1992 Miata, LS1, then LS3 swapped

[mazpower]

Updates! Lots has happened since I've been here last. Some good, some bad.

First let me give a HUGE thanks to my friend Brian at Indio Motor and Machine for helping me out with my latest build!

Last engine went boom at a local track day. 5th lap into the run, on a brief straight in between turns, loud boom at 6k RPM in 3rd gear, WOT, engine shuts down followed by an insane vibration until I press the clutch in. I pull off the track and check the car out once the tow truck comes out...no leaks, nothing looks broken. Once I'm in the pits, I find that one of the Haltech fuses are blown and the ECU isn't coming on. I fix that, crank the engine and see that the Haltech isn't reading RPMs...there's something wrong with the crank position sensor. This, along with the bad vibration, leads me to think something bad happened in the engine.

I get it back to my shop, pull the oil pan, and find this.



That's the big end of #7, still on the crank. It spun freely so it wasn't an oiling issue that broke it. I pulled the engine and stripped it down.



Fresh marks on the piston are from it hitting the head as the rod snapped.









Crank journals on #7 and #8 were in excellent condition.



The block and camshaft were trash. What ended up happening on the track was once the rod let go, schrapnel from the break hit the crankshaft position sensor and destroyed it, which blew the fuse for the Haltech and shut the engine down. This saved me more catastrophic damage like a hole in the block which most certainly would have led to an engine bay fire.



After consulting with my machinist and Scat - the manufacturer of the I-Beam rods and 4340 crank I'm running - it was determined that quench (the distance between the piston and head at TDC) was too tight and that an overrevving condition allowed piston to head contact, which in turn fatigued the rods until they broke. There were almost a dozen times where I mechanically overrevved the engine, trying to shift from 3rd to 4th and ended up in 2nd...thanks T56 shit shifter...anyways the datalogs in the ECU showed that I never went over 8500 but revving up there was obviously too much for the rods. The next engine needed to be better.

With the engine trashed, I needed a new setup. All that was salvagable was the crank, heads, and main studs. So I opted for a brand new LS3 block from GM using my Scat 4" crank, which gave a displacement of 415 cubic inches, or 6.8 liters, with 4.065" Mahle pistons, K1 H-Beam stroker rods, and a Texas Speed & Performance "Magic Stick 3" cam. MS3 is 237/242 duration int/exh at .050", .604/.609 int/exh lift, and 111 LSA. I needed new valves for the head as the #7 piston had hit the valves but not bent them, we didn't want to take any chances. LS6 valves are no longer available so I ended up with Ferrea SS valves. The heads were reworked for more flow at .300 to .550, picking up 20 cfm at .300 and .400 and flowing 295 cfm at .550. Another 15 FPS of flow were picked up across the board. We ended up with 11.7:1 compression when everything was said and done. A little high but nothing a tune can't adjust for.

Mahle pistons


Assembling the short block








Keyed SLP harmonic balancer with a ARP balancer bolt. This way I don't have to stress out setting trigger angle in the Haltech, as stock LS stuff doesn't have timing marks.


Shiny combustion chambers


A whole bunch of aluminum


And back in the car. Took 2 1/2 days of work to get running.


Finally with the car running again, I could install the AIM MXL Strada dash I had been sitting on since shortly after the engine died in February. First I needed to get the Haltech reading the vehicle speed sensor on the T56. I thought this was going to be an easy task, but no, nothing with this car is.

The VSS on the T56 is a reluctor. This means that it works like the trigger sensor on a RX-7, where you have a metal ring with teeth and a reluctor sensor...as the teeth pass the reluctor, the reluctor generates a sine wave which can be interpreted by the ECU as a trigger event. The Haltech only accepts a 5 volt square wave signal for speed...same goes for the speed input on the AIM MXL. They won't work with a sine wave. So I searched for a solution. There are converter boxes which transform the signal and even massage it to compensate for changes in tire diameter. They are $150 and above. Then there are reluctor adapters sold by Haltech and other companies that take a reluctor signal and convert it to a square wave. They are $200 and above. Lastly I could go the "fancy" route and have a trigger wheel machined to sit on one of my wheel hubs and use a hall-effect sensor, which natively creates a 5v square wave, to read speed. That would be $200-$300 and would be a lot of work.

For a while I've had a theory that a GM HEI ignition module could be used as a cheap reluctor adapter, but I never had an opportunity to try it until now. The HEI ignition module sits in the distributor of the car it came from, and processes the reluctor signal into a square wave for the ECU...it also controls timing and fires a coil but I wouldn't need all that. I went down to Auto Zone and bought a 7-pin ignition module for a whopping $27...it was for a '84 Chevy Camaro with the High Performance 305. I wired up the reluctor wires from the VSS to the inputs on the sensor, taking care to match polarity, and ran the tach output to a Timed Input wire for the Haltech, and hooked up power to the sensor. Grounding is done via the mounting holes for the sensor.

Basic wiring layout


I then got a usable signal in the Haltech and got an accurate speed reading, after messing around with the pulses per km value in the Haltech. I made an aluminum backing plate for the ignition module and put the thermal paste on it (the sensors tend to burn up if you're not careful, in a "stock" setting...I'm not running a coil off of it so it should run cooler but better safe then sorry) and bolted the whole thing down near the Haltech. Then I discovered a nagging issue with the E11v2 where it would read 400 km/h until you moved for the first time. This would really screw with my trip and main odometers, which was the reason for the MXL in the first place, so I ended up wiring the module to the MXL directly and everything works perfectly.

And damn do I love the MXL...one of the best investments for the car so far. It connects to the Haltech via the CAN bus and shows all of the sensors that the Haltech sees. You can configure 6 sensors to view in the MXL, 2 of which are displayed all the time while the other 4 are paired up and can quickly be toggled by pressing a button on the unit. It also has 6 warning lights that can be assigned to any sensor, customizable shift lights, current gear, rpm, and speed.

I gutted the stock gauges, leaving only the fuel gauge, and used a piece of aluminum to mount the MXL to. I screwed up on the hole for the fuel gauge and had to drill two so the whole gauge was visible. Version 2 of the cluster will be done in painted lexan with the "hole" over the fuel gauge left unpainted, along with a plastic ring placed between the gauge and lexan for a "stock" appearance. I'll also set up turn signal, high beam and warning lights.