[67Lemons]

I have a ‘68 400 with a set of #15 heads but I’ve been looking around for something with screw in studs & found a fresh set of 670’s with new valves for a good price. I see that they are supposed to be 72cc vs my stock 75cc heads, my ‘68 400 has original pistons so will the slightly smaller cc chamber heads bump up my compression to an unmanageable compression for pump fuel on the street? My current thoughts for a cam is an 068 with my #15 heads or Crower 60916 if I get screw in studs with the 670’s.

[steve25]

Since the 670 heads in stock form are closer to 74 CCs and now being rebuilt with a valve job your likely right back in the 75 to 76 CC area.

The closed chamber heads like the 670s are lees likely to ping and knock then your #15 heads , the emissions will not be as good, but if your going to cam the motor up it’s a moot point .

The Crower cam sounds like a good pick.
The only issue I see with that Crower cam is running stock springs ( which you should not be doing anyway) with that cams.470” exh lift.

[67Lemons]

Of course, new springs to match the cam. Any pitfalls to be aware of using the closed chamber 670 heads?

[steve25]

No, there a bolt on.

[geeteeohguy]

The 670's will work great as long as you run 100 octane fuel (if you have stock flat top pistons). IME, they will detonate just as bad as the 15's. When I ran them on my '67 400, it was ping city. When I switched to #12's, same thing. I finally ended up installing some 1970 #15 heads (87cc 455 heads, not the same as a '68 #15) and am now able to run on 91 octane pump gas MOST of the time. Running an 068 cam and flat top pistons.
670's, unless I had deeply dished pistons, would be my last choice for a street car if I wanted to run pump gas. (I have driven my '67 over 130,000 miles).

[steve25]

A question for the OP, are the valves in your 670 heads flat face and have the heads been milled?

[67Lemons]

Originally Posted by steve25

A question for the OP, are the valves in your 670 heads flat face and have the heads been milled?

I do not own these heads, I saw them listed for sale at a good price, they are at least the second set that I have seen listed locally in recent history. The 400 that I picked up is completely stock, low mileage at 40k engine that I am going to install a cam, timing chain set, valve springs & oil pump before I pull my current 326. I just figured if I swap the heads to something with screw in studs then I have a few more cam choices vs my pressed in studs on the stock #15’s that came with my 400.