The late model Mustang that rings a bell in any blue oval enthusiast's mind is the 2003-2004 Mustang Cobra. At 390 horsepower, the supercharged 4.6-liter 4-valve modular engine produced more horsepower than any other previous production Mustang in history. Not only were they fast from the factory, but they also took very well to modifications.

Case in point, our white 2003 Cobra that ran in the 10-second range on all stock internals. The risk of failure comes with any factory engine that you push the envelope with, and that is exactly what happened with our Cobra as it produced more blow-bye than we could handle. Because of this, we yanked the engine out and sent it up the road for an overhaul to the well-known blue oval shop, Ford Performance Solutions.

A Look Back at the SVT Cobra

The Special Vehicles Team (SVT) was established by Ford in 1993 in an effort to offer a higher performance, more limited production of their already famous pony car. The ’93 Cobra was given some subtle aesthetic changes by boasting different wheels, grill, and tail lights to name a few. Engine wise, the Cobra was fitted with better flowing GT40 heads, a Cobra intake manifold, and Crane rocker arms. The SN95s were the first full generation of Cobras, and they came in both early-model 5-liter forms and late-model 4.6-liter modular forms. The overly rare and highly sought after Cobra R was seen as a limited production, upper level Cobra from its Fox-body to its SN95 platforms.

The aforementioned 2003 Cobra was produced for two years beginning in '03, signifying its 10-year SVT heritage by producing an over-the-top 32-valve, supercharged mod motor that made nearly 400 horsepower. Although there were nearly 20,000 Cobras built during those two years, they have maintained a higher value than any other mass produced late-model Mustang due to its brutal horsepower achievements in both stock or modified form.

Ford Performance Solutions Knows Mod Motors - from owner Troy Bowen

“We had been building modular motors since 1995 after the Lincolns came out,” Bowen said. “We bought five of the test motors from Ford and began dissecting them. We then went to Ross to custom make some pistons before anyone else made them. We did CNC work on almost all the heads they had, even the Titan V-10s. We started getting popular with the Cobra heads and working with the guys that were doing forced induction on them.”

Our Tired 4-Valve at FPS

While pumping out over 670 horsepower to the wheels and running mid 10-second passes, the long block was performing unbelievably in pure stock form. While its fair share of fun would be had from this, it eventually went kaput. Detonation mixed with worn piston rings turned this Cobra into a 2-stroke engine, burning as much oil as it did gas. In addition to the worn rings, 4 melted valves and multiple lost valve guides added insult to injury.

The Bottom End

JE-194328 - JE 9.2:1 Pistons

Stock Manley Rods

Stock Crank

1564101 - Pacific Performance Head Stud Kit

1565401 - Pacific Performance Main Stud Kit

The first course of action to remedy the problem was to get the stock engine torn completely down. When Ford made the 4-valve, they opted for an iron block in order to increase strength for the boosted application. “The 2 versus 4-valve blocks are very similar, though the 3-valve blocks are almost their own block and makes part interchanging difficult,” Troy says. The only cleanup needed on the block was a slight .020 over-bore done on the sleeves at FPS. Head bolts were trashed in favor of a Pacific Performance 8740 chrome molly stud cut. For the bottom end, the mains received a similar chrome molly stud kit. The JE 9.2:1 dish pistons are intended for a 3.552 bore. The tops of the pistons have been thermal coated to help prevent further detonation, and the skirts have a dry film lubricant to aid in any oil starvation problems in the cylinders.

Sam sets the ring gap in the cylinders before installing them on the pistons

Hung to the JE pistons are the stock Manley H-beam rods. Ford went with these premium rods in order to ensure years of problem free service, and these were going to be more than adequate for our power needs. The crank is again a reused stock piece that was cleaned and micro polished. With the need to handle a lot more boost through the larger Whipple Charger, the rings were gapped a little looser to accommodate this. Finishing up the short block was a set of OEM main bearings.

Finishing Up The Long Block

Valve Job and Porting done by FPS

F1450P - Ferrea 37mm stainless intake valves

F1451P - Ferrea 30mm stainless exhaust valves

26123 - Comp Cams beehive valve springs - 324 lb/in Rate

798-32 - Comp Cams titanium retainers

106360 - XE266BH-116 Comp Cams modular camshafts

14122 - Aeromotive fuel rail kit

W200AX - 3.3-Liter Whipple Charger

Again, as with the block, the heads were torn down to bare castings. The first action was to weld up and repair the melted chambers. From there it was time for some machining, starting with a valve job to accommodate the over-sized heads that were going to be installed. The final machine that the heads made their way to was the CNC. Both the intake and exhaust ports got a moderate porting job to help flow the larger amounts of air being crammed into and out of the cylinders. The stock intake ports originally flowed at 238 CFM at .800 and now flow at 293 CFM. The exhaust ports increased even more with 165 CFM at .600 stock and then 253 CFM ported. “The 2-valves are very limited in the short turn areas of the head,” Troy stated. “The low floor as it rolls into the port is flat, and goes right down into the valve seat. The 4-valve has so much more area, it is just like a pocket of valves. We have picked up over 100 more CFM in porting. We have got them up to 325 CFM on the intake port. The 4-valve 5.4-liter GT heads are even nicer, as they raised for floor to help out with the short turn.”

The rockers was the only reused valvetrain part.

Assembling the heads started with new bronze valve guides affixed around Ferrea .5mm over-sized intake and exhaust valves. We settled on 37mm on the intake and 30mm on the exhaust side. Controlling the valve movement was a set of Comp Cams beehive valve springs. These springs are good up to a .500 inch lift cam that do not require any machine work to fit. The valve springs were held in place with Comp Cams Titanium retainers. The titanium versions are lighter than the stock stainless retainers and are also heat treated to increase strength to the 6AL4V alloy. Complimenting our rigid valve train was a set of Comp Cams 4-valve camshafts. The cams we selected are better suited for a supercharged street car like our Cobra, while also having favorable attributes for the strip. It carries a 230/232 duration at .050 and valve lift of .475/.45. The only part of the valve train we retained from the stock pieces were the rockers.

It was time to sandwich the heads and block together with our Cometic MLS head gaskets. Also, by using the ARP head studs over the stock bolts, we didn’t need to stretch the bolts aside from any incremental torquing. Next, it was time to move to the timing chains since this was a DOHC engine. It's important to make sure you TDC the engine and mark the chains so they are in the right place. Being off even just one tooth on your chain can result in a bent valve.

With the engine flipped on its head, Sam installed our new Canton Racing Products 7-quart oil pan. The pan allows us to keep the engine temperature lower while keeping the oil close to the pick up with the anti-slosh baffle. There is also a 1/2” NPT hole in the pan for adding an oil temperature gauge down the road.

For increased induction, we had to start with the additional fueling needed. The new 72 lb injectors were secured by Aeromotive’s new fuel rail kit that was designed specifically for the 4-valve powerplant. Aeromotive includes all the lines and fittings you need, even a convenient adaptor piece that will utilize the factory fuel pressure sensor. To aid in the Cobra’s previous power, the blower was already upgraded to a 2.3-liter Whipple Charger that saw over 20 psi. But in an effort to cram even more boost into the motor, we upgraded the blower to Whipple’s 3.3-liter version that can produce up to 30 psi, which is approximately the same power as the 2.3-liter, but on less boost.

Tips to Making a Powerful Cobra Engine Street Worthy - By Troy Bowen

“First off, put good pistons and good rings in it,” Troy said. “Next, address the head and intake flow. Make sure good port work is done to the intake. Once the port is cleaned up and working right, it will help with the combustion problems.

“Tuning is very critical on a modular motor,” Troy continued. “They are very quick to detonate and you need to make sure that the timing and fuel curves are on key. The way the fuel enters the chamber, it doesn’t have a lot of swirl. The fuel wants to throw fuel across the valve over to the far side of the exhaust. What happens is you have a denser fuel charge by the exhaust, so it burns from the intake to the exhaust side, so they have a hot spot on the far side of the piston. Some shops will start with a centrifugal map in the ECU when tuning a roots style modular motor, and they end up killing the motor. Since the Whipples are positive displacement, they are already making boost at 2000 rpm. You have to immediately pull the timing out of them due to this.”

Eagerly Waiting the Installation

While we can’t complain that we got over 11,000 highly abused miles that included over 40 runs at the track with it, it was inevitable that the stock engine was going to slowly pass away. Ford Performance Solutions was our only choice when it came to building our fresh 4-valve that we hope will produce an additional 200 horsepower to the wheels. Troy and the team assembled the engine with all of our quality goodies, and soon we will be putting the 4.6-liter back into the Cobra for some tire roasting fun.


Ford Performance Solutions


Contact: (714) 870-7935

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