Hey everyone,

New owner of a 2005 R53 Cooper S with JCW Tuning Package here! The car only has 49k miles and the engine runs great and pulls hard. I really just wanted to know the status of my motor before I put it through the stresses of a racetrack. I've read that the consistency of readings across cylinders is more important than the actual numbers, but I am a bit concerned with how low my readings are.

Cyl 1: 102psi
Cyl 2: 106 psi
Cyl 3: 105 psi
Cyl 4: 105 psi

I used a low-cost kit off of eBay (identical to Harbor Freight kit), so that may be the reason for the low readings. I also repeated the tests and checked all the fittings and got the same results. Anyone have any input on this? As I stated earlier, the engine pulls hard, has a stable idle, and doesn't have any apparent issues. Should I not worry about the low readings and just trust the consistency of the readings? Thanks in advance!

 

Your results, although consistent are lower than expected. I am guessing the tester is flawed and the compression is quite a bit higher.
Make sure the engine has fresh oil when you do the test, to give you the best test.
Don't trust cheap gauges, as they are not calibrated.

 

Thanks for the response! Is there any particular compression testing kit that you would recommend? They all look like they're from the same manufacturer and have similar boxes and layouts. I wanna make sure I don't buy the same kit rebranded for a higher price.

 

Here is the thing: If you really need to know the compression, it would be worth having one of the name brand tools like Snap on. This type is made for accurate testing. There are many good ones out there! professional tools are expensive, because of the extra work needed to ensure accuracy!
I am guessing your compression is around 150+ psi.

 

The harbor freight one I have shows 120 on healthy engines. The one you have is precise but not accurate. You can test yours on a known healthy engine for peace of mind. I'm not sure it is worth spending the money to get precision.

 

The problem I have with this, is the poster wanted to know what the real compression is! It may be 180 psi. showing 103 is not going to boost confidence, or peace of mind, for him.
If I had an engine testing at 103 psi, I would be saving for a rebuild!
I too want to know the truth, when testing compression and therefore want as accurate as possible, a tester that can achieve that.
I further notice that the cheap testers are not responsive enough to indicate valve leaks on cheap vacuum gauges. Loose valve guides will kill performance, through improper valve seating, during high rpm operations.
Nuf said.

 

Thanks for the input guys. I've taken everything you guys have said into consideration and will be looking into a Snap-On compression tester on Craigslist for $120. Although I'm pretty confident the engine is healthy, as ItsmeWayne stated, I really just want that peace of mind. Small price to pay for certainty me thinks. Cheers!

 

So if you get that high dollar tester and all it confirms that all cylinders are in the low 100s you are going to tear into the engine when it is subjectively running well?

 

Well, not necessarily. I'd postpone hitting the track and look into what might be causing the low readings. Regardless, I picked up the Snap-On kit earlier today and reran the tests to the following results:

Cyl 1: 144 psi
Cyl 2: 150 psi
Cyl 3: 148 psi
Cyl 4: 158 psi

Cylinder 1 is noticeably lower than the others, but it's within range right? Any cause for concern? I've done a fair amount of searching and have come across a variety of ranges that people suggest is ideal - some say 130-190, others say 150-170 with <=10% variance being acceptable.
Some of the time, my OCD-ness comes in handy; most of the time it's just a headache...ugh. I'll likely redo the test in a day or two to confirm the results.

 

October of '06, my shop measured my '04 Works car with 54k miles on it.

150, 145, 145, 145

Cheers,

Charlie

 

Yes, the compression is in range, so I think you are A OK on the cylinders. (20lbs is acceptable range, but not for racing) I think I would do a vacuum test to see if it is stable or fluctuating, which may indicate a possible valve guide issue. When the valves are not always seating, the vacuum gauge will flutter. You did say it runs strong, so I think it is fine!
Glad you got a good tester!

 

Awesome. Thanks for all the help guys. It's much appreciated!