Building Up A 331 Stroker Engine

Here&8217s the freshly prepped...        read full caption Here&8217s the freshly prepped bare block at the Coast High Performance shop. The block has been cleaned up with an overbore and finishing hone job to 0.030-inch. Where necessary, the block is decked and the crank saddle is align-bored.

Although our 331ci engine...        read full caption Although our 331ci engine won’t require it, all blocks prepared for stroker kits at Coast High Performance are notched for rod bolt clearance. Relative to the photograph, the notches seen here are at the 11 o’clock position at the bottom of the cylinder bore. Engines larger than a 331, such as CHP&8217s famous Street Fighter 347, definitely require this special clearancing.

The forged aluminum pistons...        read full caption The forged aluminum pistons are made especially for Coast High Performance by Probe Industries. Shown is the unique double fly-cut in the top of the piston to accommodate the Trick Flow Specialties Twisted Wedge cylinder heads we&8217ll be using.

Notice how the wrist pin is...        read full caption Notice how the wrist pin is set off-center to provide the best rod angle for our particular engine. Viewed from this angle, you can see how the metal is thicker on one side of the wrist pin than on the other.

From the side, notice how...        read full caption From the side, notice how the wrist pin is close to, but not into, the oil-ring lands. Compared to a stock piston, the wrist-pin location is moved way up into the piston to accommodate the longer rod length. This is a great feature for obtaining extra displacement without creating oil-use problems.

With the 331 piston (right)...        read full caption With the 331 piston (right) next to a Coast High Performance Track Dominator racing 347 piston, notice how the 347’s wrist pin is located way up into the oil-ring lands. This allows the use of a long, 5.400-inch rod for improved rod-length-to-stroke ratio. The positioning does cause some oil use, a non-critical factor on a racing engine. But on Coast’s Street Fighter 347, a shorter 5.315-inch rod is used, so the 347 displacement is achieved without the wrist pin going into the piston&8217s oil-ring area, a better situation for a street engine.

The extra-sturdy H-beam connecting...        read full caption The extra-sturdy H-beam connecting rods from Probe Industries are good for up to 800 hp. They are the longer, 5.400-inch length, which work in the 331 without oil-use concerns because the 331 has a shorter stroke than the 347.

The H-beam construction provides...        read full caption The H-beam construction provides both excellent strength and light weight. Notice also that 12-point cap screws are used instead of rod bolts and nuts, a preferred method for performance applications.

Although the cast crank that...        read full caption Although the cast crank that comes with the CHP 331 stroker kit is made of nodular iron, which is fine for most applications, we went with the forged-steel unit, a $300 option. Although you can&8217t tell from the photo, our crank has the narrow parting line typical of a forged crankshaft. A cast crank can be spotted by the presence of a wider parting line, usually about 1/2-inch in width.

For added oil capacity, this...        read full caption For added oil capacity, this deep front-sump oil pan from Pro Mustang Performance will fit our early car without modification. The deep sump will help prevent oil starvation, while the added oil volume will contribute to cooling.

To top off our 331, we&8217re...        read full caption To top off our 331, we’re using Trick Flow Specialties&8217 Twisted Wedge aluminum cylinder heads. These race-proven heads come with 2.02-inch intake and 1.60-inch exhaust valves. Computer-designed intake and exhaust ports, along with specially shaped combustion chambers, contribute to the power-packing potential of the Twisted Wedge heads.

The Pro Mustang roller camshaft...        read full caption The Pro Mustang roller camshaft we selected is right on target for our street package. Part number 4017, the cam features a lift of 0.493-inch intake, 0.510-inch on exhaust, as measured at the valve. At 0.50-inch lift, the figures are .212-inch intake and .222-inch exhaust. Lobe centers are 114 degrees.

Other valvetrain goodies include...        read full caption Other valvetrain goodies include these extruded aluminum roller-rocker arms, made in-house at Probe Industries. They come with locking, adjustable rocker nuts. Once you set the Allen screw, you can be confident your valvetrain won&8217t come out of adjustment. Probe can also furnish you with its Street Fighter shaft-rocker system.

Another part we won&8217t...        read full caption Another part we won’t have to worry about at high rpm is this Romac harmonic balancer. It&8217s made of billet steel and has no rubber inner component to slip during operation.

To match the Twisted Wedge...        read full caption To match the Twisted Wedge cylinder heads, the induction package for our 331 stroker will be upper and lower EFI intake manifolds from Trick Flow Specialties. The generous rectangular ports mean our engine won&8217t be running out of breath above 5,000 rpm.

Here, Mark Jeffrey is installing...        read full caption Here, Mark Jeffrey is installing the new bearings into the bare block. Jeffrey say it’s important to prelube the bearings with engine assembly lube or heavy oil before installing the crank. Don&8217t forget that the center main bearing is different because it takes the crankshaft thrust loads on these engines.

The one-piece oil seal is...        read full caption The one-piece oil seal is a nifty deal that helps ensure a leak-free engine, but it too must be lubricated before installation on the crank.

Here, the crank is placed...        read full caption Here, the crank is placed in the saddle, and the main caps have been carefully set in the correct position. Now we see the spacers for the main cap girdle being placed into position for a test-fit. These spacers must be used, as the girdle does not fit directly over the main caps.

Bottom-end strength can be...        read full caption Bottom-end strength can be greatly enhanced with a main cap girdle, as offered by Coast High Performance in either flame-cut (shown) or billet steel. In this photo the girdle is placed into position on top of the spacers. The main cap bolts for the number three journal are locating the girdle here.

According to Jeffrey, another...        read full caption According to Jeffrey, another area requiring close attention is ring-end gap. Don’t forget to check this on your go-together because they&8217re off more often than you might think. Jeffrey uses Dura-Moly rings from Childs and Albert.

When assembling the pistons...        read full caption When assembling the pistons onto the rods, Jeffrey recommends using double spiral locks.

Here, Jeffrey guides a piston/rod...        read full caption Here, Jeffrey guides a piston/rod assembly into the bore with the ring compressor already installed. In this situation, Jeffrey says it&8217s imperative to avoid damage to the crankshaft, which can be caused by the descending connecting rod. Be sure to guide the large end of the rod carefully over the crank journals.

The Pro Mustang camshaft slides...        read full caption The Pro Mustang camshaft slides into position. Use lots of cam lube here, and be careful not to dislodge any of the cam bearings inside the block. Be gentle, and don&8217t force the cam up against a hard stop.

The timing-cover holes are...        read full caption The timing-cover holes are larger than the bolt diameter, hence, the bolts do not provide correct placement of the cover. You must be sure that the flat portions at the bottom of the timing cover are exactly level with the oil-pan rails. This portion of the timing cover becomes part of the pan rail, and if they are not even, you’ll have an oil leak here. Also, if the cover is not in the correct position, your front seal will be off-center with respect to the crank snout. In this condition, the seal will be damaged when the engine is run, and you&8217ll have two leaks up front.

The last place you want to...        read full caption The last place you want to skimp is at the head gasket. Use a top-quality gasket such as ROL or Fel Pro. Here, our TFS heads are going into place.

Now is the time to install...        read full caption Now is the time to install the Probe Industries roller rockers. We used a set of Manley push-rods, and we&8217ll adjust our valvetrain before we close up the top of the engine.

With the valvetrain adjusted,...        read full caption With the valvetrain adjusted, the Trick Flow EFI lower-intake manifold goes into position. Because we’re using aluminum cylinder heads, Jeffrey reminded us that it&8217s important to use an anti-seizing compound during any assembly where the fasteners are going into aluminum components.

We&8217re going to install...        read full caption We’re going to install the Trick Flow EFI upper-intake manifold temporarily to keep small birds from nesting in the engine. It will be removed when it&8217s time to set up our fuel injection.

Here’s the Coast High...        read full caption Here’s the Coast High Performance 331 stroker ready to go into our 1967 Fairlane after installing the balancer, water pump, throttle body, and other small components.

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.

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 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, Probe Industries 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.