328 Compression Test

To low, dont buy it

Thank you

 

Did they have the throttle fully open while checking for compression? If not then that explains why the compression are low.

 

Don't know a "typical" range for a 328 compression test, but US version (9.2:1) and euro version (9.8:1) have different compression ratios so keep that in mind when evaluating what you "hear". You don't give the location where the test was performed, but another factor can be the barometric pressure -- i.e., if the test was done at high elevation = lowers the result. And finally, the gauge itself may have some error. The results being all equally low seems a little strange if it's a real problem (and not something related to the measurement method). You could ask your mechanic to do a leakdown test on a few of the lowest cylinders (if not all cylinders) to get a sort of second opinion.

 

Sometimes squirting a little bit of oil in the cylinder helps bring the compression up.

 

Yes, compression test numbers can be inconsistent based on how the test is done/atmospheric pressure/altitude, etc. The most important item is the consistency of the numbers between the cylinders. For that reason, comp test numbers are often not included in shop manuals.

The 'best' compression test is done with the throttle wide open, the SAME number of "pulses" per cylinder, NOT, "until the gauge reading quits moving upward." Six pulses is an often-used number. Also, the engine should be at/close to operating temp. That last item is very important but frequently ignored because it's a bit of a pain to deal with the hot engine/spark plugs, etc.

As Steve mentioned, a leak down test is a much better evaluator of engine condition but it takes a lot longer than a comp test and the shop would likely charge considerably more to do it. It's worth doing, though, if you are really interested in the car but concerned about the comp test.

 

Is'nt that cheating ?

 

Not really, it actually tells you a few things like if the compression increase, it means that your piston rings are sealing properly, the valves are seating properly, and valve timing are set correctly but as mentioned, it’s best to check with engine warm and preferably at sea level and with a known good compression gauge.

 

Yes, if compression increase significantly when oil is added to the cylinders it's a sign of worn rings.

 

As usual Steve is 100% correct. They are very sensitive to cranking speed too so a battery a little off will do that. I was in California and now in Texas. With our average higher temperatures I never see compression numbers like I did in California.
A cranking compression test is good for diagnosis when you know something is wrong but has so many variables is nearly worthless as an indicator of engine condition. If you are concerned about condition a leak down is the only way to go.

 

TBH, if an experienced, good mechanic THAT YOU TRUST says it's OK, I wouldn't worry about it any more.

 

Its one of the best Ferrari engines ever made so just in general I have little concern over them. Also as said a few times if it is that even my confidence would be pretty high. They don't go south with even compression often. These motors don't usually wear out, they get broken.

 

Just for comparison, when the PPI was done on my 88 328 with 84k, all cylinders were between 170-180.

 

Just another data point if it helps.

I have an 86 and the compressions were between 170 and 175 for all cylinders when my PPI was done. I also did the leak down, but that was probably overkill.

 

FWIW, usually the higher the compression ratio, the lower the compression check numbers. Sounds counterintuitive but the higher compression ratio is normally accompanied by a more aggressive camshaft which then reduces the PSI reading because some of the air being pulled in at cranking speed is shoved back out the intake tract before the intake valve closes.

For example, a 9:1 "granny motor" US V8 would show around 170PSI on a standard compression check; a shop-built 13:1 performance engine would typically show 130-140.

 

I feel a compressiontest provides a first indication only. The only real test for me is a leakdown test. This is really much more accurate

I saw engines with pretty proper compression number ( I think you can only really compare between de cilinders) which on some cilinders had very poor leakdown results compared to some other cilinders

 

About the only thing that a compression test shows you (assuming the method used was consistent across all cylinders) is the variation between the cylinders. In this case 130-145 which is a little over 10%. You definitely wouldn't want to see too much more but also likely as not if one was really bad it would also be a lot further south.

However, that in turn could also be affected by cranking speed so if the results tailed off a bit in the last few cylinders tested, then that might also be the reason for some of the variation

 

Compression tests are good for looking at cylinder to cylinder variations. If you want to diagnose a cylinder use leak down test. That will identify if the issue is rings, intake or exhaust valves.

 

Any smoke on start up? How about driving, on throttle or off throttle?

 

I recently went through this on a similar V8 Ferrari. It happened to be a 2.0 liter car, so results were magnified.

Relatively low compression numbers. But they were all consistent, and the engine felt very strong. (And I have a lot of experience with these cars, so I know what they should feel like.)

I talked to a friend of mine who has experience building engines for major race teams. The first question he asked me was “what’s the idle speed spec”. I said roughly 950 rpm (give or take). He then asked what’s the redline. I said about 7800 rpm. He said, ok, it’s a very low displacement V8 (2 liters in this case) that is made for high RPM and can’t probably stay running at a low idle (which is true). He said an engine like this has a very short stroke and high compression ratio (for what it is). That manifold vacuum will be very low (it is) and it wouldn’t be surprising to see what you would think are “low” compression test numbers.

(Note that in this particular case, this is a 2.0 liter turbo engine, so the compression ratio is actually very low. But he said the overall effect would be the same. And, a 3.0/3.2 liter V8 Ferrari engine has the same architecture, just higher displacement and higher compression ratio without the turbo.)

In summary, he said that all that matters is that the compression numbers are consistent. And that what really matter is a leakdown if you want to figure out if there are issues with the engine. We did a leakdown, and all cylinders were lower than 5%; he said the engine is very healthy, and not to worry about the seemingly “low” compression numbers.

 

i'm purchasing a similar car and the compression test came back between 180-190. Was surprised how good it was.

 

Take my input for what it is as a new Ferrari 85 328 owner and lover for years...my unit tested earlier this year with numbers between 90 to 115 and the shop said they needed adjusted and should be in the 130-145 psi range. However, after speaking with other Ferrari shops it seems the psi readings can be influenced by the actual process the technician uses to test the compressions: one or two cranks and that is the pressure reading to multiple cranks to get the highest pressure. I had a 1986 328 European model inspected back in 2015 (no, didn't buy that one) and those readings were in the range of 165 to 195 psi, which some say typically have a little higher pressure settings. In addition, a recent 1986 328 on BAT (Bring a Trailer) auction had photos of the compression test in the higher range of 170-185psi.

Hope this helps. Good luck.