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Last week I asked why the cylinder studs for a 944 where half the price of the 928 S2 when they were exactly the same length. I ordered one so I could see for myself and below is a picture of a old 928 stud next to the one I received (the longer 193mm ones) . As you might be able to see the 944 thread has fewer threads than the 928 one (approximately 20 into the block and 10 at the nut end) my question is- is that enough to hold the head when I torque it down without stripping the block, or should I bite the bullet and get proper 928 ones for more than twice the price?
Not that I am aware of, but I would think there is a reason that they are engineered that way, else why make a new part that adds to the bottom line of production.
Sometimes $ short cuts are more costly in the end
Not that I am aware of, but I would think there is a reason that they are engineered that way, else why make a new part that adds to the bottom line of production.
Sometimes $ short cuts are more costly in the end Dave
Hmm... It could be that Porsche established the part for the 928 and was shaving pennies on the 944. If the head is the same thickness and the compression is similar, then I don't see why the 944 studs wouldn't work just fine.
My thinking was that both heads are similar and rather than a cost saving exercise perhaps fewer threads means the stud is actually stronger?
Shouldn't be the case. I'm not an engineer, but if my understanding is correct, what determines the ability of the bolt to hold is the amount of thread surfaces in contact. Imagine the thread stretched out into a continuous thin 'blade' as long as the turns around the bolt. If you attached a wire to the center of the blade and pulled down against the length of the blade, you'll get more strength with a longer blade than a shorter blade.
Not to keep banging on about this but a picture of the studs ARP make for the 928 shows the same number of threads as the 944 studs going into the block (the nut end has a finer pitch though)
2.5L 8v (which works on some early 2.5 16v heads)
2.5 16v (heads got revised mid-year to have thicker head stud holes so studs got longer)
2.7 8v (the block threads for the stud got raised considerably with the block redesign for 104mm bore)
3.0 16v (raised threads, and the bigger 16v head)
bear in mind that the 928 has a 2mm higher deck height than a 944 so there is potential for a longer stud required for that reason alone.
04-03-2018, 02:12 PM
Using 944 studs on a 928 S2
