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Old 10-12-2012, 06:34 PM
oldbogie oldbogie is offline
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Quote:
Originally Posted by 79z28dude View Post
ok so im about to do a new top end on my 383....

heres what i am taking off
factory 76 cc chamber cast iron heads 8.5:1 compression
edelbrock performer intake
600cfm holley (single pumper)

heres what is in the bottom end
4 valve relief dish piston (cast)
comp cams 480 lift 280 duration
steel crank and cast i beam

heres whats going on
062 vortec 3 angle valve job (64 cc chamber) going to approx 9.4:1
i cleaned up the heads and port matched to intake
performer rpm air gap intake
670 street avenger
2 inch poly carb spacer

here is my questions
what kind of gains am i looking at?
could the set up handle 100 shot of nitrous oxide?
What exactly is the bottom end, while a cast crank is common in the SBC Chevy doesn't use anything but forged or PM rods, so where did or are they a casting come from?

There are cast pistons and there are cast pistons, are these inexpensive (that being a relative term) OEM or OEM replacement castings, or Claimer style pistons usually a hyper-eutectic with little to some heat treat to some more expensive styles with highly machined surfaces and T6 heat treatments? This gets more into the question of not so much will they take a 100 shot but rather how long are you expecting them to take a 100 shot. The temps go up the longer you keep them laughing and this is where the big problem lies. The piston is only indirectly cooled by the cooling system that's to say all of the heat the crown gets blasted by has to travel to the rings and skirt to find a way out. The only direct cooling is by oil splash unless you did something to put a spray on their underside. So cast pistons including hypers have a real struggle as the temps along with the combination of forces can get to the breaking point pretty quickly. You need to consider the pin as well because as the piston gets hot it tends to grab the pin, it the pin is only swinging in the piston and pressed to the rod when this happens the piston or the upper end of the rod gets ripped apart. Similar with the rings, the piston gets soft and the rings expand either by eating up the end gap and or the land clearance, next thing you know a big chunk of piston crown with ring land comes off, the ring can no longer stop the super hot gasses which then cut down the side of the piston.

Quality of the damper on the crank-snout also comes into play, nitrous hits the shaft really hard causing it to vibrate. If the damper isn't up to the vibes, it isn't long before the number one main gets carved out starving the number rod for oil with results you can imagine or the crank busts across the number one throw cheek, not a pretty sight either.

So the answer of how long it will live really comes down to the strength of materials in the engine how well it cools internal parts and how long you keep feeding it juice.

Bogie
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