In too many instances, engine builders or rodders tend to view spark plug wire installations as necessary evils. The engine assembly may feature thousands (or even tens of thousands) of dollars’ investment in components, machine work and assembly labor. The powerplant may spit out gobs of horsepower and torque. It may be dressed externally with gorgeous chrome, anodizing, powdercoating, polished aluminum, etc., but in too many cases, the plug wires are treated as an afterthought, running willy-nilly over or around the valve covers. Or the builder may have simply purchased over-the-counter chrome, aluminum or plastic wire looms and brackets, following traditional tried-and-true trends for their routing methods.
Since most rodders tend to desire unique custom features throughout their builds, why not continue this same methodology with regard to the plug wires?
In other words, there’s no law that says that you must copy what everyone else does.
Included here are several examples of custom plug wire routing approaches. I’m not about to claim that you’ll like each example, but the point of this article is to get the creative juices flowing with regard to the plug wire packages.
This example involved the build of a 100-percent aftermarket small-block Chevy, featuring parts including a Dart Little M high-nickel block, Dart aluminum heads, Comp Cams roller valvetrain, Moroso aluminum valve covers, Edelbrock aluminum intake, Holley carb, Edelbrock aluminum water pump, Scat stroker crank, Scat H-beam forged rods and custom JE pistons. The build featured boring and stroking to a final 383 cid. The block, water pump, cylinder head, timing cover and valve cover were smoothed/polished to a glass-like surface and finished off with a custom urethane basecoat/clearcoat paint. Various aluminum pieces (such as breathers and -AN fittings) were custom anodized in a violet color to compliment the paint scheme. In order to utilize a very cool K&N aluminum dual-carb air cleaner system (on a single four-barrel carb), we fabricated a 5-inch-diameter aluminum drop-tube mounted to our pro billet MSD distributor.
Now for the plug wires. Rather than simply organize and route the wires using readily available aftermarket brackets, looms and separators, our idea involved achieving a pseudo-plumbing appearance for the wires. We hand-bent a series of 3⁄8-inch-diameter aluminum tubes that run from the spark plug boots to the underside of the rear air cleaner housing. We used 7mm resistor-type MSD plug wires to snake through the tubes. The spark plug ends feature custom-anodized –6 aluminum tube nuts and ferrules (these are epoxied in place). At the distributor ends, the tubes terminate into the bottom surface of the rear air cleaner base using –6 AN ferrules and tube nuts. The tube nuts thread onto 1⁄4-inch NPT/-6 AN fittings (the air cleaner base was drilled and tapped for 1⁄4-inch NPT thread). Inside the rear air cleaner, the wires connect to the distributor cap, thereby hiding the distributor cap from view. Hand-cutting and forming the aluminum tubes took about 11 hours, but we felt that the results were well worth the effort. And, no, the aluminum tubes didn’t create any crossfire problems. The end result was a spark plug wire setup that’s unique and certainly eye-catching. Granted, if any of the plug wires require replacement in the future, it’ll be a pain, requiring cutting the distributor end boots off, snaking the old wire out, snaking the new wire in and then finishing the distributor ends to length, but unless this needs to be done during a roadside emergency, it’s really not that big of a deal.
I’ve seen so many spark plug wire paths used on V-8 flatheads that look just plain ugly. Most commonly, I’ve seen wires that simply crawl back from the front-mounted (and angled) distributor that just drape over the heads with no regard for appearance. When I built this flathead, appearance was key. I smoothed out the block exterior, turning the once-butt-ugly and rough casting surface into a flawless jewel, then painted in a basecoat/clearcoat red (looks like a wet red cherry). After all that work, I wasn’t about to just plop my plug wires on in the traditional fashion. The answer was actually very simple. Using a length of raw-stock straight clear-anodized 3⁄8-inch-ID aluminum tubing, I cut four staggered lengths for each side of the engine. Using off-the-shelf aluminum wire looms, I modified the looms to accept the 1⁄2-inch tubing OD and made stand-off aluminum brackets that anchor at two exhaust port bolt hole locations. Once cut to length, each end (ID) was gently chamfered and radius-rolled to eliminate sharp edges. The tubes are arranged flush at the front, staggering rearward from short to long. Each tube’s rear terminates just short of each spark plug hole centerline. This allows the plug wires to gently curve from each tube to the spark plugs, creating a symmetrical flow of the visible wires.
The distributor is located at the front of the block and sits at a pretty severe angle (angled toward the right side), resulting in the need for longer wires for the left side of the engine. The long sweep from the left cylinder head to the distributor was organized and secured using two aluminum wire looms, fastened to the block and distributor housing bolts with fabricated aluminum extension brackets. Total materials cost for the setup (minus the wires) was only about $10.
During a recent retro build of a 5.3L iron-block LS engine (overbored to 327 cid), we were faced with the common challenge of hiding the individual coil packs. GM routinely installs these coils to the valve covers, requiring some sort of cover to hide the busy coils and their harness. Of course, you can always relocate the coils to the front or rear of the engine on a custom bracket, to the firewall, inner fender, etc. with longer wires. In this case, we decided to stick with the stock coil locations but wanted to conjure a cover design that coordinated with the retro small-block Chevy look that we wanted. We made our own fiberglass coil covers, replicating (as closely as we could) old-school small-block covers. Of course, with a full cover mounted over the coilpacks, you need a path that allows the wires to reach the spark plugs. Instead of cutting slots at the outboard bottom of the covers, we cut oval holes that are just large enough to allow plugging/unplugging the wires to/from the coils. The visual result: only a short bend of wire is seen exiting the cover to each plug.
Another approach (I naturally thought of this after we made our fiberglass mold) would be to reposition the coils vertically with the wire connection pointing straight up, fabricate taller covers, place the plug wire access holes on the roof of the covers, allowing the wires to exit the cover roof, arcing down to the spark plugs. Along with a finishing rubber grommet at each roof hole, this would provide the initial appearance of a Hemi-style engine with top-located/direct-to-chamber spark plugs. The more I visualize this, the more I like the idea. I’ve convinced myself that I’ll need to try that approach on my next LS build.
I dislike the thought of draping plug wires over any valve cover. If at all possible, I always prefer to run them outside of the covers, obtaining as parallel a run as possible. In the case of a recent small-block Ford engine build, I had the Moroso aluminum valve covers powdercoated in wrinkle black and engraved/colored with a “427W” logo (this engine featured a Dart 351W block, stroker Scat setup and oversized to 427 cid). I simply didn’t want to obstruct the covers from an aesthetic standpoint. Obtaining a neat-and-tidy plug wire setup was very straightforward. Using MSD 8.5mm wires fitted with multi-angle plug boots, I used a pair of MSD snap-fit wire separators on the outboard side of each valve cover, secured (vertically) with fabricated aluminum L-brackets to existing valve cover bolt locations. Instead of using bolts to secure the valve covers, I installed a set of ARP stainless steel radius-nosed studs and 12-point nuts. The L-brackets were radiused to match the radius of the stud’s washers, essentially hiding the brackets under the washers and nuts. At the front of each cylinder head, I installed a similar loom setup, using aluminum wire separators, anchored with aluminum L-brackets to the front inboard valve cover bolt locations. This provided a very simple yet visually pleasing routing.
By the way, if you’ve never tried multi-angle boot wires yet, consider this style for your next problem child wiring job. The spark plug boots are out-of-the-box straight, but can be bent to the desired angle for custom fitting. If short straight or 90-degree plug ends won’t fill the bill, give multi-angles a try.
This example involves a Pontiac build, starting with a 455 bare block, boring and stroking to 501 cid. Although I used a set of Kauffman aluminum D-port CNC heads, the same challenge is present with all heads for the big Indian: the spark plug ports are angled, with adjacent plugs opposing each other.
Once again, I didn’t want to run the wires over the valve covers, preferring to run them in parallel along the outboard sides of the valve covers. I couldn’t (or, I should say, chose not to) utilize the valve cover fasteners to secure and route the wires, because instead of using OR-style valve covers, I went with cool race-style welded aluminum covers from PRW, which feature tube-through fastener locations at the inboard and outboard roof areas. Installing stand-off brackets at this high location just wouldn’t look right (too busy). With no practical way of securing the wires along the horizontal run, using straight or 90-degree boots would simply look way too disorganized. To ease the challenge, I opted for MSD’s multi-angle boots, which allowed me (even with opposing spark plug angles) to create a reasonably uniform rearward flow for the wires.
At the rear of the cylinder heads, I installed aluminum looms I purchased from Billet Specialties, these are designed to screw directly into the 3⁄8-inch x 16 tapped holes in the rear faces of the heads. Since the captive screws installed to the billet looms required rotating the entire loom for installation, I eased the installation (both from the standpoint of rotational clearance and obtaining a rigid desired clock position) by eliminating the existing male threads and drilling a 3⁄8-inch hole through the loom head. This allowed me to secure each loom with a polished stainless socket head cap screw, which enabled me to obtain exactly the installed position I wanted. These four-wire looms (one at each head) neatly organize each bank wire with no additional anchoring needed.
This engine was a brute from the get-go, featuring 632 inches of displacement, a Dart high-nickel Big M block, Dart Big Chief 2 aluminum heads, nearly an inch of valve lift, 16:1 compression ratio and 1,115 horsepower on the dyno (all-motor, with no nitrous). This is definitely not a boulevard cruiser, but a very radical potential streeter that, quite honestly, is dedicated strictly to the drag strip. Because of the drag race direction of this engine (as opposed to an engine that’s just for the street and show), plug wire routing of these 8.5mm MSD wires was more of a functional challenge instead of trying to create something off-the-charts pretty.
Since the MSD distributor is located at the rear of the block, and because the installed in-car setup would involve some very healthy primary header tube diameters, we had two choices: run the wires way-out from under the header tubes and nailed onto the top valve cover fasteners (running parallel along the covers to the rear or up and over the covers), or keeping the wires under the exhaust ports. Since this drag engine application will naturally require frequent valve cover removals (for checking springs and valve lash), we opted to snug the wires under the exhaust ports, behind the header tubes.
While the large-diameter header tube bends would provide adequate clearance, we installed a set of Design Engineering Inc. (DEI) thermal boots to the plug ends (by the way, DEI recently introduced an upgraded version of these thermal boots that feature a titanium weave, able to handle even higher temperatures). These boots will provide more than enough protection from nearby exhaust tube heat. At the rear of the block, we organized and secured the wire groups with MSD high-temp plastic looms (secured to the block with easily fabricated aluminum mounting brackets), and further grouped with a selection of MSD twist-on wire separators. The resulting package groups the plug wires and nearly eliminates unwanted bouncing/vibrating during the engine’s rough idle characteristics.
Be aware that the examples provided here merely serve as examples. Considering the creativity that’s alive and well within the custom community, I’m sure that others have created (or will create) even cooler setups. With this brief article, I simply wanted to raise awareness of spark plug wire routing and its contribution to overall engine appearance.
Tags: ARP, Big Block, Billet Specialties, Comp Cams, Dart Machinery, Design Engineering Inc., E3, Edelbrock, Engine Builders, Engine Dress Up, Engines, Flathead Engines, Holley, JE pistons, K&N, Kauffman, LS Engines, Mike Mavrigian, Moroso, MSD, PRW, SCAT, Small Block, Spark Plugs, Wiring