BBC 781 Flow test today

Discussion in 'High Performance Modifications' started by 1980RS, Nov 27, 2021.

  1. 1980RS

    1980RS Veteran Member

    Messages:
    5,747
    Likes Received:
    1,959
    Joined:
    Jun 17, 2006
    Location:
    MN
    So I got a chance to test a coupe of BBC heads and the extra work I did on my old 781's really surprised me. Now these heads are the 1st set of BBC heads I ever did and while they did flow pretty decent last time (1989 test) the engine I used them on in the late 90's just never made a lot of power, so after I broke a valve guide I got that fixed and had new bronze liners in them. The last guy who did the cut the heads for new 2.19 and 1.88's did a horrible job (chattered seats) so I redid that my self with my own 3 angle set job and here are the new results, how did I do?

    Intake flow, bad port
    0.100 76cfm
    0.200 141cfm
    0.300 215cfm
    0.400 271cfm
    0.500 296cfm
    0.600 308 cfm
    N/A

    Exhaust flow, No Pipe
    0.100 65cfm
    0.200 116cfm
    0.300 158cfm
    0.400 189cfm
    0.500 209cfm
    0.600 226cfm
    0.650 234cfm
    0.700 240cfm




    Now the bench operator was saying that if I did not use the burr finish my intake would have been 317 or a little higher with a smoother surface, but I am happy with this over all. Should be able to make over 600hp with these heads and I am not done with them. I will put a narrower seat on these and back cut the intake valves to get the low lift flow numbers higher. I will have a 468 to teat these on next year. My Peanut Port heads were pretty close to these except for those heads were all done on the intake side by .550 lift, which I expected.
     
    Last edited: Nov 27, 2021
    sooner likes this.
  2. sooner

    sooner Veteran Member Lifetime Gold Member

    Messages:
    1,573
    Likes Received:
    109
    Joined:
    Mar 11, 2009
    Location:
    Perry,Ok
    Very nice! Especially considering that it was the first BBC you did way back when. That .400 number is moving some volume, and it keeps on going.

    Also admire that you posted the bad port numbers. IMO this should be the standard when measuring BBC heads.

    What CC runner volume did you end up with on the short port?
     
  3. G72Zed

    G72Zed Veteran Member

    Messages:
    3,499
    Likes Received:
    1,915
    Joined:
    Sep 8, 2015
    Location:
    Canada
    Looking good 1980RS, curious, did you do the Burr finish on the complete intake runner surface ?

    I'm porting-finessing a set of BBC aluminum, and NOT going Burr finish on those, intake/chamber or exhaust ports.

    I picked up out of the box flow numbers with a little work in the runners and chamber, and saving my hands without the "chattering" LOL
     
  4. masck1

    masck1 Veteran Member Lifetime Gold Member

    Messages:
    193
    Likes Received:
    13
    Joined:
    Mar 25, 2006
    Location:
    Jacksonville Fl
    Courious to going out what burrs you used to this, do you have any pictures that you can share. If and when burr finish works correctly the BSCF will go down at the same HP which will indicate better effiencey
     
  5. 1980RS

    1980RS Veteran Member

    Messages:
    5,747
    Likes Received:
    1,959
    Joined:
    Jun 17, 2006
    Location:
    MN
    Was on another site yesterday looking at some flow data from these aftermarket aluminum heads and except for the Brodix Race Rites my 781's hung with most of them. I guess the only thing I can look at is getting the weight off the front end with the lighter heads but for 3K they are not worth it to me. Pretty darn good these old GM head designs don't ya think?
     
    sooner likes this.
  6. G72Zed

    G72Zed Veteran Member

    Messages:
    3,499
    Likes Received:
    1,915
    Joined:
    Sep 8, 2015
    Location:
    Canada
    Yep, amazing what some good-smart port work will do, quality parts and pro valve job is key.

    Too bad no one could invent the heat holding capability and core stability of Iron, but with the same weight of aluminum eh ??

    I'm working on a set of BBC aluminum square ports, flowed stock, then some mild work in the port, bowl and a little in the chamber. Burr finish, think I picked up 20+ CFM.

    Going back to my multi grit tootsie rolls and G finger short side, I'll re flow to see what I gained on texture, this might answer your question of finish, or bring up other questions.
     
    1980RS likes this.
  7. 1980RS

    1980RS Veteran Member

    Messages:
    5,747
    Likes Received:
    1,959
    Joined:
    Jun 17, 2006
    Location:
    MN
    Sounds great, will be looking forward to see the burr finish vs the smoother one.
     
  8. G72Zed

    G72Zed Veteran Member

    Messages:
    3,499
    Likes Received:
    1,915
    Joined:
    Sep 8, 2015
    Location:
    Canada
    Yeppers, I'll report back once I get back into that BBC blower build. Just got back from another dyno day.
     
    1980RS likes this.

Share This Page