The "old" Ford 427 FE side oiler has regained its popularity among both racers and street rod/custom car builders, especially for Cobra replica builders. This blast from the past is back with a vengeance.The Ford 427 "side oiler" motor was produced from 1963 through 1967 and was used in a variety of automotive performance and marine applications, most notably in the Ford/Shelby 427 AC Cobra. While the side oiler has always enjoyed a cult following among Ford types, interest in this motor is currently at an all-time high, apparently due to a strong tide of Cobra kit car builds. Given this renewed interest, we thought it would be fun to take a close look at this motor from both a restoration standpoint as well as an upgrade approach to increase power and drivability for today's performance street scene.


The original FE iron motors were not light, weighing in at a hefty 650 lbs. Of course, ours will be considerably lighter since we're using aluminum heads, intake manifold and water pump. Unlike the 428 engines, the 427 is internally balanced. The 427 FE side oiler also features cross-bolted main caps to provide added rigidity for the main caps, primarily for durability. Screw-in block plugs (instead of interference-fit "freeze" plugs) are also used. The side oiler FE block is so-named because it features oil feed to the main bearings directly from a large oil gallery that runs along the bottom left side of the block. Oil enters the passage from the oil filter housing near the front of the block. Drilled passages intersect the main gallery to feed oil to the main and cam bearings at each main web (pipe caps are used to cap-off the drillings). An oil pressure relief valve is located inside the rear of the block along the left side. The passage for this valve and for the main gallery is plugged on the block's rear face. Because of manufacturing tolerances in the ‘60s, the main cap side spacers are individually fitted and labeled. The second main cap's spacers are marked 2L and 2R (indicating left or right side), the third cap's spacers are marked 3L and 3R, etc. Service replacements for these spacers were originally available in thicknesses of 0.3767", 0.3750" and 0.3733" for selective fitting. While it's necessary to align hone any block during a complete rebuild, if the original spacers have been lost or replaced it is absolutely mandatory to align the main bores to ensure correct centerline.


Generally, when sourcing 427 pistons with a lower compression ratio in mind, you're forced to order custom-made slugs (while these motors are popular, they've not been popular enough for most piston makers to justify tooling up for all of the potential oversizes and dome volume combinations). However, things have changed. With a recent resurgence in demand, piston makers are now scrambling to offer replacement alternatives. For example, KB recently introduced ready-to-ship pistons with a choice of dome profiles. As but one example, the KB P/N KB-199 is a hypereutectic performance piston featuring a 20cc D-cup relief. When used with 76cc chamber heads, for example, final compression ratio will be in the range of 9.5:1. The minimum wall clearance for these pistons is 0.0020" (since they're hypers, the diameter won't change much during thermal ups and downs, allowing the tighter wall clearance). Compression height of this particular piston is 1.775". Pin diameter is 0.9752". Individual piston weight with pin is 830.0g (687g piston/143g pin). This lower-than-stock compression will allow the use of pump gas to suit today's street performance applications. Conveniently, this piston in a +0.020" oversize accepts standard Chevy 454 rings (5/64", 5/64", 3/16"), so rings such as Perfect Circle P/N 40203CP would be a good choice (available in standard, +0.020" and +0.040"). An example of a good cylinder head choice is the Edelbrock aluminum Performer RPM FE heads, which are offered in both 72cc and 76cc versions. Obviously, based on desired compression ratio, a bunch of piston/head combinations are possible by considering custom-made pistons.


The 427 FE side oiler has been around since the early 1960s, so finding a decent block can be a challenge. Since these motors have typically been used and abused in race cars over the years, it's fairly common to run into blocks that have already been overbored, with cylinder bores out of round, with cracks, broken walls and other maladies. A few years ago when we built a 427 FE side oiler, we were lucky enough to locate a fairly decent casting (1966 vintage) that had never been overbored for larger slugs. Two cylinders (No. 1 and No. 7) had been sleeve-repaired and all bores showed an out-of-round condition. A cleanup allowed us to use +0.020" pistons with no problem. The original 427 blocks featured fairly thin wall castings, so it's generally accepted that an overbore of +0.030" is about the safe maximum, although it's sometimes possible to oversize to 0.040", depending on wall thickness of a particular block (luck of the draw). On this particular block, a cylinder wall thickness inspection using a BHJ sonic checker showed an average thickness of 0.173", with the thickest at 0.241" (intake side) and the thinnest at 0.127" (front). As a sidenote, the outer walls (exhaust side) on these blocks are usually thinner than the inboard walls (intake side). While it would be nice to have at least 0.140" or so wall thickness for a higher compression application, we weren't planning to "squeeze" the combustion package as tightly at 9.5:1 (as compared to 13:1 or higher as found on original versions), so we felt that potential wall distortion would not be as much of an issue. Upon close inspection of this block, we found evidence of a previous mishap but we don't foresee this causing any major problems. A small chunk of block wall had been busted out of each side, but had been expertly repaired. The bottom lips of a few cylinders also featured noticeable burrs, along with a peened-over bottom edge of one of the lifter bores. Obviously, in its past life this block had been subjected to a crank/rod and cam failure, most likely the result of a nasty blip at the dragstrip. The bottom-lip burs were easily cleaned up during overboring and the block was magnetic-particle checked for cracks. It's an old and abused chunk of cast iron but it was useable. If you're anticipating building one of these 427 side oilers, you should be aware that there are alternatives to scrounging for a workable 42-year-old block. Genesis Custom Manufacturing, to cite one example, now offers a brand-new casting (in cast iron or aluminum) that replicates the original side oiler, with a host of noteworthy upgrades. The iron block material features a higher nickel content and both material versions feature thicker walls (everywhere), extra meat for machining (decks are thicker, lifter bores and cylinder bores are undersized and the main caps are one-piece beefy items that require no side spacers). Basically, this is a block that is produced using much the same approach as today's Winston Cup blocks-it's semi-finished, allowing the builder to machine to create exactly the dimensions required. I'm told that the blocks sell for around $3,000 and up (call Genesis for exact pricing). Since a decent original block with an unknown and possibly shady history sells for anywhere between $1,700 and $5,000 at swap meets (yes, I actually saw a supposed NOS block tagged at $5,000), the new Genesis casting is certainly worth considering. From a standpoint of appearance (important for customers who are building a vintage Ford or a Cobra replica), it looks exactly the same as the Ford piece, complete with screw-in coolant plugs and the exposed main cap side (horizontal) bolts. I've recently heard that Genesis was purchased by another company (the old Genesis Web site appears to have been shut down and I've tried to contact them to no avail). However, the blocks are still available. I understand that Flatlander Racing (a Genesis distributor), as an example, offers them.


• Siamesed walls for stability

• Added 0.100" material at cylinder walls for oversize boring

• Added material between water passages and corner head bolt locations to help eliminate deck surface cracking

• Added deck material to help prevent warping

• Added material to lower side of cylinder webs for increased rigidity

• Block drilled for oiling hydraulic or solid lifters

• Larger 7/16" cross bolts (vs. OE 3/8" bolts)

• Added rigidity eliminates center main bearing walk common in original blocks

• Individual traceable serial number on each block

The aluminum blocks include all above features plus added cylinder wall material to allow 0.093" thick sleeves, added material for increased thread engagement at both head bolt and cap bolt locations. Definitely check cylinder wall thickness on vintage blocks with a sonic gauge. If too thin, sleeving will be necessary. The original side oiler blocks feature spacers between the main cap sides and the block sides. Keep these in order. New aftermarket versions of this old block will feature main caps that make full width contact and don't use these spacers.