The Ultimate Guide to EFI, Part 3 – why “bolt-on EFI” is not worth it compared to proper port injection

The awesome dual-quad Edelbrock intake manifold I bought for my car was designed to fit two four-barrel carburettors (which is why it is known as a “dual-quad” set-up). Carburettors rely on swallowing fuel and air mixed together in a very roughly calculated amount, straight into the engine.

To fit EFI to my car I had to modify my awesome intake manifold, as the 2010 Corvette (LS3) fuel injectors have to be custom-fitted on the intake runners that lead to the cylinders. This is called “port injection” – where the injector squirts fuel into the intake port of the engine.


Here is the intake manifold as I purchased it. 

Beautifully TIG-welded to the manifold, Jeff ensured there was a slight bevelled edge to the FAST injector bungs. While I got weld-in bungs you can get these as a screw-in fitting, too. 


While there are some EFI set-ups that have injectors located in the throttle body itself this wasn’t going to work for my set-up for a few reasons. Firstly, I wanted two four-barrel throttle bodies to look like the old dual quad race car set-ups from the early ’60s, and there is very little space to fit two EFI throttle bodies together on one intake manifold. 


The P65 Edelbrock manifold is a “dual-plane” design where the intake plenum is divided into two chambers, with runners that cross over and have different heights. The EFI system required him to weld extra material to my manifold so the finished heights of the injector bosses would end up at the same installed heights, allowing one straight piece of extrusion to be used for the fuel rail. Jeff supplied and drilled the custom fuel rail extrusion to suit my LS3 fuel injectors. 


You can see here Jeff has left me some length so I can trim this rail down if I need to, which I think I will as the air conditioning compressor lives in that same space.


And here is the manifold set up with the air filter on top. I still need to make mounts for the fuel rails, tap the ends of the rails for fittings, get the rails powder coated, then start making my new fuel lines! 


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