Modified Mustangs & Fords
Building Up A 331 Stroker Engine
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Why a 331 instead of a 347? CHP's Chris Huff says the company originally developed the 331 in response to the early 347's reputation for consuming oil and wearing out prematurely--fine for racing but not so great for the street. Early on, the long rod used with the 347 mounted high up on the piston, requiring a wrist-pin hole that protruded into the oil-ring lands. These early pistons were also race-only, with more piston to-wall clearance than typically used on the street. Although CHP has improved the street 347's shortcomings by designing its own piston with off-set wrist-pin mounting and a slightly shorter rod, which doesn't need the wrist-pin holes in the oil-ring lands, it still offers the 331 for builders who continue to be gun-shy of the 347. According to Huff, you'll get great oil control and 100,000 miles of service from either of the CHP 331 or 347 street engines.
In most vintage Mustangs and Fords, underhood space is at a premium. With early Mustangs, Fairlanes, and Falcons, the 289 or 302 small-block is about as large as you can go without making extensive engine-compartment modifications. The good news is that with help from Coast High Performance in Torrance, California, you can pretty much name your displacement using the short-deck 302 block, all the way out to 347 ci. (In a car that will take a 351 Windsor, the displacement can reach 427!) The larger cubes are achieved by the use of a longer-stroke crankshaft and, to a lesser extent, larger bores in the block. These stroker engines give you a great power improvement while retaining the original exterior dimensions. Longer stroke in particular means more torque, so finding traction may become your newest concern in a light car like a Falcon or Mustang.
In this article, we’re going to look at the bits and pieces that go into a CHP 331ci stroker, achieved by using a crank with a 3.250-inch stroke (as opposed to the 3.000-inch stroke with the stock 302 crank) with a 4.030-inch bore. The special components make these engines different, and for this engine there are some additional things we’re going to use to make our mill extra-durable. The engine is destined for our 1967 Fairlane project car, and a durable driveline is being planned, including a super-stout Lentech AOD automatic transmission and a Ford 9-inch rear axle.
Many of the special parts going into this engine are made in-house by CHP and its sister companies, ProbeIndustries and Pro Mustang Performance. Stay with us as we put these goodies under magnification, and then we'll detail some of the assembly highlights as Coast High Performance's engine assembly expert, Mark Jeffrey, puts the 331 together.