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  1. #1
    Active Member Two Rings
    Join Date
    Apr 11 2014
    AZ Member #
    183438
    My Garage
    1986 BMW 325, 1981 VW Rabbit Diesel
    Location
    Portland

    Compression Ratio Build question

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    Hey guys,

    Finally getting my Audi motor installed and I'm having some issues calculating the compression ratio, I'm also curious as to what other owners have done when rebuilding the 2.0t.

    0.006" was taken off the head, and 0.005" off of the block.
    I purchased JE Pistons #291884.
    Bore: 83 mm
    Stroke: 92.8mm
    Cyl Head Volume: 45cc
    Dome: -0.5cc

    I'm trying to determine what thickness of gasket to use to get close to the stock 10.5 compression ratio.
    I ordered the pistons off of USP Motorsports. They advertised 10.5 ratio, but the only way I can see getting that, even assuming 0 deck clearance would be using a 0.065" head gasket. The specs on JE's site are the ones I listed above.

    I'm using this calculator:
    http://www.summitracing.com/expertad...ion-calculator

    The shop that rebuilt my motor warned me of timing issues if using too thick of a head gasket. Do you know if that applies to the 2.0T motor?

    Thanks for the help,
    Daniel

  2. #2
    Veteran Member Four Rings aluthman's Avatar
    Join Date
    Mar 24 2013
    AZ Member #
    111961
    Location
    Oakdale, CT

    Quote Originally Posted by dliff View Post
    Hey guys,

    Finally getting my Audi motor installed and I'm having some issues calculating the compression ratio, I'm also curious as to what other owners have done when rebuilding the 2.0t.

    0.006" was taken off the head, and 0.005" off of the block.
    I purchased JE Pistons #291884.
    Bore: 83 mm
    Stroke: 92.8mm
    Cyl Head Volume: 45cc
    Dome: -0.5cc

    I'm trying to determine what thickness of gasket to use to get close to the stock 10.5 compression ratio.
    I ordered the pistons off of USP Motorsports. They advertised 10.5 ratio, but the only way I can see getting that, even assuming 0 deck clearance would be using a 0.065" head gasket. The specs on JE's site are the ones I listed above.

    I'm using this calculator:
    http://www.summitracing.com/expertad...ion-calculator

    The shop that rebuilt my motor warned me of timing issues if using too thick of a head gasket. Do you know if that applies to the 2.0T motor?

    Thanks for the help,
    Daniel
    For starters, the JE pistons use a non-standard gasket to get to their advertised CR. It seems as though you have figured this out already. A stock head gasket is .8mm compressed. Using a thick head gasket can result in timing issues if you go too thick, but with the material you have taken off the head and block, you should be ok using a thick one.

    You would be at 11.3:1 CR with the above pistons before considering the removal of material from the block and head. Factoring in that 11 thousandths puts you at 11.6:1 with a stock head gasket.

    Solution 1: Run a head gasket of 0.070" I'm not sure how easy this will be to find or how cheap it will be.

    Solution 2: Buy new pistons or have your current ones milled down by about 0.040" (the slight dome means you likely won't have to mill as much off).
    -Adam

    '07 DTM A4 2.0T|6MT|EFR 7163 Twin Scroll|DoTuning|Built Motor|Meth and other go fast stuff…
    '06 A4 2.0T Quattro - RIP (Best ¼ mile pass 13.634 @ 103.30)

  3. #3
    Active Member Two Rings
    Join Date
    Apr 11 2014
    AZ Member #
    183438
    My Garage
    1986 BMW 325, 1981 VW Rabbit Diesel
    Location
    Portland

    Quote Originally Posted by aluthman View Post
    For starters, the JE pistons use a non-standard gasket to get to their advertised CR. It seems as though you have figured this out already. A stock head gasket is .8mm compressed. Using a thick head gasket can result in timing issues if you go too thick, but with the material you have taken off the head and block, you should be ok using a thick one.

    You would be at 11.3:1 CR with the above pistons before considering the removal of material from the block and head. Factoring in that 11 thousandths puts you at 11.6:1 with a stock head gasket.

    Solution 1: Run a head gasket of 0.070" I'm not sure how easy this will be to find or how cheap it will be.

    Solution 2: Buy new pistons or have your current ones milled down by about 0.040" (the slight dome means you likely won't have to mill as much off).
    Thanks for the reply. Do you think running 0.065 would be close enough. I found one of those but haven't been able to fine a 0.070 gasket.

    All the shop work has been done and the assembled block, head are at an Audi dealer and they're getting ready to assemble it, so I'm trying to avoid having to take the block back and pay for all of that work again :/

  4. #4
    Veteran Member Four Rings aluthman's Avatar
    Join Date
    Mar 24 2013
    AZ Member #
    111961
    Location
    Oakdale, CT

    This one should be about 0.070" but it's pretty expensive. Cheaper that taking your engine apart again and milling the pistons though.

    https://store.034motorsport.com/comp...bs_description
    -Adam

    '07 DTM A4 2.0T|6MT|EFR 7163 Twin Scroll|DoTuning|Built Motor|Meth and other go fast stuff…
    '06 A4 2.0T Quattro - RIP (Best ¼ mile pass 13.634 @ 103.30)

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