Compression test values for a 3.2 Carrera

[Nico911]

Hi.

I'm wondering what you guys would consider ok values for a compression test on a 1988 US 3,2L with 117 000 miles.

Also, I would like to know what a bad compression test results means. Does it mean that the piston rings are worn out, or is it about valves ?

[Arne2]

Bad compression could be either rings or valves. That's where a leakdown test helps, might be able to tell which is the problem.

On a 3.2 with those miles, I'd be more worried about valve guides.

[nettles503]

When I bought my '86 this past summer, here are the compression and LD numbers from the PPI I had done on it:

Cyl. 1: 160/10%
2: 150/8
3: 155/10
4: 155/10
5: 155/8
6: 150/8

The engine had 112,000 miles on it at the time of the test. I was told that those were acceptable for the age the engine. LD figures over 20% are cause for concern, according to this article.

Again, not the only consideration, as Arne notes. But this at least gives you something to compare to. Good luck!

[Nico911]

Originally Posted by nettles503

When I bought my '86 this past summer, here are the compression and LD numbers from the PPI I had done on it:

Cyl. 1: 160/10%
2: 150/8
3: 155/10
4: 155/10
5: 155/8
6: 150/8

The engine had 112,000 miles on it at the time of the test. I was told that those were acceptable for the age the engine. LD figures over 20% are cause for concern, according to this article.

Again, not the only consideration, as Arne notes. But this at least gives you something to compare to. Good luck!

Thanks for being so precise. That will help.

[Drisump]

As Arne says, the numbers alone won't tell you if the valves or the rings are the culprit in a low reading. A leak down test is the only real way to determine what exactly would be causing the compression loss. That being said, these engines have a very robust bottom end and seem to require attention for the valves long before rings are a concern. Valve guides and seals do often fail in around the mileage stated but won't show up on a compression or leak down test, you would just burn more oil than an acceptable amount. If buying an unknown car at that mileage, best factor in a valve job if one hadn't been done already. Cheers