2.7 Alusol jug reline possible?
 

Out of interest is it possible to reline an Alusol jug with a new nikasil (?) liner rather than bin them or is it cheaper to buy new jugs and pistons?

Lots of shops do it, try EBS racing in Reno, they have an exchange program.

It isn't really a liner (not a sleeve) - they spray the hot metal on the surface, then machine it back to spec. It is very effective, and a really good way to use worn Ausils.

Though, come to think of it, some shops will bore the cylinder out, heat it, and insert an iron liner, which is then machined to the right ID. You end up with a later day version of the Birals Porsche used on their earlier S models. The assertion is that this gives a very good wear surface as well as more dimensional stability.

I've seen it mentioned by an engine builder on here that Alusil cylinders redone in Nickasil are actually better than factory Nickasil cylinders because the alloy KS used has more silicon in it so they are more thermally stable than the Mahle cylinders.

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2.7 Alusol jug reline possible?
 

Yes, more silicon in Alusils. Nikasil is a chemical treatment, not sprayed on. It can flake off and be redone but takes best to aluminium which has not previously been Nikasil treated, therefore Alusils really good candidates for Nikasil process. They do have fewer fins 9 vs 11?) but I don’t expect this would create overheating issues, providing you’re running an external cooler.

I got that wrong - nikasil is a plating process - electrochemical might be the way to describe it?

Alusil is finished by etching, which removes some aluminum and leaves the silicon particles exposed.

Absolutely correct.

Regarding the iron liners in 911 cylinders and dimensional stability,, I’ve heard some say that for higher boost turbos, the iron liners are preferable as aluminum/nikasil cylinders can go oval. Not sure if it’s true, I’ve wondered.

In the same way that high HP applications (power adders) use steel liners inserted into the block, same goes for steel liners into Porsche cylinders. Not sure at what point this becomes necessary but certainly make stronger cylinders and improved head sealing.

Turbo’s are hot, they run hot, and the air going into them is hot. One has to trade off structural strength with thermal conductivity. At around 220 for Aluminum vs 45 for Iron thermal conductivity, aluminum wins. Turbo cylinders usually fail from detonation. Cooler more important than stronger. For the two valve engine there is no amount of boost that will change that trade off.

Other engines have water cooling, in which case that trade off flips. Plenty of cooling.

As long as you’re sending the cylinders to plate, you might consider 92mm to 2.8 with cr of 9.5 to 10.0
Bruce

Many thanks for your contribution, I managed to get smoking deal on unused set of Mahle P&C's.