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  • Miata Engine Rebuild questions

    My engine in my SuperMiata is getting a little tired and I'm thinking of refreshing/rebuilding my engine over the winter and I don't have any idea what I'm doing. It's an OEM rebuilt NB1 engine I've been running for almost 5 years (estimating 50 - 75 hours). Doesn't burn any oil over a weekend, but tuning is basically maxed out to get my class power. I also have quite a few over revs on the stock valve train which makes me nervous and I'd like to rebuild before kaboom.
    I have no experience with engine internals. I'm looking for a long lasting and reliable setup for about 140 hp with some over rev protection without breaking the bank.

    1. Where do I start to get an accurate assessment of health?
    -Compression check? - I have the gauge but never used it
    -leak down test? - ~$70 on amazon
    -judge results from this on full rebuild or just head?

    2. Just rebuild the head?
    -what are the chances I can get away with just the head?
    -what's the recommended upgraded equipment for stockish power reliable track duty? (springs, guides, valves)

    3. Rebuild bottom end too
    -generally, what can most likely be reused and what should be replaced?
    -what do I need for stockish power miata to be reliable

    4. Picking a shop
    -since most of this is the stock type of rebuild, I hoping I can find a reputable engine machine shop with some miata experience
    -Seems like paying a pro miata engine builder is a waste because I don't have to know all the tricks to comply with SM rules.
    -I'm open to any suggestions in the bay area or near.
    -Anthony
    1991 Miata - Trogdor SuperMiata
    2011 Ram 2500 - all the torque

  • #2
    1. Compression and leakdown. Kind of moot seeing as you are rebuilding regardless

    2. Do the whole long block

    3. Light double valve springs, Mazda or Felpro valve seals. The rest can be stock. Bonus points if you find a Miata engine specialist is bowl blend and deshroud, port otherwise untouched. Good bang for the buck head work.

    4. OEM is fine for the most part. For over rev protection, forged rods (Chinese is fine), ACL bearings. OEM compression is 9.5:1. 10.5:1 is the sweet spot for 91 pump gas or E85 though. Consider a piston with a bit more compression.

    5. Find a shop that knows Miata engines

    Some additional reading: http://www.trackhq.com/forums/f333/m...ng-notes-8290/
    WWW.949RACING.COM
    SuperMiata

    Aside from their cost I never understood why people race them.
    But obviously I just dont get it. -fatbillybob

    Comment


    • #3
      What Emilio said.

      Mike Haag @ Haag Performance in Sacramento is your guy. Tell him I sent you.

      If the motor is coming apart anyway do it right and rebuild the long block. Make sure that whoever you use doesn't just slap bearings and rings in it and call it good. Proper measurements and fitting, polishing the crank and cams, and cleaning the crank/block oil galleys are key to a well performing and long lasting motor.

      Mark

      Originally posted by emilio700 View Post
      1. Compression and leakdown. Kind of moot seeing as you are rebuilding regardless

      2. Do the whole long block

      3. Light double valve springs, Mazda or Felpro valve seals. The rest can be stock. Bonus points if you find a Miata engine specialist is bowl blend and deshroud, port otherwise untouched. Good bang for the buck head work.

      4. OEM is fine for the most part. For over rev protection, forged rods (Chinese is fine), ACL bearings. OEM compression is 9.5:1. 10.5:1 is the sweet spot for 91 pump gas or E85 though. Consider a piston with a bit more compression.

      5. Find a shop that knows Miata engines

      Some additional reading: http://www.trackhq.com/forums/f333/m...ng-notes-8290/
      AiM Data and Video systems, Suspension Setup, Race car builds, support, and rentals. At your beck and call.

      Mark Nichols
      Iron Canyon Motorsports
      http://www.ironcanyonmotorsports.com

      Comment


      • #4
        ^^ I actually spoke to Mike on Friday. He was very generous with his time and gave me an idea what he would recommend.

        He did start talking about plunge cuts at the end of our conversation and that got me thinking I'm paying for the spec miata expertise. Maybe I can have a better conversation with him if I have a more specific build in mind.
        -Anthony
        1991 Miata - Trogdor SuperMiata
        2011 Ram 2500 - all the torque

        Comment


        • #5
          Plunge cuts can be a good thing if the head casting has core shift in the port areas but you won't be able to see that until you get the head apart. The intent of the plunge cut (yet another SM rat hole rule) was to equalize the good heads with the bad heads and eliminate the need to cherry pick through head castings to find the 'magic' perfect head. The pc was not intended to be a performance modification. 'Intended' is the key word there... If the casting is good there is not that much benefit to the plunge cut from what I have seen. I'm not convinced of the need for the plunge cut if the head has minimal core shift as the larger port causes a loss of air velocity the air on the intake side and creates a 'ledge' on the exhaust side for air to slam in to. If we could blend the pc we might be able to solve that issue but since the blending that is allowed is almost none we have that 'ledge' to contend with.

          If you are not bound by SM rules there are lots of ways to get power from the head that may/may not involve a plunge cut. Depends on your casting IMO. Mikey can help here. Tell him what you are looking for is more of a PTE/STL type build and he'll likely shift gears.
          AiM Data and Video systems, Suspension Setup, Race car builds, support, and rentals. At your beck and call.

          Mark Nichols
          Iron Canyon Motorsports
          http://www.ironcanyonmotorsports.com

          Comment


          • #6
            I would go a different way. Do a compression test and a leakdown check, figure out if there are obvious ring problems. If the issues are mostly valves, pull head, take to your local machine shop say "gimmie valve job", pay the man $200, install the head and timing belt, run compression test again, if numbers look good, finish reassembly and go to the dyno.

            Comment


            • #7
              I won't debate the direction to go, only tell you what I had done on a '99. I had Rebello do a 0 points PT build for me almost 5 years ago now. Forged Supertech 9.5:1 pistons, no-name forged rods, race bearings, balanced and blueprinted, Supertech stiffer valve springs, billet oil pump gear, blueprinted oil pump, head shave for 10:1 CR. Engine made plenty of power for SPM for a number of years without a stand alone ECU. I had it built with reliability in mind. Overall I had a good experience with Rebello but others have not. They are also in the Bay Area.
              99 Mazda Miata SuperMiata #515 - AKA Sparky SOLD
              '91 Mariner Blue Miata project AKA Napoleon

              Comment


              • #8
                William's Rebello built NB2 was supposed to have forged rods, heavy valve springs and stainless valves, safe to 8000rpm. It had none of those and blew up after about 5 hours of being revved to 7400 a few times. That entire long block went into the trash.
                WWW.949RACING.COM
                SuperMiata

                Aside from their cost I never understood why people race them.
                But obviously I just dont get it. -fatbillybob

                Comment


                • #9
                  Originally posted by emilio700 View Post
                  William's Rebello built NB2 was supposed to have forged rods, heavy valve springs and stainless valves, safe to 8000rpm. It had none of those and blew up after about 5 hours of being revved to 7400 a few times. That entire long block went into the trash.
                  Yeah and the genuinely sucks. Unfortunately that seems to be how it goes with race shops, a few guys have a good experience and some others don't. I never checked the internal components on my build but it was strong and seems to be robust which is what I asked/paid for.

                  There's another engine builder in the Bay Area who used to work for Rebello then went out on his own. Unfortunately I can't remember the name.
                  99 Mazda Miata SuperMiata #515 - AKA Sparky SOLD
                  '91 Mariner Blue Miata project AKA Napoleon

                  Comment


                  • #10
                    Originally posted by Red_5 View Post
                    ..There's another engine builder in the Bay Area who used to work for Rebello then went out on his own. Unfortunately I can't remember the name.
                    That's Haag. With him went the Miata knowledge AFAIK. They're originally a Nissan specialist
                    WWW.949RACING.COM
                    SuperMiata

                    Aside from their cost I never understood why people race them.
                    But obviously I just dont get it. -fatbillybob

                    Comment


                    • #11
                      Emilio's link at http://www.trackhq.com/forums/f333/m...ng-notes-8290/ is like a bible and should be read every Sunday.

                      I had good luck with machine work at Victory Automotive Machine in Campbell last week, although the experience there for most people is with V8's (he called a piston from my NA6 a "cute little thing"). Vic said he had worked on Spec Miata engines before, but my build is 90% full-prep STL.

                      I gave them a box of engine parts after measuring everything twice, told them the specs I wanted, and got the parts back the way I wanted in less than two weeks at a fair price. It was a much better experience than I had with another local Miata shop earlier this year (not Haag).

                      I spent most of this past weekend assembling said parts into what appears to be a running engine, and the maiden voyage is next weekend on the residential streets of Sunnyvale. I probably should have paid for someone's experience to assemble it for me, but after a lot of searches on here, miataturbo, and a couple of calls to SCCA prod builders, figured it would be fun to do by myself.

                      The info is out there and like a lot of people say, building an engine yourself is a rewarding experience. At least for a few hours before the big kablammo. I probably won't think it's rewarding if that happens.

                      Comment

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