1999-2004 Mustang Intake Manifold Differences

Created by Jay Walling / 7 min read
Date Created: 8/13/2022
Last Updated: 12/9/2022

The 4.6L SOHC engine found in the New Edge Mustang was improved in many areas over previous years. One of these updates included the intake manifold. This article will cover the primary differences between the OEM intake and the popular aftermarket designs.

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History Of The PI Intake

On February 4, 2002, Ford issued a TSB (Technical Service Bulletin) for multiple Ford, Lincoln, and Mercury 4.6L SOHC engine models due to the plastic coolant crossover design on the intake manifold. This plastic construction would develop fatigue cracks and cause coolant seepage over time in the compromised areas. The fix was the same intake manifold but with a revised coolant crossover that was changed from plastic to cast aluminum. This redesign included a revised alternator bracket and the updated intake manifold.

1999-2004 Mustang Intake Manifold Differences  - 1999-2004 Mustang Intake Manifold Differences

Ford vs. Dorman Comparison

We will begin with the Dorman Intake manifold. This intake fits other Ford, Lincoln, and Mercury models and the 1999 to 2004 Mustangs with the PI (which stands for Power Improved) cylinder heads. Dorman supplies an intake manifold with pre-installed individual o-ring-style gaskets, alternator bracket, self-cutting screws, thermostat, thermostat gasket, and other miscellaneous hardware depending on the model of vehicle it's being used for. Some of the fastener locations do not have threaded inserts; this is where you will use the self-cutting screws that Dorman provides in the kit.

The only factory hardware that is re-used is the intake manifold to cylinder bolts, plenum to intake manifold bolts, and alternator bracket bolts. The intake runner design is different, and the manifold chamber is significantly smaller when compared to the Ford manifold. This does change where the engine makes peak horsepower and torque numbers.

Now, we can take a look at the Ford OEM intake manifold. This intake will be the same production intake from 2002 to 2004 Mustangs. No revisions have been made, and all of the factory hardware is reused. The intake that’s branded as Ford Performance is the same intake as the original, it’s just sold under the Ford Performance brand.

You will need to purchase new intake gaskets and a thermostat gasket with this intake, as the only pre-installed gasket is the plenum gasket. This intake will not affect horsepower and torque if you’re replacing an existing Ford PI intake.

1999-2004 Mustang Intake Manifold Differences  - 1999-2004 Mustang Intake Manifold Differences

Ford vs. Dorman Scenarios Pro/Cons

Depending on what intake is on your car or the situation that you’re in, you’ll find yourself needing additional parts. The first scenario you’ll run into is if you’re replacing a Ford intake with a Dorman intake manifold. This is the easiest scenario since Dorman supplies everything you need relative to the intake to install it on the car. The obvious things that you don’t get are supplies and tools.

Scenario number two will be if you are replacing a Dorman intake with a revised Ford PI intake. You’ll need an EGR bracket to intake manifold bolts, coil-on-plug bolts, fuel rail bolts, the alternator bracket, intake manifold gaskets, and thermostat gasket, and only on 1999 to 2001 cars will you need the two thermostat bolts without the studs and the revised alternator bracket designed for the aluminum crossover. The easiest method for the studded bolts is to simply clearance the stud to clear the alternator bracket.

For scenario three, and for some divine miracle, you have a 99 to 01 car, and it still has the intake with the plastic crossover, then you’ll need all of the following mentioned above except for the EGR bracket to intake bolts, coil-on-plug bolts, and fuel rail bolts. Other than what I just talked about, when swapping intake manifolds on a 99 to 04 Mustang GT, it’s important to consider other areas that may also need to be replaced. These include spark plugs, coil-on-plugs, a new thermostat, and heater hoses.

Dyno Comparison Numbers

Alright, so now let’s get to the good stuff! Are there horsepower and torque differences between the two intake manifolds? Well, we are very fortunate to have the best tool in the industry to determine rear wheel horsepower and torque, which is a chassis dyno. The data we will share with you today is from our 2004 Competition Orange GT that has been featured on our channel in a full series titled Keeping Comp. During the restoration process, I put it back on the dyno with the Dorman intake manifold still in place. The car had already had a tune-up, and the check engine light was fixed from the baseline dyno. We had also switched out and added all of the parts associated with the build; that way, we would have an apples-to-apples comparison.

Dyno Technical Data

  • Cold Air Intake
  • Off-Road Mid-Pipe
  • Borla Mufflers
  • Aluminum Driveshaft
  • 3.73 Gears
  • 18x10 Inch SVE Series 2 Wheels
  • 285/35/18 Tires
  • SCT Strategy Tune For 93 octane Fuel
  • The Transmission Is 5-Speed TR3650, And The Pull Was Made In 4th Gear

1999-2004 Mustang Intake Manifold Differences  - 1999-2004 Mustang Intake Manifold Differences

With the Dorman intake, the car made 222.4 HP at 5200 RPM and 266.2 lb-ft of torque at 3500 RPM. We swapped out the intakes and then made another run. With the Ford original intake manifold, the car made 241 HP at 4900 RPM and 274 lb-ft of torque at 4300 RPM. So if we take a closer look at the results between the two manifolds, peak gains were solid at 19 horsepower and 8 lb-ft. More importantly, the curve gains past 3500 RPM were 25+ horsepower and 23 lb-ft of torque. The increase in horsepower and torque is because of the runner design and the larger chamber volume on the Ford original intake. Driving the car around the street, you can feel the difference past 3500 RPM with the Ford intake. And just a friendly reminder, as we can’t stress this enough, individual results will vary!

About the Video

Ford & Dorman PI Intake Manifolds Explained | 1999-2004 4.6L 2V Mustang GT

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Published on 2022-08-12
In this video, Landan explains some important information regarding the Ford OEM and Dorman PI intake manifolds.
Thumbnail image of the author of this article, Jay Walling.

About the Author

Jay has written content for Late Model Restoration for over 10 years, producing over 120 articles. Jay has an extensive 25-plus-year background in automotive and is a certified Ford Technician. Read more...