OriginalSterm

Are these virtually the same with a different trade name? Or are they different compositions all together?


Can our engines have the Alusil "built up" then honed out to the stock size? Or can the Nikasil be substituted for the Alusil?

Ahmet

They are similar in that both can be linerless and need to be treated. Run a search for it.
Ahmet

Ski

Nikasil Alusil, both are mixed coatings, usually in paste forms. Nikasil is primarily made up from a Nickel base, used a lot in aircraft engines but also autos; Big BMW goof. Where Alusil is aluminum based, which is why the pistons used the iron coating. That's been my understanding...I might be about to get educated but that's okay too.

RKD in OKC

Nikasil is a coating of Nickel and Silicon that is added to a soft alloy block's cylinders to make them much harder. The downside to Nikasil is that high sulphur content gasoline can eat away the coating causing failure due to cylinder wear.

Alusil is a process where an Silcone/Auminul sleve is cast into the block and honed in an acid wash process that leaves a hardened Silocone or ceramic cylinder surface. The downside is that there are very few shops that can machine and hone alusil if the cylinders need work.

The design of these types of hardened cylinders is the opposite of a cast iron sleeves. Iron is soft and hard rings are used. Typically both the ring and the cylinder wear and need machining to be rebuilt. The idea behind Nikasil and Alusil is the cylinder walls are very hard and soft rings are used. The means typically all that is required for a rebuild is new rings. Of course, the main drive for harder sleeve designs are from the desire to use lightweight alloys for the blocks themselves.

Jeremy Himsel

The real 968 Turbo blocks were Nikasil.

sl951

Aren't all aluminum 944/928 block Nikasil?

Porsche-O-Phile

No, our engines are alusil.

Dal Heger

These are not pastes, nor are they linings. These are metal compositions. We have an alusil (basically very high silica content aluminum) block. No liner, no paste. The paste is the abrasive that the machine shop uses on a SUNNEN machine to etch and polish the cylinders when they are re-bored.

Nikasil is a very high silica content nickel casting. BMW had problems with these as the sulfur in north american gas ate away at the metal.

The rings are still the same chromoly as used everywhere else. The bonus to alusil cylinder walls is that there is only about 30% of the friction of normal cast iron cylinders.

Dal.

rc944t

I recently did all of the machine work and rebuilding of my own 944 turbo. The block is made from a high silicon content. The machine process that is used is complicated. It used brushes in the final honing process with the use of a special lapping compound. This essentually laps away the aluminum and leaves only silicon exposed in the bores. The silicon in the bores holds up beter to heat and other normal cylinder wear. If anyone needs machine work done contact me at rc65stang@yahoo.com. I have also done blocks with the cast iron sleeve deal and they seem to be holding up really well.

OriginalSterm

I found a guy local to me who will over-bore my cylinder to remove any deep scratches and have up to .040" thick Nikasil added to the cylinders. Total cost of all machine work is ~$960. I will be left with whatever bore I choose.

Pricey, but I'd have a perfect block with Nikasil in each cylinder. He said the sulfur content of the gas should NOT impact the Nikasil if done properly. He did this to his Nova that he drag races with great success.

Dal Heger

OriginalSterm. RUN AWAY!

The guys is basically sleeving your alusil block with a nikasil sleeve.. What is the point of that? Two different metals, two different expansion rates. Not to mention the problem of locking down the sleeve. Ask the guys that have spent a lot of money trying to sleeve their engines how they like it and how long they actually lasted. Just get the Alusil block rebored and properly treated (etched) and be done with it. Get new oversize pistons made and you're done. You're looking for a LOT more headaches if you sleeve.

The KISS principle works wonders.

Dal.

Chris White

(Generally speaking)
Nikasil is a coating.
Alusil is a casting.

All 944 blocks are alusil castings, (some) 911 cylinders are nikasil coated.

You can Nikasil an Alusil casting, there have been a couple of places working on this technology. You need to use Nikasil compatible rings or it won’t work well.

Keep in mind the concept is still not complexly proven – running in normally aspirated car (even a drag car) is a lot different than a turbo car. Turbos, especially our 951s, run very high EGTs as well as some pretty high peak cylinder pressures – the kind of things that are pretty tough on coatings.

It may work…but if also might fail. The technology has been around long enough that if it was a good fix I would think it would be more commonly available.

I looked into it a couple of years ago – I was quoted approx $100 per cylinder to do the coating work.

Chris White

APKhaos

Before anyone guesses again about any of this, please read THIS It gives you all the background you need to know what Chris says is right.

Its always better to have the facts, right? Here's hoping that guys who need this info will find it, and not be misled into making expensive mistakes or taking expensive but badly informed advice.

</rant>

Sorry. I'm calm now. Really. Try me.

It turns out we have a local machine shop equipped with the appropriate Sunnen, and with the hones and pastes required to treat 951 blocks. Now, if someone can find some 100.5mm pistons.......

Ben Z.

Finally somebody used the right words!

-silicONE is a polymer (think sealants, intercooler pipe connectors, etc.)
-silicA is a ceramic (think sand)
-silicON is the element from the periodic table, and it's a semiconductor, but mechancially basically a ceramic. This is what we have acting as the wear surface in our bores.