Not much- its the track and aggressive cams that suffer
Compression test CSi
- Thread starter BMW3.0CSi
- Start date
So, I triggered a discussion 
. Thx for all reactions. Already interesting to see the discussion about what the actual ratio should be for a CSi. If I look in my blue book it should be 9.5:1. See pic attached.
I didn’t saw it at first sight, but the book mentions indeed 4 table line items from below that everything above 156psi is good. It counts for all types of engine/types. Below 142psi is poor. I have a standard cam and used a simple/cheap compression tester for 30 euro which is new, but of course not a professional tool.
But I see various answers to my question, from consistent numbers is good enough to way too low. Point is that my engine is not running smooth at lower idle speed. Tending to perform a smoke test also to check for potential leaks.
. Thx for all reactions. Already interesting to see the discussion about what the actual ratio should be for a CSi. If I look in my blue book it should be 9.5:1. See pic attached.I didn’t saw it at first sight, but the book mentions indeed 4 table line items from below that everything above 156psi is good. It counts for all types of engine/types. Below 142psi is poor. I have a standard cam and used a simple/cheap compression tester for 30 euro which is new, but of course not a professional tool.
But I see various answers to my question, from consistent numbers is good enough to way too low. Point is that my engine is not running smooth at lower idle speed. Tending to perform a smoke test also to check for potential leaks.
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gazzol
Well-Known Member
With all due respect to the members the only person who answered the O/Ps question based on the facts (and therefore with any degree of intelligence) was Gransin. Spouting conversion charts and ratios is ALL IRRELEVANT unless we know that the guage is good. So all we can hope for is 6 similar numbers. I would normally interject a anecdote here but I'm in hospital with Pneumonia, hence Mr grouchy ass
How long did it take to do 6 cylinders?
I’m having it done in am at car I’m buying
73 cs
You can do a compression check on CS in an hour. Once set up, all you are doing is screwing a gauge into each spark plug hole and cranking for a few seconds. As noted, consistent low readings could be a number of things not related to the actual compression. To take out those variables, a leak down test could confirm for each cylinder if and where compression is being lost. See this link on the difference. I had both tests done for my PPI.
www.klassikats.com
Leak Down Test Versus compression Test, which is Best?
Which is the best test to perform an leak down test or a compression test? we look at the pros and cons of both tests in detail.
www.klassikats.com
When doing a compression test I would cut off the supply of gas to the engine temporarily . Too many cranks can possibly pour too much gas into the cylinders, flooding the engine, and wash off the walls of the cylinders from oil. This can both distort your readings as well as potentially damage your engine from lack of adequate lubrication. My two cents