Vilhuer

Some blocks were sleeved by factory to save them. Something went wrong in casting or machining and they would have been scrap without it. It doesn't make much sense but there were at least few made like that. Really nice work as sleeves are hardly visible at all but these blocks are useless in normal 104mm stroker build.

GregBBRD

You are falling down the slippery path, that so, so very many people, before you, have slid down.

I look back at the thread about your failure and just shake my head about the part where you state that you need to make your own mistakes to learn from...

As much as I hate to say this....you seem like a really nice guy....you might as well start saving money for the next engine, right now.

Here's is the brutal reality: Don't take it personally...but think about it.

The fact that you would even ask about reusing pistons rings in a bigger bore tells us "volumes" about your own personal mechanical knowledge. You do not have the "mechanical knowledge" to be making decisions about what pieces to use.

You need to find someone with huge amounts of knowledge about these engines and trust what they have to say....otherwise you are going to be caught in an endless "loop" of redoing this engine.

BTW...All 928 pistons (at least in our parts system...and we have the "worldwide" parts information) from Porsche come complete with rings, pins, and circlips.

mark kibort

How thick are the sleeves? more than the bore from a 100mm to 104mm? probably, huh?so, just clean up the bores and go oversized . as greg says, you then need 2 new pistons w rings. or two used pistons and a new set of rings.

since there is really nothing special with the 928 block S4 or GTS as I understand it, why not just get a used dummy block and put the GTS stuff in it?

just boring those two holes alone, and then you will probably clean up the other two holes, oversized pistons are expensive, vs some good used GTS pistons. either way, that engine has to come out and be stripped down .

I guess if you could bore it out to 968 piston size, you could then just buy new rods to match and have a near 6 liter. that would be cool, but that block with sleeves seems to be an issue with that. sounds like it is junk.

IcemanG17

nuff said........there is no arguing the success of Doc's strokers on track...

here is an observation I have found at the racetrack, regardless of engine used.... STOCK engines tend to be quite reliable (with solid oiling of course)....once you change something, say a cam, reliability drops by a cube factor..... the only other solid reliable option is a FULL built race engine with dry sump....which of course is HUGE $$$.....

The longest lasting race engines I see on track are spec miata.....wetsump and 8000rpm in 150k plus mileage engines that just run and run....they are literally bone stock...even the "built" ones are essentially "balanced and blueprinted"

Cheburator

Agreed on all points except the last one - Porsche UK will quote you separate prices for pistons/pins/rings...

Overall though the problem is there is hardly anyone here in the UK who actually has the knowledge of these specific engines in the same way as you, Marc or Karl do... Getting a machine shop to do the work is a pain, let alone to put together a race motor...

It is getting mighty close to the point where the old GT lump will go back in with the fancy big valve heads, new rings and rod bearings, and Colin's cams. That will salvage the 2nd part of the season and I will get a stroker built from scratch over a longer period...

This last sentence means that I would have to call you sooner rather than later...

BC

You'll have to pardon me- is this the motor that ran out of oil? Do we know what caused that issue originally? Was that issue fixed?

Jerry Feather

I think something is wrong about this thread. I tend to be skeptical at times and this is one of them. First, the OP never said anything about the block being Alusil lined until later in the thread, and then it sounded like he assumed it is lined because perhaps he thinks all GTS blocks are so lined. The authority here, however, suggests that, only some of the blocks were lined, and then only the ones that could be saved from some casting flaw. I would guess that is a small minority of blocks. Therefore, I would suggest that this block be verified for liners or not. If not, I still wonder why he doesn't simply bore to 104mm and put the 968 pistons in it. I think good used 968 pistons can be found for very little money and even with about $800 or $900 for rings, that will be a much cheaper cure to the problem than just about all the other options suggested here. What does anyone else think?

Much of my curiosity is because I hope to do just that to one or two S4 blocks I have for stroker conversions, someday. For me, the real question is what does it take to run 968 pistons in a bored out Alusil S4 block? For the OP, the additional question might be, can he run that much displacemnt in his race category? Thanks for any advise anyone has.

Jerry Feather

mark kibort

you then need new rods if you go that way (i think) or you need to get rods and a new crank to make it a stroker. if you just do bore, can you use the stock rods on 968 pistons??

m

Jerry Feather

I would expect that the OP would be using the stock GTS rods and then 104mm 968 Pistons.

For me, I have the stroker crank(s) and one set of 5.85 Chev rods, so all I need is to bore the block and use the 968 pistons. I have some of those also. The question is will the 968 pistons work in the alusil S4 block, or is there some kind of coating required for the pistons or the block? Thanks.

daveo90s4

Jerry, the original poster may answer for himself, but the block definitely has liners and the original poster is and has been well aware of this for a very long time. Nothing to be skeptical about here.

Erkka advises (above) that this being so, boring to 104mm (and using 968 pistons) is not feasible.

Dave

Jerry Feather

Here's the problem I have about being skeptical. He says that it is an unknown block..., then off-handedly states that it was sleeved by the factory with alusil liners....

That is what makes me skeptical because it sound to me like he thinks that all GTS blocks are sleeved at the factory.

Now, you may very well be intimately familiar with this block, but with you where you are and he where he is, I doubt it. So please don't tell me there is nothing to be skeptical about.

You are however, correct in that the OP can pipe up here and clear that issue up. He has not done so yet, so I remain skeptical.

I agree, the if sleeved, the 104mm bore will not work. I am bright enough to figure that out all by myself. But, why don't we wait for the OP to give us the actual facts about the sleeves before we try to help further with his problem.

daveo90s4

Jerry, I was just saying that there is no need to be skeptical about the original poster's comments.

Some time ago I was fortunate enough to spend the weekend at Nurburgring in the company of both the original owner of this engine and the current owner of this engine. This engine was the subject of discussion. So I start with something better than no knowledge of this particular engine.

I reiterate nothing to be skeptical about here.

Jerry Feather

Thanks Dave, for that clarification, but so far in this thread there is no indication that anyone has first hand knowledge that this particular GTS engine was sleeved by the factory. What an I missing?

GregBBRD

968 pistons require special length connecting rods for 5.0 liter (78.9mm stroke), 5.4 liter (85.9mm stroke), and 6.5 liter (95.25mm stroke) engines.

We have all versions of these rods custom built, for us, by Carrillo. We keep the rods for the 95.25mm stroke in stock. The other two versions are not as common and we custom order these rods, at this time.

The "owner" of the engine, in this thread, previously stated that one (as I recall) cylinder, in this engine has an aluminum sleeve installed. It has been suggested that the Porsche factory may have done this, when the engine was new. I an dubious about this point...it would seem that if there was a block that had a casting flaw, they would have simply "rejected" the block from the supplier. However, I can see this happening if the engine got "rebuilt" by Porsche. Irregardless, this makes this engine not suitable for boring to 104mm (unless the sleeve is thinner than 2mm on each side...which is doubtful.)

I did run dry steel sleeves in several 944 turbo engines, which allowed me to use "American" high performance pistons. in these engines. Getting the piston to wall clearance correct took a few tries (read this as: we stuck a few pistons until we figured it out).

Some of the 944 people have been successful at running a non iron plated Mahle piston (coated by Mahle and "guaranteed" to work) in those engines....apparently. The one 928 engine that we tried this in, lost the coating from the Mahle piston and we had it back apart before it had 200 miles on it. Mahle refused to warranty the pistons or the engine....

I have redone several 928 engines with "coated" pistons, besides the engine we did with the Mahle pistons....built by "others". None ran more than a few hundred miles. All were a complete mess. The coatings all failed and the aluminum pistons galled into the aluminum bores.

I believe that the only piston that will work in the Alusil bore is the Porsche "iron plated" pistons. It is a shame that no one can find out who plates these pistons for Mahle or for KS...that would solve a whole ton of problems...or create a whole bunch more problems....hard to say.

James Bailey

I once watched as a shop owner (not Mr Brown) started up a hotrod 911 engine rebuilt with some custom pistons....fired up reved up then slowly started to run slower and slower until it ground to a halt. Those inexpensive custom hi compression pistons looked a lot like a Mahle But everyone said they should work great ! Yes it seized.