Thursday, 25 November 2010

Intake Manifold - The beginning

The aftermarket fuel injection controller I will be using (Megasquirt II) is typically set up to be a speed-density system meaning the computer measures the engine speed and manifold pressure, then calculates the mass air flow into the cylinders. The injected fuel is then a proportion of that air mass to achieve the desired air : fuel ratio (nominally 14.7:1, but varies with operating conditions). Closing the loop with a lambda sensor in the exhaust stream confirms the desired ratio is achieved and if not, some 'live' tweaking can occur. This system works well, but is based on the assumption that the total air flow is evenly split between the cylinders. This is where the intake manifold comes in, as it is critical to splitting and delivering the air charge to the individual cylinders. There are a couple of options for a fuel injected manifold on the Ford 302; use a late model stock system or modify an standard carburettor manifold with injector 'bungs'. The appearance of the stock system is not really in-keeping with the look I want for the engine bay and I have concerns over how well the air will be distributed with the carb manifold (either single or dual plane). To allay (or confirm!) those concerns, I have decided to do some investigation work which involves some engineering analysis. Fortunately, I have access to a CAD workstation with CFD (Computational Fluid Dynamics) software and I will be looking at comparing the performance of the options for my intake manifold.

Watch this space...

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