Originally Posted By: mac9128
Side note I believe the 318 had a 9.2:1 compression ratio so is regular 87 octane okay or should I got a little higher? I've read unleaded gas wasn't good for the old softer valve seats so that could be an issue as well?
Compression ratio is only one factor in determining your octane needs. A second factor is how the combustion chamber was designed. That is why some older V8 engines needed 8.5:1 compression to work with a 87 octane fuel, whereas newer ones would use 9.5:1 or more.
Since you have an older engine, I think you would be better off with higher octane gasoline.
As for the valve seat issue, there are a mix of factors to consider. Some of the old engines that ran leaded fuel had no problem because they had a small cam, low redline, and the head was made of a high quality alloy. Sometimes when a leaded gas engine has this problem, someone has already had the cylinder heads rebuilt with upgraded valve seats. This is also common if the engine has been given a complete rebuild.
When valve seats are known to be too sensitive to unleaded gas, there are fuel additives that create an ash to protect the valve seat. It mimics the effect of leaded gasoline, but doesn't actually contain lead.
I suggest reading some enthusiast pages about your car. Other owners may be able to tell you if anyone had to install upgraded valve seats or use fuel additives.
