# #16 Heads (lowering compression) build recipe / suggestions



## 66CHEEVO (Jan 24, 2021)

Hi everyone, I've previously posted a few questions so i can prep myself for an upcoming rebuild.

I have a 1966 GTO with currently with a ow compression 8.00 1973 400ci X4 block ID #481988 with small valve 4X heads. 

I recently acquired some large valve (2.11 / 1.77) 72-75cc 1968 #16 heads with screw in studs. I purchased these heads in great condition not realizing what issues I would have with the high compression. 

I plan on rebuilding my 400 and hope to lower the compression so I can run it on pump gas. The highest octane in my area is 91. On this note I'm hoping to get the compression down to 9.0 to 9.5 

Looks like the most feasible option for lowering the compression is dished pistons. I still need to tear the engine down and see what I'm working with; however, I'm pretty certain I currently have stock flat top pistons. 

I'm checking to see if anyone has achieved this or if they have any build recipes or recommendations. 

I still have allot to learn and doing my research. I'm currently in the process of ordering some Ram Air D-port exhaust manifolds and a new Tri Power Carb setup through Pontiac Tripower. I'm looking to keep this build fairly stock and hoping to achieve the factory 330 - 360 HP. My car currently has a 4 speed Muncie but still need to determine my gear ratio.

I know I still need to find out what my block bore size is and if it’s even going to be rebuildable. I was hoping someone might be able to point me in the right direction with a good build recipe or for selecting the right pistons, cam and valve train kits. 
Any feedback is greatly appreciated. Please let me know if I left our any important details. 

Thank you in advance


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## PontiacJim (Dec 29, 2012)

Piratebates said:


> Hi everyone, I've previously posted a few questions so i can prep myself for an upcoming rebuild.
> 
> I have a 1966 GTO with currently with a ow compression 8.00 1973 400ci X4 block ID #481988 with small valve 4X heads.
> 
> ...



Do a search through the forums. Plenty of info on past builds. Read this as an example:









400 tear down


Hey! I just picked up a Pontiac 400 from a 71 GTO that is eventually going into my 68 goat that powered by a 557 cast engine. I’m currently in the process of disassembling the engine and nothing seems to have any excessive wear. Cam, lifters, heads… everything came off with ease. I am told thr...




www.gtoforum.com


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## LATECH (Jul 18, 2018)

You need 82-85 CC heads.

11s are 85 CCs
small vale press in studs
you will want to have hardened seats put in


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## 66CHEEVO (Jan 24, 2021)

LATECH said:


> You need 82-85 CC heads.
> 
> 11s are 85 CCs
> small vale press in studs
> you will want to have hardened seats put in


Thank you for the response. I just might go this route. I see the #11 heads have the 1.96/1.66 valves. If I go this route will I need to have larger valves installed? 
Thanks again


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## LATECH (Jul 18, 2018)

Not sure if there is enough real estate for larger valves. Probably at least a larger intake or exhaust.


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