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4.6L / 5.4L Turbocharging
When it comes to making serious power, nothing beats a turbocharger. Sure, 4.6L superchargers
rule the streets, but the reason for their popularity probably has more to do with the manufacturer’s
ability to certify the supercharger kits than the power potential. Anyone who doubts the power
potential of a well-designed turbo system need only check out the results of the comparison
between the four forms of forced induction (roots blower, twin-screw blower, centrifugal blower, and
turbos) run on the same 4.6L 4-valve ’03 Cobra motor at the same boost level. Though catalogs,
literature, and Web sites offered by some of the less well-informed supercharger manufacturers
may have you believe otherwise, the reality is that no form of mechanically driven supercharger will
produce as much absolute power as a proper turbo system. I remember reading literature supplied
by one centrifugal supercharger manufacturer that indicated that the excessive backpressure
associated with turbos would somehow offset the parasitic losses associated with driving the
supercharger. Real-world, unbiased testing performed for this book (as well as every SAE paper
ever written) has proven that with the exception of the positive displacement blowers run at low
engine speeds, no supercharger can match the absolute or average power production offered by a
turbo system. To think or suggest otherwise amounts to nothing more than marketing hype.
1700 Horsepower Ford 4.6L DOHC twin turbo engine
Topping the list of mod motor
maniacs is Accufab’s John Mihovitz.
This twin-turbo 4.6L 4-valve motor
thumped out over 1,700 hp.
While a huge fan (and student) of all things forced induction, my testing on turbo systems was
somewhat limited until I hooked up with Jimmy and Nathan at HP Performance. Using their 2-valve,
3-valve, and 4-valve 4.6L kits, I was able to directly compare turbo systems versus all three of the
popular supercharger systems. I had never seen a direct comparison of this magnitude using the
four forms of forced induction, so I decided it was high time someone showed the modular world the
benefits (and deficiencies) associated with each system. From the results it is pretty obvious that at
every boost level the turbo system will offer more power per pound of boost than any of the three
forms of supercharging. This takes nothing away from any of the blower kit manufacturers, as
blower sales should continue to skyrocket until someone finds a way to certify a turbo system for a
late-model 4.6L. Even then, superchargers will still offer advantages. The positive-displacement
supercharger will always offer more low-speed power than the turbo, though a turbo system (as
shown in the results in this chapter) will allow the 4-valve-powered Mustang to accelerate through
the 1/4-mile quicker and at a higher trap speed, thanks to the average power production in the rev
range used during acceleration. For some though, the peak and average power numbers are not
as important as the low-speed response.
700 Horsepower Twin Turbo 4.6L Ford engine
This twin-turbo kit from HP
Performance offered an easy 700 hp
and over 700 ft-lbs of torque at just 13
psi of boost.
How does one form of forced induction produce more power than another at the same boost level?
In the case of a turbo versus a supercharger, the vast majority of the power difference comes from
the fact that the crankshaft supplies the drive for the blower. Remember the power gain received by
installing your first set of underdrive pulleys? The underdrive pulleys increase power by reducing
the parasitic losses associated with driving the accessories (water pump, A/C, power steering, and
alternator). Any of the three superchargers will cause more parasitic drive loss than all of your
accessories combined. The worst offender is the Eaton M112 roots blower on the ’03-’04
supercharged Cobra motor. The drive losses associated with spinning the roots blower amounts to
well over 150 hp at an elevated RPM and flow rate. The twin screw requires less power to drive,
ditto for the Vortech, but all three require a significant amount of power to drive the blower. This
parasitic loss is power consumed and not produced by the motor, something the turbo system
avoids by using the heat energy normally expelled through the exhaust. Properly sized, minimal
backpressure is used to generate the equivalent boost pressure (a 1:1 ratio between boost and
exhaust pressure is considered very good).
990 Horsepower 2003 Mustang 4.6L DOHC motor
Replacing the factory Eaton
supercharger on this ’03 Cobra crate
motor with a more efficient twin-turbo
system from HP Performance
eventually resulted in 990 hp. Note the
2001 intake used on the ’03 Cobra
motor in place of the supercharger.
In addition to eliminating parasitic losses, turbochargers usually offer superior efficiency (they are
better able to manage air movement). Compared to a typical roots blower, a properly sized turbo
system will always offer more power per pound of boost. In terms of efficiency, roots blowers rank at
the bottom, while turbos rank at the top. Centrifugal superchargers rank high as well, not surprising
given the fact that they are very similar to the compressor section of a turbo (just mechanically
driven). The twin-screw blower ranks above the roots blower but a tad below a centrifugal. If you
check out the results of the boost comparison, this is basically the finishing order (at least in terms
of maximum power). Of course, the efficiency tells us nothing about the overall power curve offered
by each, as the least-efficient roots blower bettered all three of the other forms of forced induction
in the lower rev range. This low-speed torque production offered by the positive-displacement
supercharger makes for an impressive argument, but the rapid response rate soon gives way to the
efficiency of the turbo. The most telling aspect of the superior efficiency offered by the turbo system
is the fact that the turbocharged motor produced more power than the roots supercharged motor
well before the turbo motor reached the same boost pressure (with as much as 3 to 4 psi less
Turbocharged Ford 4.6L Engine
On an all-out race motor, the exhaust
system is critical. Check out the trick
stainless steel tubular headers,
centrally mounted wastegate flange,
and massive 5-inch exhaust tubing.
Here are a couple more examples of the power potential offered by combining Ford modular motors
with turbocharging. The 4.6L 2-valve motors are usually looked down on by their 4-valve brethren,
but we ran a twin-turbo system (from HP Performance) on a mild 4.6L 2-valve motor that produced
over 700 flywheel hp with just 13 psi of boost. We struggled like hell to exceed 700 hp with any of
the blowers, though I did eventually manage to reach 800 hp with a 2-valve motor using a Vortech
YS-Trim. The 700-hp mark came easy with the turbo kit and had I arranged additional dyno time,
800 hp would have come just as easy with more boost pressure. Things got serious while running
the ’03 Cobra crate motor. Equipped with a small set of Comp cams and an intercooled HP
Performance twin-turbo kit, the low-compression 4.6L 4-valve Cobra motor thumped out an amazing
990 hp and over 900 ft-lbs of torque at 20 psi. We may have reached the flow limit of the 57-mm
turbos, but the power output was impressive nonetheless. The ultimate expression of turbocharged
madness came when I was fortunate enough to be on hand when Accufab’s own John Mihovitz was
on the dyno with his twin-turbo 4.6L race motor. How does over 1,700 hp from just 281 cubic inches
Horsepower Dyno Chart for a twin turbo 4.6L motor Naturally Aspirated vs.
HP Twin-Turbo
NA 2-Valve GT:
347 hp @ 5,900 rpm

W/HP Twin-Turbo (9.8 psi):
613 hp @ 6,000 rpm
Largest Gain: 267 hp @ 5,800 rpm
Early 2-Valve GT: NA vs. HP Performance Twin-Turbo Kit (9.8 psi) (Horsepower)
Turbo motors kick some serious ass. A 600-hp 2-valve 4.6L motor will eat modified 4-valve Cobras
for lunch. This is even Viper-killing power, all from a mild 4.6L equipped with a twin-turbo kit running
less than 10 psi.
Toruqe Dyno Chart for a Ford 4.6L Twin Turbo motor
NA 2-Valve GT:
350 ft-lbs @ 4,200 rpm

W/HP Twin-Turbo (9.8 psi): 604 ft-lbs
@ 4,900 rpm
Largest Gain: 250 ft-lbs @ 4,900 rpm
Early 2-Valve GT: NA vs. HP Performance Twin-Turbo Kit (9.8 psi) (Torque)
The motor produced 600 ft-lbs of torque to match the 600-hp reading. Can you really use 550 ft-lbs
of torque from 3,500 rpm to 5,800 rpm? You bet!
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This has been a sample page from

Building 4.6 / 5.4L Ford Horsepower on the Dyno Building 4.6/5.4L Ford
Horsepower on the Dyno
by Richard Holdener
The 4.6- and 5.4-liter modular Ford engines are finally
catching up with the legendary 5.0L in terms of aftermarket
support and performance parts availability. Having a lot of
parts to choose from is great for the enthusiast, but it can
also make it harder to figure out what parts and modifications
will work best. Building 4.6/5.4L Ford Horsepower on the
Dyno takes the guesswork out of modification and parts
selection by showing you the types of horsepower and torque
gains expected by each modification.

Author Richard Holdener uses over 340 photos and 185
back-to-back dyno graphs to show you which parts increase
horsepower and torque, and which parts don’t deliver on
their promises. Unlike sources that only give you peak
numbers and gains, Building 4.6/5.4L Ford Horsepower on
the Dyno includes complete before-and-after dyno graphs,
so you can see where in the RPM range these parts make
(or lose) the most horsepower and torque. Holdener covers
upgrades for 2-, 3-, and 4-valve modular engines, with
chapters on throttle bodies and inlet elbows, intake
manifolds, cylinder heads, camshafts, nitrous oxide,
supercharging, turbocharging, headers, exhaust systems,
and complete engine buildups.
Click below to view sample pages
Chap. 1 - Throttle Bodies
Chap. 2 - Intake Manifold
Chap. 3 - Cylinder Heads
Chap. 4 - Camshafts
Chap. 5 - Nitrous Oxide
Chap. 6 - SOHC Supercharging
Chap. 7 - DOHC Supercharging
Chap. 8 - Turbocharging
Chap. 9 - Engine Headers
Chap. 10 - 4.6 Engine Buildups
8-1/2 x 11"
208 pgs.
340+ b/w photos
Item # SA115P
Price: $28.95
This is a great book and a
must have for anyone
considering modifying a 4.6 or
5.4 Ford for more power!
Click here to buy now!

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