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Hot Rods Engine Advise for a 671 Blower.

Discussion in 'The Hokey Ass Message Board' started by Bonehead II, Dec 23, 2019.

  1. Bonehead II
    Joined: Apr 18, 2005
    Posts: 397

    Bonehead II
    Member

    Hi Guys...need your advice on building SBC engine for my 671 Blower. An '87 and newer block 4 bolt main and one piece rear seal, Hope a Gen 1 intake will fit ?.
    Forged crank with BBC snout...Forged rods.... Forged 8:1 or 8:5:1 pistons,...This motor is for street, well 90% street . Also heads and valve size would be good as well . I have never built a blower motor before, so any advice would be appreciate. Or just go buy a crate motor, change the cam and have fun.
    Thanks...Mike
     
  2. Sounds like a good plan,,,seems like you are going in the right direction on strong parts.
    I would keep the compression low to utilize the full effect of the blower on the street.
    Build your block as strong as possible,,,that is the foundation and it will catch a lot of abuse from the boost pressure.

    One thing though ,,,why the big block crank snout ?
    For a 90% street build,,,I thought a regular forged small block crank would suffice ?

    There are a lot of talented people here,,,,they will help you plenty.

    Tommy
     
  3. DDDenny
    Joined: Feb 6, 2015
    Posts: 13,440

    DDDenny
    Member
    from oregon

    There are two camps when it comes to blown street cars, the ones that want to look racy and the ones that are racy, some can pull off both, it's hard to advise without knowing your full plan.
    As for a crate motor you want one that will stand up to the pressure a supercharger can deliver and I doubt the oem versions are up to that.
    Many of the big name engine builders offer "crate engines" also, some spec'd for blowers.
     
  4. DOCTOR SATAN
    Joined: Mar 21, 2014
    Posts: 711

    DOCTOR SATAN
    Member
    from okc

    Depends how much boost ya wanna run as to how stout it needs to be....I have heard of using a crate motor with low boost, under driven.....
     
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  5. panhead_pete
    Joined: Feb 22, 2006
    Posts: 2,414

    panhead_pete
    ALLIANCE MEMBER

    FWIW there are power adder short blocks available from vendors including Blueprint.
     
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  6. mgtstumpy
    Joined: Jul 20, 2006
    Posts: 8,056

    mgtstumpy
    Member

    • A double keyway on crank snout.
    • Vortec heads flow pretty good however earlier blower intakes won't fit due to different bolt pattern.
    • I've heard that blower engines required a degree of valve overlap as well.
    Vortec CC.jpg vortec-bolt-angle.jpg vortec-bolt-pattern2.jpg vortecpic2.jpg

    I've never built a blower engine however I seriously thought about it. I've a friend with a 671 on his 32 and he drilled and tapped both heads for water outlets as there were no outlet provisions on the intake. His car is under driven for the street, more practical that way.
    blower-boost-chart-900.jpg
    Blowerpulley.jpg
     
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  7. thirtytwo
    Joined: Dec 19, 2003
    Posts: 2,628

    thirtytwo
    Member

    I believe an earlier block would have thicker casting
     
  8. chevy57dude
    Joined: Dec 10, 2007
    Posts: 5,546

    chevy57dude
    Member

    Contact your cam manufacturer before buying one. let them know what your intended usage is. Blowers don't like inlet restriction. BIG carbs!
    Keep the distributor advance low.
     
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  9. mgtstumpy
    Joined: Jul 20, 2006
    Posts: 8,056

    mgtstumpy
    Member

    Also I'm led to believe that blowers add additional heat to an engine so don't skimp on the cooling, use a quality radiator and water pump!
     
  10. 427 sleeper
    Joined: Mar 8, 2017
    Posts: 1,022

    427 sleeper
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    It's all relative to the amount of boost and your driving style. No matter what your building, you can't go wrong with a stout bottom end, IMO. Blower motors like to breathe, so the less restrictive the top end and exhaust is, the better. Like has been said, many times, give a reputable cam grinder a call and tell him your specs and intentions, and they'll fix you right up, I like Isky but there's other good ones too. Keep it cool, a slightly conservative advance curve, don't let it starve for fuel, and you'll be in for years of reliable fun.
    Sounds like you're thinking in the right direction.
    Merry Christmas, Jedd
     
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  11. southcross2631
    Joined: Jan 20, 2013
    Posts: 3,757

    southcross2631
    Member

    My buddy had problems until he went to a double keyway in the crank. They like 2 carbs.
     
  12. 2X^ the cam for a street blown motor is the most important part. I was tuning one and the owner went through 4 cams before using a 305 RV GM cam...(he worked in a dealer)....It was a 350, forged pistons 7.6 :1 compression and 2x4 small 600 holleys on a full tunnel ram.
     
  13. dave agosti
    Joined: Nov 28, 2019
    Posts: 2

    dave agosti

    Yes, the cam timing on a blown motor is different than normally aspirated.
     
  14. Bonehead II
    Joined: Apr 18, 2005
    Posts: 397

    Bonehead II
    Member

    Thanks Guys
    I was thinking about the heads, would a stock set of heads due ? I have a pair with 76cc chamber and 1.72 intake valve and a 1.5 exhaust, I mean it is a blower and meanly for the street.....Thanks
     
  15. 427 sleeper
    Joined: Mar 8, 2017
    Posts: 1,022

    427 sleeper
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    While it would be easier to keep the compression down with the big chamber heads, the small valves and ports would cause too much restriction, negatively affecting the performance of the blower, causing excessive heat build up. You could possibly get away with 1.94/1.60 valves as a bare minimum, but in this situation bigger is better. Personally I would go with 2.02/1.60's for the street. Remember, they need to breathe, especially with that big lung on top. Keep the boost in the 5-7lb. range and you should have respectable power AND reliability.
     
  16. Bonehead II
    Joined: Apr 18, 2005
    Posts: 397

    Bonehead II
    Member

    Thank you, Mr. sleeper
    What size of chamber would be right for me.....thanks
     
  17. Always go with as big an exhaust valve as possible,,,remember,,,,the blower pushes air into the intake valve.

    Tommy
     
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  18. 427 sleeper
    Joined: Mar 8, 2017
    Posts: 1,022

    427 sleeper
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    That all depends on the style of piston you plan on using. Flat top, dished, or flat top down in the hole? What ever gets you to your target compression ratio the easiest would be the route for me. I would try to stay in the 68 to 72 cc range, give or take. Something with a chamber that doesn't shroud the valves too much. Talk to your piston manufacturer of choice and they can give you the specific's on what it's going to take. Diamond, Ross, and JE all make good stuff and their websites give compression ratios with different chamber sizes. Hope this helps.
     
  19. indcontrols
    Joined: May 29, 2013
    Posts: 88

    indcontrols
    Member

    The double key is a MUST (ask me how I know)... The setup requires larger carburetors than you would think - mainly because of the horsepower required to run the blower itself... I have run both, small blocks with 6-71's and big blocks with 8-71's, the key to them running cool and happy is most definitely timing.
    I ran a .120 over gen IV big block on the street in hot south Florida for years running 1:1 with no issues in the heat - good cooling system, PROPER TIMING, and a stall converter that keeps the blower from trying to drag you through stop lights.. MSD Boost timing master is a fantastic device, allows you to retard the timing from your dash based on boost - and its cheap.
    Some run without balancers, I have always run a balancer. Although still important, large flow number heads are not critical (the blower will solve flow problems with pressure far more easily than an atmospheric motor will) - the money is best spent on good solid bottom end parts. I have always used Callies cranks, Crower rods, Ross or JE pistons. Leave the proper room in the ring gap and don't over-tighten the blower belt and you will be surprised the longevity of a blown brute, even at higher boost levels.
    Here's a scary lesson one of my blown big blocks taught me - I was leaving a cruise-in, everyone laying down rubber, which I did as well, there was a "dip" in the road that unloaded the suspension is second, knocked the tires off, the motor went immediately to the rev limiter.... moments later, I couldn't see through the smoke, slid to a stop in a movie theater parking lot.... The blower motor revved so quick without load that the flexplate threw the counter weight off (at about mach 6), shearing off both stainless AN transmission lines and slicing off a header tube... I immediately replaced the flexplate with a JW unit, as well as add a ring guard, and re-assessed the whole car... make sure the added power is accompanied by matching components for the rest of the build !!! With great power comes - well..., other issues... header.JPG flywheel.JPG
     
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  20. dreracecar
    Joined: Aug 27, 2009
    Posts: 3,005

    dreracecar
    Member
    from so-cal

    Stock SBC does not stick out very far out of the cover, and the lower blower pulley hangs out 6". The added load of the blower flexes the hub and cracks along the keyways of the hub, then the POO hits the fan so to say
     
  21. gimpyshotrods
    Joined: May 20, 2009
    Posts: 17,147

    gimpyshotrods
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    No. Less overlap.

    You want the least overlap plausible. When both the intake and exhaust valves are open, your boost goes out the exhaust.

    This is where Lobe Separation Angle (LSA) comes into play. The bigger the number, the more boost you hold on to.

    I just slipped a cam into my blown Hemi, with a 115º LSA. Most unblown street cams are 110-112º.

    Every degree of LSA is more usable boost.
     
  22. gimpyshotrods
    Joined: May 20, 2009
    Posts: 17,147

    gimpyshotrods
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    He said '87 - up. Vortec did not start on the SBC, until 1996. Vortec describes the combustion chamber shape. Your pictures illustrate that.

    vortecpic2.jpg

    Vortec heads have fewer, all angled intake manifold bolts.

    1987-1995 SBC heads are just center bolt valve cover heads.

    Center bolt heads have the same number of manifold bolts as an old-school SBC, but the middle 4 are angled. Their origin point is on the same line as the other bolts, and most intakes can be modified to accept the angled bolts (by a machine shop).

    For the OP, not all center bolt heads area created equal. 305's in that era have bumps in the intake ports. They restrict flow, and would need to be removed. It is not hard, but it is necessary. They also have very small combustion chambers, so be advised.
     
    Last edited: Dec 30, 2019
  23. I always thought the 60,s 327 truck engines would make good blower engines. They have factory forged dished pistons.
     
  24. Budget36
    Joined: Nov 29, 2014
    Posts: 3,464

    Budget36
    Member

    Accel, maybe Mr. Gasket now, used to make an angled/wedged washer to use
     
  25. gimpyshotrods
    Joined: May 20, 2009
    Posts: 17,147

    gimpyshotrods
    ALLIANCE MEMBER

    Yeah, I remember those. I have not seen a set in a while. They should not be hard to make.
     
  26. gimpyshotrods
    Joined: May 20, 2009
    Posts: 17,147

    gimpyshotrods
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