waddisme

Here are this pics from blown motor:

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Could it be from predetonation? It happened at VIR, 71*, water temps were 203* and oil temps were 255*.

Here is my last dyno sheet:

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I thought it was a pretty conservative tune. Could it still be cracked ring and this is the damage I did on the 3 hr ride home? Thoughts?

chriswtx

I also think we see broken stock pistons from such tight top ring end gap clearances in the factory motor, when the tops of the pistons get really hot, the end top ring swells and the end gap closes to nothing and for a split second the ring locks in the bore and breaks off the top ring land. Cast pistons with tight ring end gaps don't like long, hard runs. Builds up heat in the top of the pistons...Well thats my theory anyway.

user_name

How much timing were your running?

chriswtx

After another look, that looks like severe detonation from going lean and melting the piton instead of a clean break like from a piston failure..

Robert56@RNS

I did he same thing with spray, and too much timing at 685rwtq. It also bent the stock rod.
Robert

Warp Factor

That's my theory too, except that when the ring ends butt and the ring is forced hard against the cylinder wall, it could produce enough heat to melt the ring land, as well as enough force to break it. So ring end gap might be a factor in either scenario.

Of course, detonation would contribute hugely to the heat load.

Is detonation always a factor?
I'm curious. Has anyone had this happen while using race gas with enough octane to make detonation highly unlikely?

madmatt9471

Same thing here on mine when it went, BOOST blew it out :



Thanks,Matt

peter pan

Well is the block ok? Now you will be able to forge your baby and turn up the wick

0Jake@EPP

Glad someone brought this up. Sometimes a tuner is directly blamed when it bites the dust, but it ends up being something major like such.

The heat of the chamber gets to a point and the tight end gap of a stocker is not enough.

What do the plugs say? Check the topside rod bearing? Msd coils?
There are a TON of variables when something like this happens, often its too easy to blame one little thing.

leojnknsC5

Detonation is caused by too much timing and tends to show in the middle of the piston nearest teh spark plug. Preignition is an event that occurs before the spark plug fires and may produce pressures on one side of the comb chamber near a hot spot that exceed the strength of the piston in a weak place, such as above the ring land. My guess, from here it looks like preignition or a hot spot in the chamber.

Do you spray meth? Meth will clean teh chamber and reduce or eliminate hot spots and preignition.

waddisme

I am in no way blaming the tuner here. I knew I was on the edge hp wise for a stock bottom and I was pushing it really hard at the top end of 3rd and 4th gears.

"Well is the block ok? Now you will be able to forge your baby and turn up the wick"

I have a na forged 402 al block on the way. Hopefully the old block will be OK enough to get some $$s to help with the rebuild.

"Do you spray meth? Meth will clean teh chamber and reduce or eliminate hot spots and preignition."

I had a meth kit installed but not hooked up. My tuner said there was no real need for it. Timing would back down if IATs got too high. I do not know where timing was set.

My biggest concern is for the new engine and if this was a predetonation issue or an oil starvation issue. From what I gather it is a FI issue and not a road racing issue. It seems $500 for Accusump is pretty cheap insurance for a $9000 motor. Thanks for the input.

Warp Factor

It's a fairly common failure on the stock block, and it even shows up on normally aspirated engines sometimes.

According to APS in an old thread, measuring individual cylinders showed that #5 and 7 run leaner, which would create more heat and possibly detonation. Something to do with airflow in our manifolds, and maybe the firing order I suppose.
An interesting suggestion I read was to flow the injectors, and put the richest ones on cylinders 5 and 7.

Whatever the chain of events that leads to this failure, a forged engine seems to make it much less likely, according to what I've read here. Haven't seen anyone associate it with lack of lubrication.

Edit:
The service manual puts the top ring end gap at .009 to .0149. Isn't this a little tight for FI, particularly positioned so high on the piston?

FRCTony

This is why people say not to run FI on a road course. A motor can live a long happy life on the street or drag strip. A couple of pulls on VIR's long straight, and voila.

My money is on high EGT.

MIKE-C5

ajg1915

It looks like either detonation problems or excessive heat problems that closed ring gap.

You'll know more when you get the pistons out and see if the top ring is broke.

Detonation can rattle a motor to pieces but I would have thought you would have heard a lot of pinging and loss power if this was the case.

leojnknsC5

BAcking down timing may not have saved your motor. 5 and 7 may have blown from preignition, not detonation. They are not teh same. Meth will cool, clean, and enrich teh AFratio-which directly address preignition.

ajg1915

Didn't know that, learn something new every day.

Detonation (also called "spark knock") is an erratic form of combustion that can cause head gasket failure as well as other engine damage. Detonation occurs when excessive heat and pressure in the combustion chamber cause the air/fuel mixture to autoignite. This produces multiple flame fronts within the combustion chamber instead of a single flame kernel. When these multiple flames collide, they do so with explosive force that produces a sudden rise in cylinder pressure accompanied by a sharp metallic pinging or knocking noise. The hammer-like shock waves created by detonation subject the head gasket, piston, rings, spark plug and rod bearings to severe overloading.


Mild or occasional detonation can occur in almost any engine and usually causes no harm. But prolonged or heavy detonation can be very damaging. So if you hear knocking or pinging when accelerating or lugging your engine, you probably have a detonation problem


CAUSES OF PRE-IGNITION
Carbon deposits form a heat barrier and can be a contributing factor to preignition. Other causes include: An overheated spark plug (too hot a heat range for the application). Glowing carbon deposits on a hot exhaust valve (which may mean the valve is running too hot because of poor seating, a weak valve spring or insufficient valve lash).

A sharp edge in the combustion chamber or on top of a piston (rounding sharp edges with a grinder can eliminate this cause).

Sharp edges on valves that were reground improperly (not enough margin left on the edges).

A lean fuel mixture.

Low coolant level, slipping fan clutch, inoperative electric cooling fan or other cooling system problem that causes the engine to run hotter than normal.

leojnknsC5

Meth is cheap insurance against engine damage. Dont leave home without it.

leojnknsC5

It probably came apart in very little pieces, not one large chunk.

waddisme

I haven't found any of my missing pieces. Don't know where they have gone. BTW, I heard no knocking or pinging or I would have stopped dead in my tracks.