Raceboy

As we plan to turbocharge a Euro 928 S 4.7, I'd like to know what is our piston options? I'd like to keep Alusil bore and not sleeve the cylinder.

Vilhuer

1. Lower compression on stock pistons by removing material from the tops
2. Buy set of US '83-84 4.7L 9.3:1 pistons in right tolerance group
3. Buy set of 951 pistons (I know more than dozen for sale locally) and bore block to 100mm
4. Buy set of '86 ROW 32V 5.0L 9.3:1 pistons and bore block to 100mm
5. Have Mahle motorsport make custom set
.
.
.

FlyingDog

6. Look through Mahle and KS product specs to find an OEM piston for another vehicle that meets your needs. ~$550 vs $1800+ for Mahle custom pistons

I'd go with #2.

Vilhuer

Very good Idea Matt. What other possibilities are there? Some Mercedes models perhaps. Not much else but one suitable candidate is enough.

FlyingDog

Mercedes and BMW come to mind, but I know there are a lot more. I know Mercedes has quite a few in the 100mm range.

Normy

Nobody makes a head spacer for this engine...



N!

Raceboy

I have 9 951 pistons in Tolerance Group 1 that suit for this intention but I thought perhaps there's an option to have Wiseco or Wössner pistons in right dimensions.

I know Wiseco makes custrom pistons for very reasonable price, though I'm still waiting their answer on compatibility with Alusil block.

Boring the block means I have to take it to Finland (R-Koneistos) in order to get what I want. In Estonia noone bores Alusil blocks.

I'm guessing right assuming stock pistons are cast not forged?
Since my expectations are pretty high, I would not do it with cast pistons and boring block to 100mm may harm it's integrity.
What's the opinions and perhaps experience?

928DK

Or you could get some thicker headgaskets (1-3mm watercut) steel or copper and cut grooves in the head/block

Local 928 turbo with thicker headgaskets:
http://www.thorupauto.dk/projekt-928.htm

Raceboy

I'mmostly worried about the strength of stock pistons.

My plan is to go forged pistons, stock or 951 rods, Cometic MLS head-gaskets, stainless valves all new bearings, cross-drilled crank etc.

Goal is around 600hp.

928DK

Well i dont think strength is going to be a problem just look at the project with the stock S4 pistons being machined:
https://rennlist.com/forums/showthre...=107282&page=4


i'm foremost worried about heat when sc/turbocharging (combustion chamber temp) so maybe cooling the fuel or ceramic coating is the best solution

hacker-pschorr

FWIW this is with stock pistons dished out to lower compression. This was over two years ago using the stock computers. This year I suspect more fine tuning now that the shark tuner is available. This is a 32 valve motor:

BC

I have mentioned it before , but it goes into the non-memory abyss like my BSA wheels for the porsche that were 368 dollars for all four and worked quite well in the 18" size - nobody wanted to know.

Lindsey racing, a 951 (944 turbo) tuner has been running Wiseco pistons in an stock Alusil bore at 15-18psi for about 12,000 miles that I know of with no issues. They coated the skirts with PC-9, a friction reducing material that Swaintech coatings put on. You can all call him, as I did a few months ago, and he will give you the info you need. This means, that if this continues to work, that we can make any piston design we want and whatever compression we want, and coat the skirts to work in aluminum bores.

A few pieces of info:

The new process that Mahle uses to coat the aluminum pistons is because of environmental issues with the original, much more robust process of attaching tin or iron to the aluminum pistons so they do not gaul the bores on start up and run in.

This new process is iffy at best, disastrous at worst. A few people have tried it, and it did not really work as advertised. And it was VERY expensive to get the pistons made to order.

I purchased new old stock 4.5L pisons from ebay a few years ago to build a 4.5L engine. The coating was silver, but very thin. I am stating this since many of us have not seen what it looks like, and even fewer have seen what it looks like when new. It is, as Jim Bailey has said countless times, a SACRIFICIAL coating. When you remove pistons that have been in an engine for 200,000, the pistons in the skirt area are shiney, and the coating has worn off.

That said, things on the internet are said, then repeated over and over again. Eventually it becomes fact. People stop questioning, testing.

Well, some people are testing and are a great resource to our community:

https://rennlist.com/forums/928-forum/271335-6-1-liter-stroker-short-block-for-sale.html


http://www.lindseyracing.com/Merchan...ry_Code=WISECO

https://rennlist.com/forums/showthre...highlight=PC-9

Vilhuer

Some company (not Mahle) in Germany still makes pistons using original enviromently bad manufacturing process. It could be http://www.woessner-kolben.de.

There is some company in Denmark which does Nikasil coating to just about any engine. AFAIK they haven't done it to Alusil block yet though.

FlyingDog

Hmm... isn't that something John Kuhn mentioned a few times and got blasted for?

BC

No. John.. Always advocated a nikasil bore surface with JE pistons. He liked the idea, as I do, of controlling the piston shape.