View Single Post
snowman snowman is offline
snowman's Avatar
Join Date: Feb 2003
Location: So California
Posts: 3,787
I beleive the clamping force is linear re stretch. In other words if the bolt is speced to be stretched to 0.010 inches and can clamp 200,000 lbs at that stretch, then at 0.050 inches stretch it is clamping with 100,000 lbs. For sure true if the change is small say 0.012 inches to 0.010 inches (everything is linear with small changes).

In the ARP case assume you have one inch bolts to ease the math. If stretched to spec of 0.012 inches its clamping with the full 220k lb capability, but at 0.010 inches only 183k lb. (220x.010/0.12)

Compare that with a stock Porsche torque to yield bolt of 180k lb. You ALWAYS get the maximum holding power in a torque to yield bolt because you are by definition in the yield range of the bolt.

Whats that mean, to me it means you completely wasted your money on the ARP bolt because you didn't get any more clamping power and the engine will break at the same point as a stock one would. Its even likely that you did not get to the 0.010 stretch, it all depends on the condition of the threads that day and the lube and the torque wrench, all big MAYBES. And even Porsche mechanics get lazy, why do it 3 times when one will do. Porsche engines cost way to much for MAYBE it will work.
As to millions of engines, they do not get revved to 7000 or 8000 RPM nor are they even capable of doing so, so its not a big worry. But if you are like me I rev my M635 daily driver past 7500 several times a day and have done so for almost 20 years without it breaking yet. I know its not a Porsche, but its German.

Those modern torque plus turn to angle bolts (torque to yield bolt) are neat because you get almost as much clamping force, guarenteed clamping force as much more expensive reuseable fasteners. Only problem is use once and then pitch them. And if you have a BMW M version you start out with the much more expensive bolt and torque it to yield, consequently having to pitch it and never reuse. But boy does it hold things togather.

Last edited by snowman; 01-05-2005 at 04:59 PM..
Old 01-05-2005, 04:42 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #23 (permalink)