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MSM Swap Into A 1995 Miata

This vehicle arrived with a tired, original 1.8L motor and otherwise stock drive train. The owner had desires to increase the performance envelope of the car, and had sourced their own engine from a 2004 Mazdaspeed Miata and transmission from a 1999 Miata. This swap works well because the physical engine and transmission from the newer car drops into the older car with very little modifications for fitment. Almost all changes to make the idea work are wiring, intake, or other minor changes. The motor mounts and transmission mounting are identical.

​The Mazdaspeed Miata came equipped with an IHI turbo/log manifold set up that produced approx. 175-180 hp at the flywheel. The engine was very similar to the stock 1.8 found in the '99-'00 Mazda Miatas, with some improvements and modifications to accept the turbo system. The stock Mazdaspeed engine and turbo from the factory was not a tire smoking monster, but with the right upgrades, and placed into the lighter 1995 chassis, it can be a good bit of fun.

This particular kit had received an improved intercooler, and modifications to its boost control systems to help it produce something closer to 200 hp at the rear wheels. It also included a lightened flywheel and upgraded clutch disc/pressure plate combo to handle to extra torque.

​While many important components were already taken care of, the 1995 Miata never came with a turbo from the factory, and would need several upgrades to accept the motor, turbo system, and transmission from the 2004 donor car.

​The first piece is engine management. While modern cars have engine control units (ECUs) that can be reprogrammed to handle performance upgrades, the older computer in a 1995 vehicle can not handle reprogramming for performance upgrades. When major modifications are done to the vehicle, an aftermarket programmable ECU must be installed. Sports Cars, Etc. has had good results with DIY Autotune's product line, and is a vendor of their product line.

A DIY Megasquirt ECU capable of handling the needs of this project and designed to work with this year and model vehicle was selected, and installed. Along with the upgraded ECU, the project needed better instrumentation to monitor different aspects of performance and tuning. A wideband controller and boost gauge were installed for monitoring while driving and for communication to the new ECU while tuning.

The Heart Transplant

With the computer and gauge installation completed, the next step is removal of the old engine and transmission and installation of the new components. This part is actually one of the easier steps since it drops right in after proper preparation and planning.

The Devil is in the Details

While the engine and transmission install basically just like the originals did, there are things that need to be adapted. Now it's time to take care of air routing from turbo to intake manifold, adapting the 2004 turbo exhaust to the 1995 Miata exhaust, and converting some of the original 1995 wiring to work with the various 2004 and 1999 electrical components now on the engine.
Exhaust
​
​As a general rule of thumb, turbos benefit from an increased exhaust diameter over the same engine that is naturally aspirated. Since you're putting more air into the motor, it's nice to be able to get that extra air out as efficiently as possible. A restriction in the exhaust flow can cause heat build up in the turbo system/engine, and increased boost levels that don't equate to increases in power. Just increased stress on the motor. The original stock downpipe and midpipe from the Mazdaspeed could have been adapted to work, but the exhaust diameter is not really any larger than what comes on a naturally aspirated car of the same year. That is acceptable (but not ideal) when the turbo is making factory levels of boost, but with the extra demands put on this turbo system from other upgrades, it's better to have a freer flowing exhaust system. Sports Cars, Etc. recommended using an Enthuza downpipe designed for the Mazdaspeed turbo with a diameter of 2.75". This is enough to allow good exhaust flow. While the downpipe needed to match the Mazdaspeed motor, the rest of the exhaust needs to match the 1995 Miata. The vehicle owner provided their own aftermarket cat-back exhaust of the same diameter. An adapter pipe was fabricated to go between the 2004 style downpipe and the cat-back exhaust. This adapter pipe should allow the owner to switch between any aftermarket or stock cat-back exhaust that fits on a 1995 Miata. They should also be able to use any downpipe designed to work with the Mazdaspeed turbo kit.
Intake
The next step is to address air routing from the output of the turbo to the intake manifold. The intake parts were mostly from a BEGi kit that improved the performance, which is great. The various pieces provided were all designed to work with the 2004 chassis. While many of them will also work on the 1995, it's definitely not a 100% conversion. The most important piece that will work is the improved BEGi intercooler. The stock intercooler is not great, so this is a nice upgrade to be able to reuse. 
​The majority of the BEGi hardlines that go from the intercooler to the intake manifold worked without major adjustment, but the hardlines that went from the turbo to the intercooler were too different to use. 
​The Mazdaspeed Miata comes with a an interesting strut bar that doubles as part of the vapor recovery /oil vapor scavenging system for the turbo. Since this piece physically fits on a 1995 Miata, it was installed to take advantage of the decent OEM oil catch can and other hoses already designed into the layout.
 Wiring
​Another area of adaption is handling the new modern sensors and extra inputs necessary to run the new setup.

The first part is the newer throttlebody for the MSM uses a more modern TPS and IACV. The old sensor plugs were removed and new factory plugs for the new sensors were soldered into the harness.

​Another new sensor is the GM style IAT sensor. This helps monitor air temperatures going into the engine, and is the preferred sensor for the Megasquirt ECU. The correct plug is soldered into the existing wiring harness, and the signal will be picked up by the Megasquirt. A physical bung is welded onto the intake charge pipe for the actual sensor to thread into.

From there we needed to handle the new, extra inputs that were never part of the stock wiring harness, and that the stock computer was not designed to handle. One of these new systems had to do with the 1999 intake manifold. This uses a system called VICS to help optimize air flow at different RPMs. The electronic solenoid used to help control this is not part of the '95 wiring harness, and the old computer would not of been able to accept the new input. The harness was modified to have the new plug, and the new signal wire was run back to the aftermarket ECU. The Megasquirt ECU is capable of handling several extra inputs, and will be able to run the VICS system nicely.

​The other new input is electronic boost control. The 2004 Miata ECU was capable of controlling boost levels through this system, while the stock 1995 ECU has no provisions for anything like that. In a very similar manner, the stock 1995 wiring harness is modified to contain the correct plug to work with the existing boost control solenoid, with a new signal wire run back to the aftermarket ECU. This will allow for nice, level boost under full throttle pulls.

Cranking and Running

With everything installed, the vehicle was ready for a safe road tune. After the tune, the car felt great. The current set up makes a respectable 10-11lbs of boost at 6-7k rpm, and an estimated 200-210whp.

​With the modifications already done to the turbo system, the boost levels achieved are about as high as the engine internals can safely handle. It's also right around the sweet spot of where the IHI turbo wants to operate. Beyond that, it can create more boost, but also creates much more heat. This results in no perceivable power gains since tuning must compensate for the extra heat load by reducing timing.

​The performance from this set up is a lot a fun.  200whp in a lighter, older chassis Miata is enough power to put a smile on your face.

Hours:  8AM - 5:30PM Monday through Friday - Weekends by Appointment
 Located on the Highway 29 Frontage Road near the intersection of Highway 29 and Highway 8.