Tuning my DR750s on Chrome

[Chris@Rvengeperformance]

Okay to summarize, he is what I think happened.

1)I had what I believe was a lean misfire around 4000 and 20-22 PSI. The wideband read lean.
2)I added fuel there AND gapped the plugs down.
3)Misfire seemed cured
4)ran into the misfire doing full 3rd gear pulls.
5)reduced boost
6)misfire gone, but was running mid 10s afr around 4000-4500.
7)leaned it out
8)made decent power
9)blew up the next day
10)???
11)anti profit?

So, what really happened is it was a rich misfire I misread by the lean wideband, which was caused by a misfire. I made it richer, but gapped the plugs down and the ignition was strong enough to fight it, causing unknown to me pre-ignition, beating out the bearings. By the time the tune was fixed the damage was done. If I had recognized things for what they were I could've fixed the tune and replaced the bearings and probably been okay.

All of this was amplified by the old stock shotblock making a lot of low end torque IMHO and the fact that e85 is bad for pre-ignition.

[green-lantern]

hmm, some strange info from blackstone labs:

http://www.chrisbehnken.com/files/95..._TT-061613.pdf

Looks like fuel contamination was not an issue at all and the oil did not break down. The strange thing is they detected elements of coolant. I didn't see any evidence of coolant in the oil or oil in the coolant. I also didn't see any headgasket damage that was obvious. The garage wasn't the cleanest place in the world when I drained that oil out of the oil cooler into the sample container, so it is possible some antifreeze got in there, but it makes you think.

I'm glad that the fuel content was low.

Have you had the head lift fix done? From what I understand they can leak and you pretty much don't even know it except for maybe an abnormal amount of coolant in the overflow bottle. The metal gaskets can't help much when trying to chase down a small leak ether.

[Chris@Rvengeperformance]

Have you had the head lift fix done? From what I understand they can leak and you pretty much don't even know it except for maybe an abnormal amount of coolant in the overflow bottle. The metal gaskets can't help much when trying to chase down a small leak ether.

no, waiting to hear back from ray on things and when he has a chance I'll ask him if I should do it while the heads are there.

[Chris@Rvengeperformance]

All of that still doesn't explain why my car ran so bad on the surface discharge plugs, so I am also not ruling out something wrong with the ignition system.

[green-lantern]

no, waiting to hear back from ray on things and when he has a chance I'll ask him if I should do it while the heads are there.

If the heads are up there I'd definitely do it.

[familyMAN]

Running that rich on e85 contaminates the oil very quickly as well which could cause abnormally fast bearing wear.

[Chris@Rvengeperformance]

Running that rich on e85 contaminates the oil very quickly as well which could cause abnormally fast bearing wear.

blackstore report says < .5% fuel contamination. was not the problem in my particular case.

[CoopKill]

Nice to have a definitive answer.

This could also shed light on others that have had issues such as Todd's car. Even though he was spraying 1000cc water/meth vs e85, would it not stand to reason that if rich in the same area it could cause preignition? Is water/meth susceptible to the same preignition as e85?

What makes sense to me is stressing the stock internals with the amount of torque would most likely of been fine, but with the addition of such a violent event this pushed them over the edge. There have/are others making similar/more on stock internals with no catastrophe, are there not?

[Chris@Rvengeperformance]

Really a theory still, but it is the best I have got. I would assume Todd's car did something similar, which explains the uselessness of the knock sensor at that point. With the alcohol the pistons run cooler, so it just doesn't always break ring lands like we are used to. The more alcohol the more you are just shifting the load from the pistons to the bearings.

Matt and I am sure some others has made 600 torque on a stock shortblock, but I am sure that was under a near perfect tune and normal race gas. Even at only 500 torque we are at near 80% of the torque people have made with the stock block, like you said it wouldn't take a lot to push it over the edge at that point.

I wouldn't be surprised if something similar caused familyman's stock 6G74 explosion he had.

[Chris@Rvengeperformance]

I seriously never realized that misfires were so hard on bearings, it just isn't talked about a lot and I'm sure not a pro at this. I hope someone can avoid this problem in the future due to some of the info here.

I think some of the stuff that is super obvious to pro tuners is so obvious to them they just don't talk about it or keep it as a trade secret. I can't really blame them either way.

That is one thing I really enjoyed about Trevor's build(s). You got to see every failure and the eventually fix. I think there are a lot more blown up shortblocks than people talk about generally.