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For all your Ford V8 Miata Needs!

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This is our second build, a 1993 LE which has been converted into a V8 Miata for a customer. The chassis stated out as a rather worn 1993 Miata LE that the customer found in Washington D.C. The car had 170,000 hard miles on it at the time of the conversion and had lost most of it's "special" LE accessories by the time it arrived in our shop. The chassis itself, however was rather rust-free and did not seem to have sustained and serious body damage during the 15 years since it left the factory in Hiroshima.

The first step, as always, was to remove all the Miata drive line parts and modify the firewall and engine bay to receive the 5.0. The removal process is pretty dirty and typical so we'll start off with the modified engine bay ready to receive the mighty MRM5.0 engine:

The "ears" at the back of the firewall were removed and sealed and the firewall "massaged" back about 1/2 inches with a large sledge hammer. This allows for retention of the Ford air injection system tube, part of the smog system.

The front subfame had to be modified by Martin Wilson of Monster Miata, Inc. to mount the larger engine. Here is the subframe rebuilt with the control arms reattached and ready to go in. The customer has chosen to have Shaikh of Fat Cat Motorsports create a custom Bilstien coil-over suspension for the car. The two front units are shown installed.

The engine that this car received is a Ford 5.0 originally pulled from a 1991 Mustang and extensively reworked by Tom McCully, the engine "guru" of McCully Racing Motors. The block has been completely blueprinted, bored out to 306 c.i. and honed. All push-in oil gallery caps were replaced with tapped plugs to prevent accidental leakage. The stock cam was replaced with a Ford Racing E303 and the valve train upgraded with stiffer springs to reduce valve float about 6000 rpm's. The stock iron E7 heads were extensively worked on by Tom to get them to flow reportedly almost as well as Ford GT-40's would flow from the factory.

Here it is going in:

And here it is in it's new home:

Here's the intake on and about 70% of the wiring done:

Having learned from our first build we've started including some upgrades in this build that were necessitated by the need to make things (a) easier to build, (b) more simple to build/maintain, (c) more effective or closer to how Ford intended, or (d) the fact that this chassis, being an LE has far more systems than your standard 1990-93 Miata. This first picture is an example of (a) and (b):

1991 Mustangs came equipped with a G2 alternator, as our first build was equipped with. While fine, the electric cooling fans used in a V8 conversion have a tendency to over-tax it a bit. We found on the test chassis that at night in the rain the cooling fans, lights and wipers would significantly drain the car's charging ability. In addition, the connections on the G2 were such that a large-gauge wire plug had to be almost welded to the Miata source wire to make the whole system work. The G2 also had a large external cooling fan that had a tendency to get a little too close to the upper radiator hose at times. On this build we chose to use an upgraded G3 alternator as would be found on a later model Ford Taurus. This unit almost bolted right in, uses the same belt, almost uses the exact same connections the Miata already has and, because Taurus' have electric cooling fans and quite a few accessories, will be able to more than handle the load of a V8 Miata.

Another area of improvement we saw with the test chassis was the accuracy of the oil pressure and water temperature gauges after the conversion. In the first build we used the Ford senders and wired resistors in line to try to make them accurately operate the Mazda gauges. On this build we simply extended the Mazda sender wires to the Ford sender locations and then used pipe fittings of different sizes to install the original Mazda senders in the Ford block. This should make the gauges just as reliable as they were before the conversion and should one fail it can be replaced with a standard Mazda part.

Because the customer is intending on using this car primarily as a track car he opted to leave off the AC compressor. On our test build we eventually did the same thing, and ended up replacing it with a delete pulley that allowed the retention of the late-model Ford counter-clockwise waterpump. This however became a continued struggle to make that delete pulley stable enough so that it would not cause belt wear. That, coupled with the fact that redundant pulleys and longer-than-needed belts eat horsepower made us want to find a better solution this time around. We found it in the use of a early Ford clockwise waterpump and much shorter belt. Added bonus: the clockwise waterpump and belt together are cheaper than buying a delete pulley!!!
Note, the smaller belt you see behind the main bet is the Power steering belt running the Mazda pump off of a second pulley that a friend of ours, Tony Laboy, welded onto the back of the Ford crank pulley. Thanks Tony!

One of the last major "LE issues" we had to attack was the retention of the ABS system. Building a V8 conversion requires upgrading the rear axles and hubs with hybrid Thunderbird parts which removes the stock location of the rear ABS sensors. or solution was to move the sensors inboard from the hubs (as a Miata is designed) to the differential using the Thunderbird exciter rings and some simple fabricated brackets.

The brackets:

The sensors attached to the brackets and the Thunderbird exciter rings in place:

One of the last steps will be to bleed the new 1994-97 spec Miata brakes. The fronts are larger rotors, hangers, calipers and pads, the rears only require rotors, hangers and pads to upgrade. Black car, red brakes looks pretty good...

Because the customer is planning on using this car primarily as a track vehicle we decided that an upgrade of the standard Mustang fuel rail and return system was in order. The customer decided upon a BBK billet fuel rail that we then upgraded by replacing the rubber lines that came with it with braided steel line and AN-type fittings. The crossover we fabricated out of stainless steel fuel line. The fuel system was further upgraded with the addition of Bosch "design 3" injectors, as would be found on a late '90's Ford Explorer. Currently the customer is running a stock fuel pressure regulator although it could easily be upgraded to an adjustable type should he decide to run larger injectors at some point. Here are some pics of the fuel system with he upper manifold off the engine:

At this point things were really starting to come together. The pic below was taken the last day of the build, all that is left to be done at this point is bleed the brakes and clutch and throw the wheels on:

Here's a good view from above showing how the major systems of a Ford Mustang fit very well into the engine bay of a Miata:

And now finally some pics of the car done and cleaned up:

From the side:

From the rear showing the exhaust:

With the hood down:

And what lies under that hood:

Thanks for following along with us here at McCully Racing Motors as we converted what was an unsuspecting '93 LE into the menacing road machine it now is. Still to be done is work out a few minor kinks and add a Boss Frog double hoop roll bar. An actual "factory" front air dam will be added as well once Mazda Parts figures out how to get their supply chain up and running again. Stay tuned because as soon as this car gets turned over to the customer we start on build number three, a pristine white 1990. This time we have another balance and blueprinted MRM Ford 5.0 ready to go in although this time with a full set of worked GT-40 heads and intake. Here it is eagerly awaiting it's new driveline...110 horse power no more!

-Jason McCully, McCully Racing Motors