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View Full Version : ? regarding what comp ratio actually mean?


pendejo
11-02-2004, 11:06 PM
First, I've searched for this info and have not found it anywhere. I just want to know what the number in compression ratio's stand for. Always wondered but never knew anyone with the answer.

Example 9.5:1 What does the 9.5 and 1=???

If this is in the wrong section, sorry!
A20A1
11-02-2004, 11:13 PM
how much compression there is over atmospheric pressure.

Compression : Atmospheric.

or at least that is my understandning of it.

9.5 times atmospheric pressure.
1987HondaAccord
11-02-2004, 11:14 PM
someone correct me if i'm wrong, but i believe its the ratio pressure when the cylinder is at TDC compared to BDC. so 9.5:1 would be 9.5 times the pressure at Top Dead Center as there is when the piston is at Bottom Dead Center.
A20A1
11-02-2004, 11:16 PM
I dunno, just google the darn thing. lol
Busted_Blue
11-02-2004, 11:28 PM
someone correct me if i'm wrong, but i believe its the ratio pressure when the cylinder is at TDC compared to BDC. so 9.5:1 would be 9.5 times the pressure at Top Dead Center as there is when the piston is at Bottom Dead Center.

i believe that is correct.
pendejo
11-02-2004, 11:41 PM
OK, good enough for me, thanks fellas(or ladies if they're out there:))
A20A1
11-02-2004, 11:57 PM
OK, good enough for me, thanks fellas(or ladies if they're out there:))

No worries... you can refer to ladies as guys or fellas, it happens all the time.
TheSummoner101
11-02-2004, 11:59 PM
someone correct me if i'm wrong, but i believe its the ratio pressure when the cylinder is at TDC compared to BDC. so 9.5:1 would be 9.5 times the pressure at Top Dead Center as there is when the piston is at Bottom Dead Center.
yep close to what i understand about it....

9.5 units of air compressed into the space of 1 unit...so the bigger the first number means higher compression (more gas gets compressed into smaller space, better for combustion), so more gas to burn = more power :)
Busted_Blue
11-03-2004, 04:29 AM
The Static Compression RATIO is defined as the Volume of the Combustion Chamber when the piston is at the very bottom of it's travel (called "bottom dead center" or BDC) DIVIDED BY the Volume of the Combustion Chamber when the piston is at the very top of it's travel (called "top dead center" or TDC).
POS carb
11-10-2004, 02:09 PM
compression ratio = the ratio of the volume inside the cylinder+cumbustion chamber when the piston is all the way down compared to all the way up. EX a 10:1 comp engine will squeeze 500 CCs of air to 50 CCs at the top of the stroke and then blows it up with a spark
POS carb
11-10-2004, 02:13 PM
FYI more compression = more power but once you start getting up there like 11.0:1 you start sunning into issues where the pressure is so great that the energy buildup causes the explosion to happen before the spark (aka detonation) and this is usually relieved by running higher octane gas or running longer connecting rods. This is also why running 93 octane on your 86 DX is pointless unless you have domed pistons or something.
pendejo
11-12-2004, 08:31 PM
FYI more compression = more power but once you start getting up there like 11.0:1 you start sunning into issues where the pressure is so great that the energy buildup causes the explosion to happen before the spark (aka detonation) and this is usually relieved by running higher octane gas or running longer connecting rods. This is also why running 93 octane on your 86 DX is pointless unless you have domed pistons or something.


Thanks for the info, but FYI I know that! Thanks for the replies though.