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Can anyone provide any information about boring out a 400 GTO engine. im wanting to bore it out for increased horsepower. Is there any way i can bore it out to make a 455 pontiac. Any help would be appreciated

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Just an over bore will do very little for performance. It's all about getting air in and air out. Heads and cam is where power come from. If all else is equal a .030 or .060 overbore will not produce anything extra to speak of. Work on them heads and select the right cam if you want a kick.
 

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Agreed. On overbore is used to overhaul an engine, not to produce power. These engines can be bored safely .060" oversize, after that, you'd need to sleeve it. The rule of thumb is to bore as little as possible......020. .030, .040, etc. You can overhaul an engine several times instead of once, this way. Easy to increase the power and displacement with a stroker crank kit and a well matched camshaft and set of heads. Check out Bear's 461 build on this forum.
 
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