For my EFI/ITB setup, I got almost everything in place. The biggest still missing is the linkage design between left and right banks, and throttle, of course. I made a quick mockup of the whole assembly (on a washing machine top), to study possible options.
As part of my EFI/ITB project, there’s a need for measuring the Air/Fuel ratio (AFR or Lambda), for setup and tuning purposes. Without it you will always be guessing…
The cheapest reliable option was to buy an SLC Free kit from 14point7. The assembly instructions were simple and clear and it worked at the first try. Then it was just a matter of hooking it up to a Bosch LSU 4.9 sensor bought from Ebay.
Here is the setup in all its glory, convenientely protected inside an electric shaver storage box…
Meanwhile, my active aero RC car is still undergoing parameter tuning. The wings are still not behaving completely ok, so no video yet…
I got a bit ahead (and jumped a couple of chapters), but I’m putting the finishing touches in the software, that will run in a laptop, and connect to the ECU for setup and tuning. Here’s a couple of the screens.
Let’s get on to the fuel system details. I will be using the stock Triumph injectors (from Sagem) that came with the throttle bodies as they have enough capacity to fuel, my otherwise stock, 2.7L engine.
As I already have injection on board (K-Jetronic), the existing fuel pump supplies enough pressure (about 5 bar) to feed the injectors, so one less expense… After the pump, fuel accumulator and filter, fuel will reach the fuel rails that supply the injectors. Those will be from an early Boxster. They’re not the prettiest (in the Boxster they’re hidden), but are cheap, readily available and… have the right size with absolutely no mods needed !
After passing through the rails, fuel will reach a pressure regulator. I will probably replace the one from the Boxster with an adjustable one to make sure I get the pressure I want (likely 3 bar). Finally before reaching the return line, I will add a Sytek one way valve. With it I hope to prevent the hard warm starts that I often experience. They’re due to a vapor lock condition on account of the fuel pump being close to the engine. What were they thinking at Porsche, back then ?
So i’m going to build my own efi/itb system, but how exactly ? Let’s see step by step…
Independent throttle bodies – The more complex assembly of the whole setup. Following the steps of Al Kosmal i’ll use Triumph speed triple bodies.
With an intake size of 40mm they’re a perfect match. They will be splitted to match the 911 cylinder spacing. To mate the different hole patterns and port layout, an aluminium spacer with 10mm will be used. Being wider apart than originally, custom steel levers and linkages will be designed to interconnect them. A rose jointed adjustable rod will link diagonally both cylinder banks, between #2 and #5.
For the airhorns, ITG AH34’s were choosen. With a height of 130mm, they’ll create visual and auditive impact. They will be joined to the TB’s through a rubber sleeve. For the filters, the easy choice are the ITG foam socks, although I would like to find a safe way to just use some mesh to keep the horns fully visible.
Idle air control. An old PWM-controlled valve from a BMW will be used. With the ECU controlling the duty cycle, the opening can be fully varied between 0-100%. Air will come from a separate small filter and will join each throttle body using the existing idle control lines.