I have a 4.6 stroked to 5.0. Trick flow 195r heads, edelbrock intake, small comp cams, with precision 76/75. Running on e85. Does not have the cylinder 8 cooling mod.

I bought this car assembled but needing a tune. I took the car to the dyno for a tune. Everything worked out pretty good. Got it finished up and brought the car home.
Took it to the track and made 4 passes. After the 3th pass it wasn't running well and had a miss. Got it home and cylinder 8 had 0 compression. Pulled the head off, had melted the valve and almost all the way through the head.

Head guy told me it was just bad valve from trick flow. So Had the head fixed a.d new valves in both heads. Put everything back together and the very first pass it puked what I thought was oil/antifreeze mixture. Thought it blew head gasket. Again 0 compression on cylinder 8. Pulled head off and side of piston melted, top of rod melted, and got the cylinder wall.

Now I'm scared to spend the money rebuilding to have this happen again. I tore everything apart and all other cylinders look perfect. I have taken my injectors to get tested but haven't got results yet.

Max timing was 19 degrees.
Afr at max of 8.2 on the last run.
16lbs boost

What could cause this issue?

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8.2 AFR sounds really rich, what scale is that? I have heard too much fuel can be as bad as not enough? Is it possible the coil is bad? When Matt was doing 8's for 8 he cooked a couple that was eventually blamed on a coil pre ignition.

Sorry to hear about your bad luck, I would through a junkyard 4.6 back in it until I found the cause (but I am cheap).

 

Typically when I have seen a piston like that it was from the top ring butting, the rings has no where to go so it finds a way and damages the top of the piston. Then oil is like a blow torch.

From the 1st incident , the valve damage could have been from a red hot glowing ground strap going sticking to the already hot valve and killing it. I would guess that if the ground strap was gone. Ive done it.

Notice in your last pic, side opposite of the damaged valve, you can see the surface looks like it was in a melting puddle state and the heat ended before it blew thru. All im saying is , might not have been the valves fault.

8.2 isnt completely unsafe assuming you are using e85 afr.
Consider 8.2 was the average of the whole motor. If 8 is a know issue, #8 is the plug you should be watching all the time and tuning to. If your efi has individual cylinder timing and fuel control, that one may need some work.
A safe spot is 7.5-7.6 .

I dont know the fuel flow setup on this motor. Is #8 possibly the last cylinder to get fuel on the fuel rails?

 

It is on e85 scale. I couldn't tell there was ever a miss or any problems running until it had zero compression of course.

 

What EEC are you running? Do you have a flex fuel sensor? Is that pump E or out of the can? 8.2 AFR E scale is what 12.1 on the gas scale? I run Flex, but use gas scale.

 

It's on holley dominator.
No flex fuel sensor.
Pump e
Around 12.6 on gas scale

 

I don't remember on how the rails were setup. I need to check on that.

 

I have my old push rod junk at 11.4 aft (gas scale) at 16psi and 18 degrees of timing. Not saying that's what you should do but 12.6 sounds like NA numbers.

 

Way to lean imo

 

Check the learn & Closed loop fuel correction. Pump E could have been regular 87 on a bad day.

 

Edit: I was confused, nothing helpful to contribute

 

I would think that if the entire motor was running lean then it would affect other cylinders and you may be able to pull the plugs to see what other cylinders look like. But, with #8 being a repeat offender I would concentrate on air/fuel delivery to that one cylinder.

ks

 

Did you pressure test the entire intake system from compressor cover through intake manifold?

Easiest way to melt an engine is a boost leak in a turbo application

https://www.supraforums.com/threads...stock-twin-turbo-engine.1127814/post-13994102

3 things before you tune any engine
1.pressure test
2.timing test
3. compression test

Then, for safety and cleanliness
Crankcase pressure monitoring
High quality air filtering

Many engines have some issue with rear cylinders. Usually because of intake design or valve events. For example 2jzgte and rb26 inline 6 cylinder engines both have distribution issues on the factory intake manifold. The intake needs a particular taper shape. And the valve events generally need more overlap and exhaust duration than you would think a turbo app would prefer but there it is 30 years of success. But I digress from your engine- you must find the parts that are tested to work in turbo applications and perform all of the diagnostics and then on top of that actually know how to tune it properly.