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Old 01-10-2013, 12:42 AM   #1368
Patrick Olsen
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Member#: 120
Join Date: Jul 1999
Chapter/Region: AKIC
Location: Where the Navy sends me...
1997 Legacy 2.5GT
1996 Impreza coupe


Originally Posted by Patrick Olsen View Post
Some other items of note thus far...
- The first gen engine has an interesting coolant cross-over that goes from the back of each head and crosses over underneath the intake manifold. The EZ30R doesn't have anything like that; the AVLS solenoids occupy that space on the back of the R heads. It seems strange to me that such a thing would be necessary, as there's already a coolant cross-over at the front of the engine.
Turns out the "interesting coolant cross-over" isn't for coolant at all - it's actually part of the crankcase ventilation setup. The passenger side head has a port at the top of it that connects to the crankcase. That cross-over connects the two heads; the driver side head does not have a direct connection to the crankcase. However, it does have ports in the front cam bearing cap that connect the head to the air volume contained between the front and rear timing chain covers, and then there's an opening at the bottom of the rear timing chain cover into the top of the oil pan.

As a result of the differences in the head configuration, the 30D head gaskets are different on each side of the engine, while the 30R head gaskets are the same on both heads. Based on my limited experience with engine assembly (a couple EJ25s, a SBF, and an LS6), having different head gaskets on a V or H engine is not common.

I also found something that mystified me, and I posted about it on another forum. The fuel injector ports on the heads are all joined together by a header. The headers on each head are connected by a cross-over, and that cross-over then connects to the throttle body. Pictures to explain...

Here's a shot showing the passenger side head, with the fuel rails and fuel injectors just placed in their normal position (but obviously not connected or bolted in place). Fuel supply and return are at the rear of the head (left side of the picture), and the cross-over I referred to is at the front.

Zooming in, you can see that where the fuel injector sits there is a port, and that port ties into a header that runs along the head, connecting all 3 injectors.

A cross-over connects the two heads together, and also runs to the throttle body:

Here's a shot of the cross-over going over to the driver side head:

A blurry shot of the TB. The hose from that cross-over connects to the nipple at the top of the TB. The black solenoid thingy on the right is (AFAIK) the IACV. The nipple connects to either side of the throttle plate.

So, what would this system be? The only thing I could figure is that it provides an atmospheric pressure reference for the fuel injectors, but I don't know why that would be required. As you can see in the driver side picture above, there's a normal fuel pressure regulator at the front of the driver side fuel rail, with the vacuum reference hose tapping into the intake manifold somewhere underneath. On the other few engines I've messed with, that's all there is, just that vacuum-referenced fuel pressure regulator.

One of the guys on the other forum replied:
The Germans used to run air-shrouded injectors tips for emissions reasons. There would be a small air channel to each injector that was routed to pre-throttle body air pressures. When the intake manifold and ports are under vacuum, air rushes in through the air channel and then into the port, rushing out around the tip of the injector. The rush of air atomizes the fuel better, making more of it burnable and cleaner emissions.
Apparently some Honda engines used a similar setup, called a Fuel Injection Air Control System. Interesting stuff!
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Last edited by Patrick Olsen; 12-17-2015 at 07:10 PM.
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