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Discussion Starter #1
I've got a tall deck big block chevy at 4.350 bore, 520ci. After two seasons there is a slight ridge at the top of the cylinders. I've been running steel top rings napier second. The pistons will rock a bit in the bore. I'm wondering if I should give it a slight hone and new rings or replace the block. What's the max clearance I can get away with and what rings should I use? 16-1 compression, injected Alky (M-5) and 300 shot fogger with C-12.
 

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I've got a tall deck big block chevy at 4.350 bore, 520ci. After two seasons there is a slight ridge at the top of the cylinders. I've been running steel top rings napier second. The pistons will rock a bit in the bore. I'm wondering if I should give it a slight hone and new rings or replace the block. What's the max clearance I can get away with and what rings should I use? 16-1 compression, injected Alky (M-5) and 300 shot fogger with C-12.
First thing you should do is mic the skirts and see if the piston dia is still what it was new. Many times the skirts can get knocked in several thousandths resulting in a looser piston to wall clearance. If they have been knocked in say .005-.008" then it would be time to replace the pistons.
 

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The nitrous guy
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If there is a definite ridge that you can feel, that block needs a PROPER hone to get the bores round and straight, not just a little "touch up". And that is no doubt going to make it big, in which case you need new pistons to get the clearances right.

Monte
 

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Discussion Starter #4
I'm looking for another block. This one is .100 over already. I think its cheaper to prep a block vs buy new pistons. I'd like to run it another season though, it was still making good power. Went 5.28 at 135mph progressing a 28/24 shot over 4 seconds on an air strip lol.
 

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That block should easily go another .025". Several manufacturers make a 4.375 shelf piston. Probably the most cost effective way to get your bores straight.
 

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Discussion Starter #6
I think if i'm going to buy pistons and bore the block I might as well get another block and start smaller. Then I can use my 4.350 pistons when that block gets to big for the smaller pistons. What ring package should I use? And is there a nitrous ring that's not hard on cylinders.?
 

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My thought is, if you have a "ridge" at the top cylinder bore, your piston skirts probably have enough skirt collapse that you wouldn't want to reuse them. Mic them for sure, as mentioned above. As far as rings, it's hard to beat Speed Pro Hellfires for the price.
 

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You need to measure your skirts first. Prepping a new block for pistons that have collapsed skirts is wasting money. Better off taking the block you're running now and truing the cylinders up and new pistons.
 

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Discussion Starter #10
Don't know. Its going to the machine shop. Got the pistons out and found a cracked cylinder. Going to try and hard block fill it and hone. If it won't come out nice they have another block.
 

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U gonna try to hone out a crack?? Good luck


LOL, I'm sure he left out putting a sleeve in the cracked cylinder.....at least I hope he did.
 

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Discussion Starter #13
The crack is at the bottom of the cylinder. I'll leave it up to the machine shop to decide the best route to take.
 

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I've seen some dirt track racers bring in a block that you could physically rock the piston in the hole, it was 7-8 thousands clearance. Your block is screwed, get another. The only time I use sleeves is if there is some pitting in the cylinder from water sitting in it.
 

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I've seen some dirt track racers bring in a block that you could physically rock the piston in the hole, it was 7-8 thousands clearance. Your block is screwed, get another. The only time I use sleeves is if there is some pitting in the cylinder from water sitting in it.

I've never had a motor that you couldn't rock the cylinders in the bore? 7 - 8 would be tight on my motor? Its probably about right for the OPs setup.
 

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Mine's about .009 at 4.125.
 

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The nitrous guy
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How much clearance does the PISTON MANUFACTURER say you should have. If it is looser than they say, for the piston THEY designed for the application, then it is too loose. You should trust the guys who make the parts.......who knows better than them. Me personally, I use Diamonds and some of the clearance numbers guys are talking about having here, I would consider them worn out and WAY too loose. OIL is the number ONE worst enemy of a nitrous motor, so if nothing else, I make sure the bore is tight, round and WHERE IT SHOULD BE.

Monte
 

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Discussion Starter #20
Fresh block is getting prepped. We are going to fill it first this time starting with a standard bore block. I didn't trust filling the cracked block. I'm running Race-Tech gas ported pistons. Not sure on clearance but they were a lot tighter when the engine was fresh. The steel rings are really hard on cylinders.
 
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