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Dropping compression. New pistons or heads Currently running 10.2:1 on a 358 with a set of trimmed down fast burns. 60cc chamber. Id like to get down to 9.5:1 or under for some forced air. What cc chamber would put me there or should i just swap slugs? Currendly running ross forged pistons. A head swap needs to be a raised port for a 1206 intake gasket to match my intake |
Re: Dropping compression. New pistons or heads An 8cc chamber increase will drop your CR by .81. |
Re: Dropping compression. New pistons or heads
Originally Posted by NoEmissions84TA
(Post 6277366)
An 8cc chamber increase will drop your CR by .81. Thanks for the input |
Re: Dropping compression. New pistons or heads You're welcome. I don't know how thick your head gasket is now, but you should try to keep the quench close to .040". |
Re: Dropping compression. New pistons or heads As an example: 4.04 x 3.48 60 cc head 5 cc piston .040 x 4.100 gasket .025 piston below deck Result is a CR of 10.26:1 A 64 cc head nets 9.8 A 60 cc head with a .060 gasket nets 9.78:1 The input values are a best guess but typical SBC. Verify your piston valve relief/dome/dish volume. Going from 5 cc (2 valve reliefs) to 9 cc (which I haven't come across) drops the CR to 9.8 |
Re: Dropping compression. New pistons or heads How much boost and what kind of poweradder? low boost i’d send it as is at 10:1. I would try thicker gasket first. Ease up on tune, keep engine cool and good intercooling High boost throw c16 in it or e85 |
Re: Dropping compression. New pistons or heads Gootta go back to my build sheet from a few years ago. Im pretty sure it was a.028 head gasket. I was thinkin of throwin some new afr's on whick would gain me 5cc oin the chamber. Ithimk at least 10psi intercooled. Id prefer not to swap pistons. But i will need be. Tryin to stay at 93 octane. E85 not too common around here. |
Re: Dropping compression. New pistons or heads
Originally Posted by Orr89RocZ
(Post 6277898)
How much boost and what kind of poweradder? low boost i’d send it as is at 10:1. I would try thicker gasket first. Ease up on tune, keep engine cool and good intercooling High boost throw c16 in it or e85 |
Re: Dropping compression. New pistons or heads
Originally Posted by 2slow5.0
(Post 6277903)
Gotta go back to my build sheet from a few years ago. I'm pretty sure it was a.028 head gasket. . But like I said, there are too many variables to just guess. And I'm even guessing on the bore and stroke. |
Re: Dropping compression. New pistons or heads
Originally Posted by skinny z
(Post 6277906)
It'd be tough to hit only 10.2:1 with a .028" gasket / 60 cc chamber all else being equal and standard SBC. Before you get too far you'll want to verify the values. With the above data listed a .028 gasket gets you over 10.6:1. Change the valve relief volume to 7 cc and a .028 gasket nets 10.3. But like I said, there are too many variables to just guess. And I'm even guessing on the bore and stroke. |
Re: Dropping compression. New pistons or heads On a ebl flash I never had any detonation issues on 93. Even goofin up and runnin too much timing at first |
Re: Dropping compression. New pistons or heads If its 10.2 on a .028 gasket then go with a .040-.051 and let it eat. Not even concerned with 10 psi intercooled |
Re: Dropping compression. New pistons or heads
Originally Posted by Orr89RocZ
(Post 6277929)
If its 10.2 on a .028 gasket then go with a .040-.051 and let it eat. Not even concerned with 10 psi intercooled Id prefer to not tear the bottom end apart if possible |
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