Vilhuer

I believe source is Reynold aluminum company which originally developed Alusil. Since its US company using inches is natural.

Nothing wrong except fact that good condition 968 pistons are somewhat hard to find and most S4 blocks have too thin walls. Still, 968 std size is easiest suitable piston type to find and practically only piston which works straight of the box if new made to order Molycote coated skirts custom pistons are not counted. 944S2 pistons for example are easier to find tah 968 but their skirt design is all wrong as 95.25mm (3.75") brings piston so far down in 928 block that piston skirt has to be 968 piston style to work at BDC.

Block doesn't make any difference. All 928 blocks have same height, 232mm IIRR. Using that number its easy to calculate how long rods must be when crank stroke and piston compression height is known. 2.5L and 3L blocks have smaller block height even though they use same 150mm long rods. This means 951, 968 etc pistons have smaller compression height than 928 pistons. In case of GTS vs 968 piston compression height difference together with GTS vs 968 crank stroke lenght difference is 3.4mm IIRR. This means rods must be 153.4mm to keep piston at same 928 block deck top height at TDC.

This is probably usual answer why S4, GT etc blocks which have around 116mm cylinder tower diameter are used. Most people assume its ok as everybody else is also doing it. In most cases it probably works. But if there is choice to be made between using 116 and 118 block I bet none would go with 116. In most cases thats only option and people are willing to take a risk.

GregBBRD

I'm extremely careful about which 928 blocks I use to bore to 104mm.

They must have aluminum as a main ingredient....

Seriously, I've only ever seen one block that I didn't want to use, due to excessive core shift.

Vilhuer

So your typical stroker block has around 116mm cylinder towers? Meaning under 6mm wall thickness in some places unless all cylinders are always centered. No problems, ever?

Jerry Feather

WOW!!! This is getting to a lot of great information. I hope the OP doesn't think I or we have hijacked his thread for my purposes because I think there is a wealth of information here that should help him make a much better decision about how to fix his engine.

One thought I have now is that a substitute S4 or later block can be safely bored out to 104mm, if he gets one that has little or no core shift. I suspect that with a little effort he might find one pretty cheaply, especially if he finds one that needs to be bored out already and is being held as scrap by its current owner.

Another thought is that it appears that either the 968 or the 944S2 pistons of 104mm might be used by him with the GTS crank. The real expense will be to have custom rods made, perhaps by Carillo, to match the 153.5 CTC length required to get the top of the pistons up where they need to be at TDC. I suspect that the 944S2 pistons (if they are 104mm and not a problem with the longer skirt) might be easier to find than the 968 pistons. If so they will likely be relatively inexpensive compared to custom pistons.

Therefore, the total cost should be around $200 or less for the block, perhaps $200 to $400 for the pistons, the cost of boring (?) and perhaps $2000 more or less for the rods. The 104 head gaskets are available on eBay for about $100 each. and overhaul gasket set is a little over $400. Then, to enhance the breathing of his new 6L engine, he can work the heads over with 968 intake valves and clean out the indiction a little, and have a real screamer. Those valves are also available on eBay, but I don't remember the cost. Not too much when I bought some a while back.

I guess I'll stop short of suggesting that he simply buy the stroker crank ($3000 or more) and spend less on the rods and then start his search for the 968 pistons. I suspect that will get way beyond his desired budget, and may not be worth the difference for a mere extra half liter displacement.

Jerry Feather

Vilhuer

Forget 944S2 pistons. They are 104mm but will not work without very large mods.

Problems with all your other ideas is that stroker engine is not ready before next summers racing season. Geting all needed parts takes months. Besides, 6.4L stroker will not fit to racing rules either.

mark kibort

I thought the 944S2 and 968 pistons would work the same. what are the differences?

Vilhuer

S2 has full skirt. They probably work with S4 crank but not with 95.25mm stroker as pistons come much farther down. Not without removing half of the skirt away. If anyone wants to try I know some for sale in here, IIRR its full 8 piston set in ok condition. Some say some 944 S2 pistons do not have full skirt but I haven't seen any. All 944 S2 Mahle's have full AFAIK. 968 are Kolbenschmidt's and they are different. See how far 968 pistons come.

http://www.youtube.com/watch?v=hTrl2Acrlnc

Jerry Feather

I think my idea for the OP using 944S2 pistons was with the GTS crank and not for the stroker idea. Now, I have to wonder if the 5.9 or 6L bored to 104 GTS engine will still fit the race rules??? If so, I still think that would be the bee's knees. And, if the 944S2 pistons will work, we are about half way there, aren't we? Well, not half, but some progress!!! All the OP will need is the block and rods. The rods may take a while, but not to next summer for sure.

Jerry Feather

Cheburator

You are not hi-jacking my thread at all. BUT:

I am not constrained by budget really, but by time as Erkka said...

I am not keen on sourcing second hand stuff simply because you never really know what you will get. The GTS engine that I destroyed still needed a refresh of everything except the rings, despite being only 22k miles old

The racer was built for UK and German based club racing. The UK rules are somewhat relaxed, but in Germany the maximum displacement allowed is 6.2ltrs. No exceptions - even the Vette Z06s or Vipers run to that engine size. Thus a 6.4lts 928 lump, as nice as it sounds, will not be eligible.

The scoring on the bore is 0.35mm deep at its worst. On Monday I will know whether something can be done within the existing liners or whether other options can be explored. The Woessner pistons are available and I will definitely go with them, even if I am going to 104mm. They are a much more modern design than either the 944S2 or the 968 ones, much lighter and stronger. If I am going to do it, I may as well do it right...

The heads on the engine already have 968 intake valves, ceramic coated valve seats, new guides and seals, VW lifters and opened ports, and shaved a touch. Not much more can be done to them I think...

Btw, Porsche AG offered me a GTS short block with 12mths warranty on an exchange basis for $16000 including all taxes If I had a mint 10k miles GTS, it is definitely worth considering, but for a racer?

Cheburator

Pictures of the damage

Cylinder Nr 2 with the alusil liner...


Piston Nr 2 does not look coated to me...


On a slightly better note:

Upper A-arm with an offset pin, which shortens it by 8mm in relative terms to the lower arm, thus aleviating the need to mix and match early and later styles to achieve camber greater than -2deg 30


Details of the rose-joint


Rear control arm


The rose-joints are fully rebuildable and utilse SKF/Russian bearings

Goes to show that we can get some things right too on this side of the pond...

UKKid35

Alex, I wish you luck in finding a solution for this, but surely the biggest expense will be labour not parts, so perhaps the most cost effective solution would be a new used block, rather than continued investment in Simon's recovered GTS block?

Cheburator

labour in E Europe is cheap and plentiful...

IcemanG17

I think Louie runs modified 944S2 pistons in his monster......

mark kibort

So, why the failure??? someone said that only a couple of holes are bad?? they all look destroyed in that picture. alusil liners?? i see the seam, but i remember seing what looked like a seam in other engines Ive worked on. so, its oversized or a new block?

was the failure due to some catostrophic loss in oil?? was this the accusump failure?

ugly.

mark kibort

why do you think it has liners. it seems all 928 blocks seem to have that line around the bores.
here is an 85 block