Quote:
Originally Posted by Cobra4B
What causes the breakage? The engine was only making around 370 rwhp. Is that simply too much for the actual block to to point the main bearing web fractured? What would cause a crankshaft to just snap other than bad harmonics? This was only a 6000 rpm motor. I don't know what crank it was, but I know it was quality stuff. I think the engine was 28oz balance.
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I think the first thing to bear in mind is the "only" 370 rwhp bit. These blocks are emmissions era parts that have been optimised at the factory to be cost effective to make (i.e. as little material as possible) and to withstand thier design loads. The factory hp rating for these engines would be lucky to be over 210 rwhp. So with a litte rounding we are at nearly double the factory output at 370 rwhp. I ran mine to 390 rwhp and did a 6 hour endurance race on it but pulled it after that as I expected it to chernobyl shortly thereafter.
The actual failure mode is debatable. I am sure that some are crank failures and others are web failures that cause the crank to fail. If you look at the common aftermarket band aids available (botton end and valley girdles) they target a common issue. Lack of torsional rigidity in the standard block. This is caused by the main webs having insufficient material to handle large torque loads.
If you compare the standard block to a Dart or World Products block it is night and day. The Dart block I am using has so much more material in the critical areas that it is easy to see why the standard block is a failure waiting to happen. At the end of the day there is prep that can be done to assist but the block will always be a weak link that can and is likely to lead to failure. There is loads and loads of speculative guff on the web about what the 5.0 block can and cant withstand. The best advice I saw written was why put H beam rods into a block that will fail before the benefits of the H beam rods are required.............(ditto for forged cranks as the block flex is likely to aid in breaking a forged crank).
Just one ex 5.0 stockblock runners views.........(and I never broke one)!!
Kel.