Compression

[pirotec354]

Anyone know if theres a way to measure a compression ratio without having to tear the motor down or is there now way. Because i want to run about 18 psi but i wanna be safe and see where im at with compression. Im running ten right now, but i want to be safe. Thanks in advance for any help

 

[earleys94gt]

This might help...
RSR Static Compression Ratio Calculator

or this...Compression Ratio Formula

 

[mo_dingo]

if you dont have enough engine/head info, you can do a compression test, divide your results by 14.7 and that is a rough idea of your CR.

 

[Bullitt95]

if you dont have enough engine/head info, you can do a compression test, divide your results by 14.7 and that is a rough idea of your CR.

That won't work and the result will be wrong. Cranking compression gives an indication of the DYNAMIC compression ratio which is influenced by the valve opening/closing events, particularly the timing of intake valve closure.
To calculate the static compression ratio, you need to measure the cc of the following:

1. Combustion chambers
2. Piston dish or valve reliefs
3. Head gasket bore (you can calculate the bore volume if you know the bore diameter and compressed thickness)
4. Deck clearance volume (you can calculate that from the cylinder bore diameter and deck clearance)

I'll leave out the crevice volume (space between the cylinder bore and the piston from the crown to the upper ring) because that's negligible.

 

[pirotec354]

Alright well thanx guys i guess ill just take my heads off while the car is in storage for the winter and go from there.

 

[mo_dingo]

That won't work and the result will be wrong. Cranking compression gives an indication of the DYNAMIC compression ratio which is influenced by the valve opening/closing events, particularly the timing of intake valve closure.
To calculate the static compression ratio, you need to measure the cc of the following:

1. Combustion chambers
2. Piston dish or valve reliefs
3. Head gasket bore (you can calculate the bore volume if you know the bore diameter and compressed thickness)
4. Deck clearance volume (you can calculate that from the cylinder bore diameter and deck clearance)

I'll leave out the crevice volume (space between the cylinder bore and the piston from the crown to the upper ring) because that's negligible.

I guess I should have put "rough idea" and "don't have enough engine/head info" in bold....My bad