hello NAM, so while in the process of logging in and gathering info for my tune i did a compression test.

warmed up the engine and took the plugs out and did the test 1 by 1. I was under the impression the r53 compression is 8.3

mine cylinder 1,2 &3 are consistent on 10 and #4 is 11.

Should i be worried on a boosted engine having a high compression?
it’s a 2006 MCS. 112k

thank you for looking.

 

10, 11 psi?

 

The 8.3 is the compression ratio. 8.3:1.

What you were measuring is the amount of pressure each cylinder can develop. A pressure of "10" and "11" suggests you were using a pressure gauge that reads in bar. One bar equals 14.5038psi.

Thus a 10 bar reading is 145.038 psi, an 11 bar reading is 159.542psi. Those are psi pressure numbers that sort of make sense based on my admittedly long time ago messing with compression testing engines.

The compression test runs the engine slowly, at cranking speed. This can be just 150 (or fewer) RPMs. The throttle valve wants to be fully open so there is no restriction to the air that flows into the engine. The end result is the cylinders fill up about as much as they can and the pressure reading will be pretty high. I have no numbers on what a MINI engine compression test pressure readings should be but 145psi to 159 psi ain't that high.

The concern is not so much the pressure obtained-- although the pressure readings want to be "close" to what the factory might provide in a factory engine manual -- but that they are all within say 10 to 15% of each other. What you do not want to find is one or more cylinders with a too low a reading compared to what the factory number is or what the other cylinders are reading.

 

Yes you are correct. I thought that’s how you’d read it lol like 10 to 1 in the 10 bar 😂

so it looks like I’m ok. Then. Compression is good for a boosted engine.

 

Cylinder pressure (compression test) and compression ratio are two...completely different things !
Please enlighten us, 10 and 11 "BAR"...is...what...in good ol PSI ?

Mike

 

In Bar as stated above. Not 10 psi lol

i know i have to take the engine a part to get head chamber size, bore, stroke, piston dome and head gasket to get compression ratio.

any other way on measuring it by the compression test?

I’ll have to redo the test and get the exact “psi” instead of bar. With that said. What’s the normal psi ?

 

I had to purchase a used engine for my '06 R52 from a wrecking yard last year because the original engine had issues. I strapped down the engine I bought to my trucks tail gate and connected a starter to it to crank it over.

Cold engine compression was 170 to 175lbs in each cylinder.....now this engine is a 2006 supercharged John Cooper Works model.
Engine is installed in my car and runs fine.

Just thought I would post my compression readings for you

Bryan

 

Serafin
Just for clarity, the compression ratio is set by the engine design - it won't change because of wear or mileage. There's very little you can do to change it & there's no point on a supercharged engine anyway. I think 8.3:1 sounds right for an R53 - it's probably in the Owner's Manual.
The cylinder compression test measures the pressure (in pounds per square inch, please!) in each cylinder. This will change a little over time because of a hot or cold engine, oil grade or worn rings, worn or burnt valves or a bad head gasket & a few other things. As long as all four readings are within about 10% of each other, there's really nothing to worry about. Look for something in the 150-175 lbs psi area.
A383's readings are very good & it's a JCW engine that may be a little different.
Depending on how the compression test is done, you may need to reset the fly-by-wire throttle synchronization afterward.

 

yes not trying to change or alter my compression, it was one of the forms i have to fill our when i got my tune, so just wanted to see compression still good.