400 motor with 16 or 62 big valve heads - Pontiac GTO Forum
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post #1 of 2 (permalink) Old 01-12-2018, 07:56 AM Thread Starter
 
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400 motor with 16 or 62 big valve heads

I currently have a 400 with 14 heads and the original tri power setup. I have a set of 16 heads from a 68 Firebird - big valves, screw in studs, and small chamber ~72 cc (need to get exact). I also have a set of 62 heads, but have been told the 16s flow better. I would also like to add a camshaft if swapping the heads. (My goal is to get the motor to 350+ hp with a nice broad power curve.) My concern is the compression ratio and 91 octane here in socal.

My questions are:
(1) Can I effectively lower the CR enough with a thick head gasket?

(2) Is there a popular camshaft that would not only make more power but also lower the CR? Any specific recommendations would be great!

(3) If options 1 & 2 won't be sufficient in lowering CR enough (to ~9.25:1), I guess I need to build the bottom end with dished pistons ?

Thanks

1965 GTO Convertible 3 speed tri-power drum brakes originally

Current setup:
400 cu in with tri-power
4 speed Muncie
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post #2 of 2 (permalink) Old 01-12-2018, 11:20 PM
 
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Originally Posted by cij911 View Post
I currently have a 400 with 14 heads and the original tri power setup. I have a set of 16 heads from a 68 Firebird - big valves, screw in studs, and small chamber ~72 cc (need to get exact). I also have a set of 62 heads, but have been told the 16s flow better. I would also like to add a camshaft if swapping the heads. (My goal is to get the motor to 350+ hp with a nice broad power curve.) My concern is the compression ratio and 91 octane here in socal.

My questions are:
(1) Can I effectively lower the CR enough with a thick head gasket?

(2) Is there a popular camshaft that would not only make more power but also lower the CR? Any specific recommendations would be great!

(3) If options 1 & 2 won't be sufficient in lowering CR enough (to ~9.25:1), I guess I need to build the bottom end with dished pistons ?

Thanks
All D-port heads with the big valves basically flow the same, so its your choice. Best improvements would be gasket match the intakes & 3-angle valve job. Add ARP 7/16" BB screw-in rocker arm studs and poly-locks.

Do not go with thicker head gaskets -band aide fix. Get the correct dished pistons to give you 9.0-9.3 compression.

Cams with a nice broad power curve will be those like factory - 114 LSA. Narrower LSA will typically narrow the power curve, boost cylinder pressure, and are more "explosive" but run out of steam early.
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