Introduction: Immitation Hilborn Injector

About: Senior VP of an independent oil company. Never met a hobby I didn't like!

1959 through about 1967 was a wonderful era in the subculture of drag racing. In 1959 the primary race sanctioning body, the National Hot Rodding Association,(NHRA) in its infinite wisdom decided that the most powerful fuel mixture for internal combustion engines, alcohol mixed with nitro-methane, was too dangerous and banned it. Drag racing which had been progressing at light speed, almost instantly stopped. With the most exciting class of racing virtually banned, the fan base was restless. Enter the 'blown gas' category of race car. This category had rules limiting it to door-slammer car styles, only allowed to burn pump gasoline with engines that could have GMC superchargers, that were pirated from GMC diesel engines and could have any body/engine combination. The top gas classes quickly migrated to the smallest cars available with the biggest engines available. The hands-down winning car styles were the lowly Willys pre-war cars. Manufactured from 1933 through 1942, these cars were the VWs of their era before VW was cool. Vey small, very light weight, actually pretty freaky (in a bad way!) styling for the day, they were the comic relief in the auto industry at the time. A 1933 Willys coupe could be had brand new from the factory for $325. The engine of choice was the 1954 through 1958 Chrysler hemi head which was the godfather of the choice drag racing engine design ever since.

That all changed when they were drafted into drag racing. What had been the ugly duckling of passenger car became the beautiful swan of drag racing. They were snapped up and modified in such great numbers during that period, they became rare as hens teeth today. If you find one of these cars in decent restorable condition today, expect to pay well over $50,000.

These cars were very exciting to watch race and easily took over the top spot, making people forget about the fire breathing nitro powered cars that were gone. The Willys were horrible to control for the drivers, with too much power, really bad recap racing slick tires, and jacked up front ends to try to get weight in the rear tires making them really hard to steer. Saying was "guard rail to guard rail in 9 seconds!" their era was short lived; tires got a lot better so the front ends came way down, Mustangs and Camaros with infinitely safer engineering took over class and the nitro ban was lifted. Gassers were just boring after that. Actually they morphed into the Funny Car class of today which are nothing more than the fire-breathing, no rules monster top class cars stuck inside fiberglass car bodies.

That brings me to my story. I found one of these cars, a 1936 Willys coupe, at a schoolmate's home when I was a sophomore in about 1964. I had bee reading about the marvelous Willys that had been dominating the drag racing scene so had to have that one. I got it for $75 and got a basket case of a hemi engine from another classmate for $25. To make a long story as short as possible, I have been building and rebuilding the car ever since (over 50 years!). The car was finished in its current condition in 1995 and has been an off-and-on daily driver ever since.

The classic gasser normally had the hemi engine but also had a GMC supercharger on top of the engine and the classic fuel system was a Hilborn brand '4-hole' injector with a big air scoop on top. I couldn't afford the blower and the many engine modifications necessary to accommodate that extra power but I sure needed the look of the blower scoop sticking out of the hood.

My solution was to cast my own imitation injectors to mount on my hood and buy the actual Hilborn scoop to mount on top of the 'injectors'.

Photo 1 is my car, photos 2 & 3 are vintage real race cars with real injector setups I wanted to replicate as closely as I could.

Step 1:

The first step was to make the molds for the aluminum sand casting. The first photo shows the 'match plate' pattern I made. It is a model of 1/2 of the injector body attached to a piece of plywood. This single half-pattern is used to make both halves of the final casting mold. The pattern is made from pieces of black ABS plumbing pipe which happen to be the exact outside diameter of the real injector tubes. 4 of these were cut in half and glued to the board. A 1/2" thick board was glued on edge on top of this row of tubes to act as the scoop mounting flange. I then formed radiuses between the tubes with polyester body filler.

Once the injector model was built, it needed extensions on top and bottom of the tubes to accept 'cores' that would form hollow injector tubes. You can see these in the picture as smaller diameter half-rounds extending from the main model. I made these by casting them from polyester body filler in the 'core box' described in the next paragraph and gluing them to the board. The whole pattern was painted with primer and several coats of enamel paint for a slick surface that would slide out of the sand casting mold easily.

The core box is a mold for making 4 rigid sand cores that fit in the casting mold and result in hollow aluminum tubes in the final casting after the sand is knocked out. Picture 2 shows the core box I made from ABS plastic pipe. I split the tube up the side on my table saw so the tube would expand and allow a formed sand core to come out easily. The tube is held together with a screw clamp while the resin coated sand is pounded solidly inside the tube to form the core. Note the two half-round wooden sticks that are glued on either side of the tube, these form bosses in the final casting for bolts to attach the part to my hood.

The third picture is of the plywood 'cope and drag' boxes I built for the foundry to use. These are simply two boxes that contain the sand with the hollow space for the casting that is filled with molten aluminum.

I had a small foundry in my home town so decided to have them do the casting for me. I don't have the equipment although I would like to do my own casting some day. Note in the first picture that the pattern mounting board has a wooden pin sticking up on one side and a matching hole in the board on the other side. They are exactly equidistant from the model. The cope and drag boxes also have the pins and holes so all the foundry had to do was place one of the box halves over the pattern indexed by the pins and holes, pound in the sand and pull the box/sand off the pattern and repeat the process for the other box. Then they placed the 4 sand cores on the cradles for the 4 injector tubes, pound the sand into the second box and lower that box over the first one. This yielded a cavity that formed a perfect negative of the complete injector.

Step 2: Mounting the Injector

A feature of the Willys gasser drag racing cars is most competitors employed a 1-piece fiberglass version of the complete front end of the car that easily tilted forward giving full access to the engine so it could be service quickly between racing rounds. I built a 1-piece front end for my car and needed to mount my imitation injector to it.

The injector I cast was a lot higher than it needed to be to allow me material to remove to get the perfect look. Photo 1 shows the slice I cut off the final casting to get the perfect fit using a band saw. It shows the bosses that I made in the sand cores that I could drill and tap for the screws to mount the injector to my hood. Obviously it shows the hollowness provided by the core. The wall of the tubes of the injector are duplicates of ABS plumbing pipe.

Pictures 2 & 3 show how I mounted the unit. I formed a fiberglass depression in the top of the hood to simulate the hole necessary if I had an actual blower/injector setup. I then drilled holes in the hood and matching holes in the bosses of the injector that were tapped for machine screws and the injector was bolted in from the bottom. Picture 3 shows I cut holes in the hood to match the holes in the injector so it actually acts as a functional fresh air scoop!

Step 3: The Result

Here are a few pictures of my car. I have the carnivore look I wanted yet have a mild, streetable, conventionally carbureted motor. I have received may compliments from hard-core gearheads at hot rod meets saying this is the best imitation blower setup they have seen.

I wanted to enter the intake manifold I cast for my Chevy 230cuin straight 6 engine which is much more impressive but I had entered it in a prior Instructable contest a while ago so it isn't eligible.

Casting Contest

Participated in the
Casting Contest