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Discussion Starter · #1 ·
I need a set of flat top pistons for a sbc and my buddy has a set of forged dome pistons (vernolia i believe). One valve cam in contact with the piston and the dome is destroyed. Can i cut off the dome portion of the piston to get the flat top i want? I am sure this is something circle track guys do but wasn't sure if it was reliable.
 

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Depends if it's a hollow dome or solid dome and how thick the crown is after cutting the dome off. If I remember correctly, good engineering practice dictates that the crown thickness should be about 7% of the diameter of the piston. On a 4.000" piston, 7% would be 0.280". So if you can end up with crown thickness somewhere around that number, you should be ok. If I were building a naturally aspirated gasoline motor with mild to moderate static compression ratio, no nitrous or blower, I might be tempted to go thinner if I REALLY, REALLY needed to use those pistons and had a lathe at my disposal. I might go as thin as 5%....0.200". I'm in no way suggesting that you do this, I'm just saying that I might try it if I were absolutely broke, had no other option and had to get a motor running.

Measure the crown thickness as it is now and determine the finished crown thickness after your cut. I have included a diagram of how I might do it. If the dome is hollow, measure to the deepest part of the dome with the piston positioned like I have shown here. If the dome is solid, you should be ok with just trimming it off and ending up at the base crown of the piston. If it's hollow, measure carefully and determine the ratio of piston diameter to crown thickness after surgery.....I advise that you don't cut more than a few thousandths past the base crown of the piston. The top ring land needs all the meat it was manufactured with to prevent it from collapsing and pinching the top ring.
 

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SDLuck said:
Forged pistons will be more than $300.00 and venolias maybe twice that, we used to do this with solid dome pistons back in the 60s and70s.

you can get foriegn forged pistons for under $300, and you're not comparing apples to apples. A forged piston with the crown cut down can be a lot weaker than a set of rebuilder cast pistons, then again it could be stronger.

If it was a good set of pistons, the cut was minimal, and you knew what you were doing then it'd be one thing, but this does not sound like that type of situation.

depending on the application he may be better off with a set of hypereutic or cast pistons, we don't know.
 

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Discussion Starter · #9 ·
This is gonna be a NA motor so i think i should be okay. Like techinspector said gotta find out if they are solid or hollow dome, and thanks for the diagram very helpful. compression will be like 9-9.5:1. This wont be a motor where forged pistons are a must but might as well put them to use. I also do have access to a lathe.
 

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ap72 said:
you can get a set of flat tops for less than $100 shipped to your door... Why even worry about salvaging these pistons?
Not trying to take this to far off topic, but I always think of hotrodding as using what is at your disposal and not buying un-necessary things :thumbup:
 

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there is a cost to this- time. I used to pour out all the time I could on a project in the name of saving a few bucks, then I realized that in some cases spending a few bucks not only saves you some time but can result in a better final product. A nice set of 2VR KB's would cost less than $200 and probably suit his application really well. If he needs to go even cheaper go with the SpeedPro 4VR's cast in India, they're not a great piston but for DD they'll work fine. Next step down from that is Badger, which again isn't great but may work- they're like $50 a set. If the face of the piston can handle it it may not be a bad option to turn them on the lathe, but there are other options that may work better. I don't have the piston in hand so I don't know what to make of it.

Keep in mind these are used pistons and have had valve contact.
 
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