compression?
Thread Starter
Junior Member
Joined: May 2003
Posts: 495
Likes: 0
From: Sicklerville, N.J., USA
compression?
i bought a motor that was supposly built all motor but im not sure how can i check the compression without pulling anything apart.. i want to go turbo on this motor but dont want high compression any suggestion's?
Junior Member
Joined: May 2005
Posts: 157
Likes: 0
From: Rockville, MD, USA
Re: compression? (Honda Crx)
If you feel you can assume that it isn't bored out and the head is stock (edit and the pistons are stock): you can determine compression (approximately) by measuring (with good calipers) the length the piston travels from tdc to bdc.
If you think it may be bored over or otherwise modified (likely since it's been rebuilt): about the only way to check it would be to fill the cylinder with a measured (will need an accurate way to measure it, to atleast 1/10 of a cc) amount at tdc. Then measure how much more fluid (again very accurately) it takes to fill the chamber at bdc. You would also have to use a very thick fluid (such as say 100 weight motor oil, or gear lube) to keep from losing a significant amount (again small losses will give inaccurate results) of fluid between tdc and bdc etc. You would then reduce the ratio of bdc to tdc to the lowest common denominator (pass math?).... and approximate it in terms of 10:1 10.2:1 etc.... (edit: temperature and time variations would also give inaccurate results... aka leaks and expansion. Would also have to accurately check the level to some predetermined easily seen spot in the chamber (say maybe top of spark plug hole)) (you're on your own for getting the oil back out) (screwed up valves, rings, pistons, so forth will null all results) (etc...)
So.... just throw the motor in (yes... disregard the above theories), and see if it pings with 87 octane... if it does figure it's greater than say.... 9:1.... then try 89.... if it pings assume it's greater than 10:1.... if it pings with 93 assume it's greater than 10:1 (and that something is likely wrong with the motor) if it pings with race gas.... FIX IT (teehee)
I'm sure someone will pipe up and correct inconsistencies in this... so i'm not gonna waste time worrying about details... i'll let you figure the little stuff out.
Modified by civic_dork at 6:53 PM 8/31/2005
Modified by civic_dork at 7:04 PM 8/31/2005
If you think it may be bored over or otherwise modified (likely since it's been rebuilt): about the only way to check it would be to fill the cylinder with a measured (will need an accurate way to measure it, to atleast 1/10 of a cc) amount at tdc. Then measure how much more fluid (again very accurately) it takes to fill the chamber at bdc. You would also have to use a very thick fluid (such as say 100 weight motor oil, or gear lube) to keep from losing a significant amount (again small losses will give inaccurate results) of fluid between tdc and bdc etc. You would then reduce the ratio of bdc to tdc to the lowest common denominator (pass math?).... and approximate it in terms of 10:1 10.2:1 etc.... (edit: temperature and time variations would also give inaccurate results... aka leaks and expansion. Would also have to accurately check the level to some predetermined easily seen spot in the chamber (say maybe top of spark plug hole)) (you're on your own for getting the oil back out) (screwed up valves, rings, pistons, so forth will null all results) (etc...)
So.... just throw the motor in (yes... disregard the above theories), and see if it pings with 87 octane... if it does figure it's greater than say.... 9:1.... then try 89.... if it pings assume it's greater than 10:1.... if it pings with 93 assume it's greater than 10:1 (and that something is likely wrong with the motor) if it pings with race gas.... FIX IT (teehee)
I'm sure someone will pipe up and correct inconsistencies in this... so i'm not gonna waste time worrying about details... i'll let you figure the little stuff out.
Modified by civic_dork at 6:53 PM 8/31/2005
Modified by civic_dork at 7:04 PM 8/31/2005
Thread
Thread Starter
Forum
Replies
Last Post
bxsi
Forced Induction
8
Mar 18, 2004 07:36 PM
boostedinteg03
Forced Induction
4
Apr 11, 2003 12:47 PM