Rennlisters,

Question for pro and well informed diy.
Both Porsche and BMW, a big worry is bore scoring.
Wondering if the search for improved efficiency is partly to blame.

If you could do a experience check in your head - is the scoring you are aware of mostly in automatic transmission cars?
I seem to notice, in the quick shifting to a higher gear, more engine lugging.
Engine lugging to my knowledge, causes higher cylinder pressure, among other issues.
Possibly piston instability?

If you are shifting a manual transmission, at least for me, I tend to bring revs higher than an auto would.

So the meat of the question is:
Does shifting to a higher gear, and incurring engine lugging, contributing to bore scoring?

 

No, it is a piston design problem or a manufacturing quality issue with the bore coating.

 

There have been automatic transmissions in cars for 70+ years, lugging them around in the highest gear. Bore scoring has only become a wide spread issue since auto manufacturers started going to the cheaper to produce cylinders coatings in alloy engine blocks rather than the proven tech of iron blocks or alloy blocks with iron sleeves.

 

Comparing auto trans from 50 years ago to today’s and saying it doesn’t contribute to the issue is a little off base.

Was hoping an explanation regarding the lugging of the engine contributing to a cold engine would exacerbate the bore scoring.

A recommendation to alleviate bore scoring is low rpm, mild throttle opening till engine is warm.

If you drive a modern auto from Porsche or BMW, from cold, it will hit the highest gear possible.
When you then try to speed up, with a still cold engine, you have just the opposite, a high throttle opening low engine speed and lugging. Which contributes to higher cylinder pressure and possibly skirt to cylinder slapping.

Maybe I am way off, but explain why….

 

Agree with using iron liners. Had several I6 Volvo turbo engines with alloy blocks and iron liners. Low performance by today’s standards but they lasted.

 

No it isn't. It is a solid historical precedent.

It has been explained. Lugging is bad for an engine but it is not the reason for the bore scoring. Vehicles with iron based coatings driven the exact same way don't suffer from scoring. What's causing these modern engines to bore score is the use of inferior cylinder coatings. It's just that simple.

 

This video lists Porsches that suffer from bore scoring and those that do not. The ones that do not all have iron based cylinder coatings.

 

This video shows how bore scoring is eliminated in M97 engines via replacing the OEM coated cylinders with ones made with iron liners.

 

I have seen videos explaining what the major factor is regarding materials and solutions. Understand that.

I am trying to explain the outliers.
If the cause is only materials change/ coatings, why are not all of the engines constructed this way affected?

Different oil? Different gas/ with different additives?

Trying to come up with why a small percentage. Gotta be something besides bad luck contributing.

The tech in me wants more of a solution than “Low rpm low throttle opening till warm” or rebuild the engine with different p&c ‘s.

 

All the inferior coated engines are or will be affected at some point. The biggest determiner has been ambient temperature. Cold starts in sub or near zero temperatures are killers. Vehicles in warm climates have significantly better longevity but eventually they will succumb and score their cylinder walls.

This is all out there as public knowledge. Automatic, or manual transmission, it doesn't really make a difference.

These engines eventually blow themselves up prematurely realative to the exact same vehicle equipped with iron lined cylinders. 996 Turbos and 996 C4Ss are perfect examples. They are the same vehicle except for the turbos and engine internals. Turbos have iron lined cylinders and will run for 200k miles plus easily. C4S engines are all time bombs.



PCA did a 4 part series on it.

 

I think the root cause is the variable manufacturing quality of the cylinder wall or piston skirt coating, inconsistent coating thickness or material consistency. This is a manufacturing process control issue.

 

I have no doubt there were inconsistencies in the coating process. But beyond just a manufacturing issue Porsche and several other manufacturers has stopped using these coatings that caused all the issues and moved on to others. That tells me the entire technology was flawed from the get go.

 

No.

Bore scoring is:
- mismatch of wear couple: insufficient piston material hardness and microsurface, insufficient cylinder material hardness and microsurface, insufficient thickness of expendable wear materials
- insufficient management of particles created by products of combustion which contribute to cylinder wall and piston abrasion

In summary: sh1tty design and extreme cost reduction perpetrated by the automaker.