Anything look suspect or dangerous in this tune?

[aaronc7]

Hi, been on here for a few years now to read and learn. First post.

Recently had some engine damage @ the track. Still tearing the engine down to see exactly what happened and what needs fixed, but the leading theory right now is bad knock which led to other bad things happening.

I have had zero issues with the engine, tune, knock etc. running on the track before. Over the winter/spring the only thing I did was- new valvesprings (single beehive to BTR duals), new NGK TR6 spark plugs (had TR55 before) and got a retune on the dyno. I have a FlashScan V2, but this tune was done on the dyno with a shop.

Overall mods I have a 2003 Corvette C5 Z06 w/ mild 226/230 .604/.604 113 EPS cam, AI ported 243 heads (stock valves), headers/xpipe.

Anyone see any red flags in the tune? I see some stuff that I think may be suspect, but I want to hear the real experts' thoughts. I have also included a stock tune file in the zip file for easy comparison/see what has been changed vs going thru table by table. They are EFIlive tune files.

Thanks guys.

[joecar]

I'll take a look later tonite.

What damage did your engine suffer...?

[aaronc7]

I have not pulled the heads off yet, I think that will tell the whole story. Will be having that done soon.

In the meantime the facts are
-tapping noise at idle, sounds like top end. goes away if engine rpm increased above 1500 rpm
-nothing obviously wrong with valve springs, valve tips, rocker arms, pushrods (pulled valvecovers off)
-cylinder 7 spark plug bent 'back' a few mm
-cylinder 7 leakdown 14psi when pressurized to 75psi. seems to be leaking into cooling system and crankcase (but not hugely more than other cylinders).
-oil has slightly murky appearance, more evidence of water getting into oil.

my leading theory right now for root cause is the tune, but really won't know more until I get the heads off.

Thanks for the help!

[Tinbender59]

sounds like a head gasket???

[aaronc7]

Yes I think head gasket would be best case scenario, assuming nothing else major. Worst case cracked piston or cylinder wall. Need to ID the source of the tapping as well. Hopefully only a lifter or something.

[joecar]

#7 sounds worse than just head gasket.

[joecar]

I looked over your tune, it seems ok, VE is a bit bumpy.

[aaronc7]

Thank you sir, I appreciate the feedback. Yes I think the tuner was just lazy with regards to the VE. My main concern was some of the knock tables-- tables like Knock fast attack rate values were halved and knock limit in/out PE mode table significantly reduced compared to stock values.

[joecar]

I'll look closer at the differences from stock in your tune.

[Tre-Cool]

When you say track are you talking circuit or strip?

If you have spark plug damage, something has broken off and hit it. water alone wont do that.

I'm thinking piston to valve clearance has changed with the new springs? Was clearance or preload checked with the new springs fitted just in case?

Also curious to know was the dyno a load bearing / eddy current style one or inertia?

[aaronc7]

2.75 mile road course. I never get below 50 mph so I don't think IAT was too bad, but I did not log IAT. I use a lap timer with Bluetooth OBD dongle, so I only had limited params logged: rpm, speed, throttle. I kept an eye on digital readout of oil temp, never got above 260. Coolant I was looking at the analog gauge, it never hit 220, I would guess 210 max. I can verify that there was no over rev or anything though from the obd log. In the video there is no audible 'oh shit' moment, my only indication was the tapping at idle below 1500 rpm when I came back into the pits.

I didn't re-check preload or anything with springs..was just a straight swap. I did the spring swap and re tune back in February or something of 2016... so I had been running this setup for quite a while, only street driving though until this last event.

It was on an inertia dyno/dynojet.

[aaronc7]

Finally got the car to a shop, they will be borescoping it today, then pulling the heads off/further inspection soon.

I did plug in the FlashScan to the car and saw that GM.ASPARK is at 100%. My idea was this would show me a 'historical knock' record of sorts. It's my understanding that 100% is high octane table exclusively, which would indicate I was not knocking on the track significantly over the session or anything... correct?

[aaronc7]

Not surprisingly, cyl 7 piston cracked in the typical spot. I had water getting into oil, but head gasket looked OK....so almost certainly there is a crack in the block. Engine being pulled today.

http://i.imgur.com/SUJPyjnh.jpg
http://i.imgur.com/1xQrvn9h.jpg

[joecar]

#7 chamber looks steam-cleaned.

[joecar]

GM.ASPARK can return to 100% fairly quickly depending on the recovery rate in the tune.

[joecar]

#7 piston does not show other evidence of knock.

[aaronc7]

Thanks Joe, helpful as always- I appreciate it.

I don't have a pic handy, but the spark plug did not really show signs of knock either. Just too much heat in general perhaps, or maybe water leaking in was the root cause? Coolant temp on the gauge read under 220, I'd guess around 210. There was no audible noise or indication of failure on the track, but it was 90+ outside, humid and lots of long straights on the track-- I get up to around 145 on the main straight.

[Tre-Cool]

After using an inertia dyno to tune some cars in the Philippines, I'm not sure how anyone could ever get a tune close to spot on for fueling requirements. There just is not enough load/time held at rpm through the range to sample enough consistent data, especially if you have a slow wideband/sample rate.

That ring gap looks like it's definitely closed up too. Bugger

[joecar]

+1 without sufficient engine load, it is just about impossible to get sufficient steady-state data hit-counts in each RPM/MAP cell.


The other problem is that each cylinder fuels differently than it's brothers... and LS #7 is known to run a little leaner.

[aaronc7]

Little follow up. Car is back up and running now with a forged rod/pistons LS1/5.7.

Here's some pics of the damage. I also noticed that on cylinder 7, the piston/rod wrist pin connection is very stiff. You can move the piston on the rod, but it takes quite a bit of effort. All bearings looked fine, bummer the block is basically toast from a cracked liner.

So far my plan includes having a more conservative tune for the track... Looking for any other ways to increase cooling/coolant flow to the rear cylinders.

http://i.imgur.com/9yZEGBFh.jpg
http://i.imgur.com/kTISTjBh.jpg
http://i.imgur.com/HFSGku3h.jpg
http://i.imgur.com/zPG2t07h.jpg
http://i.imgur.com/kiKP8y1h.jpg
http://i.imgur.com/uVk7RTzh.jpg
http://i.imgur.com/z3gs7F6h.jpg
http://i.imgur.com/yAjxPQSh.jpg
http://i.imgur.com/oRnGM4Uh.jpg

[joecar]

Rod/piston being stiff: is this a cause or an effect...?

[aaronc7]

Great question, but one I am not sure about the answer. My guess is an effect

[johnv]

Perhaps add steam port vent kit for the rear of cylinder heads, a common mod for forced induction engines.
Maybe a bigger radiator and cooler thermostat.
For piece of mind go back to factory knock table settings, and maybe a bit more agressive pulling timing with IAT tables.
Forged pistons will be much more tollerant of heat and knock, and should run bigger ring gaps.