Ford Mustang 5.0L Engine Horsepower Modifications

The stock E7TE heads had been previously modified to accept screw-in rocker studs. The heads were run with 1.6-ratio, guided roller rockers.

We dusted off a production 5.0L H.O. intake and stock throttle body. The ProM MAF was used as a simple radiused air entry since the motors were tuned using a FAST XFI management system. With boost in the cards, we replaced the stock 19-lb/hr injectors with a set flowing 36-lb/hr units from FAST. The stock fuel rail was used for all testing, including with the turbo motor.

Run in stock trim, the 5.0L produced 252 hp at 5,100 rpm and 306 lb-ft at 3,330 rpm. The first performance modification was to replace the shorty headers with a set of long-tube Super Comp headers from Hooker. The long-tubes improved output from 252 hp and 306 lb-ft of torque to 261 hp and 321 lb-ft. Gains offered by the Hooker Super Comp headers were as great as 25 lb-ft.

RHS CNC Ford Heads: 354 hp at 5,500 rpm, 378 lb-ft at 4,300 rpm
Having already replaced the upper and lower intake and camshaft, the next item on the to-do list was a head swap. We chose a set from Racing Head Service. The Elite CNC heads offered everything the stock heads couldn't, including aluminum construction to reduce weight and massive flow numbers that (according to RHS literature) exceeded 300 cfm at 0.700 lift. Basically the flow rate of these RHS heads was nearly double that of the stockers. The RHS heads were outfitted with valvesprings suitable for our XE274HR cam, meaning they had both sufficient seat and open pressure, not to mention clearance for coil bind. We also took the liberty of checking retainer-to-seal clearance, but we had over 0.150 before contact. The one possible downside to the ported RHS heads was that the combustion chambers were slightly larger than the stock heads (65 cc vs 61 cc)

Holley Systemax Intake: 395 hp at 6,200 rpm, 380 lb-ft at 5,000 rpm
While we had previously replaced the factory H.O. intake with the performance-oriented GT-40, we suspected the GT-40 was now limiting our combination. Leafing through the list of available upper and lower intakes for the 5.0L, we selected the Holley SysteMax combo. Though impressive in as-cast trim, we sent ours out to the good folks at Extrude Hone in Paramount, California, for some magic putty porting. The results were impressive, as the ported SysteMax intake and matching 75mm Holley throttle body improved the power output of the 302 combination dramatically. Where the previous combo with the GT-40 intake produced 354 hp and 378 lb-ft, the Holley manifold upped the peak numbers to 394 hp and 380 lb-ft of torque. The majority of the power gains came past 4,700 rpm, as the GT-40 offered more torque below that point.

Zex Wet EFI Kit (100 hp): 506 hp at 5,600 rpm, 547 lb-ft at 4,700 rpm
This is where the power gains started really getting serious. Nothing adds power as easily and inexpensively as nitrous oxide. Literally at the push of a button, it's possible to add 100 hp or more to just about any combination. For our test motor, we ran 100hp jetting in the Zex Wet EFI kit. The wet kit combined the nitrous and fuel into a single fogger, which we mounted in our air intake in front of the Holley throttle body. The Zex kit included everything needed to add as much as 125 hp to our injected 5.0L (more with optional jetting). The kit is unique in that it features an optional controller that is capable of learning the TPS voltage to ensure the system can't be activated unless the motor is running at wide open throttle. This is a nice safety feature, although it doesn't prevent the user from engaging the nitrous too early in the rpm range (something that will create havoc).

HP Performance Turbo Kit: 622 hp at 5,800 rpm, 637 lb-ft at 4,700 rpm
The final modification applied to the 5.0L was a single-turbo kit from HP Performance in Roswell, New Mexico. The kit featured a 67mm turbo, an air-to-air intercooler, and 44mm wastegate. All of the exhaust tubing featured Jet Hot-coated to maximize heat energy to the turbo, while the intercooler was sized for maximum heat rejection. Look for this kit combined with a larger turbo on a 400-plus-inch stroker in the near future, but we have successfully run the system at over 1,000 hp, so it was more than sufficient for our mildly modified 302. Use of the nitrous and turbo kit is why we installed the forged crank, rods and pistons. The kit taxed the 36-lb/hr injectors on this application, so we manually raised the fuel pressure on the boost-referenced regulator to 60 psi (from 43 psi in NA trim). This provided plenty of fuel to keep the air/fuel mixture safely at 11.5:1.

Next we replaced the factory intake with a FRPP GT-40. The GT-40 was run with an AccuFab 65mm throttle body, which was worth a few extra horsepower.

The GT-40 induction improved the power output from 261 hp and 321 lb-ft to 280 hp and 326 lb-ft. The gains were significant above 3,700 rpm, though the GT-40 lost out to the stock intake below 3,200 rpm.

Knowing the stock heads are restrictive, we replaced them with a set of RHP Pro Elite heads. The RHS heads offer aluminum construction, CNC-porting, and a host of other features.

We selected the smaller 205cc Pro Elite heads. According to RHS, the 205cc intake ports flowed nearly 300 cfm-roughly double that of the stock heads....

....The RHS Pro Elite heads featured a 2.05/1.60 valve package and 65cc (measured) combustion chambers. Compared to the stock heads (61cc), this dropped the static compression by roughly 0.4 points.

The Pro Elite heads were run with 1.6-ratio, aluminum roller rockers from Comp. After re-installing the GT-40 intake on the RHS heads, we were rewarded with peak numbers of 354 hp and 378 lb-ft of torque, gains of 40 hp and 30 lb-ft over the stock heads (measured peak to peak).

Thinking the GT-40 was holding back our combination, we replaced it with a Holley SysteMax. Run with the SysteMax upper and lower, and matching 75mm Holley throttle body (shown with turbo combination),....

....the normally aspirated 302 produced 394 hp and 380 lb-ft of torque. The ported Holley SysteMax lost out to the GT-40 below 4,700 rpm, but offered over 50 hp past 6,000 rpm.

The Zex Wet EFI nitrous kit features a single fogger nozzle to combine fuel and nitrous. We mounted the nozzle in a radiused air horn in front of the throttle body.

Engaging the nitrous all but transformed our 302 into a stroker 408, as the chemical warfare upped the peak power numbers to 506 hp and 547 lb-ft.

The final modification involved the installation of a single-turbo kit from HP Performance. The kit featured an air-to-air intercooler, Tial wastegate, and this 67mm turbo capable of easily exceeding the power limitations of our production 302 block.

The final modification involved the installation of a single-turbo kit from HP Performance. The kit featured an air-to-air intercooler, Tial wastegate, and this 67mm turbo capable of easily exceeding the power limitations of our production 302 block.