Sorry about my mistake then - I thought the wrong year (6/2002 I thought) for the fitment of the Euro3 engine - just goes to show, you can't trust parts catalogues
Well, I can tell you that the pistons and piston rings are different between the 32301 and 32310 engines. I have just machined my 32310 pistons to accept the earlier rings.
The later rings are low-friction (the second ring and oil control rings are narrower, and the top ring is cast iron rather than steel). They are a lot more expensive than the earlier rings, and given that the earlier rings are made out of better materials (chrome top ring), I objected to paying that difference.
This is of little consequence to you, but is a difference between the engines, which would lead to a theoretical increase in efficiency of the later Euro3 engine. However, I suspect that the later 2mm oil control ring was not effective in my engine, which had massive oil consumption of 1L/600km (though it will take at least a month to measure the difference my rebuilding efforts may make. I'll report back, and I'll be measuring economy on the same trips
<The next part of the post is just my ranting about this subject - mostly my own opinion - feel free to disregard or at least take with a pinch of salt>
A little more about the oil control ring. Its purpose is to scrape most of the oil off the cylinder bore walls, leaving a thin and important film for lubrication of the piston - during combustion, this oil is burned. It is therefore obvious that if the oil control ring does not remove enough of the oil, more oil will be burned. My theory is that there is no visible quantity of blue smoke because the oil burning is at a continuous and relatively slow rate, unlike for other common causes of oil burning (leaks down valve guides, leaks through compression rings/blowby) which cause immediate puffs of blue smoke.
The oil control ring has two ring surfaces plus a centre section that has holes or slots to allow the excess oil to drain away. The earlier 3mm oil control ring has the slots, while the later 2mm oil control ring has only very small round holes. In my engine, I found most of those holes blocked with carbon. We can therefore surmise that cleanliness and quality of the oil has a significant effect on how well this later design works.
No two engines are exactly the same and I suspect that my engine was not 'run in' properly, which basically entails a good thrashing under varied loads so that the rings bed in (wear against the bores to create a smooth fit) when the engine is new, and NOT the gentle treatment that many people associate with 'running in'. I suspect mine crawled around in Singapore traffic (the Selespeed computer shows mostly 3rd gear driving and very little 5th gear driving). Engines that get a good thrashing perform properly - I can think of so many examples over the years of old FIATs I've known - and race engines are a good example. They go out on full noise more or less right away and get excellent compressions and low oil consumption.
Modern synthetic oil has, in my opinion, created this problem of gently-driven engines not bedding-in properly. Engines once came new with a particular oil in them, which was then drained out and changed after a short interval (1500km). But then in the late 90s, manufacturers did away with this 'first service' and supplied the car filled with oil that must last for 20000km. It is not unique to the Alfa 156 - I have heard of the same problems with many modern cars. I took my engine apart after 237,000km and there is almost no wear at all - that's great, except that the other side of the coin is that the same quality of the oil caused the rings to never bed-in. The crosshatching (helical scratches made at 30-degree angles) was exactly even around the bore with no evidence of the rings wearing it away. I haven't seen that before, especially not in an engine with 237,000km. It looked just like one that I took apart at 25,000km once (with the same oil-burning problem). This time I carefully honed away the glaze and restored my own style of crosshatching (a 'burnished' look) and I look forward to finding out whether it works out better. Of course I want it to, with all the personal touches I've made to the engine
I'll be running on a plain mineral oil for at least the first 1000km.
At the same time, the extended oil change intervals recommended by manufacturers also, in my opinion, cause problems when the car reaches middle-age - the oil is far too dirty and the carbon buildup I mentioned before must be more likely, especially when engines are used in adverse conditions (the fine print ALWAYS advises that oil should be changed more frequently for engines used in heavy traffic, dusty conditions, etc.)
I'm sure there are lots of people out there with the later 32310 engine where the oil control rings are working fine and oil consumption is low, so I am not saying that it is a bad design - just that some engines (like mine) may have turned out bad as a result of gentle treatment in early life, and then insufficient oil changes or poor oil quality later.
<end of rant>
As for the reduction in power compared to the earlier engine - it could be all sorts of things that cause that - fortunately I don't drive at full power (contrary to what you might think by now) and I found my 156 to be a very pleasing blend of economy and performance. It used much less fuel than it was supposed to, and it seemed to go well. 5bhp less? Who cares... "Don't worry, be happy" would be my advice...
If you want lots of power buy an old Alfa 164 with the 3L 12-valve V6 - I have two of them and I'm sure they would run rings around my 156, but I think I prefer the 156 at least in some ways... and it uses a lot less fuel. I shall be happier still if I manage to solve the oil consumption problem. I decided it was more beneficial (for performance and for the environment) to reduce the oil burning than to have this theoretical efficiency gain from the low-friction rings. And anyway I was quite keen for an engine-rebuilding project after at least ten years of no engine rebuilds being necessary in my cars
It would probably have been cheaper to just carry on putting oil in