# Can '670' Heads work on a 1966 389 engine with stock pistons?



## Ozzie (Aug 24, 2009)

Question: Will 670 heads work on a 1966 389 engine with stock pistons? Would the reliefs in the 389 pistons clear the large valves in the 670 heads?


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## 646904GTO (Feb 10, 2008)

The 389 had six valve reliefs on each side of the pistons. The compression will be higher though. The 670 head was closed chamber and is about a 68cc chamber and I have been informend has different valve angles.


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## Too Many Projects (Nov 15, 2008)

Everything I've heard about this swap says no. Supposedly the valves will hit the pistons. Where's geeteeohguy ? He's worked on these for many years.


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## geeteeohguy (Feb 2, 2008)

I had a friend who used to bore 389's to .060" over....that allowed him to use stock (std) bore 400 pistons and later heads. Worked for him. With the stock pistons, the valve angle/position is wrong. '67's had bigger valves, and at a different angle. good luck.


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## Ozzie (Aug 24, 2009)

Thanks gentlemen for answering my question.


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## geeteeohguy (Feb 2, 2008)

I just found out from a machinist that most aftermarket pistons for 389's have a "double eyebrow" indentation on them instead of the stock "single eyebrow". This is to allow a wide range of cyl. heads to be used. With aftermarket pistons, you CAN run any head on the 389. But if still stock, no go.


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## PontiacDave (Jun 9, 2009)

Wait a minute......I have a 1965 389 with cast replacement 0.030 over pistons so it definitely has 389 pistons. I installed 670 heads (it had #77) before I even heard of the different valve angle and piston reliefs issues. I am 100% sure I have only 4 vale reliefs. I have been using this combo for several years with no issues at all.....I am not sure what cam I have. I believe that makes a huge difference on clearance if there is an issue but I am no expert at any of this. I was happy at the results though....the engine definitely gained some horsepower and a bunch of torque.


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## geeteeohguy (Feb 2, 2008)

With 4 valve reliefs, your replacement pistons are the "unversal fit" double eyebrow type. They are fine for both the 389 heads and the later 400 heads, as you know.


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## PontiacDave (Jun 9, 2009)

That's really odd.....I distinctly recall when I did the head swap that the pistons had a 0.030 on it and it definitely had only 4 valve reliefs, not the "universal" 8 relief style. There is a huge difference between them so it was very obvious. One thing I am not sure about is which set of valve reliefs I have....the 389 early style or the 400 later style. Could I have originally had the later 400 style reliefs and that is why the valves clear? How could it be 0.030 over with 400 style reliefs.....that would make it a 400 piston with a smaller than standard bore size. If I had 389 heads on with 400 pistons wouldn't the valve hit also? I just looked down my spark plug hole with a lighted bore-scope and for sure do not have the universal style pistons. I am confused :confused


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## geeteeohguy (Feb 2, 2008)

I don't know what to tell you, but obviously, your pistons are correctly relieved for the later heads, because the engine runs without bending valves. I had a friend who used to punch 389's out .060" just so he could use standard 400 pistons and save money on the rebuild. Whatever you have in there, it's working, so put the plugs back in and go drive it!!!!


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## plmberkevin (Aug 16, 2009)

Best thing to do is to put clay on the piston set the head down on motor and bolt it down.Slid in the 2 push rods and turn the motor over and take the head back off and look whats going on.Or take it to a shop and have them do it.


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