cygnusx1 Posted January 31, 2006 Share Posted January 31, 2006 I was wondering what the weak links are in properly tuned turbo (stock internals) motors. In other words assuming, no detonation, what breaks most frequently? And how much power/boost did it take? Quote Link to comment Share on other sites More sharing options...
violacleff Posted January 31, 2006 Share Posted January 31, 2006 Seems like Shane ran 26psi for years without blowing his. If I remember correctly, he was also running a 125 shot of nitrous as well. I was always hoping mike on3go was going to take a stock block to its limits per some of his older posts, but he changes engine plans like underwear. Quote Link to comment Share on other sites More sharing options...
thehelix112 Posted February 1, 2006 Share Posted February 1, 2006 I've got a stock long block atm save ARP head studs and a very mild cam. Will let you know. It would also seem to be a matter of what you use it for. A track raced car is going to break something a lot sooner than a street car I would have thought. 26psi would be awesome! I hope to get it up around 22psi on 98 octane pump fuel. Also, the harder you rev it the more likely it is to break, which is another saving grace of forced induction, you don't need to spin them overly hard. My redline is set at 6500 atm, mainly due to my baby cam. What are other peoples at? Dave Quote Link to comment Share on other sites More sharing options...
mobythevan Posted February 1, 2006 Share Posted February 1, 2006 I remember reading threads about the crankshaft breaking, but that is the only blow up stuff I remember reading on the forum in 3 years. See if somebody who broke a crankshaft turns up in this thread. Quote Link to comment Share on other sites More sharing options...
thehelix112 Posted February 1, 2006 Share Posted February 1, 2006 Broke a crankshaft? Jeez you'd be doing well. Even the 650hp SCCA turbo L28s only ever bent them didn't they? Dave Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted February 1, 2006 Share Posted February 1, 2006 I was always under the impression that 100% stock short block was good to 350 or maybe 400 hp at the wheels. Though I can't say anyone ever actually specified WHAT gives out at that level, not that I remember anyways. Quote Link to comment Share on other sites More sharing options...
TheNeedForZ Posted February 1, 2006 Share Posted February 1, 2006 I think the stock 9mm connecting rod bolt is the weakest link. It has undercut radii right under the bolt head, reducing the diameter to nearly 7mm. Quote Link to comment Share on other sites More sharing options...
thehelix112 Posted February 1, 2006 Share Posted February 1, 2006 Surely that is only a limitation if you are revving the bejesus out of it though? Dave Quote Link to comment Share on other sites More sharing options...
TheNeedForZ Posted February 1, 2006 Share Posted February 1, 2006 I suppose stock bolts are good for the street...There is a race mod mentioned in "how to modify..." book that uses 3/8 chevy bolts(no undercut) and modified stock rods. That's just for race cars. I'd definitely do that mod if I can find a machine shop good enough to perform the specifics. Usually when a rod bolt fails, the rod also fails and will poke a hole in the engine block. The crank journal is also scored and becomes unusable. One bad rod is enough to kill everything...That's why I will do the chevy bolt mod if I can. Quote Link to comment Share on other sites More sharing options...
pjo046 Posted February 1, 2006 Share Posted February 1, 2006 ARP rod-bolts don't cost much. Neither do ARP-main studs or head studs. If you use all that along with some good main and rod bearings, shouldn't everything hold up well if you avoid detonation and don't rev past 7K? That's where I plan on setting my RPM-limiter. I to am wondering about this. Of course I have already also got myself a set of JE forged pistons and a 1mm HKS steel headgasket. Should I even worry about something breaking? Or will I be fine pushing this to it's limits as long as I pay good attention to the A/F ratio? I have a good intercooler to cool the incoming air from the T3/T04B, and full programability from the TEC3. I guess the connecting rods are a weak link on my setup, but with the relatively low RPM-limit that shouldn't be a problem either. I mean, how many of the top-tuned L28ET engines on here are actually using aftermarket forged connecting rods? Quote Link to comment Share on other sites More sharing options...
Cody 82 ZXT Posted February 1, 2006 Share Posted February 1, 2006 Seems like Shane ran 26psi for years without blowing his. If I remember correctly, he was also running a 125 shot of nitrous as well. I was always hoping mike on3go was going to take a stock block to its limits per some of his older posts, but he changes engine plans like underwear. I don't know how he was running 26psi. I've got his old computer and trust me I can't run anywhere near 26psi with it. Quote Link to comment Share on other sites More sharing options...
TimZ Posted February 1, 2006 Share Posted February 1, 2006 RING LANDS!!! Come on guys - you're telling me you'd expect to break a crank or rod bolt before breaking a ring land on the stock cast pistons? I'm willing to bet money that 99% of the failed stock block turbo motors involved ring lands giving way. Quote Link to comment Share on other sites More sharing options...
thehelix112 Posted February 1, 2006 Share Posted February 1, 2006 Well I feel kinda dumb now that Tim mentioned it. I wonder though, if you controlled detonation, how much would a stock cast piston cope with? Dave Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted February 1, 2006 Author Share Posted February 1, 2006 My original post indicated "without detonation". Of course detonation will kill it sooner. I guess the motor is really tough 'cause so far nobody has stepped up and said that theirs actually has failed from power limitations. Quote Link to comment Share on other sites More sharing options...
mobythevan Posted February 1, 2006 Share Posted February 1, 2006 assuming no detonation like he said, I wouldn't expect the ring lands to go first. These theoretical threads are fun anyway. Quote Link to comment Share on other sites More sharing options...
iaconsultants Posted February 1, 2006 Share Posted February 1, 2006 Well I will admit that I have destroyed a number of engines running turbos, superchargers and NOS, but that is the name of the game when you try to get out as much as you can out of a motor. Stock cast pistons for 240 through 280 cars can easily break piston lands with a slight amount of detonation at 12 to 15 psi boost so I would not go that way at all. I have done that a few times because of no money back when I was in College. You can run cast turbo pistons from a 280zxt and that will handle 15 psi maybe a little more with detonation but they will go also. Once again I have done this and it is not the right choice either but much better than the stock pistons. You can run trw forged pistons which will easily go to 18 to 20 psi with some detonation and still be okay, but if you get hard detonation or run more boost then they will start to melt down and will also crack the lands. I am still speaking from experience. The final solution that worked is to o-ring the head and block with concentric O-rings and put crush wire in them which will make a good seal/crush on the head gasket. If you run a lot of boost you will strech the head gasket by the number six near the water jacket and the o-ring grooves and the crush wire will eliminate that. Polish the head chambers and valves so that they are at a shine and don't forget to grind down any high spots or sharp areas (hot spots) like between the valves. This will reduce some of the areas that cause detonation. You can have your piston edges turned off so they are not so sharp which is a detonation problem place and then you can have the pistons ceramic coated around the cylinder surfaces so that you protect it from the heat and actually help the lubrication process. Also polish the top surface of your piston, because with forgings and cast pistons there are usually some kind of finish machining being done and believe it or not those small grooves can be a source of hot spots. If you still or just have detonation issues you can always run a water/methonal injection system to dial it out and make sure that it is timing/ boost driven and that you use 40/60 water methanol mixture for best results. I have done all this and more things so I am just letting you know what works so that you can get into the boost you want and reduce/eliminate/counteract the detonation pains. good luck and feel free to ask me about this kind of stuff since I have been doing turbos/superchargers on all kinds of things for around 25 years including a 900 Nija turbo with intercooler and a viper twin turbo. My current Z will be getting an LS1 or LS6 twin turbo which I am designing now. Quote Link to comment Share on other sites More sharing options...
vashonz Posted February 1, 2006 Share Posted February 1, 2006 Which computer do you have. I have his old SDS, he said it was programmed for ~25psi. I don't know how he was running 26psi. I've got his old computer and trust me I can't run anywhere near 26psi with it. Quote Link to comment Share on other sites More sharing options...
ToplessZ Posted February 1, 2006 Share Posted February 1, 2006 I have heard of 500 hp on a blow through setup with a stock shortblock. I do believe the head was worked though. This was done with low compression in one cylinder. It was the guy who sold the purple imsa widebody to a guy wanting to do the Rb 26 swap in it. Can't remember the names right now but I believe that dyno charts where posted. Quote Link to comment Share on other sites More sharing options...
TimZ Posted February 1, 2006 Share Posted February 1, 2006 This was done with low compression in one cylinder. i.e., broken ring land I guess my point was that there is virtually no way that you'll get to the point where you are breaking cranks/rods/rod bolts/etc., without the ring lands going first. If anybody claims otherwise, then they are either very, very lucky, or mistaken. Quote Link to comment Share on other sites More sharing options...
drzed Posted February 1, 2006 Share Posted February 1, 2006 I ran all last year at the track at 19psi on a bone stock bottom end with just new rings and bearings. Ended the year at 21 psi for the last 2 nights. No failures at all except for the headgasket leaking a very small amount of water externally down the side of the block each run - doesn't leak on the street at all unless it's under full boost. I run conservative timing and good fuel - always avoiding detonation like the plague!! I also have an intercooler the size of my rad to keep the intake temps cool. Quote Link to comment Share on other sites More sharing options...
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