There is a lot of reasons as to why OldIron440 and I are saying – but neither was explaining why.
First of all the /6’s that FMJ’s use are Smog Engines using a Smog camshaft – neither does a thing for performance or fuel mileage.
The best thing to do is to build your /6 to pre-smog specifications and then you will get the best fuel mileage and power.
I’m not sure what the compression ratio is for that engine, but if using 87 octane fuel, I wouldn’t go much more than 8.7 to 1 compression ratio.
If willing to pay for higher octane fuel on every fill-up, then sure, I’d go higher than that.
Typically, Smog-er camshafts do not have a lot of lobe to them. Also, metal hardening is better now than it was way back then. Camshaft lobes might wear faster than any other component on the engine – as the mileage goes up. I have seen some camshafts, with roughly 100k miles on the, with almost no lobes on one or more cylinders.
I’m not talking about a race camshaft – but something like an RV cam that has a bit more lobe to it.
Back in the day, the different camshaft levels were: stock, RV, a level under performance, performance, then a couple more rungs before you get to race (and so forth).
Almost all cars run better with the RV level camshaft, over a stock grind. All power accessories will work, smooth idle, and so forth, as well.
If engine appears it has 177k miles, I would change camshafts and lifters, even if going back to a stock grind, because of lobe wear. Most likely I would purchase the next higher level camshaft (a couple of rungs under performance – but above stock).
There is nothing worse than having a camshaft with its lobes worn “round” or close to it.
Going back to compression, the higher the compression ratio is, the more efficient engine will be and thereby more power it can produce. Some say for a street car 10 to 10.5 to 1 is the sweet spot. The problem is it requires 93 (or higher) octane to run – for each and every fill-up.
I suspect that is not what you are looking for?
Anything above 8.0 or 8.1 to one has got to be a good thing (note: I don’t know what it should be at) – but I wouldn’t plan on going higher than 8.7 (or so) to one ratio – which allows for machining mistakes that might push it to 9.0 to one.
I do not know what the /6 measurements are, to machine off – but I would measure and re-measure before machining – for it can’t be un-done.
BudW