grumpyvette Posted July 11, 2008 Share Posted July 11, 2008 I get asked all the time, "should you re-use those stock rods, when I rebuild my 350 or when I build my 383 stroker" most sbc gen I stock rods are designed to be cheap, and dependable in engines spinning under 6000rpm that make under 400hp, this is one area where Im simply amused at the lack of thought shown in sellecting components, by some guys. most chevy small block rods are VASTLY inferior in strength to many of the mid range and better aftermarket rods available. a 7/16" cap screw type ARP rod bolt is EASILY 200%-300% stronger than a stock 3/8" factory rod bolt and frankly, the cost & TIME to correctly modify and prep stock rods is a total waste, its almost always cheaper to buy decent aftermarket rods. example http://www.sdparts.com/product/12495071/5700quotPMConnectingRods.aspx $265 for a set of stock rods and then you should still have ARP bolts installed, pollish, ballance and sized your looking at easily $500-$600 or more for a set ready to run compared to something like this below its a joke http://store.summitracing.com/partdetail.asp?part=SCA%2D6570021&autoview=sku http://store.summitracing.com/partdetail.asp?part=SCA%2D25700716&autoview=sku keep in mind theres far stronger rods available if you have some extra cash, and that connecting rods and thier rod bolts are under a huge amount of stress at high rpms....one rod bolt stretching at high rpm will usually result in engine failure and its comon for only the intake, valve covers, distrib, and water pump and a few other parts to be salvagable if that were to happen at high rpms...stretch a rod bolt and the piston contacts the head, or bends a valve, the rod bends, the heads destroyed, the block can be history and it can go down hill rapidly from there as fragments work thier way around thru other of the moving parts as the engine locks up Quote Link to comment Share on other sites More sharing options...
Jerminator96 Posted July 12, 2008 Share Posted July 12, 2008 Good advice. There are always stories of the guys running serious power on a stock bottom end, or stock crank and rods. I think those stories give guys a false hope for their old worn out bottom end. I've seen one stock crank and rod 355 LT1 with a blower lay down 480rwhp (550ish+ bhp) but you have to ask yourself why?It's not worth the risk in my opinion, or as my Grandfather always said, 'Do it once, do it right.' Quote Link to comment Share on other sites More sharing options...
grumpyvette Posted July 13, 2008 Author Share Posted July 13, 2008 ITS not generally HP but RPMS or lack of lubracation to the bearings that kills rods, I know guys with turbo cars that have carefully reworked stock rods pushing over 700 hp but they don,t generally exceed 6300rpm, rods generally fail in TENSION when the rod or rod bolts stretch /stretchs not in compression due to cylinder pressure. thats why the 7/16" rod bolts are so much better, as the bolts are the weakest component in most designs on the compression stroke the whole rod structure resists deformation on the exhaust stroke the rod bolts are playing crack the whip and the rods trying to keep the piston from pulling/distorting it maybe 25-40 thousands it takes to prevent head to piston contact, and the bearing shells from distorting ,under the load so they don,t loose the oil pressure support, if the rod elongates and hits the head or valves in valve float bad things cascade into worse things fast. the rod bolt cross setional area is generally far smaller than the rod itself and if the piston compresses the rod a few thousands on the power stroke there not much effected, but let the rod stretch and bad things happen real fast. a 7/16" rod bolt is about 20% larger in cross section than a 3/8" rod bolt and the L19 ARP steel in the better rod bolts is easily 50%-100% stronger than the stock rod bolt steel in many cases, giving a decent aftermarket cap screw rod design a significant strength advantage Quote Link to comment Share on other sites More sharing options...
Jerminator96 Posted July 13, 2008 Share Posted July 13, 2008 I see what your saying. I guess the high hp failures are more likely related to crank walk from extreme cylinder pressures. Quote Link to comment Share on other sites More sharing options...
dr_hunt Posted July 14, 2008 Share Posted July 14, 2008 I see what your saying. I guess the high hp failures are more likely related to crank walk from extreme cylinder pressures. Chevys, fords and mopars of the v8 category don't experience crank walk. Your thinking of dsm motors. Quote Link to comment Share on other sites More sharing options...
Jerminator96 Posted July 14, 2008 Share Posted July 14, 2008 Am I in error on my definition of crank walk? I was under the impression that under extreme cylinder pressure the crank would actually lift the mains and stretch the main cap bolts? Is this something completely different? Quote Link to comment Share on other sites More sharing options...
f430360e Posted July 14, 2008 Share Posted July 14, 2008 I think what most people refer to as crank walk is a thrust bearing failure, and results in crankshaft play along the axis of the crank. Quote Link to comment Share on other sites More sharing options...
dr_hunt Posted July 14, 2008 Share Posted July 14, 2008 Having been building engines for 34 years and having knowledge of the DSM's I can tell you that I have not seen a v8 ford, chevy, mopar experience separation of the main caps from the block except in the early chevy 283's which were weak 2 bolt blocks. Even so the thrust bearing would keep it fom walking. The DSM's eat the thrust and the crank walks to the point where the counterweights hit the block. I have seen that. I have seen fords v8's 302's split in half. I have seen sbc's lift the heads. I have never seen crank walk or thrust failure except when having torque converter issues. My opinion and experience only though. Quote Link to comment Share on other sites More sharing options...
Jerminator96 Posted July 14, 2008 Share Posted July 14, 2008 Well you have me by a large margin on experience Doc. I have a good amount of knowledge, especially in the physics of designing high hp mills, but I just don't have enough builds under my belt.I have seen the aftermath of a chevy 396 (SBC with 2 bolt mains) that supposedly walked the crank, but that would be the only one I've seen, if that is what actually happened.Thanks for the clarification.Jeremy Quote Link to comment Share on other sites More sharing options...
ragefear Posted July 17, 2008 Share Posted July 17, 2008 IDK, my step dad has been running stock rods, not so sure about the crank, in his race truck which is an 80 chevy pickup for over 10 years (same stock rods) and runs consistant mid 12s. In a car we believe its good for at least a mid-high 11 second run. At the tree he revs the motor up to about 7K before dumping the clutch, he was also told that his bog warner tranny would never hold up to that... never had a problem with it. I'm not saying they are bullet proof and I was quite surprised to learn that they were stock but hey, whatever works. Quote Link to comment Share on other sites More sharing options...
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