Compression ratio drop's how much
Thread Starter
Burning Brakes
Joined: May 2003
Posts: 1,035
Likes: 9
From: Hernando Beach Fl
Compression ratio drop's how much
I am looking at a 406 bored .030 with TRW-L2489 pistons, These are 11.06 to 1 with 64cc chamber heads, If I went with 76cc aluminum heads, what would that reduce the compression to? I am also considering the comp cam 480 lift with 230 duratiuon. Thanks in advance for your opinions and comments.
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Where did that 11.06:1 figure come from? Do you trust it? The only way to really know the compression ratio is to measure the deck height, figure in the head gasket compressed thickness (or volume), the piston dome or dish volume, and measure the cylinder heads to be sure they are what you think they are.
If you have confidence in the 11.06:1 number, you can figure the number of cc's above the piston by comparing it to the swept volume. Simply add the 12cc's (76-64) to the, above piston volume, you derived above, and re figure.
RACE ON!!!
If you have confidence in the 11.06:1 number, you can figure the number of cc's above the piston by comparing it to the swept volume. Simply add the 12cc's (76-64) to the, above piston volume, you derived above, and re figure.
RACE ON!!!
Melting Slicks
Joined: Nov 2002
Posts: 2,460
Likes: 5
From: Wheaton IL
The best way (not the easiest) to achieve a desired compression ratio is to use flat tops and choose a cylinder head combustion chamber volume and deck height that gets you where you need to be. Big pop-ups and large volume chambers increaes the chance for detonation.
And to CFI-EFI's point, always take the required measurements. My stock 1966 block turned out to have a .31 deck height on one side and .41 on the other. I compensated by using two different head gaskets.
Three most important factors
1. Deck Height
2. Cylinder dome/dish volume
3. Combuston chamber volume
can be adjusted by doing the following
1. Changing cylinder head volume (mill/unshroud)
2. Changing deck height
3. Piston selection
4. Head gasket selection (compressed thickness)
Good luck
Brian
And to CFI-EFI's point, always take the required measurements. My stock 1966 block turned out to have a .31 deck height on one side and .41 on the other. I compensated by using two different head gaskets.
Three most important factors
1. Deck Height
2. Cylinder dome/dish volume
3. Combuston chamber volume
can be adjusted by doing the following
1. Changing cylinder head volume (mill/unshroud)
2. Changing deck height
3. Piston selection
4. Head gasket selection (compressed thickness)
Good luck
Brian
