VK Commodore EFI Systems
The EFI from the VK can perform very well, despite being very simple - almost to the point of being crude. The system has few inputs, and has no feedback devices such as oxygen sensors etc. The injectors are wired in two groups of three, but all fire simultaneously at 120deg intervals. The manifold design provides very good midrange torque and is suitable for engine speeds up to about 5500rpm - ideal for a strong street car. A bit of judicious portwork at the transition area leading up to the gasket face should pay off with even more flow and power. The relative crudity of the fuel control makes the fuel economy from these units less than spectacular and in fact better economy can be had from the Varajet equipped engines. Improvements to the controls make these units perform even better, with gains in both power and economy. There are limitations with the stock ECU with regard to compatability with longer duration cams. Aftermarket, tunable ECUs are readily available though, as are bigger injectors and throttle bodies etc. A popular budget mod is fitting the 808 Delco ECU from the JE Camira. These are cheap, programmable (using something like Kalmaker) and able to use additional inputs such as exhaust oxygen sensors. I won't go into much detail here on EFI's but there are plenty of people out there who have used these successfully, and there are some good how-to's on the web.
The strong point of the EFI system is the midrange torque provided by the long manifold runners, and this manifold also works very well with LPG. For an LPG-only engine the compression ratio can be raised to make up for the slight drop in output that LPG normally brings. There won't be any distribution or fuel drop-out problems and you'll get a nice flat torque curve...
Be aware that the EFI manifold becomes quite restrictive at higher revs and flow rates - say around 5500rpm/180hp and up. There is a substantial reduction in area for a distance of about 100mm back from the gasket face, and there isn't enough wall thickness to open them up without first building them up with weld. And even if you did open them up it's likely that the runners would be too long for high rpm work anyway. For practical 12 port street car projects though, a VK EFI may well be the best choice.
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| VK EFI manifold sectioned to show the 40mm ID runner entries. |
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| This shot shows how the manifold runners neck down as they approach the head. |