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GTX B6T Rebuild Options - Opinions wanted

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    GTX B6T Rebuild Options - Opinions wanted

    The B6T in my GTX has 220k mi and consumes oil pretty consistently. It occasionally smokes pretty good at startup. I've installed a GT25 turbo on it and miss the down low power and quick turbo spool up - though I dig the top-end with 20psi =)

    So it's time to rebuild the motor. My goal is to get about 230hp with as broad a power band as possible. The GTX is just my fun daily driver so I'm not looking for anything too extreme.

    I've pretty much written off the BPT motor swap due to the fabrication required and the cost. (maybe someone can make a case to convince me otherwise) My current though is to find a 91-93 automatic transmission Miata 1.6L (big nose crank and 9.0:1 CR) engine to swap in. I think the higher compression ratio will give me the better low end and quicker spooling I'm looking for.

    Since I'm relatively new to the Mazda scene, I could use some help with my options, so some discussion points:
    1) Are there any serious draw backs to the AT Miata 1.6 block swap that I'm missing?
    2) I understand I'll have to swap over the B6T oil pan, cams, and take care of some coolant routing. Is there anything else I need to swap over?
    3) I read the Miata rods supersede the B6T rods, does this mean they are better? Should I / can I swap the rods?
    4) Should I just re-use the whole GTX head on the Miata block?
    5) Will the 9.0:1 CR give me the performance boost I'm looking for?
    6) I haven't read much about people using the Miata engines, is this an uncommon swap?
    7) Is there some other option I haven't even considered?

    PS, I'm running full standalone, so I have no worries about fuel/spark control, if that factors in at all...
    ///SpitfireEFI.com -- MegaSquirt GTX Install

    #2
    Originally posted by bham_gtx View Post
    Since I'm relatively new to the Mazda scene, I could use some help with my options, so some discussion points:
    1) Are there any serious draw backs to the AT Miata 1.6 block swap that I'm missing?
    2) I understand I'll have to swap over the B6T oil pan, cams, and take care of some coolant routing. Is there anything else I need to swap over?
    3) I read the Miata rods supersede the B6T rods, does this mean they are better? Should I / can I swap the rods?
    4) Should I just re-use the whole GTX head on the Miata block?
    5) Will the 9.0:1 CR give me the performance boost I'm looking for?
    6) I haven't read much about people using the Miata engines, is this an uncommon swap?
    7) Is there some other option I haven't even considered?

    PS, I'm running full standalone, so I have no worries about fuel/spark control, if that factors in at all...
    Ok,
    1. No oilways are tapped (not that difficult really but something to account for)
    2. I can't think of what else is involved but keep in mind the block is longitudinal instead of transverse.
    3. No. B6t rods are better.. They just stopped making them. Use the stock gtx rods if you can.
    4. This one I can't remember on.. Maybe someone else can fill in this gap...
    5. Yes.. quicker spool, and more low end. (I think the BPT will give you a better response. I've driven many GTX and by far the most fun was a BPT swapped GTX, which I now own.)
    6. Its uncommon only because there's so many turbo blocks and they're nearly bulletproof. It would almost be better to just swap out the crank and the piston, or get some wiseco 9.0:1's for a Miata and throw them in.
    7. Get a BPT, you'll be way happier. Ever down in Portland? I'll give you a ride. It's really not that much fab work. The hardest part is finding front axles to hybrid to make it work.

    1988 White GTX - #1 parts
    1988 Black GTX - #2 reliably broken touge monstar (294,000 miles no rebuilds) - dead
    1988 Blue GTX - #3 in progress (view here)
    1988 Blue GTX - #4 BPT swapped weekend warrior.
    1988 White GTX - #5 Rally car

    Comment


      #3
      To me it seems like the the only thing the BPT is getting me is an extra 0.2L of displacement... Don't get me wrong, I know it will make a big difference, but I'm not sure I want to go down that path right now...

      So based on your feedback, it seems like the second best option is for me to refresh my B6T block by:
      1) Installing a 1.6L Miata "big nose" crank
      2) Keeping my B6T rods (upgrade rod bolts)
      3) Fitting 9.0:1 Wiseco pistons
      4) Get the B6T block bored/honed/cleaned
      5) Get the head surfaced refreshed with new valves/guides/seals

      ...hmmm now that I write it all out, it seems like a lot of work/$$
      ///SpitfireEFI.com -- MegaSquirt GTX Install

      Comment


        #4
        it's an extra 50hp stock. and a totally different power band for a weekend of work.

        but yes.. that would be my suggestion if you don't want to go BPT.

        1988 White GTX - #1 parts
        1988 Black GTX - #2 reliably broken touge monstar (294,000 miles no rebuilds) - dead
        1988 Blue GTX - #3 in progress (view here)
        1988 Blue GTX - #4 BPT swapped weekend warrior.
        1988 White GTX - #5 Rally car

        Comment


          #5
          What all is involved as far as "Fab work"? I've been told that you need to notch out the frame rail and make a new pass-side motor mount. What are the 'hybrid axles' made out of?

          I guess I need to poke around here for some BPT install build diaries.... The lame thing is that I've got to get a new custom exhaust manifold and down pipe made for the GT25R.
          ///SpitfireEFI.com -- MegaSquirt GTX Install

          Comment


            #6
            ive also been wondering what was all needed in swapping a b6t with a bpt.
            88 Mazda GTX- rusted dalmation, it runs?
            00 Ford ZX2- red terd, mods: slow
            00 Ford ZX2- purple ricerocket, 302whp/298wtq - SOLD

            Comment


              #7
              you pretty much nailed it..

              the hybrid axles are bpt inners and b6t outers. must be 4wd stuff is the important part... The downpipe should work with some minor modification since the BPT is going to be tilted slightly.

              1988 White GTX - #1 parts
              1988 Black GTX - #2 reliably broken touge monstar (294,000 miles no rebuilds) - dead
              1988 Blue GTX - #3 in progress (view here)
              1988 Blue GTX - #4 BPT swapped weekend warrior.
              1988 White GTX - #5 Rally car

              Comment


                #8
                The wiring will be a little different. The easiest would be to get a BPT harness too, but i know you can modify the existing harness to make it work.

                1988 White GTX - #1 parts
                1988 Black GTX - #2 reliably broken touge monstar (294,000 miles no rebuilds) - dead
                1988 Blue GTX - #3 in progress (view here)
                1988 Blue GTX - #4 BPT swapped weekend warrior.
                1988 White GTX - #5 Rally car

                Comment


                  #9
                  Originally posted by bham_gtx View Post
                  What all is involved as far as "Fab work"? I've been told that you need to notch out the frame rail and make a new pass-side motor mount. What are the 'hybrid axles' made out of?

                  I guess I need to poke around here for some BPT install build diaries.... The lame thing is that I've got to get a new custom exhaust manifold and down pipe made for the GT25R.
                  B6T's have been know to make plenty of power so dont worry. there are tons of miata guys that keep the B6 and go turbo. i would look into swapping in a BPT transmission, it will be stronger then the stock GTX tranny and also give you a viscious center differential.
                  "See that car, in the 80's that car was deadly." Random man to his son while passing the GTX in a parking lot

                  Originally posted by neuspeedescort
                  the proper spelling would be "Launchabilitiness" i do believe.
                  -88' Mazda 323 GTX, 1.8t, Modified Magazine May 2012
                  -88' Mazda 323 GTX, caged and ready for dirt
                  -93' Mazda Miata, half caged
                  -09' Mercedes C63 AMG
                  -87' Toyota Land Cruiser, 33's with slight lift, safari style!

                  Comment


                    #10
                    Its true... good power can be made on a B6T... But it's not going to have the low end a BPT has. Take into consideration my street car is BPT but my rally car is b6t. It's mostly due to the fact that I have so many B6T spares.

                    1988 White GTX - #1 parts
                    1988 Black GTX - #2 reliably broken touge monstar (294,000 miles no rebuilds) - dead
                    1988 Blue GTX - #3 in progress (view here)
                    1988 Blue GTX - #4 BPT swapped weekend warrior.
                    1988 White GTX - #5 Rally car

                    Comment


                      #11
                      Ok, so it sounds like the "hybrid axles" shouldn't be a problem if I get the BPT / trans with cut axles on it. I can combine what I have now on my GTX with those and be all set, right?

                      Is the BPT transmission identical to the B6T(GTX stock) trans as far as mounting/interfacing? I guess I would have expected it to be slightly different than the stock trans since the block is longer/tilted.

                      I'm not worried about engine management or wiring harness adaptation since I'm running stand alone and have a lot of automotive wiring experience.
                      Last edited by bham_gtx; 03-05-2010, 07:45 PM.
                      ///SpitfireEFI.com -- MegaSquirt GTX Install

                      Comment


                        #12
                        Greg Downing has a couple of good write-ups on the yahoo forum. One is for the BPT with the BF tranny (IIRC), the other is the full BPT and BG tranny swap. Lots of good info there.

                        Comment


                          #13
                          If I recall, the GTX rods are as thick as (or thicker than) those in Chevy's 350 V8s. They're good. My GTX makes pretty decent power, and we stayed with them. We did upgrade to Wiseco forged pistons.

                          One other thing I'd recommend...look into a lightened flywheel.

                          Have fun!!

                          Regards,
                          Joel
                          1988 323 GTX - Heavily modified

                          DJT Motorsports (Oak Park, MI) - like no other

                          Comment


                            #14
                            Go with a BPT - the powerband of the BP is way flatter and smoother than the B6. I went from FWD B6T to boosted BP and AWD - the power is incredible, its an entirely different beast. 808 convinced me to do it, and its soooooo worth it

                            Edit:

                            If you are going to stick with a B6 - grab one from an n/a capri and throw your rods in it - its already setup for FWD. Miata's B6's have the same block but everything else is setup for RWD operation
                            1991 Capri XR2 "GTXR2" BPT AWD Bastardization/conversion
                            1991 Isuzu Impulse RS Turbo AWD

                            Creator of the B6T Rocketchip
                            www.werbatfik.com

                            Comment


                              #15
                              It's true... Rocketman and I talked for months before he broke down and listened to me. And now he wouldn't trade it for the world.

                              1988 White GTX - #1 parts
                              1988 Black GTX - #2 reliably broken touge monstar (294,000 miles no rebuilds) - dead
                              1988 Blue GTX - #3 in progress (view here)
                              1988 Blue GTX - #4 BPT swapped weekend warrior.
                              1988 White GTX - #5 Rally car

                              Comment

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