4.6L 2V Hybrid Horsepower

Words And Photos: Richard Holdener

Magnum PI. For the skinny jean crowd out there, the name is synonymous all that was cool in the 80s. Put down the e-cig and web search Ferrari 308 GTSi or world’s most amazing mustache, and you will come to better understand the true definition. Once enlightened, you will immediately recognize that we have taken grand liberties with its use as applied to the lowly two-valve, Modular Ford motor; but the power gains offered by this exercise were at least Magnum in scale. Given the choice between power sliding around paradise in a prancing horse or medaling with a mod motor, we’d join Rick and TC every time, but not all of us have a Robin’s Nest we can call home, let alone a rich benefactor. For us everyday Mustang folk, mods to our PI mod motors are about as close as we will ever get to Magnum status. Not to worry, these upgrades will make any 2V stallion show taillights to the famous prancing pony, even with mega mustache behind the wheel.

Introduced in the Mustang in 1996, the 4.6L two-valve mod motor replaced the legendary fuel-injected 5.0L. The new modular motor was supposed to make up for the lack of displacement with technology, namely a set of whazoo overhead cams. While this cam positioning suggested added rpm potential compared to the traditional cam-in-block position, the two-valve was anything but a high-rpm terror. Even the double throw-down, four-valve Cobra motor made peak power below 6,000 rpm. The initial two-valve offerings were rated at just 215 hp, which rose to 225 hp by 1998 before Ford stepped up to the revised 260-hp, Power Improved (PI) motor. Though ported heads and a cam upgrade can be applied to either motor, the most successful combination is to install the ported PI heads on the earlier, non-PI short block. The non-PI motors combined small-dish pistons with larger combustion chambers, while the PI motors reversed this situation with small chamber heads and larger dish pistons. The best combo is to install the small-chamber PI heads (which also flow better) on the small-dish, non-PI short block. 

To illustrate the power gains offered by this package, we purchased a 1996 non-PI 4.6L motor from the local wrecking yard. These motors are plentiful and were also available in 4.6L trucks, but with a different intake manifold. Our plan was to take the high-mileage, non-PI, 4.6L 2V motor and upgrade the heads, camshafts, and intake. Though PI components already make a nice upgrade to the non-PI short block, we took things one step further, but using ported heads and a pair of COMP camshafts. Use of the PI heads required the matching PI intake, which is a good upgrade over the longer-runner, non-PI intake. Before replacing all the stock components, we ran the 1996 4.6L on the dyno to establish a baseline. The mod motor was run with a Meziere electric water pump, a set of Hooker headers, and FAST XFI/XIM management system. Also present was a set of FAST 36-pound injectors and fresh Lucas synthetic oil. Run in this configuration, the non-PI motor produced 259 hp at just 4,700 rpm and 339 lb-ft of torque at 3,400 rpm. Oddly enough, this 4.6L did indeed offer more torque through most of the rev range a stock 5.0L tested under the same conditions-maybe overhead cams really do work!

With our baseline set, off came the stock non-PI heads, intake, and cams to make way for the upgrades. First on the list were the PI heads. We sent our PI heads out to the flow experts at Total Engine Airflow (TEA). Though Trick Flow Specialties now offer the only after market set of 2V heads, we opted to simply port the PI heads and call it good on this one. The porting from TEA increased the flow rate substantially, from 174 cfm to 226 cfm, while the exhaust increased from 125 cfm to 209 cfm. Working in conjunction with the ported heads was a pair of COMP XE270AH cams. Middle of the three Xtreme Energy shelf camshafts available for the PI motors, the 270 camshafts offered .550-lift (both intake and exhaust), a 234/238-degree duration split and 113-degree LSA. The final modification included the factory PI intake manifold topped with an Accufab 75mm throttle body and intake elbow. Like the heads, the PI intake was a performance upgrade over the earlier, non-PI version.

Many enthusiasts shy away from the Ford mod motors because they fear the overhead cam design. Fear not, as cam swaps on this motor are no more difficult than on a conventional small-block Ford. Put the motor at TDC, line up to the timing marks on the crank and cam sprockets with those on the chains and you are off and running. After bolting the ported heads on using Fel-Pro gaskets and ARP head studs, we had the PI/non-PI hybrid motor up and running in no time. After tuning the FAST 36-pound injectors with the XFI management system, we were rewarded with a Magnum-sized increase in power. Equipped with the new PI components and COMP camshafts, the 4.6L hybrid motor produced 407 hp at 6,100 rpm and 393 lb-ft of torque at 4,900 rpm. The new combo offered all the low-speed torque of the stock non-PI motor with a radical new top-end charge that would suck the headlights out of any PI-driven Ferrari. Never known for their torque, the 4.6L exceeded 350 lb-ft from 3,700 rpm to 6,100 rpm. Combine this power potential with cost and availability and this modified two-valve motor might just qualify as a Magnum PI after all.

The graph illustrates that there was plenty of power hiding in the little two-valve Ford motor. Despite the high-rpm promise of the OHC design, these early non-PI motors were tuned for torque. In stock trim (with headers), the 1996 non-PI motor produced 259 hp and 339 lb-ft of torque. Peak power occurred at just 4,700 rpm-not exactly what you would call rev happy. After upgrading to COMP 270 cams, ported PI heads and the matching PI intake, the hybrid 4.6L produced 407 hp at 6,100 rpm and 393 lb-ft of torque at 4,900 rpm. What Mustang owner would want an extra 140 hp?

Sources

Accufab
accufabracing.com

COMP Cams
compcams.com

FAST
fuelairspark.com

Holley/Hooker
holley.com

Lucas Oil
lucasoil.com

Total Engine Airflow
totalengineairflow.com