oh dear!

Grunter, yes I agrre with what you said and Jeff taylor said. Its seems that the fuelling needs to be just right. To be over fuelled is just as bad as detonation and can cause your rings to go south. It seems the mix is really hard to get when boosting goes over 10psi and becomes more and more critical the more boost you give it. Softer top rings and forgies will only delay the ineviatble if your fuel mix isnt right. Im thinking great power is available in a decomp A series if you are using a good injection system and ECU...of course this cost money, but its money that would never break, unlike engine internals and would seem like the area to keep developing. Once we get that right then we can get the engine internals sorted to get even more boost. Im thinking once fuel is right then i reckon we can boost 40-50psi with the right engine.

hmmm
A12 with 40psi


Now your thinking

yep i reckon......we need a bloody good tuner and ECU though...thats gonna cost

Ring lands dropped out in several pieces when I popped no 4 piston out of the block. no damage to anything other than the piston though.

But here's the wierd bit:
I cc'd the chambers and the compression ratio was 9.7:1 (I had been told it was still stock)
and the cam had some wierd specs, 310 deg of exhaust duration and 280 deg of inlet duration (something like 290&240 @ 40thou lift)

I was doing the cam specs with feeler guages rather than a dial guage so the results aren't spot on, but its a hell of a lot more radical than I thought. And it doesn't really add up with the torque curve either. you would expect a cam like that to peak a lot later.

could be the stock inlet manifold holding it back I spose.

Anyways, it will go back together with pulsar ET pistons and 8.5:1 or 9:1 comp, detailed combustion chambers and 5psi & a blower grind cam & I think it will be good and reliable.

sounds good, those et pistons can take a beating, with a lower comp ratio from these dished pistons and chamber modds i reckon you could run 10psi+ again without pinging give it a go before dropping the boost you may be suprised

I couldn't get the E15ET pistons to go in without a lot of extra work. the compression height is 33.5mm on the ET vs 30mm on the A15. Could be done, but the cost was going to get silly. Best to go back to an A14 for ET piston upgrade. I have gone with another set of stock (oversize) pistons, decent rings & bearings. cleaned up and dished out the combustion chambers while I was at it which should drop the comp ratio a bit.

I also retarded the cam by 5 degrees to hold onto the pressure for a bit longer before the exhaust opens. Will mean that everything else happens later too though so it may just be a pig.

Should be running in a week or two.

I woiuldn't advise doing that. With a blown motor you need to open the ex valve a bit sooner. This helps evacuate the higher volumes of gasses, which are the byproduct of forcing in the charge at the other end. This is why blower cams have a wider lobe separation angle. Nitrous cams have an even wider separation angle for this reason.
How much overlap does your cam have? With the incoming charge getting forced in, The purging of the spent charge at TDC on the exhaust stroke will happen at lower revs. Unlike on an N/A motor where the scavenging effect relies on higher gas velocities occouring in the upper rev ranges.

Hmmmm. Interesting.

The main reference book I am working from is Supercharged! by Corky Bell. He is a bit of a clown, oversimplifying everything- but one of the main points he raises is that combustion takes longer in a blown motor, with considerably more combustion pressure still in the cylinder at 90+deg ATDC than in a NA engine.- hence the decision to retard the cam & hold the pressure in for longer. It was a big call potential gains are probably small, but potential losses may be huge, and be a pain to fix. I'm in it for a laugh though, so its all good.

My cam is supposed to be a 30/70 (110 deg lobe separation) I got the numbers checked with the cam grinder while it was apart. the tappet clearance reccommended by the cam grinder was 20 thou though, which is amost twice the standard clearance. This may explain the difference between the official specs and what I got when I measured it.

The other effect of retarding the cam timing, will be raising the powerband further up the rev range. With a blower you don't need to be pulling monster revs. To quote dodgeman, "just grab another gear and hang on".