I searched and found no threads that had contested or suggested this and so I figured it might be a potential design oversight.
It has been the policy of Automation that design options which would require drastic changes in cylinder head geometry are chosen at the family level rather than at the variant level. These features include camshaft configuration, number of valves, and whether or not the engine supports variable valve lift i.e. having two different cam profiles. It occurred to me today that direct injection is not receiving this same treatment though it possibly should.
My interjection is this:
Direct injection should be a feature explicity chosen for an engine family to support just like VVL and should NOT be chosen as a feature of a variant.
Because just like camshaft configuration, valve number, and VVL, direct injection requires extensive design consideration for the head itself unlike other fuel system options which only affect the design of the intake plenum. Heck when swapping between carburetion and single point EFI, the intake plenum may not even change hence why so many late '70s and early '80s cars have it. Direct injection is significantly more complicated however.
Direct injection first of all requires consideration of fuel injector placement and associated port geometry. This is especially problematic for multivalve SOHC engines which are already make spark plug placement difficult. There is also high pressure fuel rail routing to consider since direct injection systems run at extremely high fuel pressures on the order of 100 atmospheres.
Also, because the air-fuel mixture is no longer helped in homogenization by the intake plenum, special considerations need to be made for piston and combustion chamber designs to ensure proper mixing and even burn.
Because of these factors, adding a direct injection system to an engine already in production that was never designed for it would require some heavy modifications if not a clean sheet head design. Thus it seems to be receiving special treatment compared to especially VVL.
So a question:
Has this discrepancy been considered? If it has, then out of curiosity what was the reason that direct injection is allowed the leeway that it has? If it has not, then what are the devs’ thoughts regardless?
If this is indeed an unnoticed discrepancy, my suggestions for addressing it would then be one of the following:
Direct injection, like VVL, should be chosen as the feature of a family and only then may it be used.
Direct injection could remain a variant option but if direct injection is added in a facelift / is not originally included in the initial production variants, adding direct injection should incur an engineering time penalty proportional to the number of variants in production. (This option would be as if the engineers chose to use the same cylinder head for all variants. And as any engineer knows, modifications in one thing often have unexpected effects on things that you thought would be inconsequential.)
Direct injection could remain a variant option but incurs a flat higher engineering time if not one of the original production variants, and a flat higher production units cost if produced together with non-DI variants since it would need a different cylinder head. (This option would be as if the engineers chose to use a different cylinder head just for the DI variant)