SBC 400 w/late model 350 heads into 73 Z-28

Discussion in 'Engine Topic' started by ttmm, Jan 4, 2009.

  1. ttmm

    ttmm New Member

    26
    0
    Dec 29, 2008
    San Antonio, Texas
    Recently bought a 73 Z with the original but tired L-82 350. I pulled the 350 to save it for future rebuild to return the car to original someday and installed a small block 400 in it's place. That is where the questions come in.

    1. The SBC 400 runs very strong but vibrates hard as RPM increases. In the 67 Camaro with Turbo 350 trans the SBC 400 ran smoothly so am suspecting that it is not matched to the stock 11.5 inch clutch that came behind the 350 in the in the 73. I seem to remember something about SBC 400 being internally balanced/SBC 350 externally balanced. Am I right, and if so, what flywheel do I need to eliminate the vibration?

    2. The temperature sender taps in the 202 heads on the SBC 400 are 1/2 inch, so the 3/4 inch senders from the 350 won't work. Which senders do I need to enable my temp gauge to work again?

    3. We installed later model electronic ignition with the SBC 400 and have not attempted to reconnect the factory tach. Is it simply a matter of attaching the factory tach lead to the TACH terminal on the electronic ignition distributor cap or is other modification needed?

    Thanks in advance!
     
  2. Kamikaze

    Kamikaze Veteran Member Lifetime Gold Member

    The Sm Blk 400 was externally balanced and the harmonic balancer is different. All 350's were internally balanced.
    What you might need to check besides the balancer is if the right flywheel is on it.

    If you can find a good NAPA store with a knowledgable counterperson who can read parts books, they can check the Echlin books to see what sending unit with the right size threads, match the ohms of your 350.

    Attaching the tach to the TACH terminal on the HEI is just what you need to do!

    Good luck!
     
  3. tom3

    tom3 Veteran Member

    10,485
    26
    Aug 1, 1999
    ohio
    Might locate a tap on the intake for that temp sensor? Sometimes there is one not used near the thermostat housing in front.

    My tach on the 70 works good connected to the tach terminal on the HEI unit from a mid 70s car.

    If your flywheel is an aftermarket billet piece you might cut the weight off the flexplate and weld it on the back side of the flywheel, careful to get it lined up right. Probably not possible to weld on a factory cast/forged piece. Or maybe try this Ebay piece:

    [​IMG]

    http://cgi.ebay.com/ebaymotors/Smal...temQQimsxZ20090101?IMSfp=TL090101118003r31511
     
  4. Battmann

    Battmann Veteran Member

    705
    1
    Sep 12, 2007
    North Chili, NY
    just throwing this out there - not related to your vibrating problem.
    do your 350 heads have steam holes in them? i had to have my 350 heads drilled to match the steam holes on a 400 i built years ago.
     
  5. cmonson

    cmonson Veteran Member Gold Member

    4,134
    0
    Apr 7, 2006
    Calgary, Alberta
    your 400 is most likely externally balanced, which means there needs to be balancing weights on the balancing damper, and the flywheel.

    Your 350 is internally balanced so the damper and flywheel do not have weights on them.

    By chance did you use your 350 flywheel and damper for your 400 swap? If so, there lays your problem.
     
  6. ttmm

    ttmm New Member

    26
    0
    Dec 29, 2008
    San Antonio, Texas
    The damper was not changed after pulling the SBC 400 from the 67, but the flexplate from the automatic was changed out with the flywheel from the SBC 350 to match the 4 speed, so apparently therein lies the problem as I suspected.

    Is a counterweight as pictured available separately to apply behind the stock flywheel, or is there a specific part number/application for a SBC 400 11.5 inch clutch flywheel to quote to a supply house, or must I modify the 350 flywheel to add the appropriate counterweight?

    On the temp senders, the intake would have been my first option but I have no additional tap available there so have to find alternates. The Z-28 has two, one on each head, one being the type with the tab (idiot light sender I am guessing) and the other being the stud with nut (gauge sender I am guessing) so I need to deal with both.

    I appreciate all the helpful info, will post a picture if someone can tell me how!
     
  7. ttmm

    ttmm New Member

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    0
    Dec 29, 2008
    San Antonio, Texas
    Ooops, yes, forgot to mention that when I had the 2.02 heads done I had the cooling holes bored to fit the SBC 400 also; good catch! This 400 has dish pistons stamped "30" so I am guessing it was bored .030 when built before I bought it. If so, what CID would it have now? Thnx
     
    Last edited: Jan 7, 2009
  8. cmonson

    cmonson Veteran Member Gold Member

    4,134
    0
    Apr 7, 2006
    Calgary, Alberta
    are you sure it is 11.5" clutch. all of the flywheels for SBC I have seen at either 10.5" or 11".

    assuming it is an 11", below is a link for an externally balanced flywheel which is what you need.

    http://www.jegs.com/i/Hays/490/10-132/10002/-1

    I would NOT run it anymore with the incorrect flywheel...
     
  9. ttmm

    ttmm New Member

    26
    0
    Dec 29, 2008
    San Antonio, Texas
    Maybe you're right about the clutch size, I had noticed that it was bigger than the clutches I am used to seeing so assumed it was an 11.5 but will verify when I pull it before I buy anything. And no, I won't be driving it anymore until repaired; it is back up on jack stands already. The cold front came in this morning, just in time to make it more fun pulling the transmission again...
     
  10. cmonson

    cmonson Veteran Member Gold Member

    4,134
    0
    Apr 7, 2006
    Calgary, Alberta
    also, reading your temp gauge issue.

    all early sbc heads that I have ever seen either come with a 1/2" NPT tap for a temp sending unit or after about 1986, they came with 3/8" NPT.

    I assume you are looking for a 3/8" sending unit.

    If so, then a GP Sorenson part # TSU64 should work in the 3/8" NPT tap.

    also you referenced 202 heads. what are 202 heads? Do you mean the intake valve is 2.02? do you know the casting number on the head?
     
    Last edited: Feb 13, 2009

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