MN

Would something like this also address the oil consumption problem of my 92' GTS?

Rob Edwards

No. But it will exacerbate your wheelspin problem.

TexasDude74

Having 7 litres instead of 5.4 with the stock breather system on a GTS would not be an improvement, I would wager it would make the problem far worse.

jeff spahn

I'll wait patiently then. My 928 isn't going anywhere.

ptuomov

4.25x4.00 would be 454 cid, which is about 0.4L more than 4.25x3.75 or 426 cid. It's hard to think of what parts of the block, girdle, and the pan the crankshaft and rods would _not_ hit if you'd go to the 4" stroke. ;-) Still, with enough determination and money anything can be done.

123quattro

4.1" is not an uncommon stroke on a GM LS and can be spun to 7k rpm. That works out to 465ci/7.6L.

ptuomov

In case this is in response to my post, I didn't mean that it would break at high rpm. I meant that you'd actually have to clearance the girdle, pan, and the block in a major way for a 4" stroke crankshaft with rods attached to freely rotate in the 928 crankcase. Not that I am an expert in strokers, just that I've seen photos of the fit with a 3.75" stroker cranks.

Vilhuer

Very interesting development. As block cracking is a worry would adding block concrete help? Water depth can be reduced without problems I think.

Ducman82

very nice. could they be used with out the stroker cranks?

123quattro

Tuomo, I only meant 4.1" is a common stroke for a crankshaft. Obviously that would require even more machining.

Erkka, if you fill the block it will be stronger, but also run hotter. If you do a half fill on a block you need to run a big oil cooler to offset the cooling loss.

Jim Devine

Unless there is a reason to use the 928 motor IE:
needs to be there to race a class or just want original, there is another option.
Something like an all aluminum big block Chevy
easily makes 600 hp, doesn't require a custom Moldex crank, has an oiling system that works, uses readily avail pistons, heads that will flow for 454 cid. etc.
http://www.donovanengineering.com/Blocks/Dscn4464.jpg
Engine weight with aluminum block/ heads is
550 +-

FBIII

How do you seal the liners in the bottom of the block? I think this was an issue Bob Devore had wrestled with in his 2 valve engine development back in the early Devek days.

TexasDude74

Everyone here has been beaten over the head with chevy options, this thread is about big block porsches.

Carl Fausett

Yes, the big bore sleeves could be done with a stock crank if you want, no problem.

The stroker crank we are using has a 3.75" stroke, and we have to do light die-grinding on some cradles to clear casting flanges out of the way for that. It just fits. I have my doubts I could get a 4.0" stroke crank to spin in a 928 - but I haven't tried. Just saying the 3.75" is pretty damn tight.

docmirror

By the time you're done with a BBC in decent fettle(+500HP), you're around $9k or more. Then, add the cost of putting that in the 928 and it's starting to sound like real money. If you already have a 5/5.4L Porsche block with reasonable condition, I can't see changing to a BBC for any reason.

<edited to correct mistake>