Articles on Engine Design

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A snippet about oxygen sensor location from a Coyote engine swap guide:

If the Oxygen Sensors Must be Moved
FRPP's engine harness and controls package supplies two wide-band oxygen sensors that are designed to mount in the stock '10–'11 Mustang GT locations. If the factory headers don't fit your old chassis, the relative sensor position may need to change on any new exhaust. If that's the case, position each sensor so it can sample from all four cylinders on one bank (for example, in the header collector). Ford also frowns on altering sensor wire lengths, claiming that such alterations can degrade sensor function. If the headers won't permit sampling all four cylinders without harness mods, Ford says the least harmful alternative is locating the sensors to sample one cylinder per bank: "The cylinders that have on average the closest air/fuel ratio to the bank average are cylinder No. 4 on Bank 1 and cylinder No. 7 on Bank 2; the next best choices are No. 3 and No. 8."

https://www.hotrod.com/articles/hrdp-1306-ford-coyote-engine-swap-guide/

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https://saemobilus.sae.org/content/2016-01-2252

Formation of Intake Valve Deposits in Gasoline Direct Injection Engines
Gregory Guinther - Afton Chemical Corp. , Scott Smith - Afton Chemical Corp.
Journal Article2016-01-2252
ISSN: 1946-3952, e-ISSN: 1946-3960
DOI: https://doi.org/10.4271/2016-01-2252
Published October 17, 2016 by SAE International in United States
Formation of Intake Valve Deposits in Gasoline Direct Injection Engines
Sector:
Automotive
Topic:
Engine lubricants, Combustion and combustion processes, Gasoline, Engine cylinders, Lubricants, Valves, Wear
Event:SAE 2016 International Powertrains, Fuels & Lubricants Meeting
Citation:
Guinther, G. and Smith, S., "Formation of Intake Valve Deposits in Gasoline Direct Injection Engines," SAE Int. J. Fuels Lubr. 9(3):558-566, 2016, https://doi.org/10.4271/2016-01-2252.
Language:English
Abstract:
Gasoline direct-injection (GDI) engines have a well-known propensity to form intake valve deposits (IVD), regardless of operator service, engine architecture, or cylinder configuration. Due to the lack of a fuel-washing process that is typical of Port Fuel Injected (PFI) engines, the deposits steadily accumulate over time and can lead to deterioration in combustion, unstable operation, valve-sticking, or engine failure. Vehicles using these engines are often forced to undergo expensive maintenance to mechanically remove the deposits, which eventually re-form. The deposit formation process has not been well-characterized and there is no standardized engine test to study the impact of fuel or lubricant formulation variables. To meet this need, a proprietary vehicle-based GDI-IVD test that is both repeatable and responsive to chemistry has been developed. Using a vehicle equipped with a 2.0L turbo GDI engine, the mechanisms leading to deposit formation have been studied and analyzed, and found to be a combination of engine oil, engine-wear elements, unburned fuel, and exhaust gas contaminants. The rate of accumulation was also found to be affected by engine lubricant formulation variables.

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Some support for popular PFI additives in the service of keeping intake valve deposits at bay
http://casestudies.atlanticmotorcar.com/mini-cooper-engine-problem-carbon-deposits-on-intake-valves/

How To Prevent Carbon Deposits On Intake Valves
An ounce of prevention is worth a pound of cure, so here is what you can do to help prevent this from occurring with your beloved Mini, BMW or other vehicle. How fast the intake valves get dirty does not seem to be a function of fuel quality. Rather, it appears to be influenced most by driving habits, and how often the engine oil is changed. Oil vapors and combustion byproducts that are drawn back into the intake manifold through the crankcase ventilation system seem to contribute most to carbon deposits on the intake valves.111

At the Atlantic Motorcar Center, our advice is to change your oil every 3,000 to 5,000 miles if you only do short trip stop-and-go city driving, or change your oil every 5,000 to 7,500 miles if you do mostly highway driving. If you want to minimize carbon buildup on the intake valves, don't push your oil change intervals to 7500 miles or longer unless you are using a high quality full synthetic oil (which usually has less volatility than conventional motor oil).

We also recommend the monthly use of a fuel additive, like Lubromoly, or Chevron Techron, while these cars are direct injection, and as such the fuel does not inject onto the back of the valve, but rather in the cylinder itself, we've noted that cars using these products experience considerably less carbon buildup.

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Gen 2 3.5L Ecoboost engines (dual injection PFI DI) get upgraded timing chains among other things:

New 3.5 EcoBoost is equipped with a two primary chain system (there is one separate timing chain driving each cylinder bank). The cam chain drive sprocket on the crankshaft is a double gear arrangement. New chains are also more durable and less prone to stretch due to an increased thickness of the side plates.

https://www.motorreviewer.com/engine.php?engine_id=144