Sunbeam Alpine V6 Restomod: Carburetor And Throttle Linkage

With the engine bay coming along nicely it was time to decide on the fuel system delivery. Until recently, there wasn’t much choice in terms of non-carbureted options. In deciding what carburetor to buy, I stumbled onto Electonic Fuel Injection (EFI) for carbureted cars. These EFIs look similar to carburetors but are in fact semi-fuel injection units. The technology is relatively new and the market is just emerging. We had a major decision on our hands. Go with a conventional Holley 390 carb setup or venture into unknown territory and install an EFI onto our engine? This wasn’t an easy decision.

From my previous discussion on the Offenhauser Dual Port intake, finding a two-stage 4 barrel EFI setup would be difficult. After searching through several manufacturers, I whittled down the prospective EFI companies to Holley and Fitech. These two seemed to be the leaders in the development of this new technology. However, the problem with the current offerings of EFIs with a 4 barrel setup is most are designed for single or dual plane intake manifolds. This would not work with the current Offenhauser intake manifold.

Holley 2 Barrel EFI
Original 2.8L V6 Single Plane Intake Manifold
Original 2 Barrel Carburetor Spacer

Another problem with the EFI option is the cubic feet per minute (cfm) our engine was going to pull was well below what is required for a 4 barrel EFI unit. The Holley Sniper EFI 4 barrel kit can pull up to 800 cfm. The Holley carb pulls a max 390 cfm so if we were to find a 4 barrel two-stage EFI kit, the injectors would be working on 50% of their duty cycle which the Holley tech told me was not ideal for the setup. However, Holley does make a 2 barrel solution with which pulls in a max 580 cfm. This option was quite appealing but another issue popped up. How do we install the 2 barrel EFI onto the engine?

The answer is use the original single plane intake manifold. Like all things, the install of the 2 barrel EFI to the single plane intake would not be simple. When these engines were built, it was the height of the gas crisis of the early 70s. Emissions development was in its early stages. On the Mustang II V6, there is an exhaust gas recirculation (EGR) spacer which allowed a small amount of exhaust gases into the intake manifold to help with emissions and fuel efficiency. As shown in the pictures above, this rotates the carburetor slightly on the intake. In order to correct this rotation and block off all of the EGR ports a special adapter would need to be fabricated to allow for the 2 barrel EFI. We approached a fabricator and he didn’t see a problem with manufacturing the adapter. 

Now that we had figured out the options for the EFI setup, this left us with two options. Option 1 is to use a Holley 390 two-stage carburetor with the Offenhauser performance intake manifold. Option 2 is to us the Holley 2 barrel EFI with the original single plane intake manifold with a special manufactured adapter. We milled on this decision for quite some time. 

Holley 4 Barrel 390 Carburetor
Holley Secondary Jetting Kit

After deliberating for a few weeks and double-checking with Holley on the EFI setups, we decided to go the traditional route with the Holley 390 cfm carburetor. Our main reasoning was the carbureted 4 barrel intake manifold was more of an upgrade than the EFI using a single plane intake manifold. It seemed to be a step backward by restricting the flow of the carburetor/EFI through a 2 barrel and a single plane early emission intake manifold. The install had also never been done before and would have been a first. With my engineering background, I was more than willing to try it but we ran the risk of spending thousands of dollars on something that may or may not be an upgrade. In theory, it made sense, but we were unwilling to step into completely unknown territory when we were just barely figuring out the conversion. Conventional wisdom ultimately won out and we purchased the Holley 390 carburetor with a secondary jetting kit. Luckily, we put the oxygen sensor on the exhaust and a beefy alternator in case, somewhere down the line someone tries the 2 barrel EFI and it is successful and from what I hear, people are getting close. 

Intake Filter Cover with a push button release
Intake cover has the required clearnce of the hood
Transmission linkage was in conflict with the valve covers

Once we received the carb, the task of bolting everything up was up next. The first task was finding a small low profile air cleaner. I quickly found an air cleaner on Summit’s website and decided to install a push-button release for it too. This push-button release is pretty slick since it uses a latch to remove the air cleaner instead of the standard wing nut and gave us even more clearance between the hood and air cleaner. After the installation, we checked the clearance and had no issues with the installed hood. The only snag we had was with the throttle bracket on the carburetor. The automatic transmission hookup on the carburetor was fouling the valve covers and a quick visit to the Dremel solved the issue immediately.  

Stock throttle linkage
Second attempt of throttle linkage
Final decision of the throttle linkage

The next item to address what the throttle cable install. The standard Holley throttle cable system for this carburetor uses a two-spring system which works well but a fellow Sunbeam V6 suffered a blown engine at the hands of this throttle setup. The two-spring system failed when one of the springs caught on the other spring and destroyed the engine when the engine got stuck at open throttle. I ordered a Moroso throttle return spring kit which is shown in the second photo, but it too didn’t seem to fit well with the setup. On the third attempt, we ended up going with a Summit Racing billet aluminum throttle cable bracket. This option felt sturdy and fit nicely above the valve covers. I had to extend the carburetor studs but a quick Summit order fixed this. 

The completion of the fuel delivery was a great milestone for the project. We had finally decided on a path for the fuel system and given ourselves options in the future with a possible EFI setup. Things were starting to materialize and the car was becoming… a car. Next up for the project was the interior, which of course is the next plausible step. Motor on.