Mamimum safe over bore on a 400 Chevy - Chevelle Tech
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  #1  
Old Dec 23rd, 07, 10:15 PM
bardall1 bardall1 is offline
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Smile Mamimum safe over bore on a 400 Chevy

I ran accross a local guy trying to sell what looked like a super nice and cleaned 400 block. In checking the bore I noticed that it is already .030 over size and will need to go out more to clean it up etc. Is this a good deal or is the .030 already at its safe size? Another thing does anyone out there in Chevelle land do business with Street and Performance out of Mena Arkansas? Brodix and Street and Performance are both super top companies and are both in Mena Arkansas. Has anyone out there done business with these folks and a person who works on enginess at S&P named Brian S ? Thanks
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  #2  
Old Dec 23rd, 07, 10:17 PM
pdq67 pdq67 is offline
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Default Re: Mamimum safe over bore on a 400 Chevy

Isn't it like .040" over for a 400 SB unless it sonic check's out OK to go more??

pdq67
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  #3  
Old Dec 23rd, 07, 10:22 PM
furball8994 furball8994 is offline
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Default Re: Mamimum safe over bore on a 400 Chevy

I don't know the Co's But as to the 400. It all depends on the block. I have seen some bored .060 over others that were maxed at .030. The block really needs to be sonic tested to check wall thickness before trying anything over .030.
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Old Dec 23rd, 07, 10:29 PM
DOUG G DOUG G is offline
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Default Re: Mamimum safe over bore on a 400 Chevy

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Originally Posted by furball8994 View Post
I don't know the Co's But as to the 400. It all depends on the block. I have seen some bored .060 over others that were maxed at .030. The block really needs to be sonic tested to check wall thickness before trying anything over .030.

IMO
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  #5  
Old Dec 23rd, 07, 11:00 PM
trmnatr trmnatr is offline
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Default Re: Mamimum safe over bore on a 400 Chevy

It depends on the block, some can go .060", some can not

I do suggest if its a race engine having the water jackets filled {half fill} after hot tanking and the machine shop preps it to be filled then you bore it with a torque plate, this will make it as stable as possible
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Old Dec 24th, 07, 9:45 AM
BillsCamino BillsCamino is offline
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Default Re: Mamimum safe over bore on a 400 Chevy

I've got a fresh, just out of the machine shop last week, .040" 400 block. Checked fine.
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  #7  
Old Dec 24th, 07, 11:00 AM
fabio fabio is offline
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Default Re: Mamimum safe over bore on a 400 Chevy

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Originally Posted by BillsCamino View Post
I've got a fresh, just out of the machine shop last week, .040" 400 block. Checked fine.
lucky dude, enjoy it. But to the original poster make sure to get it sonic checked as some will clean up and others will be to thin. These blocks are hard to find. I looked for 8 months and the one that I found was cracked along the main webs. Make sure if you buy the block that the guy will return your money for the block if the machine shop says it's no good.
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Old Dec 24th, 07, 11:58 AM
gcoats gcoats is offline
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Default Re: Mamimum safe over bore on a 400 Chevy

If the block is already @ .030 over...it's just about impossible to take it to .040 over. It can be done IF the cylinders wore evenly and IF it don't have much taper by someone on a CK10 power hone (or equivalent), IF you can find someone who wants to fool with it. It is a PITA, to say the least.
SOME 400 blocks can go .060, but for most .040 is pushing it pretty good.


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  #9  
Old Dec 24th, 07, 1:17 PM
racecar100 racecar100 is offline
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Default Re: Mamimum safe over bore on a 400 Chevy

For what it's worth ,these blocks are getting harder to find so don'tcull,l it just yet. As Greghas said.if it isn't wore much hone it to .040 if it is too bad go to .060. As scott said
have it sonic tested if possible. Ihave built many .060 overs with good results.I wore one
out had .065 pistons made, wore it outthen went to.070 still going.Always hone with
deck plate, gaskets and studs or bolts you are going to use. Diferent strokes for diferent folks.Personly I have no need for hard block..I had one coustmer that ran 8 years with the same block no hard block. Door car ran 5.11 in 8th 1 4b no nitrous. Now pick your own poison. Thanks[ olddog ]
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Old Dec 24th, 07, 3:19 PM
BillsCamino BillsCamino is offline
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Default Re: Mamimum safe over bore on a 400 Chevy

Heck...we're building another 400 right now that's only .030" over. The .040" over block is gonna sit for now. We just ran both thru the machine shop.
Also have a spare 400 block in my shop that's standard bore.
All the above are 2 bolt mains.
Seems like I've been covered up with 400's lately...
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Old Dec 24th, 07, 4:39 PM
BillK BillK is offline
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Default Re: Mamimum safe over bore on a 400 Chevy

bar,

First of all, its really no problem to go .040" if you have a good honing machine. The block is probably worn 2 or 3 anyway, that only leaves .007 to hone, heck we pretty much always leave .005 when we bore them anyway.

Now, I might get some grief about this, but has anyone here actually had a problem with a .060" over bore on a 400 that they can swear was caused by the fact that the block was bored .060" ?? I dont want to hear about the overheating, I think that is bull. If its overheating, its because it is making a lot more power than the cooling system is designed for, not because it is .060 oversize.

Maybe, just maybe, on an all out engine with a blower or lots of nitrous, you might build enough clinder pressure to cause a problem but ....... if you are making that type of power you should be using an aftermarket block, or filling the stock one anyway. All of the major piston manufactuers make .060 over pistons for 400s, they would not doo it if there was a problem.

Just my opinion,
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  #12  
Old Dec 24th, 07, 5:16 PM
John D John D is offline
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Default Re: Mamimum safe over bore on a 400 Chevy

The question is about overbore sizes, .030, .040, .060
Well, lets flip the question to what it really is....

Based on personal or professional opinion & experience, what would be the maximum safe overbore on 400 without the expense of sonic checking or block filling?

Question 2:
IF the block was sonic checked, and is intended to be filled, what is the minimum allowable cylinder wall thickness??
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  #13  
Old Dec 24th, 07, 9:05 PM
BillK BillK is offline
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Default Re: Mamimum safe over bore on a 400 Chevy

John,
My personal opinion:

1. For most street engines, I see no problem going .060 on a 400. That is without sonic testing.

2. With sonic testing, on a street engine I would be happy with .090, on a race engine or something with boost or nitrous I would personally like to see .125 or more, especially on the thrust side.

I have a 400 block at the shop we will probably sonic test on Wednesday. It is already .030. I will post the results after we test it.
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  #14  
Old Dec 24th, 07, 9:52 PM
gcoats gcoats is offline
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Default Re: Mamimum safe over bore on a 400 Chevy

[quote=BillK;1622923]bar,


Now, I might get some grief about this, but has anyone here actually had a problem with a .060" over bore on a 400 that they can swear was caused by the fact that the block was bored .060" ?? I dont want to hear about the overheating, I think that is bull. If its overheating, its because it is making a lot more power than the cooling system is designed for, not because it is .060 oversize.



Just my opinion,
Merry Christmas to all [/quote

I have seen 2 400 blocks that failed @ .040..both busted cylinder walls out. One was a 5.7 rod/11:1 bracket engine with a fair many passes on it, no NOS or alky, the other a 6" rod 12:1 circle track engine (on alky, the tune up could have caused it so I guess that one is a toss up). These were both "511" blocks.

Seen one "509" block that was .060, 13:1, on alky, bracket engine...lived a long happy life with a "half fill". After four seasons it finally cracked a wall..but it was four long, hard, high RPM seasons that would have gotten the best of nearly anything. I've used a couple .040 "509" blocks that lived just fine.

And no, it's not that bad to hone a .030 block out to .040, but it is a little time consuming, and hard on honing stone sets..most machinists won't fool with it simply because there's more money to be made in less time fooling with something else.
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  #15  
Old Dec 24th, 07, 11:51 PM
trmnatr trmnatr is offline
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Default Re: Mamimum safe over bore on a 400 Chevy

The further you bore it the better it will be if you fill the block. We used to use concrete umpteen years ago when dad was doing it then our machine shop switched to an epoxy filler that does not crack like concrete fill.

It all also depends on clylinder wall clearance and piston material too, i would say {no proof-just me thoughts} that a forged piston would put less stress on the cylinder wall than a hyper KB piston etc

Another thing is are you running steam holds? Another thing that helps is to have a machine shop tap into the back of the cylinder head and run a coolant line from the back of the cylinder head to the front of the intake manifold and run the rear bosses of the intake to an adaptor plate under the thermostat housing, this helps pull the heat out as fast as possible

I dont like to run a thermostat or a restrictor plate, this is the return for hot water to go to the radiator to be cooled, i like to play with the pulleys to find the sweet spot, the performance market is starting to realize this as they now make restrictors to limit the flow in the lower hose so the water stays in the radiator to get cooled longer and the water gets to the radiator quicker without a restrictor plate
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