Back to square one with the GTS race motor. Arghhh! Help needed...
#46
Addict
Rennlist Member
Rennlist Member
The question I seem to have now is where did the minimum wall thickness said to be 6.35mm come from? That really sounds scientific and perhaps well engineered to be so precise. However, when that is converted to inches it comes out to just about exactly a quarter of an inch. That sounds more to me like someone, perhaps who even is very knowledgable, simply said " you need the keep the wall thickness about a quarter of an inch, then it got converted and became a sort of gospel at precisely 6.35mm.. I have to wonder what the data is that might actually support that limit.
For me, the question is, what is wrong with using stock 968 pistons in a bored out 928 block (any one that is appropriate) with a stroker crank that is designed to use the chevy rods, and using the 5.85 CTC rods?
For him the question is which rods would he use with the GTS crank and bored out S4 block to 104mm and 968 pistons?
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.
#47
Former Vendor
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.
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.
#48
Addict
Rennlist Member
Rennlist Member
#49
Rennlist Member
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
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
#50
Addict
Rennlist Member
Rennlist Member
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.
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.
#51
Rennlist Member
I thought the 944S2 and 968 pistons would work the same. what are the differences?
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.
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.
#52
Addict
Rennlist Member
Rennlist Member
http://www.youtube.com/watch?v=hTrl2Acrlnc
#53
Rennlist Member
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
Jerry Feather
#54
Rennlist Member
Thread Starter
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
Jerry Feather
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?
#55
Rennlist Member
Thread Starter
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...
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...
#56
Drifting
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?
#57
Rennlist Member
Thread Starter
labour in E Europe is cheap and plentiful...
#59
Rennlist Member
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.
was the failure due to some catostrophic loss in oil?? was this the accusump failure?
ugly.