Alusil Pistons
 

Hi Guys, I'm tearing down a 3.2 engine that is turbocharged and it has Alusil barrels. It will be getting forged turbo appropriate compressaion pistons. My question is twofold:

1. Can any 95mm barrel be safely bore out to 98mm?
2. Given they are Alusil I'll need pistons that have a ferrous coating on the skirts. Are these available and if so where from please?

Yes I can probably have them Nikasil coated (limited reading) but why not explore the Alusil option?

Thanks.

1. No, you cannot bore 3.0 95mm to 98mm, you can bore 3.2 95mm however.
2. You’ll have to ditch the alusil or have them plated in nikasil or buy new.

Isn't it possible to bore 95 mm alusils to 98 mm and then nikasil plate though? (clarification on #1 above)

Easy answer is yes, you can bore them and coat them with Nikasil.
The trick with 95 mm cylinders with CE rings is that they really won't go out to 98.
What we do is bore them to 97mm.
Two reasons: 97mm leaves enough thickness at the CE ring
Second: 97 mm allows you to use factory 930 3.3 pistons or if you want custom compression ratio, you can still use 930 97mm Geotze turbo rings.

We might have both 97mm freshly Nikasil cylinders on the shelf.
I also believe we have a low mileage set of 97mm 930 Turbo Ps&Cs

Which brand piston are you opting for?

I dont know yet Mike. I'm assessing options. I just seems strange that nobody sells a custom piston for an Alusil cylinder. I understand Mahle have the patents for the necessary ferrous piston skirt coating but you'd think with all the Alusil out there someone would have found a way.

Thanks Henry. Just to clarify it's a 3.2 95mm barrel, not a 3.0. Maybe you're referring to the sealing ring that is on the 3.0 and not on the 3.2? If so is 98mm possible?

They are 3.2, not 3.0. Per the original post.

Try calling CP-Carrillo if you haven't already. They have strong tech support, and expertise with Porsche. They may be familiar with alusil and possibly have an opinion.

So I just called them. The tech sales guy said they have a piston coating called TD14 for the skirt that makes them Alusil compatible. Either didn't know or wan't prepared to elaborate on what TD14 is, but if you take it at face value it seems they are available. I guess the next chalenge will be correctly honing the Alusil bore. I'm still looking for a reason why this isn't a popular pathway for people...

You're right I read it wrong. Same information applies.
Alusil can be Nikasil coated, if the 95 has a CE ring 97mm is limit.
You can coat pistons to become compatible with Alusil (Reynolds Aluminum Silicate) but Porsche never used Alusil on an air cooled Turbo.

If you read the LN Engineering info on their Nickies product they state low silicon aluminium is used (extruding not casting) which results in double the thermal conductivity compared to factory cast cylinders. Alusil has an even higher silicon content (it's how that alloy works) so perhaps Porsche didn't like to use it in turbo applications because of its thermal properties...

Ring compatibility/availability can be a challenge.
Plus, Alusil is less durable in high heat environments.

It’s not a popular pathway because after you come down from the sticker shock of new cylinders and think about the pros and cons its more logical to just bite the bullet and open your wallet. Check around put up a want ad in the classifieds you might be able to score a good deal.

The issue is not thermal conductivity it's about cylinder pressures and surface durability.
Even at low cylinder pressures, ring to cylinder contact creates pressure that often cause gulling and poor oil ring function.
Almost every automotive company that have introduced Alusil blocks have had warranted issues with massive unpredictable oil consumption.
Many of those issue have been resolved but never in air cooled Turbo engines.
Thinking outside of the box is cool [even at times cost saving] as long as you don't mind doing it twice. Good luck.

Nikasil plating alusil cylinders isn't cheap but also isn't crazy expensive. Finding a good set of used nikasils is another option.

For those that have experience with the 97mm Turbo Barrels:

- seeing as this are already 97mm, is boring to 98mm acceptable?

- is there a reason that Porsche didn't put fins on the top half, considering a turbo application is likely to produce more heat?

- Are there any dimensional differences that need to be taken into account when machining heads, in order to maintain good sealing?

- is there a reason that Porsche didn't put fins on the top half, considering a turbo application is likely to produce more heat?

Early turbos (3.0) and later turbos (3.3 in 965) as well as 3.6 turbo engines all had full fins. It was only the mid 3.3 turbos that did not. Mahle 98mm turbo cylinders are full fin as well.

john

My wife's 2008 Cayenne had galling of the Alusil cylinders in the V8 block. Fortunately, it happened just before it hit 48,000 miles. Porsche supplied a replacement engine, but the troubleshooting and installation was on me.

First question is yes. You can bore the 97mm turbo cylinders to 98.

Second question why? Porsche was having cool down leakage/seeping from the head to cylinder joint. The Dilavar studs weren't helping so they were looking for a way to keep expansion rates from top to bottom of the cylinder consistent. Remember, 911s are mostly oil cooled and the cylinder fin are mainly about pulling heat out of the heads. When they went to the partial fins they added the radiator style cooler.

Third: the cylinders are dimensional the same until the 993 twin turbo engines.