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 Bore .60 over too much?
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Cowpatty69
Cochise

USA
222 Posts

Posted - 05 Dec 2017 :  10:09:23 PM  Show Profile  Reply with Quote
Hey All, just looking for your opinions here. I recently dropped of a 1968 400 YS block (9790071) to be dipped and checked. They let me know that it was currently at .40 over and would need to be .60 over to clean it up. I brought it back home to think about it. I have a complete 557 block from a 77 TA available that is bone stock, but not near as desirable as the 1968. Is .60 over too much for a 400ish HP build that will probably be driven under 1000 miles a year? Complete 400s have really jumped in price and don't show up like they used to. Thoughts? Thanks in advance!

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GtoGuy32
Crazy Horse

USA
851 Posts

Posted - 05 Dec 2017 :  11:54:28 PM  Show Profile  Reply with Quote
Did they sonic check the walls?

If the walls are too thin, you could have cooling issues.

I know lots of guys have gone 0.060", but every block is a little different. Pontiac did pretty well with preventing a lot of core shift.
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Cowpatty69
Cochise

USA
222 Posts

Posted - 06 Dec 2017 :  5:05:27 PM  Show Profile  Reply with Quote
I don't believe it was sonic tested, or at least they didn't say anything about that, but felt confident that .60 over would be no problem. I guess, all things being equal,my question is would a "good" block bored .60 over typically last the same as the original under the same user conditions?

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Cowpatty69
Cochise

USA
222 Posts

Posted - 10 Dec 2017 :  4:00:55 PM  Show Profile  Reply with Quote
Well, the consensus I'm getting from my hot rod buddies is that a 60 over bored block should last quite a while under normal conditions. I did put this block out on ebay just to see if there's any interest or need from somebody doing a "numbers matching" gig. If not, I may start collecting the rebuild parts as I go.

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Lee
Sitting Bull

166 Posts

Posted - 18 Dec 2017 :  2:36:16 PM  Show Profile  Visit Lee's Homepage  Reply with Quote
I've gotten non-standard overbore pistons from RaceTec (founded by the former owner of JE Pistons). Most pistons are either .030, .040, or .060" over. RaceTec made me a set that was 0.015" over, with a custom dish to get the compression ratio where I wanted, and price was rather reasonable.

You may not really need an additional .020" overbore, but they just THINK that is the next size up. Talk to the shop, and see if a .010 or .015 overbore will be sufficient.

CURRENT: '73 T/A clone, starting to get less boring!...
67 Firebird (sold) 11.27 @ 119.6 Feb. '05 issue HPP
69 Falcon wagon, 10.51 @ 130mph Feb. '10 issue PHR (sold)
72 Cutlass Convertible, first car, owned since '82, now with a 6.0 LS, mild, putting just under 400 hp/tq to the wheels.
www.LNLPD.com
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Cowpatty69
Cochise

USA
222 Posts

Posted - 19 Dec 2017 :  10:47:13 PM  Show Profile  Reply with Quote
Thanks for the reply Lee. They recommended. 060 as a minimum to clean it up. I've had the block out on ebay with the usual lots of watchers but no bidders, but could be expected with local pick up only. I have found some rebuild kits at Summit and obviously ebay pistons included $400-$800, and am considering an inexpensive "stock " build of 350-400hp, just for the rebuild experience with my son. I don't have anything I'm looking to put a monster build into.
Anyone had experience with an eBay kit like below?
https://www.ebay.com/itm/Pontiac-400-Engine-Kit-Pistons-Rings-Timing-Oil-Pump-Rod-Main-Bearings-Gaskets/172016187369?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2055119.m1438.l2649



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Edited by - Cowpatty69 on 19 Dec 2017 10:49:41 PM
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Miles
Cochise

Canada
207 Posts

Posted - 11 Jan 2018 :  09:27:46 AM  Show Profile  Reply with Quote
I have my 428 at 65 thou over. I don't know if they have any more material around the bores than a 400 would.
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