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.040 pistons for a 402

 
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seventy468
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PostPosted: Tue Jul 14, 2009 10:37 pm    Post subject: .040 pistons for a 402 Reply with quote

Where can I get .040 over pistons for a 402? yeah I know .040 is somewhat odd so lets look past that. anyone know where I can find a set? Its not that bid of deal if they have to be custom, Im just curious and I know you all are the best at BBC.

Or... if you think going .060 over would be safe (on the block) I guess I could go that route.

I am looking for 13:1 CR.


Thanks!
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squeeezer
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PostPosted: Wed Jul 15, 2009 9:11 am    Post subject: Reply with quote

im not a bbc guru but.......

.060 is not a big deal on a bbc like it is on a sbc

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af2
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PostPosted: Wed Jul 15, 2009 1:30 pm    Post subject: Reply with quote

Need to know what heads/cc's and compression/ pin height.
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seventy468
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PostPosted: Wed Jul 15, 2009 3:19 pm    Post subject: Reply with quote

well i knew most bbc's would be ok.060 over but for some reason seems like someone told me the 396/402 bbc ran a little on the thin side when it came to the cylinder wall thickness. however that was just heresay. as for heads and what not.. that is still up in the air.. i just havent seen many .040 over pistons for a 402 so i was trying to find a place to start.. but looking more like ill just have .020 taken out.
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af2
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1933 Willys Coupe

PostPosted: Wed Jul 15, 2009 5:48 pm    Post subject: Reply with quote

seventy468 wrote:
as for heads and what not.. that is still up in the air.. i just havent seen many .040 over pistons for a 402 so i was trying to find a place to start.



How are you going to get 13:1 pistons not knowing the the head cc? There is 23+- cc's on the different heads. .040 pistons are pretty common. The dome size is not. You need to figure out what chamber you want then get pistons that match.
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seventy468
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PostPosted: Wed Jul 15, 2009 10:57 pm    Post subject: Reply with quote

I understand, my thoughts originally were that if I could find a .040 piston (because I thought they were a little more rare than they apparently are) I would shoot for 13:1 (it doesn't have to be exact...) and taylor my engine to those pistons. I do understand pistons usually come last when it comes to building the engine on paper.. but due to the fact that I didn't think those pistons were as available as apparently they are, I was unaware that I had that option.
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Big Dave
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PostPosted: Thu Jul 16, 2009 8:38 am    Post subject: Reply with quote

If you are thinking price point a custom piston doesn't cost that much more as all pistons are custom, they just build a lot of them on spec and all you are paying for is the paperwork to process the order. Order a piston to fit your head.

All blocks are made since 1967 are thin wall, but that thin wall has more meat in it than a 400 small block so going 0.060" over is no big deal (I have bored them 0.125 over a number of times and they ran for years as a 427). Are you building a race motor? (one must assume so at 13.5:1 compression) and the fact that you are playing with a 396 at all tells me you're running some class race that restricts the motor to stock sizes. Either way pistons if not a consumable are made to fit the head and the rest of the motor rather than being a restriction to designing a motor. To get your desired compression ratio you order a piston to fill the head with as small a dome as you can obtain to promote flame travel. Squish in an open chambered big block is just about non-existent as it is more of a hemi head than a wedge but you need to promote complete combustion and prevent detonation by limiting hot spots in the chamber as a result of a dome isolating a portion of it.

Big Dave
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