How to Check Compression

  1. krazykuda

    krazykuda Well-Known Member FABO Gold Member How-To Section Editor

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    krazykuda submitted a new Article:

    How to Check Compression

    Read more about this article here...
     
    Last edited by a moderator: Jan 2, 2017
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    • krazykuda

      krazykuda Well-Known Member FABO Gold Member How-To Section Editor

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      Close! This will be posted in the official "How To" section for reference. :glasses7:
       
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      • txstang84

        txstang84 Well-Known Member

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        • krazykuda

          krazykuda Well-Known Member FABO Gold Member How-To Section Editor

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          • RustyRatRod

            RustyRatRod Lemmie see your b00bs. FABO Gold Member

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            Great stuff, Karl.
             
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            • krazykuda

              krazykuda Well-Known Member FABO Gold Member How-To Section Editor

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              Thanks Rob!

              I've been meaning to write this for a month now and have had most of the pictures. Just had to finish up a few and reformat them for posting.

              The thread that you've been helping Bad Sport on today prompted me to finish it and write it. Hopefully with what you've posted in his thread and what I've covered in this one will help him (and others) understand compression better.

              I haven't had a chance to fully catch up in that thread yet, just a quick glance, but your posts look very helpful on that one, and I want to see what you have posted for my knowledge. You cannot ever stop learning, there's always someone who can teach you more than you already know, if you keep an open mind and not think that "you know it all" and stop listening and learning. I learn alot from your posts, as you know what you're doing.
               
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              • RustyRatRod

                RustyRatRod Lemmie see your b00bs. FABO Gold Member

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                It's good stuff. A lot of those figures are already known if you buy new parts......BUT it always pays to measure anyway as small variations in machining tolerances always exist. Your method is a sure fire way to get it dead nuts right.

                And as for my "knowledge" I can put what I know on the head of a pin.

                With room left over.
                 
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                • krazykuda

                  krazykuda Well-Known Member FABO Gold Member How-To Section Editor

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                  Yes, that's why I do it this way. It takes all of the variation and guess work out of it. You can find out exactly where your parts are at - no bull sh!t. And with materials and tools that most people have in their garages or can get at local stores at an affordable price.

                  Example: The heads may have been decked by my head guy to maintain flatness. Most 360 heads are 72 cc, but these came out to 69 cc.

                  I would have never guessed or believed that this engine was below 8.0 compression, if I didn't measure it and do the calculations. Now, I just have to measure the piston deck height to find out how much more I need to to increase the piston compression height to get this between 9.2 - 9.4 compression where I want it.

                  If you don't know the full history of your parts, it may cause errors in your compression calculations if you don't measure them and assume that they are like the others. You don't know if your block or heads have been decked by someone who owned them before you and could throw off your compression. If you want it done right, you should check them yourself to make sure.


                  Don't sell yourself short. There are many things about engines and cars that you know that I don't. I have a good knowledge of Mopars and engines, but by far, I don't know everything. And there are many people out there that know some things that we don't know and we can learn from them. I try to keep learning so I can keep getting better and better.
                   
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                  • 1967 'cuda

                    1967 'cuda Dropped on Head as a Baby

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                    I really want to thank you guys for taking the time to pass info on.
                    :prayer:
                    It seems that I'm constantly having to study up on stuff I want to do. In some cases I'm totally in the dark.
                    :read::study:
                    My memory isn't what it used to be anymore and I sometimes have a hard time absorbing new info. But I'm not to the point where I'm drooling on myself yet (knock on wood).
                    :dontknow:
                    Thanks again!
                     
                  • krazykuda

                    krazykuda Well-Known Member FABO Gold Member How-To Section Editor

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                    • 4spdragtop

                      4spdragtop CONGRATS NORTH AMERICA! FABO Gold Member

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                      Awesome write-up Karl! Looking forward to doing this on a couple small blocks in the near future!
                       
                    • krazykuda

                      krazykuda Well-Known Member FABO Gold Member How-To Section Editor

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                      Hey guys, I mis placed my beaker and just ordered another one. The link above is for a GLASS beaker.


                      Here is a link for a PLASTIC beaker. I recommend the 5255-5 (250 mL with hex base) or the 5250-5 (250 mL with ROUND base). Both sell for $3.20, however they zing you on the shipping.

                      Shipping for one is $17.95
                      Shipping for 6 of the hex base is $18.75
                      Shipping for the round base is more expensive (heavier - I don't think that they heard of the flat rate boxes....)


                      Point being, get with a buddy or two who needs one and split the shipping to make it more cost economical.

                      Here's the link:

                      http://www.mansionschools.com/gradu...HXmNt6mE1Zj0o3GmRtHZL1vyIkEzpMLAMHRoCrKzw_wcB


                      *Note - the part number in the link and the description do not match. The part number is for the round base, and the description says hex. The numbers that I listed above are correct. If you just order off of the internet page, you will probably get the round one.

                      Here is a link to their catalog page with the proper part numbers:

                      http://site.mansionschools.com/lib/0139/catalogpages/0139CatalogPage20130074.jpg
                       
                    • krazykuda

                      krazykuda Well-Known Member FABO Gold Member How-To Section Editor

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                    • gorgerider

                      gorgerider Well-Known Member

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                      As a former chemist, I know there are two types of graduated cylinders - TD ("to contain"), and TD ("to deliver"). This is based on water at 60 F and is due to the surface tension of water (solvents have a negative meniscus and water has a positive meniscus). Since we're measuring water, and we're delivering to the cylinder, find the TD grad. cylinder. And if you have access to a burette, it'll eliminate the funnel and provide real control for adding the water. Borrow one - they're spendy.
                       
                    • DesertRat

                      DesertRat FABO Gold Member FABO Gold Member

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                      Glad to see this popping back up. KK, you did a stellar write up and explanation of the process. I am going to do most of this starting tomorrow and I have already built myself an Excel spreadsheet with all the calculations in it so I can see if my effin cam has enough duration to let my motor live or if like everything else, I wind up with another cam and one on the shelf. Good information and if you have a Vet supply close, you can buy the 60CC TD syringes very reasonably.
                      cheers all---DRO:)
                       
                    • gorgerider

                      gorgerider Well-Known Member

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                      Any chance we can make this thread a sticky?

                      And yes, I went for the burette. Much more accurate volume measurement.
                       
                    • krazykuda

                      krazykuda Well-Known Member FABO Gold Member How-To Section Editor

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                      It was, but they then moved it into the "How to Article" section... You can find it there also...
                       
                    • gorgerider

                      gorgerider Well-Known Member

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                      Thanks for the lead.
                       
                    • MileHighDart

                      MileHighDart Well-Known Member

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                      Anyone care to take a poke at the math part of this for me?

                      I'm totally lost on the calculations. I pulled the heads off my 318 just to get these measurements.

                      Bore 3.940" - .030 over 318

                      Stroke 3.31" - standard 318

                      Combustion chamber 65cc

                      piston to deck volume 10cc

                      Head gasket is .050" thick

                      Head gasket opening size is 4.1875"

                      A little help here would be great!
                       
                    • mderoy340

                      mderoy340 Well-Known Member

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                      8.78:1
                       
                    • MileHighDart

                      MileHighDart Well-Known Member

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                      Thanks mderoy340,

                      That's a little better than I thought it would be.
                       
                    • oldskool979

                      oldskool979 Well-Known Member

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                      Thx for the instruction and illustration. Great presentation.
                       
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