blown 87

If there was only some one he could call for help, some one that had been down that road before.

atb

Jerry, when I referred to Mahle's I'm talking about the OEM's from Germany, not the Mahle Motorsport pistons that are domestically made.

Jerry Feather

Thanks Adam. I think I realized that already.

I also think that there is a lot more expertise on this forum than the one(s) sitting back feeding their face with popcorn and their brains with doggie do do stories, and their little fan club, that have a lot to share with those who might be interested is something besides unnecessary expensive parts and fiction about crankshaft metal.

Thanks for your help with my question.

Jerry Feather

GregBBRD

ShawnSmith

I feel like I'm watching someone plead for a cup of water as he pees all over a stack of fine glassware and a pitcher full of Evian...

atb

Here's a quick comparison shot of the KB, Mahle, and S4 piston.

And my apologies - I mispoke when I spoke of rod interference with the skirt (there can be some clearance issues with the big end of some rods, but that is with the block not the piston), in digging up this picture I was reminded that the issue was the Mahle piston skirt contacting the crank throw of the stroker crank.

atb

Here's another view that better shows the difference in skirt design.

jeff spahn

Is that a pre 90 piston for the S4?

atb

Out of an '87 squirter block.

T_MaX

What ever happen to the DEVEK crew, didn't they do a ton of this kind of stuff?

daveo90s4

The right hand piston in post #21 must have an (extremely) offset rod

John Speake

The race car in my avatar uses a set of old 968 pistons in an overbored block, crank and rods from GregB. Two seasons of racing so far.

T_MaX

John, what if any are the differences in your crank and rods than stock?

John Speake

The crank is of course a long stroke crank to get the 6.4litres with the 104mm 968 pistons. I think it is Moldex, but was certainly bought from GregB with the rods which I understand are custom Carillo. I wasn't directly involved with the engine build but was very much a DIY effort.

Now the car is on ITBs with the ST-Alpha, those internals are getting some hard work :-)

Vilhuer

There is more than one possible problem. Counterweights can be so large that they will hit KS 968 pistons so that is not just Mahle specific. That can be fixed by removing material from counterweight outside edge.

What is non KS 968 piston specific is that 928 block is not build to have pistons move so far down as 95.25mm stroker crank makes them come. Full skirt in Mahle pistons can touch non round side of the bore at BTC.

Third issue is rods. Besides of Chevy rods upper end problem its possible lower end does not have enough room to rotate when connected to stroker crank. There are two problem areas in block. Bottom of bore gets affully close to rod bolt. Other place is easier to sort by machining material off from crank cradle same way as factory did for GTS block.

All three problem areas can be seen in this video.