Boomerang Baba

Need your help again.
I have a 93`GTS engine that has done about 220 000 km and needs to be overhauled.
My mechanic split the engine and measured the cylinders. Its up to ,8mm worn in 1 cylinder. Basically I have been told that I need to bore it and get new pistons.
We found out that they can be up to 103mm in size.
I have found a company in Sweden that can do Alusil bore. And at a decent price too. I then was tipped about Ross Pisons and contacted them. Sure they can make custom pistons for me. They requested one of the original GTS pistons and I sent it to them. So they are ready to go ahead and make 103mm pistons for me and make a special coating that will be suited for an Alusil block.
But....
Now a friend told me that the coating they are using might not be up to scratch and will clog up the cylinder walls etc...
I need Nikasil coating instead...
But thats very expensive over here...
Please advice...
Can I use these custom Ross pistons with coating for alusil?
Or shall I go another route?
Thanks. Michael

namasgt

I have read that non factory coated pistons were used in Alusil bores, and it damaged them, they were supposed to work but apparently they did not. So people have been using Nikasil coating for their bores.
If you search you can find threads about this subject.

read through this and see if it helps,

https://rennlist.com/forums/928-foru...or-alusil.html

123quattro

Why not just pick up a couple sets of 968 pistons at 104mm and get your block bored and lapped for them. They are designed to run in an Alusil block.

Boomerang Baba

Thanks guys!
Reading that thread that you linked to me now NamasGT.
And Mr 123cquattro...
I cant have more than 103mm bore in my GTS block....
May I find 103mm 968 pistons somewhere..?
Cheers and thanks to both of you!

slate blue

There is no 968 pistons that are 103 mm. Have you already ordered/paid for the Ross pistons? If you have had them made what size are the pistons that you have had made? That is what size are the pistons, not the bore.

Greg

Boomerang Baba

Hi Greg,
103mm is the size of the pistons.
Any bigger than that and there wont be enough of the original sleeve left...
One cylinder was worn to 0,8mm I think it was.
Almost a whole mm.
I havent ordered yet luckily!
Ross Pistons have one of my original GTS pistons.
I have fortunately been holding back...
I cant afford a multi thousand dollar screw up like you had with Malhe.
Also I cant believe that these large and well reputed companies cant make amends when they screw up..!
Please advice me Greg.
You seem to know alot about this.
Cheers.

Boomerang Baba

Hey I may have mistaken one Greg for another Greg...!)))
But either way I am very keen to hear what you Greg Downunder have to say about my situation.
Cheers mate.

slate blue

I'm glad you haven't committed as yet, this is what I will probably look at, given I am in the same situation as yourself with Nicasil, I am going to look at getting my pistons chrome nitrided and then a coating of diamond like carbon. It is quite common to have dlc pistons now in LeMans engines and of course F1 engines, but just because it is good for them doesn't mean it will be good for us.

However I have been reading up on this a bit, you have another option, but it is in Switzterland, they coat alloy bores, it is similar to Nicasil and the current LeMans winning engine uses it. Can't remember the name right know but Google those facts and it should come up, they just opened a plant in New York too, I don't believe you need to dip the block like Nicasil either as it is sprayed on and then cut with a diamond, it is something like sumi or sumo.

Back to the DLC the study I saw an except of had gains of around 2% in power and my guess is that the silicon wont abraid the DLC or the chrome nitride. However I would never use Ross pistons with a DLC coating on the street. They are 2618 pistons and the DLC has no cushioning effect like many resin coatings. This is done to stop some NVH issues and the big piston to wall clearance you will need to run, hence my question about what size the bore will be because it will need to be larger if you use Ross pistons than if you use Genuine Porsche pistons or pistons made from a similar material.

Greg

slate blue

Found it,
http://www.sulzer.com/Portaldata/7/R...Cullough_e.pdf

Greg

Boomerang Baba

Hi Greg,
I just heard from a fellow in Sweden that has a 948.
He took a S4 engine and put it in a 944. The thing is very light and he has bored the engine till about 5,5l and has BMW M5 air intakes from the 90s. Air goes straight into that thing man and increase hp significantly in itself. He is running Ross Pistons with some special coating (Its black and made for alusil) in his newly bored alusil block.
He has done about 20 hours dyno testing and 14 hours racing with it.
No problems he says....
What do you think?

slate blue

It is could be PC-9 from swains, if it is that is good as I have one set of pistons with that on them. However do you realise that the piston wall clearance will be considerably bigger? This can lead to noise depending on various factors. Your clearance would be at the lower end of the range as it is a street engine but you still need to get it right.

Just because it works in one persons engine doesn't mean I want to repeat it. For a purely street engine that is mostly stock I would prefer to use the high silicon pistons. This is what the original pistons are made from. It does have better wear properties. From talking to various people I believe that Mahle may over state the wear problems with 2618 or in this case what Ross make their pistons from. Something you should know is that Mahle did tell me no OEM car manufacturer uses 2618 in a production car.

I have a set of 2618 pistons for a 4 valve engine but it will be a high horespower engine and probably requires this material. Back to the main issue, will the coating last? Less than a week of running is not enough for me. Also the rocking of the piston because of the greater clearance needed will in my opinion place greater stress on the coating.

Can you get chrome rings for this size or will they need to be custom made? Can you explain why you want to go down this route? Have you looked at a thin alusil sleeve to repair this one cylinder?

Greg

Boomerang Baba

Hi,
What is 2618..? Some aluminim alloy..?
Ross Pistons also deliver piston rings.
I dont know what type they are...
Well my mech has told me that we can use the engine as it is with new original rings that I bought,
but that it will consume oil and maybe even have blue smoke...
I would like to get this engine in order and put in a car. Maybe my race car.
Then it will be used a few times a year under intense conditions.
I was told last night by a buddy with the exact same problem with his GTS engine,
that 928 Int or one of those vendors sell original Porsche pistons that are oversized and at a discount!
Maybe that is something to look into...
It wouldnt make my engine much larger tho....
Would love to get more power from displacement...
Cheers mate.

Vilhuer

I'm trying to have Ferrostan coated pistons made for friends 100mm low CR build. I believe Ferrostan is name of the coating used in original pistons meant for Alusil made by Mahle and Kolbelschmidt. It seems even Wössner http://www.woessner-kolben.de uses something they call Molykote nowdays instead of similar process as Mahle did way back. I'm still hoping original stuff is available somewhere somehow but it looks bad.

Boomerang Baba

I am all confused now...
Some people tell me that the Ross Pistons will be fine and that they use the right coating.
A nice chap in Southern Sweden is running such in his bored up 5l unit in his 944 Race car.
But like Greg mentioned, he had only done a few miles on his engine...
I could just put he original pistons back as I have new rings on them and the tops are overhauled.
But my mech says it probably will have blue smoke or at least burn oil alot...
928 Int sell GTS pistons at a discount these days. 100,5mm in size.
They are original Porsche and would give me a very fresh original spec engine.
But I was thinking I might as well try customs pistons and bore it up to 5,8l or whatever 103mm will give me. That should give me maybe 50 extra horses and nice torque...
Please advice...
Erkka, didnt you bore up and overhaul one of your GTS units?
Cheers, Michael

Vilhuer

Not exactly but something similar. I had '86 32V S block machined to 104mm to work with 968 stock size pistons. It was done without deck plate and wrong way in other ways also. Result was out of round and hourclass shaped cylinder walls when heads were mounted on the block. This means block is useless without boring it, this time correct way using deck plate and slowly enough not to distort towers, to 104.5mm 968 oversize or some other 104mm+ size. There really isn't enough material in that block for oversize 968 pistons. Other option is to insert dry steel liners and use some custom pistons which then do not need skirt coating. I'm looking into this now and probaly end up bulding two engines, one each for both GTS using similar 103mm piston design. This will be little under 6.4L with 95.25mm stroker crank for 5sp and 5.7L with GTS crank for automatic. Friend wants to have low CR 100mm pistons for 5.4L GTS crank SC engine and thus we are looking manufacturer which can still produce Alusil pistons old enviromentally unfriendly way. It seems some later style coating is only option. They are probably better and better as more engines are done with them but I'm not yet convinced they are relialble enough to take a risk in using them. At least not all of them made by just any company.