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Thoughts on this compression test? 996 Cup

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Old 03-05-2018, 08:19 PM
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spiller
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Default Thoughts on this compression test? 996 Cup

Hey guys,

I've been on the hunt for a 996 cup for a while and just had a PPI done on a car with the following compression test results.

1: 210
2: 211
3: 210
4: 208
5: 205
6: 210

The owner claims approx 2000 kms (20 hours or so) on the engine since it was refreshed but does not have any invoices as it was rebuilt many years ago when still in the hands of a pro team. The car has not been raced since 2009. This seems like a good spread to me? Is a leak down test necessary in light of these results?

TIA
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Old 03-06-2018, 02:27 PM
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Steve113
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Great numbers drive the hell out of it . I wish mine were as good
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Old 03-06-2018, 07:00 PM
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spiller
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Originally Posted by Steve113 View Post
Great numbers drive the hell out of it . I wish mine were as good
Thanks, good to hear. This is what I hope to do!
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Old 03-06-2018, 07:45 PM
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Can you have someone go in with a Modas device and software to query the ECU to see what is says about hours on the engine? I find that "estimates' by sellers of the number of hours on an engine are notoriously wrong. If it was last refreshed by Porsche Motorsport (at whatever facility), the ECU engine hours would have been reset by them and the engine would likely have been sealed. Is it? If not, then the hours on the ECU may not be meaningful. Also if Porsche did the work, you can probably get the receipt for from them for whatever was done. If not, maybe someone at the Pro Team still has records of the rebuild that you could acquire. Though those leakdown numbers look good, they don't tell the whole story, and it would be nice to get the rest of it.
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Old 03-07-2018, 03:22 AM
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spiller
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Originally Posted by Rob S View Post
Can you have someone go in with a Modas device and software to query the ECU to see what is says about hours on the engine? I find that "estimates' by sellers of the number of hours on an engine are notoriously wrong. If it was last refreshed by Porsche Motorsport (at whatever facility), the ECU engine hours would have been reset by them and the engine would likely have been sealed. Is it? If not, then the hours on the ECU may not be meaningful. Also if Porsche did the work, you can probably get the receipt for from them for whatever was done. If not, maybe someone at the Pro Team still has records of the rebuild that you could acquire. Though those leakdown numbers look good, they don't tell the whole story, and it would be nice to get the rest of it.
note these are not leak down numbers, only compression. From my take a leakdown tells you the condition of the top end and compression the condition of the rings? Neither tell you how the bottom end is going? Have I got that right? The shop who did the inspection suggested doing a compression test first and if it was suspect they would then do a leak down. They said they have another car in their shop with 3 events on the motor producIng only slightly higher results.

The car is located in Australia (where I am) and is an ex-carrera cup Australia car. Last raced professionally in 2005. The story goes that it was refreshed at the end of the season and they could not find a driver for it the next year/they switched over the 997 cars. Total kms on the car is 11,200 so it has not been used extensively. The pro team is unfortunately now defunct/merged so it would be tough to track those records down. The rebuild was done by the team I believe, not Porsche Motorsport. Supposedly no one in Australia has access to the equipment to read the 996 cup ecu so buying a 996 cup is a bit like walking down a dark corridor. A lot of the cars here are like this with not much history. It’s only had two owners however so at least it’s not as much a story of fourth and fifth hand information.
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Old 03-07-2018, 01:15 PM
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Sorry, I "misspoke" when I said "leakdown numbers." I meant to say "compression numbers." Both tests provide an overall indication of the "sealing" health of the top end -- rings, valves, head gasket, and diagnosis of cracks or holes in cylinders, heads and pistons. The compression test is a good procedure to do first, and if a problem is detected (say, a cylinder with more than 10% variation from the average compression), follow up with a leakdown test would allow more specific diagnosis of where a problem may exist within the top end (rings v. valves, for instance). But I have also found that leakdown numbers can be very flaky, and that just as with compression numbers, they're more useful in a relative (comparative) sense than on an absolute scale. That said, I think your compression numbers look very good, and I probably wouldn't bother with a leakdown on that engine. As you've noted, neither compression nor leakdown tests give you any sense of the condition of bottom end or of any of the other parts in the engine. There's only so much you can reasonably do to diagnose internal condition. Another test you could run is on the oil -- to see if there is high metallic content that would indicate wear of bearings or other components. You could also remove and disassemble the oil filter, inspecting for traces of metallic flakes. Has it actually sat around since 2005 without being run? I hope not, because that's really not great. You can get corrosion in the cooling system in several critical places (engine-mounted heat exchanger, cylinder liner/water jacket o-ring sealing surfaces, head frost plugs) from stagnant water or coolant that can be a problem. This is especially true if the system had straight water in it. It seems odd to me that the engine was (or may have been) rebuilt in Australia, which is no small feat, yet no one in Australia has access to the equipment needed to read the ECU? It is not that hard to get this equipment (I have different versions in my home garage), and I would certainly think someone down under should have it too. You can buy what you need for a few hundred dollars; PM me if you'd like further guidance on that. Anyway, I know what you mean about buying a Cup -- that it's like walking down a dark corridor. The trick is to get some night vision goggles!
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Old 03-07-2018, 08:43 PM
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Originally Posted by Rob S View Post
Sorry, I "misspoke" when I said "leakdown numbers." I meant to say "compression numbers." Both tests provide an overall indication of the "sealing" health of the top end -- rings, valves, head gasket, and diagnosis of cracks or holes in cylinders, heads and pistons. The compression test is a good procedure to do first, and if a problem is detected (say, a cylinder with more than 10% variation from the average compression), follow up with a leakdown test would allow more specific diagnosis of where a problem may exist within the top end (rings v. valves, for instance). But I have also found that leakdown numbers can be very flaky, and that just as with compression numbers, they're more useful in a relative (comparative) sense than on an absolute scale. That said, I think your compression numbers look very good, and I probably wouldn't bother with a leakdown on that engine. As you've noted, neither compression nor leakdown tests give you any sense of the condition of bottom end or of any of the other parts in the engine. There's only so much you can reasonably do to diagnose internal condition. Another test you could run is on the oil -- to see if there is high metallic content that would indicate wear of bearings or other components. You could also remove and disassemble the oil filter, inspecting for traces of metallic flakes. Has it actually sat around since 2005 without being run? I hope not, because that's really not great. You can get corrosion in the cooling system in several critical places (engine-mounted heat exchanger, cylinder liner/water jacket o-ring sealing surfaces, head frost plugs) from stagnant water or coolant that can be a problem. This is especially true if the system had straight water in it. It seems odd to me that the engine was (or may have been) rebuilt in Australia, which is no small feat, yet no one in Australia has access to the equipment needed to read the ECU? It is not that hard to get this equipment (I have different versions in my home garage), and I would certainly think someone down under should have it too. You can buy what you need for a few hundred dollars; PM me if you'd like further guidance on that. Anyway, I know what you mean about buying a Cup -- that it's like walking down a dark corridor. The trick is to get some night vision goggles!
Thanks for the informative post Rob! You've put my mind at ease somewhat as what you have said about compression vs leak down is pretty much in line what the race shop said (and it makes sense too). I did not think of the oil analysis, that is a good idea. I will look into doing that, hopefully when I own the car. I'm not sure if there is a local Australian place that offers this service but I could always send internationally to Blackstone. The car was last professionally raced in the 2005 Carrera Cup, but was then used for a further 4 years in club type racing by the current owner before he crashed the car at Bathurst. A brand new front tub and all front panels + various suspension components were fitted and he has not driven it since. It has been started regularly but not been on a track in this time. There are no fluid leaks according to the PPI which was a pleasant surprise. I expected at least some RMS seepage. Some of this info might sound less than ideal, but it seems to be similar with a lot of the 996 cups in Australia at the moment in that they haven't been used much at all in recent times. Most tend to run 997s as they are still eligible for GT3 cup challenge here and seen as the superior car. I specifically want a 996 for my own reasons so this is what I am up against. I think its worth at least catching a plane to test it on track, which I will hopefully do next week. Regarding the software/hardware to read the ECU, it sounds ridiculous that practically no one in Aus has access to this but it's apparently the case. I will PM you about that as I'm keen to learn more about it.
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Old 03-08-2018, 03:32 PM
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My SC had good compression and leak down numbers. Wish I would have had it scoped....5 pistons beat to hell, heads were garbage and one rod was so far out of spec I am surprised it didn't grenade. So, I am skeptical of those tests now....



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Old 03-08-2018, 11:58 PM
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They don't tell the whole story, BUT they are a quick way to see how well 'sealed' the motor is.

What was rattling around in your motor?

Ray
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Old 03-09-2018, 12:24 PM
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John H
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Nothing. Someone took it apart and slapped it back together with parts from a bin somewhere. Valve springs and retainers weren't even Porsche parts according to my shop.
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Old 03-09-2018, 06:48 PM
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Laurence Gibbs
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Just to clarify John, are you saying you got those numbers and then tore the engine down and found that damage?
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Old 03-09-2018, 06:55 PM
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I got reasonable numbers given what I was told about the number events on a recent rebuild. Assuming, of course, the shop that did the PPI actually did a leakdown/compression on it. Still pissed about it. Writing my last check on the new motor next week.
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