Fourtitude.com - Lowering CR ABA Block w/ 1.8 Head
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    1. Junior Member
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      10-11-2019 09:31 AM #1
      As the title states, I am looking for a way to reduce my CR using the ABA block with a 1.8 head. I am going Turbo, and not wanting to run into issues with CR. I think the CR with a 2.0/1.8 is 10.3:1, anyway I can get that down to, say, 9ish?

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    3. 10-11-2019 10:03 AM #2
      double metal head gaskets.

    4. Junior Member
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      10-11-2019 11:02 AM #3
      MLS from a 2.0 16v? or from something different?

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    6. 10-11-2019 01:15 PM #4
      the very one think the 8v and 16v are the same though.

    7. 10-11-2019 01:16 PM #5
      they are very strong gaskets, so no problem stacking 2 together.

    8. Junior Member
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      10-14-2019 07:59 AM #6
      Next question, related. Is there any bottom end components I could swap to reduce my CR? Trying to reduce it to a minimum of 9:1, but would like to get a little lower than that.

    9. 10-14-2019 08:29 AM #7
      You could shave the pistons but you would need to get them out and a machine shop to shave them down. If you really wanted to try your skills, you could open up the combustion chambers with a die grinder. Unshrouding the valve area and enlarging the combustion chamber area would reduce the compression a bit. You'll need to cc the chambers when you are done to keep them all the same. I've done both for different reasons and it worked for me.

      Buying pistons would be the best bet but then the block may not have the right clearances for them.

    10. Junior Member
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      10-15-2019 07:55 AM #8
      I'm not too familiar with CC'ing combustion chambers. But, out of curiosity, Would a 1.6 crank do me any good? I know the stroke is significantly shorter in a 1.6, like 9 or 10 mm difference.

    11. 10-15-2019 10:36 AM #9
      Don't get me wrong but I believe you are way over your head with this project you are doing. I'm not saying you can't or are not capable.

      To lower the compression ratio, you need to increase the combustion chamber. It's that simple. That can be done by getting pistons that do that. Milling the tops of the pistons or increasing the combustion chamber. Yeah, people have double stacked headgaskets but that is shear butchery.

      Changing the crank with a 1.6 would probably not allow you to use the rod/piston combination. Buying shorter [2-3mm rods] ain't going to happen either.

      So it all boils down to this. Do it right or keep it stock till you have the money to do it right. Changing pistons properly is not cheap. It's not that you can slap some pistons in the block and call it good. There is a good chance the bore will not be the correct size [which is why a good machine shop will not bore a block without having the pistons]. Go ahead and double stack gaskets. It has been done before but I think it's a poor way to go.

    12. Junior Member
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      10-23-2019 07:41 AM #10
      I am relatively aware of what I am getting in to, and the nuances of getting machine work done. My curiosity was more towards the availability of off the shelf / stock components from other engines that may reduce the price of my build. Thank you for the info Butcher

    13. 10-31-2019 09:04 PM #11
      you could have the aba block skimmed down by 2.2mm and fit a 1.8 crankshaft. will only leave you with 1847cc but will be bang on 9.0-1 cr

    14. 10-31-2019 09:15 PM #12
      or, if you just swap the standard gasket for a 3.5 mm one. you will have 8.94-1 cr.

    15. 11-01-2019 08:39 AM #13
      With all that shaving [which would not be good when it comes to headgasket sealing] the cam timing would be seriously off and the timing belt may not be able to be adjusted properly. If you could find a headgasket that thick, you would have the same issue.

      Sadly, sometimes to do it right costs money. This is where the OP is at. They do not want to spend money and are looking at half a$$ ways of making it work. Shaving the pistons or CC'ing the combustion chambers is the best cheap way. Remember, I think doubling headgaskets is just plan stupid.

    16. 11-01-2019 01:27 PM #14
      maybe combining a little head chamber carving with a 2.5mm head gasket would be the way to go

    17. 11-01-2019 01:34 PM #15
      when I done the 2E block swap on my old mk2 (same block as aba) the dot on the back of the cam pulley wouldn't line up as well as it did on the 1.8. think the cam was very slightly retarded, so if a 2.5mm gasket was used, that would be corrected

    18. 11-01-2019 01:42 PM #16
      if you were to work the chambers alone, you would need to remove about 10cc. which is a bit more than I would be willing to risk, especially on a turbo engine

    19. 11-02-2019 08:12 PM #17
      Get out of the 90s

      They supply many choices:

      https://www.cometic.com/i-24766447-v...tegory:1280264

    20. Member
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      11-10-2019 07:38 PM #18
      2 ABA headgaskets and ARP headstuds to hold it down and together.

    21. 11-17-2019 08:15 PM #19
      studs require constant retightening until the gaskets are squished flat. They are not really practical unless you pull the head lot.

    22. 11-18-2019 06:18 PM #20
      I think the op has done a runner

    23. Member Junkyarddawg's Avatar
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      11-20-2019 08:14 AM #21
      There are definitely many different ways to arrive at your desired compression ratio and trying to do it on a budget is why many of us choose
      to build VAG engines but a few things should be considered before choosing what ratio to go with and what your goals will be.
      Many motorists and enthusiasts are not aware of how important fuel quality and octane ratings are on a high performance engine and when
      an engine has been fitted with a turbo, it is "high performance" and high quality/octane fuel becomes a requirement and in many cases
      fuel mileage is not part of this recipe. Once we understand this we realize that committing to use of high octane fuel in a high performance
      application becomes more of a requirement than a preference. It just doesn't make a lot of sense to build a high performance engine to
      run on low octane fuel because of the risk of engine damage and lack luster off boost performance, and when on boost, the ecu pulls all the timing
      because the knock sensor is constantly maxed out. Additionally the hardware part of a turbo conversion is the easiest part but procuring a safe tune can be lot harder.

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