommy
     
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  25. well then no compression drop necessary. ;)
     
  26. Bandit Billy
    Joined: Sep 16, 2014
    Posts: 7,647

    Bandit Billy
    ALLIANCE MEMBER

    More than I care to admit. I have built entire cars for less tho not as cool.
     
  27. Pete1
    Joined: Aug 23, 2004
    Posts: 1,969

    Pete1
    Member
    from Wa.

    A REALLY good 4 miles to a gallon flathead street engine will cost 30 G's these days.
     
    Bandit Billy likes this.
  28. Seems to me the way the exhaust is on the Cadillac flathead that it is simple to fab a turbo setup. Go with an intercooler, that will help the lack of airflow. Turbo may not be as traditional. But seems the easy way to fit it all under the hood and be easily reversible. I think 10 psi on an otherwise good condition stock engine may be pushing it. Maybe 7 psi, would be kind of like a 11 to 1 compression.

    Plus turbo is not putting the forces on crank snout. Although not knowledgeable of the Cadillac crank snout strength, just a point of consideration.

    Sent from my SM-G950U using The H.A.M.B. mobile app
     
  29. lippy
    Joined: Sep 27, 2006
    Posts: 5,533

    lippy
    Member
    from Ks

    No matter what anyone says there's only one way to know. And that's blow and go. Lippy
     
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