Back in the olden times, we built engines from used stuff. We searched for good used blocks and heads, dropped them off at the machine shop, and waited weeks or even months to get them back. And we liked it, sort of.
Today, many of the old-school machine shops are gone, leaving us fewer options for rehabbing our old junk. What’s more, most of the good block and cylinder head cores in the salvage yards have long been picked over.
But thanks to modern technology, the aftermarket offers a cornucopia of brand new blocks, cylinder heads, assembled short blocks, and compete crate engines. The Ford Performance Parts BOSS short block assemblies are a good example. Available in 347, 363, and 427ci displacements, the BOSS short blocks are built with all-new, quality components like SCAT forged cranks and rods, MAHLE forged pistons, and Clevite main and rod bearings.
Story Overview
Learn how to build a powerful 347ci small block Ford using a Ford Performance Parts BOSS Short Block Assembly
Short blocks provide a great foundation for an engine build and allow you to add the cylinder heads, camshaft, and other parts of your choice
Learn engine building tips from professional engine builder Jeff Latimer
The short blocks are based on the Ford Performance BOSS iron block. It’s cast from diesel grade iron, feature four-bolt main caps, and has plenty of material in key areas like the decks and main webs. That means strength is not an issue. The blocks are compatible with roller camshafts and retain the dimensions of the original 260/289/302 and 351W engines so they accept most factory and aftermarket components.
Here’s a quick overview of the BOSS short block assemblies. All are internally balanced and require a neutral-balance flywheel and harmonic damper.
My neighbor, Erick, is building a ’66 Mustang restomod for street use. He wanted an engine with a broad torque band, smooth idle, and plenty of grunt for the traffic light Grand Prix. We enlisted the help of engine build Jeff Latimer to spec the engine. He saw the BOSS 347 short block as foundation for building great power. A call to Ford Performance Parts and a short block arrived at Jeff’s shop.
Jeff built an engine my neighbor could grow into. He opted to follow the basic recipe for the Ford Performance Parts Street Cruiser crate engine that makes 365 horsepower and 400 lbs.-ft. of torque. As a performance engine builder is wont to do, Jeff incorporated some ideas of his own. We’ll cover those in the photos.
On the dyno, the 347 put out 371.3 horsepower at 5,500 RPM and 419.4 lbs.-ft. of torque at 3,800 RPM. That’s a healthy street engine with a smooth idle plus plenty of power for freeway use and Saturday drag racing. Let’s see how it was done.
The BOSS series of short block assemblies are some of the best Ford Performance Parts has offered. Take the BOSS block for example. Cast from diesel grade iron and designed with additional material in key areas like block decks and webbing, the block’s strength is superior to any Ford OE block ever produced. The BOSS block can handle 1,000 horsepower. (Image/Summit Racing)The lifter valley has additional material around the lifter bores along with previsions for the factory roller lifter retainer used in this build. (Image/Jim Smart)The Scat 3.400-inch stroke steel crankshaft is secured in the block with four-bolt steel main caps. There’s plenty of cylinder skirt in this block for piston stability too. (Image/Jim Smart)The Mahle forged pistons are flattops with two valve reliefs to work with a variety of aftermarket cylinder heads. (Image/Jim Smart)Jeff Latimer opted to use a COMP Cams Magnum hydraulic roller camshaft for this build. It specs out at 206 degrees duration @ .050-inch and .533-inch lift with a 100 degree lobe separation. The cam helps build power in the 1,200 to 4,500 RPM range, making it ideal for street duty. (Image/Jim Smart)Every engine build brings its share of challenges. Jeff discovered clearance issues between the cam plate bolts and cam sprocket. He countersunk the bolt holes in the plate to provide the required clearance. (Image/Jim Smart)I’ve never understood why replacement timing cover gaskets for small block Fords are not trimmed to the timing cover. Jeff doesn’t understand that either. He trims the excess from timing cover gaskets to give his builds a clean look. (Image/Jim Smart)Another issue is improperly installed crankshaft seals. The seal lip must face the crank to prevent oil leakage. (Image/Jim Smart) It is a good practice to never to install an oil pump right out of the box. Jeff opens up the Melling high-volume pump, checks clearances and surfaces, and fills the pump cavity with engine assembly lube to ensure good oil pressure during initial startup and break-in. (Image/Jim Smart)The COMP Cams Ultimate Timing Set is fully adjustable to fine-tune cam timing. It features a pre-stretched dual roller chain that eliminates any timing variations and a billet steel cam sprocket with a Torrington thrust bearing for reduced friction. The timing set is adjustable up to six degrees advanced or retarded in two degree increments. (Image/Jim Smart)Jeff believes you can never overlubricate an engine build. He generously lubes all moving parts during assembly. Prior to fire-up, he fills the oil pan and spins the oil pump to make sure oil is flowing to the rocker arms. (Image/Jim Smart)The COMP Cams Roller Lifter Installation Kit uses a ‘spider’ and lifter links to hold the lifters in place. This is the same setup Ford introduced the roller-cammed 1985 5.0L engine and has stuck around because it works. You may opt to use retrofit-type linked lifters instead. (Image/Jim Smart)Jeff stresses how important it is to confirm true Top Dead Center (TDC) on number one cylinder before degreeing the cam. If you are not at true TDC, valve timing will not be accurate. That costs horsepower. There’s also the risk of valve-to-piston contact if you don’t confirm true TDC. (Image/Jim Smart)The numbers on the Mahle pistons confirm piston deck height—how far they are into or out of the cylinder bores. These are minus numbers, which indicate how far into the bore the pistons are. Because these short blocks are production pieces, we were pleasantly surprised how consistent the deck height numbers were. (Image/Jim Smart)Degreeing a cam confirms actual valve timing events versus the cam card. The card for our COMP hydraulic roller shows the intake centerline to be 106 degrees, which is four degrees advanced. Jeff went with a 105 degree intake centerline which will increase low speed power. It will also keep cam timing from retarding if and when the timing chain stretches. (Image/Jim Smart)The Ford Performance M-6049-X2 cylinder head is cast and machined using all-new tooling and assembled with premium-quality parts. It is the best all-around head for this application. It flows very well—the intake side flows approximately 230 CFM at .600-inch valve lift, and the exhaust side flows approximately 160 CFM at the same valve lift. Features include: 188cc intake/63cc exhaust runners 64cc combustion chambers with stainless steel 1.940-/1.540-inch valves 1.207-inch single valve springs rated to .600 inch of valve lift Increased section thickness in critical areas for port work Be careful with head gasket selection. Ford Performance specifies #M-6051-CP331 or #M-6051-S331 gaskets. The Fel-Pro head gasket we used is also a good choice. (Image/Jim Smart)The X2 heads use pedestal-mount rocker arms. These Ford Performance pedestal rocker channels tie the rocker arms together to keep them properly centered over the valve stem tips. One channel connects two rockers together. Jeff used Ford Performance rocker pedestal shims to accurately set valvetrain geometry, adding or subtracting shims as necessary. (Image/Jim Smart)Jeff chose COMP Cams Ultra Gold ARC full roller rocker arms for the 347. The 1.6 ratio rockers feature CNC-machined aluminum bodies and precision trunnion bearings that can handle aggressive valve spring pressure and valve lift. Here, proper valvetrain geometry is confirmed and valve lash set. Jeff tells us you need to aim for the narrowest roller tip pattern possible on the valve stem tip. The rocker’s roller tip should begin toward the intake side and travel toward the exhaust side. (Image/Jim Smart)Jeff chose the recommended Ford Performance Parts neutral balance harmonic damper for our BOSS 347 build. Always us the proper harmonic damper tool for a smooth, non-violent installation. (Image/Jim Smart)Edelbrock’s Performer RPM Air-Gap manifold is a great all-around intake manifold for street and track use. It combines the long, tall intake runners and generous plenum of the basic Performer RPM and added an open air space to separate the runners from the heat of the lifter valley cover. That cooling effect provides a denser air/fuel charge to help build more power. (Image/Jim Smart)Holley’s 670 CFM Street Avenger carburetor is a solid choice for a street-oriented performance engine. The vacuum secondary carb comes with an optimized street calibration but like all Holleys, it’s easy to fine-tune for your specific engine combo. (Image/Jim Smart)The MSD Pro-Billet “Ready-To-Run” distributor has a magnetic pickup for accurate timing. It will smooth out the engine’s idle, improve starting, and perform at much higher RPMs. As its name implies, it is ready to run and eliminates wasteful misfire. The distributor has an adjustable mechanical advance to fine-tune the ignition curve to match your engine’s needs, plus a vacuum advance canister to help improve fuel economy if you’re into that sort of thing. (Image/Jim Smart)On the JGM Performance Engineering dyno, our Ford Performance 347 performed cranked out 371 horsepower at 5,500 RPM and 419 lbs.-ft. of torque. Those are very solid numbers, but the short block is capable of handling 500 to 1,000 horsepower if new owner Erick decides he wants more go-power. We’re grateful to Ryan Peart at JGM for his valuable time on the dyno. (Image/Jim Smart)Jeff wraps up the Ford Performance 347 build and dyno testing with a wipe-down and pre-delivery prep. It’s fully assembled with headers, front accessory drive, ignition wires and plugs, and other parts. All the new owner has to do is plunk it in his Mustang. (Image/Jim Smart)
Jim Smart is a veteran automotive journalist, technical editor, and historian with hundreds of how-to and feature articles to his credit. Jim's also an enthusiast, and has owned and restored many classic vehicles, including an impressive mix of vintage Ford Mustangs.
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