| |
Labor Day Putting down your wrenches or time for
MORE wrenching? 
Plenty of places to share. | | Click on image for the lowdown. 
====
| | | Forums66 Topics128,006 Posts1,055,267 Members48,418 | | Most Online14,466
Apr 26th, 2026 | | AD Chevy Trucks  Over 6,000 pictures Brad Allen has an awesome collection of Chevrolet factory pictures that he has set up from film strips. Check them out!
Lots of work on Brad's part ... pure enjoyment (and references) for you!
| | THANKS!
For helping keep this great
old truck web site
on the Internet for over 30 years! and not clogged down
with Ads!  Again, thanks!
| | | | Joined: May 2005 Posts: 1,624 Shop Shark | | Shop Shark Joined: May 2005 Posts: 1,624 | I have an engine in desperate need of a rebore. The manual states the piston compression height is 1.805”. Compression ratio is around 8.5:1. In searching various web sites for oversized pistons, I find flat top pistons have compression height of around 1.775”. Are the piston manufacturers assuming one is going to mill the heads and block to bring the compression ratio back to 8.5:1?
Thanks.
Six volt guy living in a twelve volt world
| | | | | Joined: Feb 2004 Posts: 29,742 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 29,742 | They're probably reducing the compression height on the oversize piston to keep the original compression ratio the same with the enlarged cylinder volume. Unless you're running a racing engine, all the .030" lower compression height will do is give you a little more valve to piston clearance. It probably won't make a noticeable change in power, even on a dyno run. PM me with some details, if you like.
Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!
| | | | | Joined: May 2005 Posts: 1,624 Shop Shark | | Shop Shark Joined: May 2005 Posts: 1,624 | I would have thought just the opposite. By lowering the compression height with the added increase in bore size that would lower the compression ratio.
Six volt guy living in a twelve volt world
| | | | | Joined: Feb 2004 Posts: 29,742 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 29,742 | Think about it- - - -the cylinder volume gets bigger from the overbore, but the combustion chamber stays the same size. That raises the compression pressure unless the piston doesn't go as high in the cylinder. When I was going for max compression on the round track engines I would mill the block deck for zero piston deck height and use a .020" thick steel shim head gasket. Piston/valve clearance, especially with a radical cam, got very critical. Sometimes I had to flycut the valve eyebrows in the pistons deeper.
Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!
| | | | | Joined: May 2005 Posts: 1,624 Shop Shark | | Shop Shark Joined: May 2005 Posts: 1,624 |
Six volt guy living in a twelve volt world
| | |
|
|
| |
