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    MLS head gaskets

    Where is everyone getting their M20 MLS gaskets?

    MLS head gasket from IE has gotten stupid expensive. ~$350 with shipping.

    I'm only seeing 85mm bores from Cometic on their M20B25 page.

    TCD has 0.120 but doesn't answer the phone. And doesn't state bore.

    VAC only has 84mm in 0.080. I need 0.120.

    ??

    "And then we broke the car. Again." Mark Donohue, "The Unfair Advantage"

    Das Beast build thread

    #2
    VAC will do custom sizes, won't they?

    I called them a few weeks ago and they told me if I was willing to wait a bit they would have something made.

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      #3
      VAC had an 85mm 0.098" in stock so I ordered it. Talked to a guy who sounded knowledgeable. He said 0.5mm outside the bore is fine. Had done it on many M20s. Dropping .022" from .0120" won't raise compression enough to cause detonation at our boost levels. It's going for a re-tune on the dyno in any case.
      "And then we broke the car. Again." Mark Donohue, "The Unfair Advantage"

      Das Beast build thread

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        #4
        i paid like $215 for a custom one direct from Cometic to suit 86 mm bore (86.5 mm gasket bore).

        The bore of the stock HG is 85.5 mm vs 84 mm bore so need not worry
        89 E30 325is Lachs Silber - currently M20B31, M20B33 in the works, stroked to the hilt...

        new build thread http://www.r3vlimited.com/board/showthread.php?t=317505

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          #5
          Looks like VAC is offering a good section of the Cometic catelog. Next time I can just go with C4394-120, 85mm bore / 0.120". Or stick with C4394-098, 0.85mm / 0.098" like I just ordered.from VAC.
          "And then we broke the car. Again." Mark Donohue, "The Unfair Advantage"

          Das Beast build thread

          Comment


            #6
            Maybe I missed it in your thread, but WHY .120"? Did you shave the block to get the .5mm compression height back?

            You will make more power out of boost, spool easier, and require less boost for similar performance with the higher compression. Don't fall into the old way of thinking that you need to be 8.5:1 or less. I was putting turbos on detonation-prone 9.6:1 GM engines many years ago. Apples to apples, the same turbo system on differing compression levels, the higher comp will make more power, more efficiently.

            Going from a stock .068" to .098" would drop the static a little more half a point, .120" would be about a full point.
            john@m20guru.com
            Links:
            Transaction feedback: Here, here and here. Thanks :D

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              #7
              I was concerned about detonation at high boost so went 0.120 on the first build. Like you said, wasn't an issue at 7.8. So we're back to 8.3 with the 0.98. Should make over 300HP at 10 psi. What are you running on boosted cars?

              Thanks for the tips.
              "And then we broke the car. Again." Mark Donohue, "The Unfair Advantage"

              Das Beast build thread

              Comment


                #8
                Originally posted by dvallis View Post
                What are you running on boosted cars?
                Stock compression, or more. Stock 8.8:1 with stock cam (more trapped mass than a 272/284 etc) easily accepts boost without fear of excessive detonation. I wouldn't hesitate to boost a 10.5:1 m20 if it used the hemi 885 design (provided iot had a matching cam).

                EDIT: I have also reused many of a MLS gasket. Just drill out the rivets, clean all the viton off, and put a light layer of copper coat on each layer as you set it on the block. Never had an issue. In fact, when the block and/or head wasn't shaved, I will coat that side(s) with copper to keep the gasket from weeping.
                john@m20guru.com
                Links:
                Transaction feedback: Here, here and here. Thanks :D

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                  #9
                  We're running an 885 head with 284/272 cam, 0.050 lift over stock. Pistons are 0.5 mm below head deck due to 130mm eta rods. Measured 0.150 clearance (clay) piston to valve. Sounds like we could go 0.050 on a MLS head gasket, get the compression up and still be good.
                  "And then we broke the car. Again." Mark Donohue, "The Unfair Advantage"

                  Das Beast build thread

                  Comment


                    #10
                    OK, since you didn't shave the block you are around:

                    9.3:1 with .070" gasket: https://www.zealautowerks.com/advanc...00,7200,1500,0

                    8.7:1 with .098" gasket: https://www.zealautowerks.com/advanc...00,7200,1500,0

                    8.4:1 with .120" gasket: https://www.zealautowerks.com/advanc...00,7200,1500,0

                    BUT! Now you have a HUGE squish/quench band that also tends to cause detonation since the fuel charge has ample space to congregate there (tight squish propels the charge into the spark plug). With a .098" gasket and .019" down in the bore (.5mm), you have a very excessive .117" piston to head clearance, and .139" with a .120". Ideally, you want to be in the ~.040" area and the .120" gasket puts you almost 100 thou over.

                    Honestly, with your setup, personally, I would just use the layers of the MLS gasket you need to get to .040" and not worry about the static comp. .050" would get you close to stock specs, and still only have 9.7:1 (one point over a stock b25).

                    Now, since you have such low compression and a longer-than-stock duration/overlap, you are bleeding even MORE trapped mass out of the cylinder - ie lowering effective/dynamic comp ratios, thereby further negating the fear of detonation. IMO

                    What is your cranking compression? If it's in the 140-150's, right? If so, you have plenty of room on that cam to go higher. A stock healthy 8.8:1 m20 will do about 170psi cranking and easily take 20psi and 400+hp, so long as you can keep the head down. I wouldn't be concerned with adding a turbo anything below 200psi cranking.

                    john@m20guru.com
                    Links:
                    Transaction feedback: Here, here and here. Thanks :D

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                      #11
                      Right. We're at 150 psi static compression.

                      This is a great post. Totally changed my thoughts on the head gasket. Called VAC back and changed to a 0.040. Should have a 10:1 compression ratio and 190 psi static compression.
                      "And then we broke the car. Again." Mark Donohue, "The Unfair Advantage"

                      Das Beast build thread

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                        #12
                        190 sounds about right. With a 272 cam and 9.4:1 our car is 190psi and the stock cammed car is just under 200.

                        Just make sure you verify your tune with a detcan on the dyno. The added compression does decrease the spark advance window (not as forgiving if the tune doesn't match).

                        You are going to like the extra grunt. This thinner gasket will raise the power under the curve in the lower RPM's, and increasing the comp will add a fair bit of torque everywhere else, too.
                        john@m20guru.com
                        Links:
                        Transaction feedback: Here, here and here. Thanks :D

                        Comment


                          #13
                          Dyno tune for sure. Back to Roman at Boost Logic. I ran into him yesterday dropping off the downpipe for its GT30R refit at an independent TIG shop. He was happy to see us going GT30R. Haven't told him about the new compression ratio yet. He'll be excited. (Dyno Geek)

                          We have bad compression (120) on #4 and #5. Valves and piston crowns look fine. Suspecting broken rings. We're using Deves 2297 (1.5 / 1.75 / 3.00 mm, 4 piece oil ring). Any advice here? One piece more durable? Upgrade to pistons with better ring options?
                          "And then we broke the car. Again." Mark Donohue, "The Unfair Advantage"

                          Das Beast build thread

                          Comment


                            #14
                            Ring options are limitless, you can have them made to order.

                            Usually, prior to pulling the engines apart after a failure, I will use the compression tester end, thread it in the spark plug hole, put piston to TDC power stroke and use an air regulator to slowly pressurize the chamber. If its a failed intake valve, air escapes the TB, exhaust valve will be tail pipe, and oil dipstick indicates rings.

                            Since the turbo ate itself, I wouldn't be surprised if junk got under a valve and tweaked it. Last year we checked a motor post-race because two cyls were at 180psi vs the 190-195 they were before green flag. Turned out two exhaust valves were ever so slightly bent - not enough to make it run rough even. Good thing too, because the bearings only had about 50hr on them and they were looking ripe, so they got swapped out along with the valve job.
                            john@m20guru.com
                            Links:
                            Transaction feedback: Here, here and here. Thanks :D

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