How do we know when we're approching mechanical limits?

Hey guys,

So I've been wondering this for a while, and I guess I never really could answer it.

When it comes to tuning NA + T engines, where they're not designed for the extreme load that a turbo can induce, how do we know when we're pushing too hard?

My personal example is my Subaru EZ30 Turbo with a Precision 6262. The car is on E85 and my previous tuner had it lift the heads on the dyno, where I learned that it was targeting high 20's in the ignition table with the boost controller having the turbo spool as quickly as it can. Given the motor breathes well and the rear housing is a .83 on a mid-frame turbo, it came on quick, and I suppose the cylinder pressures during combustion simply increased too rapidly. He didn't explain to me what his process was, but I'm assuming he either pushed the timing until it stopped making power, because in the usual circumstance, on 98RON pump fuel, it would've been knock limited, as most of these EZ30's are, even stock.

I don't blame him because, shit happens, but I'm curious, is there any way to know when we're going too far? Is there anything that might've been indicative that a failure was imminent? Or is it really just a game of luck and experience?

We haven't blown anything up since then which is cool!

For the most part, things are fine... until they aren't. Every engine is going to have different strengths and weaknesses - the trick is in knowing what your engine's are, and working around that.

It's mostly trial and error, and for the most part there are people who have already done the expensive part in finding where pistons fail, rod's bend or snap, head gaskets fail and head bolts/studs stretch and allow the head to 'lift' and the head gasket to fail - as in your case.

For the most part, it isn't how quickly the pressure rises - this is generally a good thing, provided it doesn't cause detonation, and it helps for efficiency and MBT - but the peak pressure reached.

Going too far can mean a lot of things, but if you're referring to ignition advance on E85, it can be tricky.

People often end up far beyond where they should have stopped advancing timing on ethanol because they think if the engine doesn't seem to be knocking, it must be OK. That's not the case, and component failures become more likely when ignition is over advanced. Without knowing all circumstances in your gasket failure I'll just say it seems to have been a factor in your case.

Gord's point about knowing what the physical parts can handle is a good one. If the information isn't readily available, then you learn as you go.

If I may add:

It is important to make "Double"-sure that there is no timing drift as RPM increase.