I am in the last stages of rebuilding a 1.8L motor for my 1975 914. I shall be using a 9550 cam from Jake Raby and 96mm pistons and cylinders. Everything else is stock. I plan on using it with the stock L-Jet fuel injection. The engine is aimed to be installed in a daily driver.

I am trying to decide what to do about the compression ratio. From computing it over and over it appears that if I don't put any spacer rings, nor head gaskets, I end up with a CR of about 8.5:1, which is a bit higher than what I originally aimed for (I wanted 8:1 to stay on the safe side). However, if I put the VW recommended spacer rings (1.6mm) between the cylinders and the crankcase, then I end up with a CR of 7.2:1 which is way too low.

Two questions:

a) Would a 8.5:1 with the 9550 cam (fairly mild, only slightly more aggressive than stock) work well on 91 octane gas? Could it perhaps even be run on 87 octane?

b) If not, and I want to get down to 8:1, where can I find spacer rings of thickness of about 0.6mm?

Thanks,
Andrei.

I am already running a Raby 9590 (they don't sell the 9550 anymore) in Betty's car. I use the head gaskets, and it works great with 91 octane.

I got several sets of them from a parts store BAP/GEON near me in various thicknesses. When I got them I found that they had a slight burr from being stamped out so was careful to grind off the sharp upset edge, then measured them with the calipers. I found one set had variation in thickness within the four pieces so ordered another identical set to get four equal ones. They're not expensive--fit under the cylinder base & didn't use any head gasket.
I don't think 8.5:1 is too much to worry about as Jake commented that the actual dynamic CR on an 8:1 setup is probably about 6:1. 92 or 93 octane should be fine.
IIRC the stock 1.7 engines had over 9:1 and required premium fuel.

You can stack up to 3 shims per cylinder base, so if you take 3 sets of the gasket set base shims you are getting close to your .6mm.
I think pelican parts sells these shims individually.