View Full Version : Compression Ratio's????
drft86
11th April 2006, 06:55 PM
hey all
just wondering if someone would know how to convert a compression figure into a ratio thanks.
eg 190psi = 9.5:1 compression or whatever
would be a bit of a useful thing to know if someone could help please
thanks jason
SprinterTRD
11th April 2006, 10:32 PM
I dont think it can be done as the compression you measured is effected by to many things, like cam profile,
you will also have to know what temprature you did the test at.
aaaaah
11th April 2006, 10:36 PM
Compression ratio is the ratio of the total cylinder volume to the volume of the compression chamber. Plain and simple.
Hen is a total nutcase
12th April 2006, 01:36 AM
TRD man is on the money. Cam overlap will affect the psi reading you take during a compression test, as will many other things.
Maybe you should ask what is a typical reading for whatever engine you have. However consistency across the cylinders is more important than the absolute value.
Hen
biggo
12th April 2006, 03:58 PM
Yair and what happens when u add boost?
Does the compression multiply it or what?
Drift Love
19th April 2006, 09:31 PM
to get an exact compression ratio u need to know the area in the chamber at bdc and tdc
if the motor is stock u should b able to look up the compression ratio from toyota or somewhere like that
the psi reading has nothing to do with compression ratio cos if u have a dead ring or a stickey valve u may have no compression but it will still have the same compression ratio
hope it helps
AE86GT
19th April 2006, 09:38 PM
you can get a reading by doing a compresion test psi or kpa
SprinterTRD
19th April 2006, 09:46 PM
You can get a pressure reading but you cant work out the compression ratio
Drift Love
19th April 2006, 09:51 PM
yeah u can get a compression reading but not a raitio from doing a compretion test
shift_rook
19th April 2006, 09:51 PM
Also there is a percentage leakage test for non static compression testing , but yes you cannot work out the compression rate from any of these tests .
AE86GT
19th April 2006, 10:03 PM
True
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