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Discussion Starter · #1 · (Edited)
Interesting technical read.

Arriving at our 9A2 Direct Fuel Injection, the article concludes:
"one of the most important aspects of high pressure (over 3,000 psi in current versions) DFI is that it is the first EFI system to surpass the fuel atomization capabilities of the original Bosch timed MFI systems. The evaporative cooling effect imparted by atomization of the fuel charge is further exploited by it being injected directly into the combustion chamber, which greatly improves resistance to detonation and allows higher compression ratios and/or turbocharger boost levels to be realized."

Related quote from another source:
"The side-mounted direct injectors have been moved to the top,next to the spark plug. The injectors now spray at 3625 psi, nearly double that of the old injectors. The combination of a top spray and higher injection pressure creates a finer atomization of the fuel, resulting in a better fuel/air mix in the chamber. To further improve on combustion efficiency, key to improved fuel efficiency, the intake ports were refined to allow for more tumbling of the fuel mixture within each chamber. As a result, there are fewer raw particulates in the exhaust. "

In other reading I've seen references to this ultra-high-pressure DFI having been pioneered in the 919 race-car's turbo-four, which faced draconian fuel consumption restrictions (together with high power requirements) in the WEC LeMans Prototype formula. Racing improves the breed.....

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151 Posts
DFI and gummed up intake valves

Has Porsche found a solution for the problem of gumming up intake valves in DFI engines? BMW pretty much solved the problem in their engines. After 2012, the turbo MINI engines didn't have this problem.
I only have 20,000 miles on my '17 CS and have no symptoms. But in the older MINI turbo engines the problem would show up after 50,000 or more miles.

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157 Posts
Despite manufacturers’ initial issues with implementing GDI such as prematurely failing pumps, coking intake valves and low speed preignition, there’s no denying its significant contributions to reducing fuel consumption and decreasing tailpipe emissions.

EU, EPA/CAFE and motorsport sanctioning organization “draconian” requirements have again compelled engineering staffs to action.
That GDI 718 exhaust drama on overrun in sport mode is a nod to clever programming, too.

I do miss tweaking my erstwhile Holley, Weber, Solex and Rochester carburetors on occasion. ;)


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157 Posts
DFI injection strategies
Depending on the operating condition, the following injection strategies are selected:

Depending on ambient temperature:
• 3x during the intake stroke
• In case of extreme cold, 3x during the compression stroke
Catalytic converter heating
• 2x during the intake stroke, 1x during the compression stroke

Warm-up phase
• 1x during the intake stroke
Acceleration with low to medium load
• 2x during the intake stroke

Operating temperature
• Single injection for small and medium load
Acceleration at high load
• 2x during the intake stroke up to 3,500 rpm
• 1x during the intake stroke above 3,500 rpm

The central injector position and the increase in the fuel pressure (to up to 3625
psi /250 bar) optimize mixture formation and the combustion behavior to such an
extent that it was possible to dispense with the secondary-air injection process
previously used to heat up the catalytic converters. This makes it possible to achieve
lower untreated exhaust gas emissions and to comply with all required exhaust
emission values.

That's a lot of code!

Service Information
2017 Technik Introduction
718 Boxster/S (982)
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