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5.0 Mustang Intake Manifolds - Tech Stroker K.O. Punch
Testing A Real Heavyweight: The TFS Box R Intake
Grab any issue of MM&FF and read through the ads to see how many intake manifolds are currently available for the long-since-dead 5.0L Mustang. Don't get me wrong-the first car I ever purchased was an '88 5.0 Mustang LX, and if things go as planned, my new son will be driving it as soon as he gets his license. Despite the absence of the car that started an industry, manufacturers continue to not only sell products for the 5.0, but also design new ones. At last count, there were about a zillion intake manifolds for the 5.0, but how many are there for the larger 351W-based motors?
While the 5.0 Mustang was born with a 302 under the hood, a great many owners have discovered the tremendous power offered by a substantial increase in displacement. In addition to the often-discussed peak power numbers, the benefit of a stroker combination is the impressive average power gain. Stick your foot in the throttle of a stroker and you are immediately rewarded with a surge of power.
While the 5.0 motor is the basis for a great many buildups, the basic architecture is somewhat limited in terms of displacement potential. The limiting factor is based around the relatively short deck height. Physically, there just isn't enough room to substantially increase the stroke and provide enough room for a reasonable connecting rod length and compression height for the pistons (for proper crown strength). Combine this with a cylinder wall thickness that usually only (safely) accepts a 0.030-inch overbore and you have dramatically limited the possible displacement. A production 302 can be bored and stroked to produce as much as 355 inches, but most stick with 347 inches.
Small-block Ford owners looking for additional cubes are required to step up to the larger 351 Windsor block. With the taller deck height (the measurement from the crankshaft centerline to the block's deck), the 351W can easily achieve displacements topping the 400-inch mark, the most common (for a production block) being 408 inches. Where the power gains offered by a 347 stroker will be noticeable, those from a 408 will be noticeable. To put this into perspective, a 347 will generally produce an additional 45 hp over the 302, but a 408 will offer 106 hp (given the same specific output). In addition to the improved power output, the 408 will also likely offer an additional 100 lb-ft of torque (everywhere).
But it's not all gravy, as there are problems associated with the larger-displacement motor. One area that needs to be addressed is the induction system. We mentioned that intake manifolds abound for the 5.0, but pickings are considerably slimmer for the larger 351W motor. No serious enthusiasts in their right minds would think about running a factory 351W truck intake on a performance stroker, so it's off to the aftermarket for a decent performance manifold. Not only does a manifold need to fit the taller-deck 351W, but it must offer enough flow to support the power needs of a larger stroker version. After all, a 408 stroker's airflow needs are different from that of a standard 351. Restricting the breathing of a stroker motor is like not having the displacement in the first place. Properly topping a stroker motor will result in a knock-out punch for any street Stang or other fast Ford.
While carbureted intakes are obviously avail-able for the 351W motor (and stroker variants), we wanted to run an EFI system on our 408 supplied by Coast High Performance. The big-inch street motor featured a 4.00-inch crank attached to a set of forged connecting rods and dished pistons. The dished pistons were employed to produce a pump-gas-friendly 10.2:1 compression ratio. You may remember this 408 buildup from the AFR 205/TFS 205 head shoot-out. While that test was run with a carbureted intake, we decided this motor deserved an EFI intake designed with street use in mind, since not every Mustang owner wants to get rid of the driveability and fuel mileage offered by the factory EFI setup.