I have a block that is .30 over. I would like to use this - how far can you go without imposing any probllems. I know you can go as far as 60 but many machinists want an unhoned block to work with. If I use this .30 over block, what am I up against?????
How Far Over Can You Punch Out A Sbc
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Depends largely the amount of power you ant to make. .060 is safe for most mild street stuff. You need walls that sonic at .150 or better.
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what your up against is what shape is the bore now in? the machinist should be able to tell you. Most small block`s can go over safely to .060 over, but if you plan on going over more it would be wise to have it sonic checked. Last I hear .080 over has become common practice, but I`d recommend sonic checking first.
Don`t have your block bored more than needed, as boring it bigger doesn`t help power output much.
Don`t have your block bored more than needed, as boring it bigger doesn`t help power output much.
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239 Posts
If it was me, I'd go .040, if possible. Then you have the option of going .060, if you wear it out, or break something.
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boring doesn't make power and it only yields a few extra cubes. Its not worth the effort or cost. The only time boring is worthwhile (of course) is when the bores are in need of it, and then only enough to clean them up. Why go more than you have to? All its going to do is cost you money in the long run when you're trying to rebuild the thing again and find out you need a new block this time.
K
K
I have no iontentions of making the bore as big as I can. The reason for my concern is that I have a .30 block handy for a 383 build project. When I had told my machinest of what I have he was not exactly happy about it. He said that if he has to, depending on the condition of the cylineder walls he may have to push it to .60. Even though you can go to .60 he said he does not like to do that - he takes a conservative approach. Sooo i was wondering is he being overly conservative or not!?!?
They would'nt be making and selling 0.060" oversized pistons if block weakening was a major issue. Your machinist probably has easy and cheap access to virgin blocks thru his contacts for when he needs one, and therefore could not understand why someone would want to go 60 thou over. I guess because it's because you're not made of money right? It's also probably an ethical issue for machinists and he's probably just protecting his own reputation. If you're really worried you can always pour block hardening compound into the water jackets. The piston manufacturers would have feed back records on going 0.60" over and you can always give them a call for a different point of view.
Being in the trade you soon predict the verdicts when you send something out. Every time we sent radiators to specialists for a flush we get a reply that the cores have cancer and require a recore. But after they patch up the old cores due to the customers lack of funds the radiators miraculously go on to out last the car! The world's full of drama queens.
Being in the trade you soon predict the verdicts when you send something out. Every time we sent radiators to specialists for a flush we get a reply that the cores have cancer and require a recore. But after they patch up the old cores due to the customers lack of funds the radiators miraculously go on to out last the car! The world's full of drama queens.
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2,240 Posts
Nobody hear can answer that question. You need to load the block in question up and take it to the machine shop. He can check the block out and tell you if it's any good. If it is at .030 now, the next step would be .040 and the .060. He will be able to tell how much is needed when he checks the block out.
I have a .060 overbore in my blown 388ci SBC no problems yet. I rana .040 over 385 for years no problem. It all depends on the block you have. Since they are cast and some have core shift, not all blocks are created equal. If you have a good casting going .040 or .060 over is not an issue.
Royce
I have a .060 overbore in my blown 388ci SBC no problems yet. I rana .040 over 385 for years no problem. It all depends on the block you have. Since they are cast and some have core shift, not all blocks are created equal. If you have a good casting going .040 or .060 over is not an issue.
Royce
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1,072 Posts
Yep, what Royce said. Only way to know is a sonic check. alot of 350s will go to .060...but not all
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3,532 Posts
Make sure the machine shop you go to uses a torque plate when they bore the block. That will get the cylinders referenced where they will be with the heads torqued on.
I would not really sweat .060 over. I think this is really alot of hype. Taking .030 out of the cylinder is only .015" per side.
I wouldn't really worry about it on a hot street engine. If it were highly stressed race engine, that's another story.
I've got an .080 over 350 and it runs fine.
I wouldn't really worry about it on a hot street engine. If it were highly stressed race engine, that's another story.
I've got an .080 over 350 and it runs fine.
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