Cheburator

After a proper teardown of my GTS race motor I got some more "great" news from my mechanic. Cylinders 2 and 6 are toast as the pistons have scoured marks on the walls. Another four cylinders are suspect but the mechanics thinks it is better if we do all eight bores in one go. The GTS rings are still good on all 8 pistons.

Now then, where can I find oversize GTS pistons without having to sell my 7 month baby daughter into slavery in order to pay for them?

Seem to remember that Erkka said that Woessner in Germany would do a set? I had a look at their catalogue and there is nothing on offer for the 944/968/928 range. Moreover their pistons are designed for Nikasil bores? Woessner sells Nikasil liners. Given that my GTS block was sleeved by the factory with God knows what maybe that's an option?

JE pistons? Do they make anything compatible with alusil?

Would I be able to re-use my GTS rings - they are virtually brand new...

Dr Nick of Orange Car fame on here suffered a terminal failure on his V8 M5 alusil engine where the siamesed bore was damaged. A local shop repaired it by installing steel liners allowing him to run higher comp/cheaper JE Pistons. Before you slate the shop for steel sleeving an alusil block - they have built the fastest E36 M3 in Europe (3.4ltr 420BHp) and one of the fastest E46 M3 GTRs so they know what to do with engines...

Any other suggestions?

993turbo

The rings should not be re-used if you go up a size.

Do you have a picture of the ''scoures''?

slate blue

Alex this is sounding like a nightmare It is also sounding like a stroker job so that you can do away with all the Porsche parts inside that block.

Have you fixed the crank issue as yet? If not I would consider the stroker, I don't even know if the oversize pistons will be available. Another board member John Gill is getting some pistons made up very soon for his GT. The design is very similar but different compression height and bowl volume.

Or what about use another block and then fit the existing GTS parts into the new block?

Also there is a strong chance of a bulk order later in the year for lightweight race cranks, hopefully 5 cranks and they will be competively priced. Maybe something to think about.


Greg

Vilhuer

For Alusil compatible Wössners contact Chris White at 944 Enhancement, http://www.944enhancement.com. He is also Rennlist member and active at 944 section. Just yesterday I measured set of Wössner 100mm low compression 32V pistons which has skirt coating for Alusil. They all were within 0.44g of each other straigth out of the box. Wössner can make sizes like 101 and 102mm in case block is worse than what stock oversize pistons can fix. They aren't exactly cheap (little under $2k) option but factory GTS oversize pistons will probably cost 50% more. While at it you can have them in 103-104mm depending on blocks you have available and max engine size you can have. I know there is question of will aftermarket coating work or not. There are some local 951's which have used Wössners and survived Nurburgring flat out for many laps and long distancees at autobahns.

I would also order them with slightly (0.1-0.2mm less) smaller compression height than 968 pistons. If you later on need to change crank you could then just use same pistons with 95.25mm "std" size stroker crank and 5.85" SBC rods. Only drawback is that new different lenght rods are needed with GTS crank also making first build more expensive. You can also set compression ratio to what you want and pistons are much lighter than stock. In case of friends 5.4L 100mm set 510g vs GTS stock 720g. Add aftermarket rods and you can easily loose another 50g per rod. Together thats 2kg off from rotating mass. Friends GTS crank needs to go to heady diet in balancing.

Jerry Feather

What would it take to have it bored out to 104mm and go with a set of 968 pistons?

Cheburator

Thanks Erkka,

I have sent an email to Chris.

Nikasil plating the block is not an option. This service here is at least twice as expensive as in the US.

At the moment it is down to two options - Woessner pistons with aftermarket coating/oversize alusil bore and JE pistons/grey cast iron sleeves slip fitted

Thanks for the replies, will keep you updated...

P.S. Porsche have the pistons in stock - £279 or $452 each and the rings are £840 or $1360 for all 8 so that's out as an option...

123quattro

I would look into getting a block Nikasiled in the US and shipped to England. That would be cheaper than getting it done there it sounds. I shipped a Tcase over for my Range Rover once from Ashcroft. Similar weight for the item vs a 928 block. I took about a month on a boat, but was only about $300.

Nikasil just seems like a better option. Then you can run newer/cheaper piston designs (that weigh less).

Cheburator

A supplier of Woessner custom pistons has come forward within the last 2 hours. Not the cheapest, but apparently to OEM quality and the price includes Pistons, Rings, pin and clips. The cost of the pistons is comfortably 50% less than the cost associated with shipping the block to the US, getting it nikasilled and then fitting JE Pistons and then shipping it back to England. Add the time and then it looks like no racing this year at all as I would be lucky if I see "change" out of 3 months...

If I go with Woessner I am looking at getting the pistons done in 4 to 6 weeks and then a week to put back together the engine in the worst case...

Still waiting on costings for JE pistons in grey cast iron sleeves...

Vilhuer

What bore size you plan to use? Closer you get to 104mm more likely it is you will end up with wrong shape cylinders unless machining is done exactly right. For 103-104mm you definitelly need torque plate to simulate head. Its good idea to use it even in 1st over size boring. Also add spare head to another side to really simulate conditions when engine is put together.

Cheburator

Nothing as radical as 104mm... Remember it is an unknown block, which was sleeved by the factory with alusil liners... At the most I will be going with 102mm I think... Still waiting on the mechanic to come back with available options... 102mm gives us 5.6ltr, add 11.5:1 compression, already have the super-duper heads and exhaust, Colin's cams when they turn up.... (Colin, do you hear me?) Should be a nice combo for endurance racing...

Btw, what headgasket should I use?

Vilhuer

If it has Alusil sleeves forget about it. You can't go any larger than 1st oversize 100.50mm. See how thin those sleeves are at bottom end. They aren't more than 2.5mm or something similar. Only top few mm is wider as sleeve shape is T looking from side. Rest is only few mm. thick. If you want to use that block with anything larger you need to change Alusil sleeves to iron. Then you can get anything up to 104mm. If you emd up with iron sleeves you don't have to use Nicasil. You can for example get pistons with low friction coating.

In case you end up with 104mm use 968 gaskets. For every other bore larger than 100.50mm you need Cometic's. They can do at least 103mm. Both block and heads have to have very smooth surface with them. Much smoother than what machine shops are used to do but usually they can do it. At least by doing final finish by hand.

Cheburator

Point about liner thickness well made... Perhaps we can machine the liners away and go back to the original block walls... It all depends on what the mech says. He is 2500km away Thanks on the info about the headgasket...

Damn, it is getting to the point where the old GT motor will go back in and get tuned to a milimetre of its ability to produce power and take it from there...

mark kibort

pictures of the bores. I would just clean up the bores, and get 2 oversized pistons and call it a day. it would be cheap and done. now, why are the walls scored?? that sounds odd? something drop down in there. engine been apart before?

nicasil is a tough deal. the ring packages are very critical as well, especially the oil control ring. you need the right coating or it will chew up the nicasil in a few 1000 miles. alusil would be my choise and I would find 8 968 pistons and be done with it. But, if all the rings are new, this sounds like someone built this motor wrong. what rings did you use? the ones that scored the cylinder, why would you consider using them again. the fact that two cylinders were scored makes me even more suspicious of the builder. thats an assembly issue or something falling into the engine issue, but twice???
damaged on initial start up when built? on assembly?? not ring gapped correctly?? lots of possiblities.

Vilhuer

Top few mm will mess up that plan. Its so wide than part of it will remain even when block is bored to 105mm. Maybe it could work as seam is above 1st compression ring but I would not want to try with expensive pistons. Its either 100.50mm or new liner. There's no chance geting around it.

mark kibort

why was the GTS "sleeved" at the factory with alusil liners?? I have never heard of this? true??

you cant use JE, unless you nicacil. so, that rules that out for you

sounds like the best choise, since you are boring anyway, is to bore to 104mm and use 968 used pistons. (and then find the stroker crank)

otherwise, just get a cheap 5 liter block and put your pistons back into it, and find 2 used GTS pistons.
why would you want to bore your current block when S4 bocks are so cheap? (and then you have to worry about oversized pistons.)

I think you need to show the pistons in picture form as well as the bores.

what happened to the original motor to have it have "new rings" an earlier rebuild? this mechanic do it for you?? lots of possiblities here!