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by Jon Mikelonis

1983-1988 Thunderbirds provide a nice platform for Ford enthusiasts looking outside the brutalized Fox Mustang market or pricey musclecar arena. For those not willing to deal with the collectible Turbo 4-cylinder found in the TurboCoupe, quite a number of these birds came equipped with the 5.0L powerplant. Combine the 83-88 T-bird's Fox platform with a 5.0L and you can have a unique, modern, and unsuspecting piece of FordMuscle. Keep a sharper eye out for a 5.0L conversion and you can even find a TurboCoupe that has been "improved" with a 5.0L, this way you can have all the fun of a 5-Speed, snappy TurboCoupe suspension, and access to all the easy power upgrades associated with the 5.0L. That's what the guys at FordMuscle found in the 1985 Thunderbird TurboCoupe pictured above.

For all intents and purposes, our 1985 Thunderbird was equivalent to a Fox Mustang with a Mass Air 5.0L. The previous owner had done the right thing by transplanting an HO motor from a "California" 1988 Mustang GT. Very little had been done to the motor other than the addition of a Ford Motorsport E303 cam when we purchased the car in November 2008 for $1800.00. The previous owner did a commendable job transplanting the 5.0L into the original 4 cyl. Thunderbird. All the sensors and wiring were installed properly, usually on these transplants you find omitted and cobbled together harnesses. In fact, this conversion even passed California's rigorous Bureau of Automotive Repair inspection. All these factors led to a confident decision at purchase.

Baseline Dyno Pull
It didn't take long before we were eager to upgrade the nearly stock 5.0L with heads, intake, throttle body, and headers. Even before making new component decisions, we got the Thunderbird on a dyno to establish a baseline.

Here's the Thunderbird getting hooked up the rollers.
The Ford 5.0L H.O. powerplant is incredibly predictable. We guessed 210 horsepower and 250 ft. lbs. of torque. The final numbers were 207/245.

Top End Component Selection and Installation
We've played around with all sorts of 5.0L cylinder head, intake and cam combos. You can peruse the FordMuscle Tech and Project car archives to see what has worked well and what hasn't. In our opinion there isn't a better bang for buck than the Holley Systemax II kit. It's a complete kit - heads, intake, cam, timing chain, pushrods, headbolts and other associated parts. You can also round it out with a Holley throttle body and fuel pressure regulator as we did in this project. The kit is fairly plug and play, though there are a few things to content with, such as valve cover clearancing as you'll read below. The Systemax kit makes great power though, and that is the goal.

Not many readers will realize the extra effort involved in making a well-documented "magazine" article. If you aspire to submit a tech article to us two tips: use a tripod and photograph every step.
Many first timers are overwhelmed by the apparent complexity of an EFI motor. There is no reason to be, the 5.0L powerplant is well designed - all the connectors are uniquely shaped, it is difficult to screw up. Alleviate your concerns by taking detailed pictures and using masking tape to note the placement of wiring and odd fasteners.

An extra set of hands, plus the additional brain power, makes for quick tear down. Here Jon drains the cooling system while Chirag removes the upper intake manifold.
After disconnecting the fuel rails using a fuel line disconnect tool we can remove the lower intake manifold bolts and proceed with pulling the lower off the block.

It's best to remove the lower manifold with the fuel rails, injectors and heater core tubes still attached. We'll transfer these over to the Systemax manifold at a later step.
In line with unwritten rules of wrenching - he who own the car does the dirty work. Therefore Jon got to lay on the cold concrete and tackle the h-pipe and header removal.

The factory 5.0L headers are a nice change from the old cast iron logs of yesteryear - but they still suck. We're tossing these for a set of true shorty headers.
With the manifolds, headers and valvecovers removed we're able to access the headbolts. We're not bothering with removing the stock rocker arms beforehand. They'll simply lift-off with the cylinder head.

Five hours into wrenching comes the removal of the first 50lb. cylinder head. By this time your back is sore and the floor is coated with antifreeze. Needless to say a little caution is warranted.
Anyone who has performed a head swap before will agree this image is a project milestone. You've got everything removed down to the shortblock. Now it's a matter of cleaning up and reversing the steps.

The Systemax package comes with a decent Lunati camshaft (PN: 51027. 221/223 duration and 0.509" lift), however we opted to stick with our Ford Motorsport E303 camshaft (220/220 and 0.498" lift.) The Lunati would admittedly squeak out a bit more power, but we the specs were close enough to convince us not to spend the extra time pulling the timing cover.
Since the Systemax heads have large 2.02" intake valves it is advised to check for piston-to-valve clearance if you are using stock pistons.

Checking for "p to v" clearance is simply a matter of installing a used (compressed) head gasket, the head, and one set of pushrods, rockers and lightweight checking springs. The head need not be torqued down, just snug it with a couple head bolts.
Then we rotate the crank by hand and measure for at least .080" clearance on the intake side. It helps to have a second set of hands here. One person slowly rotates while the other pushes the valve open (easy to do with the lightweight checking springs.)

With our E303 cam and the 2.02" intake valves we measured about .040" clearance. Not quite enough, so we broke out the Isky cutting tool and put nothces in. It is time-consuming, but once you get going the piston cutting is easy work and not as damaging as it sounds. We spin the drill slow and listen carefully - the pitch changes noticeable when you've cut enough of a notch.
The end result is surprisingly pro looking. The 2.02" valve simply needs more clearance around the edges of the stock valve relief. About 30 seconds of cutting is all that is needed to yield nearly .150" of clearance - plenty of room for even a future cam upgrade.

With Jon cutting pistons and vacuuming the resulting shavings, Chirag turns his attention to prepping the new manifolds. The Sytemax kit instructions spell out what needs to be done - here I am knocking in the oil baffles.
We'll reuse all the sensors, fittings and PCV components from the stock manifold. From left to right we have the ECT (engine coolant temp) sensor; PCV valve, grommet and trap; IAT (intake air temp) sensor; and temp gauge sending unit.

Whenever you step up the heads or cam on a 5.0L engine you'll need to be able to adjust the fuel pressure. This requires an adjustable fuel pressure regulator. We're using a Holley unit.
Three allen bolts later we've replaced the factory fuel pressure regulator with an adjustable type from Holley. This will allow us to dial-in the appropriate pressure for the new fuel injectors.

Prepping the fuel rail continues with swapping the old 19lb. injectors with new Accel 24lb. units. The increase in fuel flow is required for our new power output levels. A dab of Vaseline on the o-rings and the injectors pop right into the fuel rail.
Here the fuel rail and injectors are set into place on the Holley Systemax lower manifold.

Attention now turns to assembly of the upper intake manifold. We're going to use Holley's 70mm throttle body.
Swap over the throttle position sensor, EGR and intake air solenoid from the stock throttle body and upper intake.

(Installation Continued and "After" Dyno Pull)

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In This Article...
FordMuscle's project Thunderbird gets its first major power additions. The transplanted stock 5.0L engine is getting a new top end in the way of a Holley Systemax head, intake and cam kit.

Holley SysteMAX II Engine Kit for Ford 5.0L (PN 300-501)

Find out more at Holley:

ACCEL 24lb Fuel Injectors
(PN 150824)
24 lbs/hr Static flow rating. New low-mass disc design ensures accurate metering control even at ultra-low and high duty cycles. This process ensures accuracy of 1-1.5%. Operates at higher fuel pressures without loss of metering control.

State-of-the-art manufacturing processes reduce flow deviations between injectors to improve performance. Low- and High-impedance designs available to match most commercial applications. Provides precise control of fuel delivery and atomization for increased power, improved throttle response and better fuel economy.

Find out more at ACCEL:


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