Quote:
Originally Posted by Gach
The killer for the cast crank, is rpms. 625-650 hp at 5500 rpm Will live a long Life. But not something making that kind of hp shifting at 6500. Back in the 80’s early 90’s when we were pushing the hp limits which meant raising rpm levels. To get past that 650 hp. The stock cast cranks wouldn’t live very long. So back to a safe level of 625-650 hp keeping rpms at 5500 rpms. In the 80’s bracket racing running 10.30’s shifting at 5500 over 200 passes. It lived. Of course those were 12.1 compression motors.
Today building a 500-600 hp motor on pump gas and aluminum heads with at most 11.00 compression Iron heads 9.5 compression. Keeping peak power at 5500-5800. Cast crank has a much better chance of living a good life. But the killer is ( and I know most are automatics now ) is the 4 speeds and missing a shift and the motor going to the moon. And of course donation especially the definition that you don’t hear. The 2 biggest killers of cast cranks. Before you know it you’re riding around doing burnouts quarter mile passes with a cracked crank but you don’t know it. Especially with today’s gas which is critical not having any detonation. I’ve just seen it happen so many times.
Difference is with good steel crank and rods 6500 or going to the moon 7-8000 isn’t going to hurt anything. The experiences haven’t been through all this, and learning the hard way. So in the end what did you save. Of course there are combos making 500 hp that just die at 6000 rpms. So those are kind of safe.
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I agree. RPM`s and detonation are killers. But, I also believe that to be true with the block too. So, I believe if one builds a 455 combo to break a factory crank, he will most likely start to crack main webs as well.
I don`t see putting a forged crank in a factory block if the original crank is good. I won`t use a china cast crank. I think a forged crank IS a good idea in a 400 type build at 550 hp and up with 6200 plus rpm`s.