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  #1  
Old 11-21-2006, 05:15 PM
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Default over bore on a 340

Will a 71 model 340 block stand 4.125 bore? I know it will need to be sonic checked, but wondering if it would stand it. I've been running it at 4.100 for a couple of seasons and wanna rebuild it using shelf chevy pistons.

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Old 11-21-2006, 06:14 PM
BJSracing BJSracing is offline
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I would have the block sonic checked to see if it will clear. The other problem you may run into is the pin height on the chevy piston. Remember that a 360 I know that you are building a 340) is 3.580" stroke and a Chubby 350 is 3.480" stroke. And the pin height is different in the two pistons. You may run into some clearance problems. Also the pin diameter is different. You can bush or hone to make the pins work but the height may cause a problem. I would be suprised if the block passed the sonic check to go that far. You are already getting close to the limits of the block as it is.
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Old 11-21-2006, 06:20 PM
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I know that... its a 340 with a 3.58 stroke (dragon slayer), 6.2 chevy large journal rods (.927pins). I need to know if the bore of 4.125 will work in a 340 block.
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Old 11-21-2006, 08:07 PM
sanborn sanborn is offline
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Wow, I think you are real lucky to be able to bore to 4.100" safely. We have never been able to do that in race engines---we always seemed to split cylinder walls.

I would be real cafeful and sonic test before boring to 4.125". An "X" block is borderline, a stock block is real questionable.
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Old 11-21-2006, 11:06 PM
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Sanborn This motor has probably been the best motor I've ever had. Bought it dirt cheap like 8 years ago. I raced it on pavement for two seasons, didnt even freshen it up the first season. Then bought a late model changed the intake and ran it in it for a season. Put it in another car and ran it some more before I got another motor and put it in the car. It was run before I got it. Originally built in 92. Has ran every season except about 2 1/2 seasons. To my knowledge it has always been the 4.100 bore with a standard length 6.123 rod and a forged 3.31 stroke. The cylinders are in pretty rough shape. I have a dragonslayer crank and a set of rods all new laying here and I was wanting to get a set of pistons to put a motor back together. I know all eight cylinders have sleaves in them and the outside diameter of them is 4.190. So not counting the block I would only have .0325 to the side of just sleave. I'm kinda leary of this block but I dont have the money to buy another. I dunno what to do....
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Old 11-22-2006, 12:02 PM
it's all dodge it's all dodge is offline
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Wouldn't the valve reliefs not quite line up if you used an off the shelf Chevy piston, since small dodges are 18*(?) heads, and Chevys are 23*(?)????
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Old 11-22-2006, 05:26 PM
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yeah most of the time they have to be modified anyway. Looks like either go custom and hone to fit or sleeve the block back. Probably go custom.
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Old 11-22-2006, 07:45 PM
sanborn sanborn is offline
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If you go custom piston, then order the pistons in whatever size you want. We often order pistons .002"-.005" larger. It makes no difference to the piston manufacturer and the cost is the same.
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Old 11-23-2006, 11:55 AM
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Yeah we ordered two sets at a time one the bore we wanted and another .005 over that when I worked with the cup stuff. We used the blocks two races and scraped them.
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Old 11-23-2006, 06:59 PM
sanborn sanborn is offline
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What happened? We have been getting several thousand laps between honing oversize on our "R" block---and we only hone .005" over.
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Old 11-23-2006, 10:38 PM
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That was on the nextel cup stuff.
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