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  • Too Close for Comfort (Displacement)

    Howdy,

    So I've been having a very hard time finding a suitable STD bore block for my F motor build which would give me 181cid on a 183.99cid limit. I have a 0.030 block which gives me 183.87cid but that just seems way too close for comfort...

    Will either get me a tear down if I set me a record?
    Central TEXAS Sleeper
    USAF Physicist

    ROA# 9790

  • #2
    The answer is - maybe. Remember, we check (on your style engine) with a NASCAR-style pump and the results are corrected for in-cylinder temp. Usually we can work with the pump values and recheck the temp correction to verify. If it just WON'T come out below the max displacement you might have to pull a head to certify the record.

    Remember that when you come up to the inspection station following your back-up run you'll need to pull a valve cover and back off one set of valves as the pump needs a sealed cylinder. Please prepare for that as you wait in the inspection lane! You'll need tools, etc. and someone with the car (probably YOU in this case) who knows how. You wouldn't believe how often folks show up with no ability to do this.

    EDIT:

    Almost forgot - when you're ready to install the heads you can set up a visit with an inspector from SCTA who will measure the actual bore and stroke and seal the engine. Once sealed you can run all year without pumping or teardown. Generally they'll seal the pan to the block (maybe use a wire seal in place of one pan bolt) or the block to the head. The idea is that you can't replace the rotating assembly without breaking the seal. The visiting inspector will make notes in your logbook so be sure you have one. From that point forward the SCTA "knows" that engine as long as the seal is intact. If you have to tear it down (say for a repair) you'll have to have it re-sealed.

    Hopefully Dan Warner will check in if I missed anything significant.

    Dan
    Last edited by DanStokes; September 26, 2013, 06:47 AM.

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    • #3
      Originally posted by CTX-SLPR View Post
      Howdy,

      So I've been having a very hard time finding a suitable STD bore block for my F motor build which would give me 181cid on a 183.99cid limit. I have a 0.030 block which gives me 183.87cid but that just seems way too close for comfort...

      Will either get me a tear down if I set me a record?
      What kind of engine and whats the std bore.

      Comment


      • #4
        With the SCTA you are allowed to "pump" the engine for displacment IF it is within 3% of the maximum or minimum displacment limit (pg. 12 H.1 3rd sentence) 2013 SCTA rule book. As you are, either the 181 or the 183.87 while legal, you would not be allowed to pump. So direct mesurment is your only option unless you follow Dan's 2nd bit of advice and have the engine sealed during assembly.
        Last edited by Dynoroom; September 26, 2013, 03:50 PM.
        There are very few people in this world who's opinion I value, you are not one of them.

        300 in 1999

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        • #5
          Not knowing how far along you are with the build have you thought of offset griding the crank to drop part of a cu in?

          Nick

          Comment


          • #6
            Originally posted by miketblsr View Post
            What kind of engine and whats the std bore.
            Buick V6, STD bore is 3.800in

            Originally posted by Dynoroom View Post
            With the SCTA you are allowed to "pump" the engine for displacment IF it is within 3% of the maximum or minimum displacment limit (pg. 12 H.1 3rd sentence) 2013 SCTA rule book. As you are, either the 181 or the 183.87 while legal, you would not be allowed to pump. So direct mesurment is your only option unless you follow Dan's 2nd bit of advice and have the engine sealed during assembly.
            Sounds like I shouldn't really worry about being "too close" as even with the stock STD dimensions, I'm in disassembly territory. I while I might have someone who can seal the engine close by, I don't know if I can afford the service.

            Originally posted by nickleone View Post
            Not knowing how far along you are with the build have you thought of offset griding the crank to drop part of a cu in?

            Nick
            I could but I've got the only 2.66in aftermarket crank I've run across yet and I don't want to cut it down unless I'm doing something like shifting to a 3.900in bore or something radical or I've damaged it in a block failure.
            Central TEXAS Sleeper
            USAF Physicist

            ROA# 9790

            Comment


            • #7
              There's no charge though if travel is involved it's courteous to take care of those expenses. Seems like there would be someone in CO Springs or maybe Denver who could do this. Sometimes the inspector gets tipped but there is no expectation of that - the inspectors are not in it for the money.

              Dynoroom is, of course, correct.

              I'd call the SCTA office and see if there's an inspector in your area. That would be the quick and dirty solution.

              Dan

              Comment


              • #8
                Are you looking at off the shelf pistons? Check the catalog dimensions, tolerance and clearance. I'd bet you need to hone to beyond 0.030" to use shelf stock pistons.

                Also, have you measured every throw of the 2.66" crank you have now? You are close enough that you need this info to decide.

                Sounds like you need custom +0.010" pistons and a worn, but unbored block.

                Comment


                • #9
                  Originally posted by Aircooled View Post
                  Are you looking at off the shelf pistons? Check the catalog dimensions, tolerance and clearance. I'd bet you need to hone to beyond 0.030" to use shelf stock pistons.

                  Also, have you measured every throw of the 2.66" crank you have now? You are close enough that you need this info to decide.

                  Sounds like you need custom +0.010" pistons and a worn, but unbored block.
                  Crank has been checked out and it's between 2.655 and 2.660 on all of the throws.
                  I already have standard bore pistons, not married to them but $175 for the set of 6 is hard to walk away from. The machinist (who has done 200+ at Bonneville) thinks the piston to wall will be fine for a race car on a non-hashed standard bore block. If I could find one I'd be happy to see if it'll work.

                  If I have to go with custom pistons, I'll probably make them for 0.030 over. Not because I want the last sliver of displacement, but because 0.030 over block are a whole lot easier to find. The block is likely the weak point of the whole engine, the main webs aren't up to big power without some trickery with more than just a steel girdle.
                  Central TEXAS Sleeper
                  USAF Physicist

                  ROA# 9790

                  Comment

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