| heads together, but also working up a set of NA heads for a non-turbo shortblock I rebuilt last week (another project I'll reveal upon completion ;-), but I wanted to take a moment to show those of you who dont know about this what the whole "Soft Valves" fiasco was all about. In the 1st Zs of the 1989 production run there was an issue with the alloy being used for the intake valves. They referred to this as "soft valves", although this isn't entirely correct. However, what happens to these valves is a severe pattern of wear on the valve face itself, the area of the valve that contacts the valveseat to seal the combustion chamber. This wear pattern is clearly visible once the valve is removed but there are other indications that soft valves are present. Because of the wear, the valve will 'sink' into the head. As this wear occurs, it happens unevenly around the face and it prevents the valve from completely sealing up. An engine with low compression is an indication of this, but keep in mind, this isn't the only possible reason for low compression. Additionally, since the head of the valve is 'sinking' into the cylinder head, it is lowering the compression of the engine (on top of the leaking valve). Performance will suffer dramatically on engines with this problem. Fortunately, Nissan caught this problem pretty early and began using a different stainless alloy for the intake valves. But, the funny thing is, they called the bad valves 'soft valves' when in fact, they are actually harder than the new alloy being used. I had various different valves Rockwell hardness tested several months ago, the "soft valves" had a rockwell hardness of 32 whereas the newer alloy has a rockwell of 27. I guess "soft valves" makes more sense to most people as being the reason for the wear, but its a more complicated issue of valves 'bouncing' off of seats and impact being the cause of wear, so I've been told. You can have too hard of a valve apparently. Here's some pictures I took: This is a picture of the soft valve next to a new valve installed into the combustion chamber. Note how one valve is about 0.030" lower than the other. (Black-headed valves are what you are looking at, not the shinier exhaust valves)
 And here is a picture of the same two valves, side by side. Note that the good valve on the left has a flat "face" (grey area) where the valve on the right has 3 distinct angles worn into the face (shiny area). These angles you see are the shape of the valveseat (30^, 45^, and 60^ angles) which have 'worn' into the valve. The greying of the valve face on the left is due to valve lapping compound, a silicon-carbide "grit" suspended in a water substrate - used for seating the valve to the seat. The compound is not present in the picture, but you see how the surface is prepared with it (and if you look at the bottom-center of the pic of the valveseat, you can see the greying of the 45^ face there too). 
Just another pic:
 I have a whole box of these soft valves that came out of a '90 cylinder head - all of them are worn to some degree or another like this. This was the worse of them all.
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Nissan Soft Valves. I've been working on putting my TT - 
