High Compression Discussion
On The Tree
Joined: Oct 2004
Posts: 98
Likes: 11
From: in a large steel structure
most dome pistons are a solid dome so they end up heavy. Approximately half of that extra weight can be milled off the underside in a na engine. Piston dish volume is limited to an extent by the compression height needed so we are back to a compromise between the two in my book
What I tried to do on mine was preserve as much of the chamber as possible. Ended up with a net 1.3cc dome (AFTER valve reliefs figured in), so it's like a little flat "mesa" on top of the piston. but that got me 12.7. Not 14. And it did make the pistons heavier. I noticed that while shopping. I could get dished pistons in the 450g range all day long, but domes were in the 490-500g range all day long.
Then heftier pistons require beefier rods, and it spirals.
What I have in my head for a future build is sort of like this. Another big bore motor. Stroke as yet undetermined. Something based off the LSR casting, starting at 52cc and then running a 5cc dish to get compression into the 14-15 range. Seems like the best way to do it. Or even more extreme, a C5R bare casting in the right hands with a 30cc chamber, no milling, but then needing a 20cc dish to get into the 16:1 range.
But it's diminishing returns, and boost becomes much easier, so I see your point for sure.
Then heftier pistons require beefier rods, and it spirals.
What I have in my head for a future build is sort of like this. Another big bore motor. Stroke as yet undetermined. Something based off the LSR casting, starting at 52cc and then running a 5cc dish to get compression into the 14-15 range. Seems like the best way to do it. Or even more extreme, a C5R bare casting in the right hands with a 30cc chamber, no milling, but then needing a 20cc dish to get into the 16:1 range.
But it's diminishing returns, and boost becomes much easier, so I see your point for sure.
