Took the car out for a drive at the usual 11psi/12* of timing and all went well. Hit the 6600 rev limiter but all was OK (I think). I then cranked the boost controller to 16psi and it felt real good but then heard a consistent tapping afterwards. Limped back home and took the pan off and found bent rods. No metal in the oil or filter at all, oil pressure was where it was before. These are the floating style rods - suppose to be stronger. I'm assuming I heard the pistons hitting the crank or block. Haven't got the the heads off yet, but wanted to get some input. I thought I was pretty safe with only 12* of timing but maybe 16psi is too much with 92 octane and 50/50 water injection.

Here's what the timing/boost/rpm curve looks like - tell me if its too aggressive for pump fuel:

RPM....BOOST PSI...TIMING...AFR
3962...0.1 ..............30........13.4
4141...1.4...............28........12.8
4252...2.4...............26.5......12.4
4465...4.3...............22.7......12.2
4531...5.0...............20.9......11.8
4725...7.7...............16.1......11.6
5062...12.8..............12.0......11.6
5229...16.0..............12.0......11.5


Max rpm on that pull was only 5300. I did pull 470lbs/hr of fuel on that run + an additional 10% meth/water. Did I just make too much power, deto, too much timing???

This is a 04 LQ9 with an LS6 cam and rings opened-up. I will try and get the heads off tonight. No debris on plugs at all.

 

Typically, the lq9 is a higher compression than an lq4 in stock form. That being said, I think the boosted timing curve should be a little more conservative. Looks like youre running a total of roughly 30 degrees at 100kpa which seems a little high for an ls based engine. So if we started off high and you're pulling timing from there, it's going to be high everywhere. Seems to me you're on the ragged edge between the timing and boost and it caught up to you. Maybe a touch lean too. These ideas are just my opinion, but thats my take on what might have happened. Sorry to hear about the engine. Total bummer.

 

Got any photos Vince?
This is a bummer.
I'm not a pump gas runner. And don't know much about meth.
Do you have a log of the drive?

Ron

 

Were you data logging when you hit the rev limiter? What happens fueling wise when you hit the limiter?

 

I hydrolocked a cylinder once by leaving an injector open and it made the tapping noise once running like that, the bottom of the piston hitting the crank. Is there any blow by? It seems weird detonation could bend a rod, is there any way it hydrolocked? I have some spare gen 4 rods you can have to replace your bent ones from when I did mine, had to buy a complete set. Or clearance the bottom of the piston and run it as is

 

I did datalog this run, that where I got the rpm/boost/timing/afr figures that I listed from. Fuel pressure never dipped and was where it supposed to be - 43psi base + the boost reference.

Took the heads off. Heads, pistons, bores, bearings are all PERFECT! No signs of distress at all. Probably 5 rods are bent. Engine ran fine with the bent rods.
If it wasnt for the noise I wouldn't of known there was an issue.






I've read plenty of posts where folks ran n/a timing up until say 7psi and then dumped it all. I should of paid closer attention to what fuel was being used. But being that everything looks perfect, I can only assume too much timing at peak tq maybe???

PS - cast pistons are strong huh

 

Don't think it hydrolocked? I could see if one rod was bent but there's multiple rods bent in this case. No blow-by at all.

I'm going to replace all of them b/c the ones that dont appear to be bent just may be slightly. Is there a way to check for straightness? I'm wondering about the crank and the piston pins too.

 

That blowsss.... What efi you using? Any audible knock? It had to have some detonation.

 

Yeah, they can be checked. Either check em or replace em. The littlest bit can cause bearings to spin and rods to break. Have the crank checked too, but the pins, I doubt they'd need it.

 

whats the weight of the car?

 

What 1969x11 said: what happens to the fuel when you hit the limiter? Water and meth continue to flow? Water is hard to compress sorry your having trouble. I can't see that timing hurting anything.

 

Holley HP. I never heard any knock, knock sensors are activated however. Again pistons, cylinders, heads and plugs are perfect and not a spec on them.

Any idea how and who can check cranks out?

Its a 96 Stang, my guess is 3500 with me in it??

Not sure. Only on the rev limiter for .004 seconds, that's it. I would assume those things keep flowing or else the engine could really be damaged.

 

Bummer. I just bent a set as well. Around 20psi but I was on the limiter awhile through the traps on a pass. Pretty sure that is when mine bent but hard to be certain.

 

The GM ECM cuts fuel on the limiter.

But then, we use two steps which is a low rpm limiter, and it cuts spark while we sit there bending rods, I mean building boost. :-)

Obviously a bit different load on the engine.

You sure it didn't boost spike?
Maybe some time prior?
I'm thinking maybe something happened on an earlier drive, like when you thought the oil pressure shifted a bit?
Maybe this drive just finished them off?

 

16psi was the highest this engine has ever been along with the lowest timing at 12*. Boost curves were all very smooth. I was looking for SOMETHING that would indicate deto or something otherwise but there isn't anything else in terms of damage. Bearings (rod) look perfect and I'll reuse them. It appears the driver's side bank have all bent rods which makes sense b/c I ran a compression test before breaking it down and the drivers were all 160psi vs the pass side at 190 psi. Only thing I can think of is the rev limiter, but there's guys riding the limiter harder than me for perhaps the last 1/3 of a 1/4 mile run.

This was the last run where I think it happened:

 

To much boost on pump fuel with that compression.

 

Thanks for chiming in Hellbent. What would you limit boost to on pump fuel with this engine? Does this look like deto to you?

What I dont u/s is how guys with LQ4's which have apprx .5 less compression are running 16+ with pump fuel.

 

Have you verified the timing is correct? That 0° is actually TDC? You can configure in the holley if you want the rev limit to cut fuel/spark or both, although I would think detonation would cause broken ring lands/speckling in the porcelain of the plugs/ check marks on the piston... Not bent rods, but I'm no geologist

 

All bent on the same side of the engine...Strange.
As for 16#/alky. [We routinely run Buicks, [stock rods/pistons], pump 93, at 26#/alky.]
How is the fuel delivery plumbed?
Have you cut the treads off the plugs, and taken a close look down deep??
Reusing brgs that have been run in those rods is not what I'd do..Just sayin.

 

Not sure how to check the timing. I had the spark-only cut engaged. Think I'll change it to soft. But, no signs of deto. everything looks perfect.


Looks like the pass side are bent but ever so slighlty compared to the drivers side. -8 to fuel rails and -6 return, regulator after the rails, twin Holley fuel pump.

I looked at the plugs with a magnafying glass and it looks very clean.

At this point I can only assume too much timing at part throttle. Peak tq for an ls6 cam in a 6.0 is around 4500. At that rpm I had about 21* and 5psi.