sublimate

When steel is loaded below it's "fatigue limit" it will theoretically last for an infinate number of loading cycles without failing. In actuality steel can undergo creep (particularly at elevated temperatures) from repeated or constant loading and eventually elongate and fail. And if steel is loaded above it's tensile strength then it will fail regardless of the number of cycles (ie, you only have to take your engine up to 10,000 rpm once ).

This is unlike aluminum which theoretically has no fatigue limit, so even a small load will cause it to fail given enough cycles. In reality if the loads are kept low enough then it can last for enough cycles to have an esentially infinate life.

SharkSkin

Heinrich, those are certainly factors in the overall picture. However, piston speed must be considered separately. It is important to know how fast the piston & rings will move against the cylinder wall, and to choose materials that will stand up to the expected friction under those conditions -- or limit RPM to keep piston speed at a level that can be tolerated by the materials in use.

BC

My plan is to go as far as I can in bore, while knowing it will see boost. At least one bar above atmosphere, with respect to the CFM needs of the engine. 968 valves, and probably some 85/86 cams that may be built up a bit if needed.

The GTS crank is a great idea for me I know. I wasn't planning on the full stroker crank throw, but something in the middle, and I have the time to wait for the "crazY" people at moldex. I don't understand the crank throw thing PERFECTLY, but I do think I get it. I also need enough room on the piston below the crown for quite a bit of space before the top compression ring for more heat disipation.

I'm concerned about the cutting into the GTS crank for a bit more stroke. I was assured that it would work by taylor engine in Whittier, but I'm still concerned.

Jim bailey - 928 International

Brendan the big problem is keeping the compression ratio down while going from moving the piston only 78.9 mm 3.11 inch to the 85.9 of the GTS or the "standard" stroker at 95.25. The GTS pistons were about 25 % shorter and the wrist pin 2 mm closer to the top .

heinrich

I have a nice set of 968 pistons. How close to just installing them into my 5l block with existing setup, can I come (after boring of course)?

BC

Right Jim. Adding Bore will change this as well. A pretty big dish in the piston.

Fastest928

DONT cut up that crank. Use it as is.

Marc

sportscarclassics

Brendan,
If you cut into the GTS crank to increase stroke are you decrease the journal diameter? When guys use the Moldex or Scat cranks that use Chevy connecting rods, does the big end journals have smaller diameter? I also think the thickness of the Chevy rod is thinner? Would it be better to weld up a S4 crank to increase the stroke and save that GTS crank? I would think it cheaper to weld a standard S4 crank to increase the stroke than buy a new Moldex/Scat crank even if you have to weld the journal shoulder for a Chevy rod. Aren’t the Chevy rods shorter too?

Carl

heinrich

Relax Brothers. Crank saved

Stan.Shaw@Excell.Net

I believe welding cranks was tested before the Moldex/Scat route was chosen for stroked cranks. Welded cranks resulted in too many failures, as I recall.

BC

Louie928

Which pistons and rods if you want 104mm bore?

heinrich

Louie I am planning on coming your way this weekend ....

BC

How far is Louis from you H? In which direction?

heinrich

He's in North Oregon .... i see where you're going with this Brendan, but that is pretty far from my house