# 400CI engines..What are the differences???



## X~Nightstalker (Mar 28, 2009)

So I am upgrading my 66 LeMans 326 with a 400 or 455. 

I am actively looking for an engine.

I am finding all kinds of Pontaic 400s from the late 60's to the early 70's

Doing a complete rebuild and trying to get 350-400 HP from it. 

My question is...what are the differences between the engines from those years??

I already am aware of everything for mounting. I am just curious about the internal differences if any. I already have a Edelbrock Performer RPM manifold I am going to transfer over from the 326 plus a 650CFM carb. 

I am just trying to get a feel for how to narrow my search down.


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## busaben (Oct 30, 2008)

you shouldnt have any problem reaching those horsepower numbers im upgrading to a 400 from a 326 myself


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## 05GTO (Oct 6, 2004)

Go with a 69 or newer 400, they have 11 bolt water pumps and run cooler than the pre 69 engines. The hp ratings dropped in 71 so an engine from 69 and 70 may be your best bet for higher hp.


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## X~Nightstalker (Mar 28, 2009)

I used to have a few problems with my 326 getting too hot. That was one of my concerns. I was going to get a huge aftermarket radiator anyways and add in an electric fan. Still going to, but it would be a lot better to have a engine that runs cooler to begin with.


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## geeteeohguy (Feb 2, 2008)

Use a later 400 as stated above (more common, timing cover is available, etc.) The only real difference in early to late HP figures is due to vompression ratio and camshafts, and compression ration is controlled solely by the cylinder heads. So, you can get a common, mid '70's 400, and use better heads, and have a good runner. Be careful about compression, though. You want to run 87cc heads or larger with stock pistons. All heads earlier than '71 except for the 455 heads have 64-72cc heads, and result in 10.5-11.0:1 compression, which is unworkable on today's gas.


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## X~Nightstalker (Mar 28, 2009)

I plan on going aftermarket with everything I can on the engine rebuild...any recommendations on heads?? I probably wont have stock pistons.


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## Koppster (Jul 27, 2008)

I've got Edelbrock RPM performer heads on my 400 (out of a 76) and I'm very impressed...my entire top end is Edelbrock (carb, intake, heads & cam). Nice set up, very tight motor (I just wish the block were a 389!)


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## geeteeohguy (Feb 2, 2008)

I've heard nothing but good reviews on the Edelbrock heads. They work well, and save a TON of weight.


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## CARLOSGTO67 (Apr 14, 2009)

*389 cc -400 cc automatic to standard*

I'm swaping a automatic for a stick shift on a 67 gto,but im having troubles with the flywheel ,the flex plate it used has a 166 teeth ,and the replacement flywheel they sold to me is 168 teeth all the crank and bolt pattern is the same except for the extra two teeth ,somebody told me to change the bendix on the starter ,mine has a 9 teeth on 166 gear ring,


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