Wednesday, August 26, 2009 - 02:18 pm, by: Shane Austin(Austinisirish)
Hey all,
Firstly, I have a lightly modified 1jz soarer (ecu, front mount, exhaust, intake and boosted to 14psi)
Upon changing spark plugs, a bit of porcylin (excuse spelling) fell down into the cylinder. In gettin the porcylin out, we through a camera down into the cylinder and noticed det marks on the piston head. I dont have any images of these det marks, but I can say they were in a small patch on the cylinder... How bad are these marks? What do they mean and what causes det marks??
I want to keep workin on the cars performance but quite worried about these det marks. What would be a better option if these marks turned out epicily bad... new pistons or engine swap. Lately I have been considering a complete 2jz swap with manual conversion. Any info would be appreciated
Wednesday, August 26, 2009 - 05:45 pm, by: Walter Gillmore(Cl33pa)
my understanding is detonation is when the charge air, (air and fuel mix) detonates before reaching the compression chamber. this would damage valves and possibly cam lobes, pitting on the top of a piston is merely dirt and other junk that gets blasted in the combustion process. then shot out the exhaust. is this correct? if so then pitting on the top of your piston is not a real worry. although if gunk is gettin through you air filter and reaching the combustion chamber. then i suspect your exhaust turbine vanes on your turbo(s) will show chipping.
detonation is caused by a couple different factors from my understanding. (this is just off the top of my head, so please!!! correct me if i'm wrong!! )
1. charge air too hot = this usually happens when your turbo is reaching the limits of its efficiency range. ie. spinning waaay too fast for its size. countered by bigger intercooler, better turbo sizing for application, not running such high boost on small turbo's, the harder the turbo has to work to compress enough air to suppply the engine with positive pressure, the more heat is generated by compressing the air and the fact that the turbo's are spinning too fast for the bearings to handle.
2. too much ignition advance = a simpler one. if your spark plug ignites the charge air before it has the chance to enter the combustion chamber then detonation occurs, this form is extremely damaging to the valves, since the spark plug had the chance to fire up before the charge air got inside the combustion chamber and before the intake valve shuts, the rest of the charge air outside the chamber would also ignite, the resulting force is enough to force open a closed valve, thus damaging it by bending the stem, snapping the stem, or just destroying the whole valve, as well as possible cam damage. counter this by retarding ignition.
the first process can also damage valves this way, but usually occurs before the valves and combustion chamber entry. so detonation from charge air thats too hot usually blows intercooler piping off (if your lucky) or blowing out your intercooler end tanks (not pretty) second process can also do away with your intercooler. depending how far in the stroke your engine was from opening the exhaust when detonation occured.
Thursday, August 27, 2009 - 06:29 am, by: Matthew Sharpe(Madmatt)
Detonation outside the combustion chamber is called backfire - either through the exhaust (un-combusted fuel/air mix) or the intake system (for lots of reasons, most of them usually pretty bad)
Pre-detonation, or pinging, is inside the combustion chamber, but is caused by the fuel igniting at the wrong time, IE before or too close to when the piston has reached the top of the compression stroke. Its often caused by the ignition timing (spark) being too far advanced, but can also be caused by excessive compression, poor quality/low octane fuel, "hot" debres in the combustion chamber etc. You can usually hear it pretty clearly as a tinging noise when the engine is under load (provided you don't have a hektik exhaust and/or intake to drown it out)
Thursday, August 27, 2009 - 10:20 am, by: Shane Austin(Austinisirish)
Hey all, thanks heaps for the info... by seeing det marks i meant that I did see pitting on the top of the piston. I dont think it was caused by bad fuel as i only use 98 octane. secondly, i dont hear any pinging but mind you, i have a straight through exhaust.
I'm pretty sure it had something to do with the tune. I did have a bad tune a while ago - reference my post "riped off" in the engine management forum. That has since been fixed.
The camera we shoved down the cylinder didnt show any bad signs on the valves, so i guess i can count my lucky stars there. So my next question is now what??? Should i get new pistons or go a 2jz swap, or should i just leave it as is? either way, the next 12 months i wanna turn the car into a manual, and although i wont be flogging the car every day, i do want to be able to give it some stick without worrying about my internals.
Thursday, August 27, 2009 - 11:06 am, by: Blake Gloyn(Blakenz)
that's weird. i got told that the ringlands will get damaged well before any marks appear on top of the piston face. these 'pits' now become hot spots and encourage further detonation
Thursday, August 27, 2009 - 11:08 am, by: Cameron Laufer(Ivboost)
Pitting on top of a piston can also be caused by a leaking head gasket, coolant getting into the combustion chambers. Although this is rare it can happen.
Thursday, August 27, 2009 - 11:59 am, by: Damian Ware(Frozenpod)
Shane whilst tunning high boost engines often peak power and torque is produced at the point of detonation and they are tuned to this limit.
Every time my car has been tuned it has been tuned to the edge of detonation which produced peak power then back off a safety margin.
Detonation is always bad for an engine but under control conditions engines are tuned to allow for some slight detonation. My pulsar when cold detonates slightly with the factory tune at 2750 to 3500rpm. I have tested another pulsar same model and it does the same. My pulsar has been doing so every cold start and now has about 80,000km on it and no signs of any serious damage.
Even this slight detonation will cause small particles of the piston to be blown off and if you remove the spark plugs while on the dyno you can often see small particles of the piston on the porcelen. These particles are very small and can be approximately 10 microns in size.
Given your tuner may have been less than skilled he may have allowed the engine to detonate badly and cause visiable pitting.
If the engine comp tests and leak down tests ok don't worry about it.
Thursday, August 27, 2009 - 06:25 pm, by: Shane Austin(Austinisirish)
I'm pretty sure i dont have a blown HG... either way, its going for a 100km service tomorrow, so i'll ask the mech what he thinks of the whole situation. Will let every1 know what the go is tomorrow
Monday, August 31, 2009 - 09:56 am, by: Chris Davey(Chris_davey)
SIlly question but the pitting in the piston you are talking about is not the piston "cut out" right? No 1j piston in front of me now but from memory they have cut outs in them so just checking you know this
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