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516 to 906 head on '66 440?

Jeff_383

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Say I have a bone stock 66 440 (516 heads). One valve is bad on the 516's. Have a set of 906's that are fine shape. Is anything gained or lost by tossing on the 906's? Other than the comp drop, which is how much?
 
I was told it is approximately 3/4 of a point. The flow is slightly better since the 906 uses a larger exhaust valve.
 
Well, the exhaust valve on the 516 is a 1.60 while the 1967 and later 383-440 engines had 1.74 " valves. At higher rpms, it theoretically would make more power.
Is it a wash? Only a dyno can tell you for certain.
 
A stock 906 will definitely produce more power than the 516. CR difference is usually about 1/2 point. If you have the 906's take the time & a little cash to freshen the valve job and guides. A quick pocket port is worth a fair amount of power. A good shop can do the "pocket port" with a deep steep bottom angle on the valve job.
 
I like my 516 heads with larger exhaust valves and hardened seats. Being closed chamber, they increased my compression ratio without changing pistons. Personally. I don't think expensive porting is that much of a gain on a lower RPM engine. Those heads and a steel shim head gasket give me 9.5 to 1 compression ratio. I have heard that in some cases, a smaller port will give more air velocity and better performance................................MO
 
The 516 will work fine especially with the larger exhaust valve. Pocket porting gives a significant increase in power/torque through the entire RPM range. Pocket porting doesn't decrease velocity just improves the in & out. A little more CR is always helpful. The 516 won't flow as well at high lifts and high RPM's as a 906, but works good if the motor is a 5000 - 5500 RPM piece.
 
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