BBC 781 Head Work?

Discussion in 'High Performance Modifications' started by Wpg79Z, Feb 10, 2006.

  1. Wpg79Z

    Wpg79Z Veteran Member

    Just getting set to modify my 454 for a torquey street monster.

    Here's what I've got:
    Comp Cams XE268 K-kit (lifter, 911 springs, seals, retainers, locks, etc.)
    Comp Cams exhaust rotator elminators
    Performer Intake (no EGR)
    Dynomax headers (1-5/8 primary)
    GM steel shim head gaskets (.020 compressed - trying to bump up a little compression)
    Stock (as far as I know) '75 454 truck motor with 781 heads.

    I just took off the intake last night and this motor looks very clean inside. Still waiting to get the heads off, but am contemplating what head work to do. I'm not planning to touch the bottom end unless I find any big surprises.

    Should I just use the heads as is? Plug in 2.19/1.88 valves? Do some port work/bowl blends? Or something else? Any idea what this work would cost from a "good" shop? And what should I be asking when I start calling machine shops?
    With the combo I'm building will the big valves really help much? I've also heard that these heads are a lot more prone to cracking once you put the big valves in them too?
    I still don't know if the valve guides are sloppy or not since I don't have the heads off, and I don't know if the stock spring pockets are going to fit my 1.55" springs and rotator eliminators. So I might end up taking them to the machine shop anyway...

    Let me know your thoughts?

    Also wondering what oil and/or additives are best recommended for breaking in a new cam - especially since I've been hearing some buzz about oils not having zinc(?) in them anymore that kills flat tappet cams?

    Thanks.
     
  2. More2Life

    More2Life Veteran Member Gold Member

    202
    0
    Aug 10, 2004
    Rolla, Missouri
    I have about the same setup you have right down to the heads. If you have a machinist you can trust I would talk to him. I found out a lot of ways of getting the best bang for the buck when talking with mine. I would say porting & larger valves are gonna be your best gain with the heads, but to take advantage of them I would look at other options if a little extra money isn't an issue.
    I was told the stock 454 has about 8:1 compression. If you can afford to get dome pistons I would go that route. I raised mine to 10.1:1. from 8:1. I didn't have any work done to the heads other than replacing a couple of valves, fixing a couple of guides, milling the heads a touch, and a 3 angle valve job. I only had it bored & honed 10 over. With what I listed above and with him assembling the motor/heads and whatever minor machining costs I had, it put me back about $1000. I figure later on to look at getting a better head job......if you will. Either way I think you will be happy.
     
  3. 72RS408BB

    72RS408BB Veteran Member

    1,019
    0
    Jul 1, 2004
    DTW
    With 1 5/8 headers it will be very torquey. I say stay with the small valves and put the green in some other area. The heads I would say tootsie roll the runners and smoothem out. It will breath strong to 6gs.
     
  4. ZS10

    ZS10 Moderator Staff Member Lifetime Gold Member

    12,165
    2
    Jan 18, 2003
    BC, Canada
    I have the same heads and did my own 'clean-up' in the bowls and got them to flow quite well. I used a set of cheap new stainless valves and left them the stock size. They work very well.
    I wouldn't spend much money on them though. A couple $100 max.
    Your money is far better spent on new aluminum. There are enough choices in aluminum that when you get your comp ration figured out, you can get the appropriate chamber size to get it up at least a point.
     
  5. Wpg79Z

    Wpg79Z Veteran Member

    Thanks for the input so far...

    and my mistake - the headers are 1-3/4... too much reading about "small blocks" lately to remember the size of my own headers.

    Keep the comments coming - good to hear from people with similar set ups. Also curious what you guys are running for drivetrain (trans & rear gear) and how you use your cars.
     
  6. 1978LT

    1978LT Veteran Member

    16,280
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    Feb 24, 2002
    Poquoson, VA USA
    They make that small of a header for BBC?? 1-3/4 should make some SERIOUS low end grunt ;)

    If I had a BBC I'd blend the bowls, leave the stock valve size if you keep the small headers, and run a spreadbore carb!
     
  7. pdq67

    pdq67 BANNED

    10,496
    0
    Jul 26, 2001
    Columbia, MO, USA
    Fwiw, a 1.75" header will support a 496! I have them on mine now!

    As for heads, before I would dump a bunch of money in -781's, I would look close at Merlin ovals! What are they?? $850/pr bare?? (And I have a good set of -781's out in my garage too! BUT I bought Merlins for my 496)...

    And the only other head that works decent on a flat-top pistoned 454 P/U motor at about 8 to 1 CR. is the E-brock 100 cc "ROVALS", AND I am not a fan of "ROVALS"!! Give me true oval ports is all!!

    Cut these to 90 cc's and then they will be GOOD flat-top piston motor heads, imho!!

    I have a bare set of old -206's in the garage at 96.7 to 98 cc's that I want to play with some time on another stock, low compressioned 454 P/U motor.

    pdq67
     
    Last edited: Feb 10, 2006
  8. bigblock chev

    bigblock chev Veteran Member

    120
    0
    Jan 5, 2006
    hamilton
    let us know how fast you go
     
  9. 1978LT

    1978LT Veteran Member

    16,280
    0
    Feb 24, 2002
    Poquoson, VA USA
    For real?? I've seen guys use 1-3/4 tubes on 350's!! And they picked up power.
     
  10. jforb

    jforb Veteran Member

    206
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    Feb 10, 2006
    sunny southeast AZ
    It would be easier to help figure out what the engine needs in it if we knew about your plans for the rest of the car....how much highway use will it see? is mileage important? how much converter stall speed can you afford and live with (assuming it's an auto trans)?

    You can make some decent power on a big block, and put it to use, with just mild bowl cleanup, stock valve sizes, a bigger cam (perhaps 220 to 235 degrees at .050) and springs, headers, and about 2500 stall speed, with mid to high 3s on the rearend gears. The stock early iron intake and Qjet work fine for a setup like this. The improvements mainly come from the bigger cam and headers, and setting up the trans and rearend so the engine can run in the 2500-5500 rpm range.
     

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