Update on F430 Compression Test Results

Go drive it, do the test again and the numbers will be different.

The only way compression tests work is if you do them regularly and note a trend. IMHO

 

5 or 6 strokes would be normal enough I feel. I wouldn't have thought the variable valve timing would enter the equation - bottom line is valves should be fully closed on compression stroke.

Did he let you know what values he typcially finds on fit 430s using the same technique? How do these values compare to what he would consider a fit motor?

 

Smaug,

I'm certainly no expert at compression tests, but my 2005 F430 just qualified for Ferrari's certified 1-year "Power" warranty with compression test readings of 11.6-11.9 bar per cylinder (about 168 - 172 psi). I spoke with Jason at F of Silicon Valley, and he seemed very comfortable with these numbers and also iterated what jason1st suggested, that namely the numbers vary somewhat each time the test is run. Hope this helps.

 

+1

My 05 readings were 11 - 11.3. Also qualified for factory Power warranty (which I bought).

Interesting that an earlier test from 1+ year prior showed lower numbers at 10.5 - 11, with one cylinder (#8) at 11.7.

 

My compression test as well as another member has quite higher results (in bars).

Cyl 1 : 14.5
Cyl 2 : 13.9
Cyl 3 : 13.5
Cyl 4 : 13.5
Cyl 5 : 14.5
Cyl 6 : 13.5
Cyl 7 : 14.1
Cyl 8 : 14.5


http://www.ferrarichat.com/forum/showthread.php?t=324351

 

Are the numbers dependent on rpms or other factors during the test? Seems like a large range of values among different members' cars.

For example, my car was fitted with a Capristo exhaust by a previous owner. Could a 'freer flowing' exhaust system, which could ostensibly reduce back pressure, reduce absolute compression values? I found it interesting to read various threads that actually showed a loss of hp with some exhaust system mods. TIA!

 

All these figures are quite fine. It's a simple cranking compression test and this has nothing to do with the exhaust

What is more important is the difference between the cylinders. There should be no more than 10% difference between any of them.

Low compression in only one cylinder usually indicates a bad exhaust valve. Low compression in two adjacent cylinders means you may have a bad head gasket. Low compression in all cylinders would tell you the cylinders and rings are worn.

I would always claim a leakdown test if one of the figures were below 9.6 bars (140 lbs) or if there is more than 10% difference between 2 cylinders. With the leakdown test, instead of measuring pressure, pressure loss is measured by injecting compressed air in each cyclinder at 5/6 bars (75-90 psi). A leak up to 10% means the engine is in great condition. Up to 20% can still be considered as fine. Although above 30% indicate trouble.

Keep in mind that a leakdown test is not replacing a compression test. Both are complementary and very useful. For instance, you can have an engine with minimal % of leakage but poor compression test figures (incorrect valve timing if this is happening on all cylinders or valvetrain problem if this happens on only one cylinder)!

I would recommend to start with a leakdown test as it is faster to do (a threaded coupling attached to a leakage gauge is screwed into a spark plug hole) and is easier to figure out where the compressed air is leaking. But always confirm the leakdown test with a compression test.

 

SfefVan, awesome information. Thank you so much! That helped a lot!

As an aside, Ferrari of Silicon Valley could apparently not get the one-year Ferrari warranty unless the car had the stock exhaust installed. So, it's going back on. I'll decide later whether to reinstall the Capristo. Honestly, I may just sell it because I generally like my cars stock (except for an upgraded audio system!).

Great forum!