Question on EFI timing and heat soak
 

I have two questions about intake systems such as the one below (and any other variation where the injectors are near the intake ports).

http://rennlist.com/forums/upload/efi_3_watermarked.jpg

1. Is it ideal to time the injection such that the fuel goes directly into the cylinder through an open intake valve or does some of the fuel wet out the port and back side of the valve?

2. I've seen phenolic spacers used to reduce heat soak into the intake runners. Could PEEK also be used and could the intake runner be a non-metallic material? I was thinking of a composite material with high temp resin for the intake runners.

1.
Yes, at least for fuel consumption, in theory. But in reality at higher rpm they spray almost continuously even though the valve is open for just a short while, otherwise it wouldn't manage get enough fuel into the combustion chamber. The time would be to short, to deliver it.

1. As said by Magnus... BTW it is not that near on a 911 head.

2. Stock 930 runners are kind of phenolic too, so if your material is strong enough when the pancake is torqued down and withstands heat and fuel, why not? Maybe sealing could be an issue?

1. Is it ideal to time the injection such that the fuel goes directly into the cylinder through an open intake valve or does some of the fuel wet out the port and back side of the valve?

Erik,

The concept of "ideal" is difficult because emissions, economy and power are conflicting goals. In practice, OEM's time sequential EFI with the closing, not the opening, of the intake valve at low load, part throttle. This gives more consistent emissions results across cylinders.