Mongo

There's a company in the UK called AutoFarm that designed this headgasket that includes the cylinder sleeves for 996s in the event of the dreaded cylinder wall failure on those cars. The modification makes the 996 engine a closed deck design and apparently makes the motor more reliable.

Has anyone thought of this with 928s? I know I haven't heard of any sleeved 928s on this board, but it wouldn't be a bad idea to make the car a closed deck design with cylinder sleeves in the event of an overhaul.

Vilhuer

Lots of stuff in archives if you use right search words.

RyanPerrella

Autofarm does that because the otherwise good case is just thrown away. They found a reason to keep cracked cases (996 engines can crack cylinder bores) and can now fix them and resell them. Its a good money maker as the cases that are cracked were previously worth $0.00.

Not sure why you would want a closed deck though. I believe the water runs from the head into the block or vise versa on one end of the head. The head gasket has holes in it for this. If the block needs sleeves then i would just go with what Todd in GB is doing which dosent use a closed deck. The bore spacing in the 928 is HUGE so closing it would probably create more problems then it would solve. You would have to test all kinds of allows and differing tolerances so they expand with the rest of the block.

Closing a 928 block dosen't sound like a good idea to me. If you need sleeves, you can sleeve it as Todd is doing. But there would be no reason to close the block. If anything it just reduces the cooling ability of the block by reducing the amount of coolant in it and most likely also causing flow issues as well.

Mongo

I saw in one thread Sterling did this to his 928. He appears to be having good luck with it so far. I'm aware that there was extensive engineering in designing the block, but yet have no idea why Porsche engineers thought an open deck would be preferred over a closed deck design.

dprantl

This question comes up from time to time. The main reason is that there is concern that boosting an open-deck block will cause the cylinders to move around and waste the headgasket in short order. However, there are many supercharged 928s running around with years and tens of thousands of miles under boost that have not had this issue (mine included, and I'm running ~8.5psi).

Dan
'91 928GT S/C

RyanPerrella

I'm pretty sure Sterlings block isnt closed deck. i think his is just bored out, as in not sleeved, and definately not closed.

Vilhuer

Sterling's original stroker engine had dry steel sleeves and welded in deck plate.

Reason why Porsche used open deck is probably ease of manufacture. Block casting is much easier to do that way. Problems with 996 block might be reason why Cayenne block isn't open deck setup.

Mongo

http://www.928sg.com/block.htm

It's defnitely closed, but not sleeved.

RyanPerrella

Your absolutely right

so Sterling, whats the benefit? Increased rigidity on the tops of the pistons?

I will check out the page, i haven't read it in a few years.

Mongo

Yea, it's been a while for me too and I completely forgot about that website.

Rather impressive that the fill work and grinding was done. Sure as hell beats having to fab something up as a headgasket with sleeves on it.

Lizard928

his original engine was closed. His website is out of date.

do a search and I am sure you will see that he says the second time around he didnt close the deck.

Vilhuer

His original engine had also steel liners. They are right there in the pics. There's no way he could run those aftermarket pistons without them or Nicasil coating which wasn't really option back then.

Jim bailey - 928 International

The chili pepper V-8 is a closed deck low pressure cast alusil block. The open deck block probably has more to do with ease of casting than any design advantage.