piston ringland crack. Possible causes? What can cause this piston crack? If you cant see well there is a crack on the side of the piston between the first 2 rings, and a piece came off. Fortunately it didnt came off the piston and made no damage to the cylinder. It just had no compression and very much smoke came out of the breather. The engine is a vg30det, cima single turbo. I just had my new poncams fitted and i raised the pressure to 1.5 bar(21 psi). Single turbo precision pte5857 billet. I'm guessing it around 450 hp. So this the limit of the det pistons????
I think you answered your own question. Why do car parts break ??? when they are subjected to forces greater than the strength of the metals
I wonder, are the tt pistons stronger? They are supposed to hold power around 600 hp. Why mine broke at 450 hp when they are sopposed to be the same as the tt ones? There was no marks of detonation and the engine is very clean with perfect cylinder measurements at all. I was running a litle lean but i dont believe that this was the problem. I was running 11.2-11.4 afm. the egt never get above 900 c
Was the car run on the dyno at 21psi to check air/fuel ration and for knock? And yeh Id say thats pretty close to the limit of standard pistons/rods. Especially on a 20yr old engine.
No dyno run. I have a wideband o2 meter in the car and i have many logs swowing the afr. 11.2 to 11.5 the leaner spot. Today i also found some small cracks near the spark plug housing at cylinder 1,2,4,6. Should i replace them? Pics from the heads is coming
At that boost you need to run the A/F @ around 12.2, personaly I would not run a boost pressure above 17psi on standard pistons.I run 14psi max in my ZX. Looks to me that the engine has det.on full load .[is the piston from the back pots?]
Those are the ringlands that are damaged. 11.5AFR is fairly rich and aslong as the timing wasn't too far advanced it should have been a safe tune unless you copped a bad batch of fuel. In the end though, 20+ year old parts won't last forever and at 450rwhp it was a matter of time. Every car and engine is different, just because one VG30 makes 600hp on stock bits doesn't mean the next one will.
Without doubt caused by detonation, as are the cracks around the plug bosses. Both these are caused by excess heat and pressure. AFR is not the most important thing when it comes to detonation, what matters most is the amount of timing. Stock pistons will take well above that boost and hp level providing they are ok to start with.
Detonation?? There is no signs of detonation at any piston or head. They are all clear as new. As for the timing it is stock, litle retarded at the midle range. When we tuned it we used a knock monitor and there was no knock. I ll post some pics of the other pistons too
Detonation?? There is no signs of detonation at any piston or head. They are all clear as new. As for the timing it is stock, litle retarded at the midle range. When we tuned it we used a knock monitor and there was no knock. I ll post some pics of the other pistons too
Stock timing higher up in the maps is probably 3 degrees or so too much for that amount of boost, assuming your fuel is similar to ours. Post up good photos of the tips of the plugs, my bet is there is little silver balls on the end of the thread, peppering on the ceramic and a white electrode. Cracks in the plug bosses are sure signs of detonation. Coupled with cracked ring lands, I have no doubt that detonation caused this. You will not always see detonation signs on the piston crowns, if you do it is extremely bad knock. I will also guess that is number 4 piston?
No its number 6. The fuel i use is 100ron. The plugs are ok too, with no signs of ware. Bkr7e ngk cooper pkugs i use. I ll post pics ar i get home
Just because there are no visual signs of detonation, does not mean its not happening. That engine could have been rattling its head off and NEVER fizzed any metal off the pistons. Just because you cant hear it NEVER means detonation is not happening. Ring land cracking is a classic sign of prolonged and repeated knocking. The cracking around the plug holes is also a bit of a worry indicating prolonged and excessive heat which may cause pre-ignition, or spontaneaous ignition of the fuel before the spark event. Pre-ignition is a totally different animal to detonation. The amount of horsepower you produce is almost irrelevent to a piston, cast or forged. The amount of abuse the pistons recieve in the form of grenading OR pre-ignition is what does the damage. Forged pistons will tolerate more abuse rather than allow higher powers. L8r E
This is an important point of two conditions that are confused with the same issue. Pre-ignition, and detonation. or Knock and lean ignition. They are regularly confused with each other. You overly rich running may actually be contributing to pre-ignition, in an area normally devoid of air/fuel mixture <the ring lands>. It was Henry Ricardo (do a wiki search on this genius) who first identified there is a difference. Detonation will lift metal off the piston crowns whereas pre-ignition will unevenly load pistons especially in the, sparkplug threads, valve seats, rings and ring land area (any area that has features that oppose each other). Pre-ignition is hard to hear over the engine operations, but can be observed in high air fuel raitos (hint), and mis-fires. As pre-ignition upsets the complete combustion process of the engine, and can occur at any point of the combustion cycle. Also, for the Vg30DE I found that the engine carries over a lot of free oxygen, see here, so be cautious relying purely on air/fuel ratios and detonation sensors.
"SORRY" As I said before it is a DETONATION problem ,can be caused by injectors maxing out ,advanced timing , running lean , type of fuel , lack of cooling [ hot spots ] , wrong heat range of plugs and sharp edges [bures] inside of cobustion chambers.It is too late now the damage is done . get your self some new heads & Pistons do a rebuild then drive it carefully to a good expirianced Dyno tuner lots of $$$$$$ later problem fixed.
As everything shows detonation caused this. That's exactly what i'm going to do. New heads-pistons and i will examine carefully all the engine. The bad thing is that there is not a good exrerienced tuner here that works with 300zx. So i have to either do it myself, or go to a good tuner for hondas that i know and tell him exactly what i want. How can i get a trustable warning for detonation? Does knocklite-knocklink works ok or should i buy a more expensive knock analyzer like phormula ks4?
