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400 bored 60 over

  
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400 bored 60 over

 
towacoman towacoman
New User | Posts: 13 | Joined: 01/09
Posted: 04/14/09
07:47 PM

I have a 400 that is bored 60 over. The engine needs to be freshened up again.
What is the most that this engine can be bored? Thanks  

blackbird72 blackbird72
User | Posts: 186 | Joined: 08/07
Posted: 04/14/09
08:17 PM

What's the block no. and year? Early 400's can go more than .060 if your sonic check is good.

Geno  

towacoman towacoman
New User | Posts: 13 | Joined: 01/09
Posted: 04/14/09
08:20 PM

The block is a 1970, I will have to find out the other numbers, How much do you think I can go?  

flynryan flynryan
User | Posts: 151 | Joined: 01/09
Posted: 04/16/09
04:11 PM

Pontiac blocks are great for going up to 60 over. Some engines, such as a Cleveland are too thin for even 30 over. However, it is never recommended to go more then 60 on a Pontiac. In order to do so you will have to sonic check the block. Then you will need to have custom made pistons and rings. That will cost well over $1000 alone. Then you will have to rebalance the assembly as with any time you change pistons, but now you have a larger piston so you have to add heavy metal to the crank, which costs more.

When a shop does a sonic test they just check a few locations in each cylinder. So they can miss a thin spot where a casting mark is, or rust occurred, or if the block had core shift, then the bore may be off centered and when machined leaves one side much thinner. Under the best scenario you still have a 30+ year old block with thin walls. If it over heats even once, say good buy to the block and all the machine work.

Option #1- find a piston brand that has allot of expansion and requires a larger piston to wall clearance such as .006 or even .008. Then you may be able to stay at 60 over. Have the block measured first with a torque plate on it and do not drive untill it fully warms up.

Option #2- just get another block. Pontiac 400's are still plentiful and shouldn't cost more the $200 for a good one that has been mag tested.

Good Luck  

Pontiacman8 Pontiacman8
Moderator | Posts: 5778 | Joined: 02/08
Posted: 04/16/09
04:30 PM

I would not recomend boring it more than .060 over and the year don't really matter as far as thickness the local machine shop I use has sonic tested a lot of pontiac blocks and the thickest block measure so far was a 1972 455 and the thinest block measured was also a 1972 455 so the saying that the older blocks are thicker is not always true.  
Engine builder,self taught auto body guy.
Horsepower sells engines and torque wins races

Pontiacman8
Pontiacman8
Pontiacman8

towacoman towacoman
New User | Posts: 13 | Joined: 01/09
Posted: 04/17/09
07:05 PM

Thanks for the info guys  

pontiac426 pontiac426
New User | Posts: 1 | Joined: 06/10
Posted: 06/30/10
07:55 PM

I GOT A PONTIAC 400 BORED .30 AND HAVE PORTED VAVLE JOB EXT..ON THE 6X HEADS ...AND AN AFTERMARKET  CAM FROM COMP CAMS..HOW MUCH HP..AND TORQUE SHOULD I HAVE??  

idrivejunk idrivejunk
Addict | Posts: 5162 | Joined: 12/09
Posted: 07/01/10
04:44 AM

Welcome, pontiac426.

Guys here can answer that, but will need a lot more specs on your setup.

If you post a new topic (thread), you may get more attention. Smile  
idrivejunk

Pontiacman8 Pontiacman8
Moderator | Posts: 5778 | Joined: 02/08
Posted: 07/01/10
05:26 AM

+1.  
Engine builder,self taught auto body guy.
Horsepower sells engines and torque wins races

Pontiacman8
Pontiacman8
Pontiacman8