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    #1

    unusually high compression

    So when I bought the car I immediately did a compression test. 180, 180, 180, 179,178,180. From what I have read online that is about 20 psi higher than it should be. Doing general google searches some people say carbon build up but their compression numbers vary ALOT more than mine do. Any definitive way to know why I have such high consistent compression?

    Some background info. The car started its life out as a auto and was swapped for a 5 speed e. Not exactly sure if anything has been done to the e. I also have a rough idle problem and run rich, but I am pretty convinced its the ICV just haven't gone around to cleaning it out.





    My don't quote me list:

    Originally posted by george graves
    I could be wrong, but I don't think it's a smog test type of thing. IIRC think it's against CA law to *sell* a dual outlet muffler as a replacement for a car that came from the factory with a single. But don't quote me on that.
    Tags: None
    #2
    Your head is thin?

    The eta has higher compression numbers? An RV cam? (low overlap cams tend to
    build higher low- speed (static) compression)

    If it's not pinging or knocking, I'd be all sorts of tickled over the consistency,
    and go drive it and change the oil often and love it and hug it and call it George.

    (sorry, forgot the pills this morning)

    t
    now, sometimes I just mess with people. It's more entertaining that way. george graves

    Comment

      #3
      Originally posted by TobyB View Post
      Your head is thin?

      The eta has higher compression numbers? An RV cam? (low overlap cams tend to
      build higher low- speed (static) compression)

      If it's not pinging or knocking, I'd be all sorts of tickled over the consistency,
      and go drive it and change the oil often and love it and hug it and call it George.

      (sorry, forgot the pills this morning)

      t
      Thats the thing, it makes sense that the 2.7l should have a higher comp but from the few forum posts I have read its quite the opposite. Low compression for etas. unless its a super eta? all I know for sure is that some part of the egine is pre 87 becuase the diagnostic port in the engine bay is a 15 pin connection not a 20 pin found post 87, but to me that doesn't say much if the engine itself was frankensteined from I and etas. Unless I am wrong?

      A thinner head is what I initially assumed but if one of the POs had done that I assumed they would have gone outta their way to do some easier mods as well like having the more desired diff, right now it has the stock eta rear diff. beyond the high compression numbers it seems very stock but well maintained. They did keep the higher RPM reading I cluster which speaks to the cheapness of the swap.

      TBH I don't know much about RV cams but I have only ever heard about them in the context of larger 8 cylinder vehicles. Great for torque @ the low end and better MPG, but if the PO wanted a cruising torquey e30 I am sure he would have gone with a different rear diff (shorter rear diff?) on top of the rv cams which would have compromised his MPG but given him a little bit more of a torquey ride.

      Lastly I did do an oil change immediately and hoped I didn't hear any knocks. Not sure if you can mask a ping with thick oil or additives but I heard non pre nor post oil change (used thin oil temporarily).

      lol and Im not complaining about the consistency or the fact that its an e, love it. Thats why it is sitting on jack stands getting complete overhaul of engine, suspension, interior etc...

      Lastly I can't ask the more recent PO because he is a scammy slick talking jerk off. If you ever meet an albert herrera in or around houston beware.





      My don't quote me list:

      Originally posted by george graves
      I could be wrong, but I don't think it's a smog test type of thing. IIRC think it's against CA law to *sell* a dual outlet muffler as a replacement for a car that came from the factory with a single. But don't quote me on that.

      Comment

        #4
        High, consistent compression numbers? And it drives fine (you didn't mention otherwise, so I'm just assuming)? Not seeing the problem here :)

        I guess it could be a super eta (if I remember correctly, those have domed pistons)

        Maybe the head was milled and a thinner HG was installed? Who knows. I'm sure you'll find out when you tear everything apart.

        Comment

          #5
          Have you considered the possibility that gauge could be wrong? I had the inverse problem with a consumer grade compression tester once. It indicated low numbers across the engine. But when I ran a leak down test to find out why, those numbers were very good. Which didn't make sense unless one of the tools was lying. Since I could not hear escaping air anywhere it seemed that the compression gauge was bad and that my professional grade leak down tester was correct. I replaced the compression tester with a professional grade gauge and got normal numbers.

          Before going nuts, test again with a different gauge.
          The car makes it possible, but the driver makes it happen.
          Jim Levie, Huntsville, AL

          Comment

            #6
            Originally posted by jlevie View Post
            Have you considered the possibility that gauge could be wrong? I had the inverse problem with a consumer grade compression tester once. It indicated low numbers across the engine. But when I ran a leak down test to find out why, those numbers were very good. Which didn't make sense unless one of the tools was lying. Since I could not hear escaping air anywhere it seemed that the compression gauge was bad and that my professional grade leak down tester was correct. I replaced the compression tester with a professional grade gauge and got normal numbers.

            Before going nuts, test again with a different gauge.

            +1 on that... or be fine with the good numbers :)

            Comment

              #7
              That could be a possibility, I don't own a compression tester and I rented it from auto zone. I just figured since the gauges are pretty basic that there isn't much to break. It drives fine, like I said there is an idle problem but I suspect another part. Ill have to get a hold of another gauge and check, possibly buy it instead of renting another.

              Lastly, when I tear it apart what should I be looking at for signs of a milled head? If I get consistent compression numbers I would be hesitant to tear it apart and look.





              My don't quote me list:

              Originally posted by george graves
              I could be wrong, but I don't think it's a smog test type of thing. IIRC think it's against CA law to *sell* a dual outlet muffler as a replacement for a car that came from the factory with a single. But don't quote me on that.

              Comment

                #8
                Originally posted by joncrz View Post
                Lastly, when I tear it apart what should I be looking at for signs of a milled head? If I get consistent compression numbers I would be hesitant to tear it apart and look.

                There is no reason to tear it apart

                Comment

                  #9
                  You would be a fool to tear it down, those are perfect numbers. Compression testers are for comparing numbers from cyl to cyl and and not the actual numbers ;)
                  My M20 Frankenbuild(s)
                  4 Sale - Fully Built TurnKey Megasquirt Plug and Play EMS

                  Comment

                    #10
                    Originally posted by whodwho View Post
                    You would be a fool to tear it down, those are perfect numbers. Compression testers are for comparing numbers from cyl to cyl and and not the actual numbers ;)

                    I know... but I am just itching to know about this e30. Ive googled the hell out of the key words e30 engine Identification which hopes of finding info on every specific part of the engine, turns out you have to disassemble it to really know about your engine. Its frustrating and the fact that its solid speaks volumes how I should not touch it (besides timing & other general maint. stuff) but I reached out here to hopefully find out some obscure and easy way of finding out why high compression. I guess there is no easy way to without risking compromising the overall health of my engine. I did have someone interested in swapping it for an e24 shark and I might take him up on it just so I can leave this e30 in pristine condition without me breaking it further.





                    My don't quote me list:

                    Originally posted by george graves
                    I could be wrong, but I don't think it's a smog test type of thing. IIRC think it's against CA law to *sell* a dual outlet muffler as a replacement for a car that came from the factory with a single. But don't quote me on that.

                    Comment

                      #11
                      Oh yea, I forgot to say that I did the compression test on a cold engine. Theoretically once warmed up the numbers should be higher, which really is blowing my mind. should I be running on higher octane fuel?





                      My don't quote me list:

                      Originally posted by george graves
                      I could be wrong, but I don't think it's a smog test type of thing. IIRC think it's against CA law to *sell* a dual outlet muffler as a replacement for a car that came from the factory with a single. But don't quote me on that.

                      Comment

                        #12
                        What year is the car? What head does it have (casting number)? Stock injectors? What ECU? These are a few things you can check without taking anything apart, though injectors can some times be a pain. You can also try to get the casting numbers off the block.
                        90 325i DD/Track
                        03 Durango 5.9


                        Originally posted by e30mpg
                        It is recommended to get new gasket but this is R3v and we just copper spray that shit......slap biotch on and tighten to tq.

                        Comment

                          #13
                          sounds healthy to me. the absolute # isn't important - you can't tell the CR from it really, and your #s are very close together which is good.
                          Build thread

                          Bimmerlabs

                          Comment

                            #14
                            Couldn't hurt to use someone else's gauge to double check your numbers.

                            ETA engines until Sep 1985 had higher compression engines. 11:1
                            Still, at static atmospheric pressure you should only be showing 161psi on your cylinders (give or take 5 for error and atmospheric differences).

                            ETA engines after that dropped to 10.2:1, or 149psi to the cylinders.

                            You can tell the difference by the stamp on the block. 27 6KA is pre 09.85, 27 6EB is post 09.85

                            Comment

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