This page is devoted to the hybrid engine rebuild.

Thanks go to Glen N for advice, encouragement, and use of his warm shop; to Hiroki C for help pulling the engine, and installing the rebuild; and to Julian P for suggesting the MX3 donor idea.

The B6T rebuild quote was about $700 for the head, and $1600 for the bottom, which stopped me cold. But, another friend, Julian, pointed out that the Mazda MX3 from 94-96 used a DOHC B6 4-cylinder block, and that it should swap. The key thing is these cars show up at Pic'n'Pull style wreckers now in Canada, while there are never any 323 GTX or Ford Capri's. (The B6T Capri was not sold in Canada). And I had seen one a few days before at Pic'n'Pull in a car with a crash-wrecked front end, so I knew the engine was running. Hiroki, my fab guy from page 1, came out and helped me pull the engine, and it cost only $130.

The plan was to pay to rebuild the B6T head, and put it on the MX3 B6 block. Does this combo work? Yeah, but it is not quite bolt on, and you need parts from the B6T bottom end.

First, the MX3 uses 9.0 compression, while the B6T is 7.9, so I will have to think about using octane booster to get at least 93 if I get detonation. But people turbo the 9.0 compression Miata B6, so it can work.

Second,, has it been done and described for others? Not that I could find on the web. Web searches turn up swapping the B6T exhaust manifold and turbo onto the MX3 engine, with a complaint it does not quite fit. Also, the MX3 head (which breathes better) has been swapped onto the B6T bottom, and mated to the B6T turbo mani. But there are extra oil galleys on the exhaust side that had to be plugged on the MX3 head. Other turbo's have been put on the MX3 engine, with a need for a piggyback or standalone ECU to control spark timing and air/fuel ratio.

Third, could I figure out what had to be done? I thought so, and that's described below.

Oil Pan Swap and the Foyer
Not only did my wife have to put up with an engine in the foyer so the JB Weld could set, she had to help me carry it in! But besides earning nights on the couch the photo above shows the B6T oil pan on the MX3 block. This swap had to happen, because the MX3 oil pan does not mate to the B6T G25mr series tranny. (The B6 MX3 uses the f series tranny). Plus, the B6T oil pan already has the turbo oil return tap in place. With the swap done the G25mr tranny bolts right on.

Clearancing for the Turbo
For some reason Mazda put a round bell shape on the MX3 block to match the tranny shape of the f-series, whereas the B6T block just has wings sticking out at the bottom and a symmetric tower shape at the tranny end. This bell prevents the turbo from sitting properly, and had to be ground away. The photos show the bell and the grind. There is about 3 thou of clearance now for the wastegate actuator.

Plugging the Oil Galleys
The pics above also show the extra oil return galleys on the exhaust side. I thought the B6T head gasket would just block them off, no problem, but no. They are half outside the block so are not covered. They need to be plugged. The hole diam matches either a 3/8 pipe thread tap drill or 5/8 standard thread tap drill size, so no drilling is needed.
Holes were tapped with 3/8 pipe thread. Brass 3/8 blind plugs were ground shorter, and the thread was tapped deeper, so they could be screwed down below the upper deck of the block.
The tap broke off in the block and the air turned blue!! I had to go very deep to get the plugs to turn below the deck, and it simply required too much force. I ended up just grinding the tap down to the deck. Both plugs (thinking of the tap now as a leaky plug), were then sealed with JB Weld Epoxy, and sanded flat with a palm sander.

Lesson Learned
It would have been easier to grind the brass plugs down to the deck than grind the broken tap, so I should not have been so determined to sink the plugs. Or better still, I should have used 5/8 diam set screws and tapped standard thread. A standard tap bites only near the tip, whereas the tapered pipe thread tap bites along the whole length, drastically increasing friction and the needed torque the deeper one goes. Since I was using JB weld to seal the top of the plug anyhow I did not really need the sealing power of the pipe thread.

Turbo Oil and Coolant
The turbo oil return was on the B6T oilpan so that line was covered. But the oil galley line for the oil feed was not on the MX3 block. I found a nice $67 product on the Flyin Miata website to run an oil feed for their turbo install on later model B6 or BP blocks. But they were out of stock on one part, and shipping UPS to Canada adds $50 bokerage fees (crooks in my opinion). So I assembled a similar system for about $60. (Click on Instructions on this Flyin Miata link if you want to see their install pdf www.flyinmiata.com/turbos/index.php)

Autometer part 2269 adapts from Mazda's 1/8 BSPT thread to 1/8 NPT. Then an 1/8 NPT 3-way T goes into the adaptor, an NPT to AN (or aeroquip) #4 adaptor, and an AN #4 fitted braided stainless steel oil line hose (3 feet long) connect to the T, and the stock oil send threads into the other opening. (BSPT male works in NPT female, but NPT male does not fit BSPT female, go figure!) All of this goes into the stock oil send location beside the oil filter. I later took out the stock pressure send and put in a 1/8 NPT connector to a mechanical oil pressure gauge instead.
The turbo end was harder. The fitting is 1.75 mm pitch, 8 mm diam into the turbo, with a 1 mm pitch, cone-shaped tip-fitting to the oil input feed line. I could get an aluminum adaptor from MOPAC with the 1.75 mm pitch for the turbo end, converting directly to AN to mate with the braided steel oil line hose, but was told the thermal expansion mismatch of aluminum and the hot steel of the turbo would lead to big problems. Dunno if thats true (steel bottom and aluminum head after all) but I accepted it.

The stock turbo oil line is 1/4 inch steel, and it is double flared like a US brake line to fit the cone shaped tip from the turbo. I was able to take a 12 inch long 1/4 inch brake line, cut one end, and put on the 1 mm pitch fitting of the stock oil feed line, then re-flare the cut brake line. (My flare leaked, but Glen redid it for me and it sealed well.) The other end used a brass brake connector to 1/8 NPT adaptor, then a steel NPT to AN adaptor to connect to the braided steel oil line. Parts were from MOPAC and Parts Source fittings & screw shelf, but they could also be had at Bumper to Bumper.

The turbo water line return was handled by using the B6T coolant bypass tube, which has the needed branch tube on it, rather than the MX3 bypass line, which does not.

The B6T block has a turbo coolant feed tap right from the block, the MX3 does not. I decided to cut the rubber coolant line from the intake manifold, which feeds the oil cooler collar on the B6T and then goes to the heater core, and splice in a T. This should ensure enough pressure difference across the turbo for good coolant flow. The diam of the rubber hose is odd (i.e. metric), and I could not get a good brass plumbing fitting T for the job. So I cut the MX3 bypass coolant tube near a tap line, and fit it into the rubber coolant tube from the intake manifold. See above photo. A narrow bore heater tube then runs around to the turbo coolant intake. A barbed hose connector joins the original turbo inlet hose to the new feed. The original had the right type of bends in it, so that I could avoid the kinks that would have come from trying to run the new line all the way to the turbo.

Other Adaptations
The top B6T timing belt cover piece is needed, but the bottom two pieces are the same on both blocks.

The water pump to hose fitting needs to be from the B6T to fit in a Festiva engine bay.

The front-of-the-engine mount needed to be from the B6T, since the parts we fabbed were for that design.

The MX3 long nose crank fittings are a lot different than those on the short nose B6T, and the timing belt drive and crank pulley from the MX3 had to be used. The crank pulley is for a flat serpentine style belt, whereas the B6T is a v-groove. Swapping the crank pulleys might be possible, but I was not sure what would come apart without breaking. Instead I used the water pump pulley from the MX3. The MX3 alternator was bad, and my B6T alternator had been rebuilt. But I could not just swap the pulley as the shaft diam is different. An alternator shop had a flat belt pulley that worked on the B6T alternator. An MX3 belt must be used, obviously.

The oil pump must be from the MX3, because the crankshaft diam is different from the B6T at the pump.

Results
It worked! It is burning oil on startup right now, but it clears in 5 min or so. The diagnosis is that one of the valve stem seals in the head rebuild is bad. I will have to take that up with the rebuild shop.

On summer tires and icy winter roads a test drive seemed scary fast. I could not keep my foot in it, because the wheels kept breaking loose. With Bridgestone Blizzacks at the Ice Race School on the lake it behaved much better. But with each shift it would easily break the tires loose and spin up to the rev limiter!

Its going to be great I think. The higher compression should give better low end torque than the B6T, and that is really useful in ice racing, where you have to drop the revs to get the tires to bite before you can stomp it into boost.