Would 2 different piston sizes cause a problem
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Teching In
Joined: Mar 2012
Posts: 7
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From: Oklahoma
Would 2 different piston sizes cause a problem I'm in the process of rebuilding my LT1. It was a 383. It's at the machine shop getting work done and they keep running into issues and the price keeps going up. The current issue is that they see some rust and pitting and they don't think a hone will be good enough so they want to go with oversize pistons. I don't want to buy all new pistons and have them punch the block out to a total of 40 over so he suggested only doing it to the cylinders that need it. 2 maybe 3 cylinders at 40 over and the rest at 30.
My questions are has anyone done this and how were the results? It would be a balanced rotating assy but what about the offset compression? Would it even be noticeable at idle? Would it need retuned or would there not be enough difference? I just don't really know what to think about it right now and I would like some opinions.
My questions are has anyone done this and how were the results? It would be a balanced rotating assy but what about the offset compression? Would it even be noticeable at idle? Would it need retuned or would there not be enough difference? I just don't really know what to think about it right now and I would like some opinions.
As long as it's balanced I don't see where it would be an issue in a mild build. It's not perfect but not really going to cause any issues. I know it used to be done in stock car racing because they would almost always pull one of the two front spark plugs to tech the engine so the other 4 or 6 would be bored to gain some additional power.
I'm good friends with an old school machinist. hes very very particular about things. he told me years ago it was common to do that sort of thing when money was and issue or they just needed to get something back on the road. Many many engines have been done this way. You already know what the COMMON accepted practice is. Others will tell you bore all the cylinders and replace all the pistons. Its very easy to tell someone to do that when they arent the ones paying for it. Will .010 difference in piston size make a difference? no.
edit: unsure of whether the block is already .030 over or they plan on doing some .030 over and some .040 over. IF THATS THE case, just do all of the at .040, if not, just fix the defective cylinders. i have run engines with mild rust pitting and they ran just fine. As long as nothing catches the rings.
edit: unsure of whether the block is already .030 over or they plan on doing some .030 over and some .040 over. IF THATS THE case, just do all of the at .040, if not, just fix the defective cylinders. i have run engines with mild rust pitting and they ran just fine. As long as nothing catches the rings.
I personally would not do it. I'm guessing you want to reuse the .030 pistons as much as you can. I would sell those pistons to recoupe some money and go .040 on all cylinders. That is just me.
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TECH Resident
Joined: Jun 2011
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How well is the engine going to be balanced with pistons being different sizes? And you'll have slightly different compression ratios on some cylinders. Plus some cylinders will need more fuel than others (beyond normal cylinder to cylinder a/f variance). You'd need to be conservative on the fuel side as to not have the larger bores with higher compression from running too lean.
Doing it on a grandma's driver might be one thing, but on a performance motor? Yeah, it's not our money, but even if things were tight, I wouldn't do it. This is a little different than "should I go with the Garret or the BW budget turbo" type of decisions.
Doing it on a grandma's driver might be one thing, but on a performance motor? Yeah, it's not our money, but even if things were tight, I wouldn't do it. This is a little different than "should I go with the Garret or the BW budget turbo" type of decisions.
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