Part Three: Better Intake Manifolds
3. While you might expect the slightly wilder cam timing to trade low-speed power compared to the stock combination, our top-end mods improved power everywhere, from 3,000 rpm all the way through 6,200 rpm. Had we elected to tug the new combo down to 2,500 rpm during the test, it would have been better there as well. The peak numbers improved dramatically, from 268 hp and 318 lb-ft to 405 hp and 393 lb-ft. The engine speeds for these peak numbers rose as well. Where the previous combination produced peak power at just 5,100 rpm and peak torque at 3,600 rpm, the new combo produced peak power at 6,000 rpm and peak torque at 4,900 rpm. Measured peak to peak, the power improved by 137 hp and 75 lb-ft, but elsewhere along the curve the gains exceeded 150 hp and 130 lb-ft of torque.
Use of the PI heads required a matching PI intake manifold. The PI intake was topped with
Changing the big three resulted in significant power gains. The modifications increased th
Rather than running the PI intake from the Mustang, it is possible to top the 4.6L with th
It should be noted that it is possible to further enhance low-speed (below 4,000 rpm) torque by replacing the composite Mustang PI intake with the aluminum truck version. This will improve the torque production by 15-20 lb-ft below 4,000 rpm, but the tradeoff will be a loss in power from 4,000 rpm to 6,000 rpm (25-30 hp). If sub-4,000 rpm is most important for your application, you would be best served by dropping down in cam profile to the XE262AH profiles to better match the truck intake. The trick divided plenum in the truck intake greatly improves power between 2,500 rpm and 3,000 rpm using Helmholtz resonance tuning, something not available in the Mustang version. Of course you are now free to toss in a stroker short block under the combo or add nitrous or forced induction, but that is a test for another day.
2. The truck intake also features a unique divided plenum. The plenum volume has a definit
3. A servo-activated divider is used to separate or join the plenum volumes. This activati
1. The difference in height between the truck and PI intake is visible in this photo. The
4. Use of the truck intake will improve power production up to 4,000 rpm. Unfortunately, t
The Final Word
The dyno results reveal that there is plenty of power to be had even with nothing more exotic than a stock, high-mileage short block. Topping the stock non-PI short block with ported PI heads, a set of aggressive but streetable Comp Xtreme Energy cams, and a PI intake manifold, improved power production by as much as 140 hp. Obviously it would be better to start this buildup with a fresh short block, but if money is tight (isn’t it always?), then adding the right top-end package to your 4.6L or 5.4L mod motor can offer huge dividends.
Stock Vs Big Three ’98 4.6L 2V Ford
It is immediately obvious from the power curves offered by the stock ’98 4.6L two-valve motor that Ford was not concerned much about high-rpm power. Run with no accessories, long-tube headers and a FAST XFI management system, the wrecking yard wonder produced just 268 hp, though a fairly impressive 322 lb-ft of torque. Credit the long-runner intake, small intake ports and mild cam timing of the early non-PI motor for its torque nature. Replacing the big three performance components (heads, cams and intake) resulted in a sizable jump in power. Adding the ported PI heads (which also increased the static compression), the wilder (but still streetable) Xtreme Energy cams and matching PI intake manifold improved the peak power numbers to 405 hp and 393 lb-ft of torque. Despite the more aggressive cam timing, the top-end package improved the power output from as low as 3,000 rpm (even lower had we lugged the new combo down at 2,500 rpm) out past 6,000 rpm. This is a combination that will start by feeling pretty good when you put your foot down and then proceed to feel really good as the engine speed increases.