What the Hell Happened to Project Silvia?


Ok, except for two things. There is actually a change in oil passages between an S13 and S14. The variable cam timing actuator needs oil pressure and the S14 takes the oil passage from the block that was originally intended for the chain tensioner and re-purposes it for the cam timing. The S14 chain tensioner is then fed by an oil passage that not only doesn’t exist on the S13 block, but comes from a place on S14 block that doesn’t even exist on the S13 block. Put an S14 head on an S13 block and that passage will be dangling in space. Bummer. My plan, then was to plug the S14 head’s chain tensioner passage and drill a new one in the front of the head which I could feed with an external oil line.

s14 cylinder head

The cad-plated hexagonal doodad top center is the solenoid that sends oil pressure to the VTC actuator. The Sharpee marks are my attempts to trace the oil passages.

S14 vs S13 cylinder head

Stacking an S13 gasket on the S14 head, it’s easy to see the difference in oil passages. On an S13, oil feeds up around the head bolt hole right in the middle of the picture and pressurizes the timing chain tensioner. On an S14, that same oil feed is used instead for the VTC actuator. The diagonal oil passage just up and to the right of that hole is added on S14s to supply the chain tensioner. Problem is, as you can see from the S13 head gasket, there is no block there on the S13. I’ll plug this hole and feed the chain tensioner with an external line.


Things start going badly…

Shop #1:

Sometime in early December, 2008, I dropped by Cosworth USA, handed the head and valve guides to Eric Hsu, and told him what I was trying to do. And then a month went by. 

Slipping the head in the back door was my first mistake. Had I gone through the front door, someone from Cosworth’s machine shop would have looked at what I wanted to do and immediately said no. Instead, my head was put on a shelf and everyone went home for Christmas break. After they came back, Eric finally took it over to the machine shop where it was put in line. When it finally got to the front of the line, someone looked at what was needed and finally said no.

Turns out Cosworth’s machine shop is set up for doing a relatively limited number of things over and over very precisely. Subaru heads, MZR heads, EVO heads, etc., They have the tooling they need to do the jobs they do, but none of those jobs, apparently, involve reaming valve guides to 7mm. (Turns out the brand new guides I got are intentionally undersized and are intended to be reamed to size). They simply didn’t have the tooling to do what I thought was a simple job.

Shop #2:

Eric suggested I take the head down the street to Tom Fujita at Port Flow. Tom was rightfully skeptical when I told him what I wanted to do, but had me leave the head with him for a week while he tried to figure out if he could help. One week later, right on schedule, the answer was no. Reaming the guides to size wasn’t the problem, installing them in the first place was. Both the DE and DET valve guides have the same wall thickness, which means the OD of the DET guide is 1mm larger than the OD of the guides already in the head. Swapping guides would mean opening up the guide bore in the cylinder head casting. This is not a normal procedure, so there is no spec for how much of an interference fit is needed, and he had no tooling for it anyway. It seemed theoretically possible, but Tom didn’t want to risk it.

In the week it was there, Tom did get me three steps closer to being finished though. First, he decked the head just enough to give me a nice flat gasket surface. Second, he plugged the tricky, diagonal chain tensioner oil passage, and finally he put my head on his fancy vacuum cleaner thingy that measures how well your valve seats are sealing. This confirmed that the intake valves were sealing perfectly well and didn’t need to be touched. The exhaust was also sealing, but changing valves and guides would require a fresh exhaust valve job anyway, so that was irrelevant. 

S14 sr20det oil passage plug

Drilling out and tapping the chain tensioner oil passage shouldn’t have been hard, but being a diagonal hole, I didn’t want to risk screwing something up. Tom did it for me. in this shot of the head surface, you can see parallel cut lines form Tom’s milling of the head, and the finer crosshatched pattern from Dan Paramore’s hand finishing of the same surface.


1 comment

  1. I forgot how much I missed Project Silvia. I was an avid reader of Sport Compact Car when it was still in print form. I was happy to find out Project Silvia is still in work, as of this posting anyways. Now that I’m here I’ll have to catch up with all the turbo japanese goodness. Thanks for bringing this back guys!!!

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