so glad I have done the A15 conversion lol not a massive increase but definitely noticeable...
although i havnt really been driving it too hard it does grab and spin second, and it even chirps THIRD hahahaha! sad i know ;)
might have to look at gettin a H165 LSD though, for a bit more fun lol
mine is a '78 model ute so i have the H165 but how much roughly is a LSD centre and does anyone still do them new?

Mine use to chirp in 3rd, then I got sticky tyre's. I miss my ass-end over taking me

What are the specs of your a15? Im thinking of doing an a15 but wondering if its really worth it over an a14... Ive spoken to a few ppl who have raced a14's and they seem to be popular as they rev hard but are a nice square engine.

Im pretty sure from memory someone did a run of h165 lsd for around the 1100 mark a little while back, do a search on here?

Give us a vid!

hahaha cool, cant give u specs its a secret... lol jokes nah its all stock man. had big plans for building a mild one but A12 threw a piston so the A15 sittin in the shed got a quick stock rebuild to go in lol

Topgear here builds torsion LSD for h165 for 1100 new!

O_O Threw a piston! How on earth?
Thats grouse then if its just a stocker a15.
Im thinking of going 20 thou over with a set of flat tops (depending on price :S) Have a set of twins here to go on too. Depending on budget maybe a mild porting with some big valves to go in also.
But to begin i should probably do the couple of little niggily jobs ive gotta do on the mild a12, get the funds up and then go bigger :S haha
At least ive pretty much got all of the bits i need to do it, but the machining will be a killer!!

well it didnt 'throw' a piston lol my bad, the piston chipped around the outer skirt, it must've been dropped when they did the rebuild and had a hairline crack or something in it, coz the guy I bought the ute off told me that it had just had a recent rebuild and dyno tuned hahaha, they dyno'd it at tafe or something, made 52hp lol i wanna get it dyno'd now to, just so they can check that the mixture isnt to lean etc...

my old a12 did the same thing. I chipped a piston. We had two ideas, it happened during travelling at around 110km on a freeway. it was less than 1000km after the rebuild. The engine was stock.
First though was that the head has some pitting in on of the water galleries next to piston 3 (the piston that chipped the worst, there was some slight chipping on 4 as well..) the idea was that a small amount of water somehow made its way into the top of the piston and being hot as it was doing 110km and had been for around 2 or so hours the water does not compress therefore chipping the piston.
The other idea was that the rings may not have been trimmed to fit perfecting and as the engine got nice and warm they expanded which caused the bad scoring in the bore.
either way it sucked that it happened haha.
Got a nice mild a12 now though ;)

It's probably not the coolant. Generally if it leaks enough coolant into a cylinder to hydraulic lock at all (and it actually takes a lot of water, and at a high rate of flow too - because it will just push small amounts of water out of the gap and into the combustion chamber space, get to TDC, initiate the burn (technically a touch before TDC), piston travels down and back up and it will then push the water (or perhaps steam by this time) out the exhaust valve/port) So it isn't likely that. Also - if it DID hydraulic lock, it typically won't just chip a piston, it'll break it and likely bend (or break/damage) a rod or even the crank in really bad cases.

It certainly can happen (piston damage) if the ring end gaps are too close, and the rings expand and close the gap entirely. This will tend to rip/snap the piston crown above the top ring right apart.

Without seeing pics (and I realise i'm discusing 2 engines here and they weren't necessarily the same exact situation in each case) - but based on the description of the piston crown/combustion chamber, it 'sounds' like it might have been seeing some smaller (but still significant) amounts of detonation or pre-ignition. This can very easily happen on a freshened up motor - for a few reasons -

first, it possibly has gone to the next oversize piston during the rebuild. in which case, with no other changes, you have a little bit more capacity, still being squeezed into the same combustion chamber, so the compression ratio will have been raised. Even if it is std size pistons, it's also likely the head will have been freshened up, and a surface grind to clean up the cylinder head gasket mating surface - well that will slightly reduce combustion chamber volume. So again 'unexpected' (so to speak) increase in compression ratio. if it was just 'safe' from detonation with the comp ratio it ran before the rebuild, then it would just be over the line into the danger zone after the rebuild. It doesn't take much and the damage doesn't 'heal' so it accumulates over time.

second - on a related note, factory distributor advance curves were worked out and 'right' when new (sometimes on some cars in general the factory advance curve is a little compromised which could affect performance a little bit, but was necessary for emissions compliance or something like that) - ok asuming this curve was pretty good, well the springs inside the dizzy will have sagged a little bit, so you'd see the mech advance coming in a little earlier than originally (hey, they are getting up towards 35-40 years of age). This won't affect max rpm timing much, since it travels out to the max possible timing, but it _will_ mean there's a little bit too much advance coming on a little earlier in the low-mid rpm range.

third - depending on how the engine running in process is done (and I don't want to go off on a big argument over which way is best, as there's some pros and cons to various techniques/timetables) - anyway - if you do the 'nice and easy' running in, not going too hard for a few thousand kms (as I said, there's pro's and cons and this method would/will work, but it is important to drive it accordingly until the process is complete) - anyhoo, if the run in process is the slow and steady option, it _can_ mean that even at 1000km on the clock since the rebuild, there still might not be full or complete bedding in of the rings. If the ring seal isn't optimal by then, well some combusion gases will get past the rings. This will pressurise the crankcase, and then other pistons, on their intake stroke will see some seepage of blowby gases (or even some tiny amounts of oil being pushed up past the rings) coming up from the crankcase and bypassing the rings, and getting into the combustion chamber/cylinder area, just before that cylinder starts its compression stroke.. Which means the incoming air/fuel is contaminated by blowby gases and even some oil, and this lowers the effective octane of the fuel, and this will also lead to the onset of either detonation or pre-ignition.

Another thing about detonation/preignition - you can usually hear it at lower rpms if there is too much ignition advance, and you floor the accelerator - that rattling knocking sound over and over and over. BUT - at much higher rpms, with the engine well into its powerband - well all the 'proper' noises that an engine makes at full throttle and near peak rpms, well that can easily 'drown out' or cover up/conceal any knocking/detonation sound.

Obviously it depends on teh severity and duration, but detonation will leave the piston crown surface with what looks like tiny craters on the moon, or something like htat. and if harsh enough, it can hammer and break piston rings and or break the piston crown (often you find both have occured simultaneously, it's a little rarer to just see one or the other by itself.

When you are just on the borderline of detonation (etc) where it is just starting, or just on the verge of happening, you'll also tend to find that it doesn't happen to each cylnder/piston the same. there's a couple of reasons - primarily two:

1. mixture distribution - plain and simple, esp with factory intake manifolds (esp from 30-40 years ago for mass produced cars where reliability and affordability was more important than getting every last possible % of performance out of the setup) some cylinders will run leaner than others some richer than others. Some therefore more likely to detonate, some less likely to do so. we might be able to improve that one - it depends, we'd have to locate which are the troubled ones, then try and see if subtle alterations to the intake manifold or carb position or jetting improve things Or of course we could switch to twin carbs, esp something like dcoe webers - each cylinder will (or at least potentially can) get its proper and even share of air and of fuel.

2. Cylinder to cylinder heat variation. Due to the way coolant flows through the block, mostly from front to back, then up to the head then toward the front nd out (there are transfer holes along the length of the head/block to allow some coolant to shortcut and get to the front of the head to help this situation) - anyhoo, it gets hotter and hotter as it continues it's journey. So since #1 cylinder sees the coolant first, it will (usually) run cooler, but as the water passes back past each cylinder, it will heat up more and more and cool each cylinder less and less. Then it does the return trip through the head. Now (relatively speaking) the coolant around #4 (but in head not the block) will be cooler than that that gets to the front of the head, which is warmed as it passes each chamber. So therefore, whilst #1 cyl 'should' be cooler #1 combustion chamber is likely the hotter. Since most of the burn takes place in the top 1/3rd of the cylinder bore and the chamber, the heat in the chamber is arguably more critical than how hot the cylinder is.

They cancel each other out a bit, but you'll generally still find that one or perhaps two of the 4 cylnders will (with identical comp ratios and fuel mixtures etc) be closer to detonating than the rest.

This isn't a 'cheap and easy' problem to solve. On various factory engine based racers over the years, engine builders have done all sorts of mods, drilling/welding up/enlarging/reducing various coolant passages or pathways to redirect coolant. Some even have additional external pipes routed into the waterjackets in the block or the head, so they even things up temp wise. But usually this will only 'improve' things not totlly solve them, and can cost insane amounts of time effort and money. At the height of the british supertourers (very roughly speaking it was the 1990's from early through till late 90s) - massively highly developed 2 litre engines - with custom heads, blocks cranks, you name it - probably costed around 3-4 times what a v8 supercar cost to build (esp allowing for inflation rates etc). Anyway even with these literally $1 million budgets, they still couldn't get the cylinder temps 100% equal. So they ran the same fuel map for each cylinder (so as not to waste fuel, esp if a long race where buckets or enrichment fuel for cooling just would use too much fuel over the race and require more frequent pitstops etc) - anyway they basically ran a separate ignition timing map for each cylinder.

Obviously that can't happen on a datto with conventional ignition. So what option might we have? Well what most people would do, and it is the affordable and safe option, is simply to run less timing or less compression ratio. That keeps the 'hotter' cylinders safe, but then the 'cooler' ones will be running less compression ratio than they could otherwise handle safely. the trick is simple enough. (and I didn't think of this myself, it's been done by a bunch of people over the years) - anyway IF it can be 100% for certain known which are the offending cylinders, then the combution chambers for those cylinders could be carefully opened up a few more cc's using a die-grinder. That will lower the comp on the 'risky'cylinders but retain it on the 'safe' ones..best of both worlds.

I realise it is too late to do this to the current motors in question, since the damage has already happened, but I thought I'd bring it up for trivia's sake

Well John has covered so many hypotheticals very well,I will bring to the table some more likely ones,Old often machined cylinder heads on most cars first thing I would check is that the head has been machined square and all the chambers measure up with close to even combustion chamber volumes.
Plenty of engines have been cooked in the past and someone just machines the head flat and bolts it on with a new gasket,Most bend up in the middle so when refaced end up with more being machined from the ends of the casting so the #1 and #4 cylinder chambers can be a lot higher compression than the centre cylinders.

Especially with an A series engine where pushrods and no cam tunnels like an OHC engine mean no warning sign of a Cam binding when you try turning it often means many now rather elderly A Series heads are best carefully checked or they will detonate on the end cylinders because of those problems.

First easy check for this problem is a straight edge along the Rocker Cover gasket surface,They were originally machined flat and square to the head gasket surface when they left the factory so a simple test like this will show any potential faults before they cause a problem with a built engine.

Mostly either Ring Gap as John pointed out or the above scenario as I have elabotated on are most often the cause of detonation caused Piston Damage or Seizure related stress failure's.