Six_Shooter's money pit and time vampire... v.240Z

[34blazer]

If Turbo Buicks can push a 3600 lb car well into the 10's with a stock long block, or even champion irons (which flow significantly less then LX9 heads) and get into 9's, then I think there should be no problem with the LX9 making good power to get those same numbers in a chassis that weighs far less.

Bigcheese and I were talking about options for a custom billet cam for the VVT, but most grinders won't touch it for less than a Grand, and thats a big IF, they want to even try it.

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I don't see any signs that detonation had caused this, there's no pitting or silver flakes that would indicate that was a problem.

I've considered going LZ9, and I can get as many complete as I want for about $225 CDN each, but I'd still be rebuilding it with aftermarket parts, because I'm just at that point I don't want to screw with stock internals anymore. I've read about and kept my eyes on a few LZ9 swaps and builds, and it just seems that the cam is a real issue. Going to bearing spacers and a standard cam just seems like leaving something out. Like there's something being left on the table. Like getting a piece of apple pie on your plate, and even on your fork and then not eating it. I don't want to mess with VVT right now, even though there's a few options to control it (VVTuner, MS3X, etc), there seems to be some debate on exactly how it works, and I really don't want to spend time on figuring that out right now. There doesn't seem to be much improvement available in the heads. I'd have to completely rework the belt drive and a few other challenges that would likely come up. Overall I just don't see any appreciable reason to go to an LZ9 over using an LX9.

The LX9 will have plenty of potential for what I want to do. It already has more power than I can really use, but my plan is for more... along with plenty of suspension changes to actually use it. If I ever need to go bigger than the LX9, I don't think just a displacement increase will do it, I think it'll have to grow by a rather large cylinder count as well. I have access to the engine I speak of, with a couple hair dryers hanging off of it, but I don't have the $10k or so it will cost me to get it in my hands, before even fitting it to the car. That $10k is a SMOKING deal too. I know of only one other 240Z with that engine.

So, I'm sticking with my plan of going with a built bottom end to handle the power I want to make, both peak (dyno queen numbers) and everyday pound on it power.

I had bought a used 3.4 iron head pushrod engine long ago that had been rebuilt. No idea on the pistons used, or ring gap. I boosted that baby with 10-12 lbs of boost and a 100 shot on top of it. never had a ringland issue in that engine. Bent 2 rods though. 500+tq at the crank. Detonation will destroy ringlands fast. if you posted pics of tht I haven't looked at them yet so sorry if it wasn't detonation.

I say move to a lz4 or lz9 engine instead of a rebuild. Mars seems to have good luck with his on about 550-600 hp on stock internals. you already have a cam too, that you can swap into the 3900 if you wanted. plus the lz4/9's are now pretty cheap, and you can get them with low to medium miles for under $800. Thats the cost of forged pistons for a 3400.

Again...not enough top ring gap. Hyper pistons don't use normal piston ring gap rules, and boosted hypers even less so.

I don't think the lower part of the piston failed first, because you have two pistons with ringland damage, of the same type. I have never seen a piston break the top ringland from being slapped against the head-the top ring will just not allow that much compression there.

To be sure, you'll want to go over all the other pistons with a picky eye...look for cracked ringlands on otherwise undamaged cylinders.

Try to get photos of the ring gap faces...if they are shiny, they have butted together. If the ring gap was big enough, you shouldn't see any shiny or fretted marks on them

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It's MORE than enough ring gap, think what you want, but the ring gap was plenty. I have one piston with ring land damage. The one that I mentioned in my previous post was a different set and different part of the piston and also had stock ring gap when I ran them. Considering that the contact pattern in the head shows a clear indication that the ENTIRE outer ring (top) of the piston tells me that it didn't fail first. That the entire pistons was pushed into the head, and not parts broken off that got caught.

I've ran hyperutectic pistons with less ring gap and similar levels of boost on similar bore engines and never had a ring pinch. I don't see how the piston material effects how the ring reacts to heat. *facepalm*

I'm replacing the rods and pistons with aftermarket parts now anyway.

[Xnke]

Again...not enough top ring gap. Hyper pistons don't use normal piston ring gap rules, and boosted hypers even less so.

I don't think the lower part of the piston failed first, because you have two pistons with ringland damage, of the same type. I have never seen a piston break the top ringland from being slapped against the head-the top ring will just not allow that much compression there.

To be sure, you'll want to go over all the other pistons with a picky eye...look for cracked ringlands on otherwise undamaged cylinders.

Try to get photos of the ring gap faces...if they are shiny, they have butted together. If the ring gap was big enough, you shouldn't see any shiny or fretted marks on them

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Not enough ring gap, looks like. Detonation severe enough to break off that much of the ring land would show up in you cylinder head combustion chambers, or on the undamaged area of the piston as little pockmarks. What did you open the rings up to?

Keep in mind hypereutectic pistons require a much larger (20 to 30 percent, in many cases) top ring gap compared to a non-hypereutectic piston. The top rings on my 3.4L are gapped at 0.028", compared to 0.018" that would normally be fitted to that engine. All because I'm running 3400 hypereutectic pistons.

Ring gap was around .022" IIRC, I'll have to go back over the formulas again (or measure them) but they were on the large side of what my engine builder friend recommended and what I found from other sources, I don't see this as a ring gap issue, I just see it as the piston getting pounded on for months well beyond it's designed stress limits. With how there is literally nothing of the skirt left on #4 I would have to think that the skirt/bottom of the piston failed first and then because the rod pulled out of the piston, when it came back up it pushed what was left into the head causing the ring land to break, and then causing the rod to fail, which just snowballed from there.

I've only had a couple of times when I got some detonation, because I tried something different with the tune, and immediately went back to what I was running previously.

Good thoughts.

This (green) block was the one that had the headgasket blow, I swapped bottom ends at the time since I had another bottom end, and really didn't know the history of the one that was in the car.

The head gasket blew on #3 and while that rod did suffer damage from this, it was an innocent casualty from what I've been able to determine.

The pistons in the green block were not original to the block. After I had the issue with the ignition module going haywire and spinning the engine backwards, I swapped it out for the green bottom end, when it also got a cam upgrade and new bearings, since there was a sound while cranking I just didn't like, but couldn't find the source of it. Maybe that source was piston #4, but I didn't see anything when I looked them over. I didn't want to use these pistons, but I found one piston from the original set for this block with a broken ring land between the top and middle ring, so I swapped all of the pistons.

The car has been a little rich under boost for the last few weeks, because I scaled the fueling parameters to have a bit more head room in the VE table, where I was maxing out the VE. I was getting it closer to where I wanted, just didn't get it there. Every time I've pulled plugs on this engine they always look decent to slightly rich, depending on how long after pounding on it I shut it off.

[Xnke]

Not enough ring gap, looks like. Detonation severe enough to break off that much of the ring land would show up in you cylinder head combustion chambers, or on the undamaged area of the piston as little pockmarks. What did you open the rings up to?

Keep in mind hypereutectic pistons require a much larger (20 to 30 percent, in many cases) top ring gap compared to a non-hypereutectic piston. The top rings on my 3.4L are gapped at 0.028", compared to 0.018" that would normally be fitted to that engine. All because I'm running 3400 hypereutectic pistons.

[34blazer]

I ventured back to the beginning of the thread, right around the time where it cooked a head gasket. Looks like the same cylinder? May have slightly uneven airflow distribution with that upper intake. Have any old spark plugs, or the current ones to peek at? Im curious to see where the AFR's were at just before it went kablooey.

[Superdave]

Nice Carnage!

[34blazer]

I'm interested in what you come up with for pistons/connecting rods

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Usually hit 6300 to 6400 RPM. A little lower in first, I think I had the shift light set to 6000 RPM for first gear. I have taken it close to 7000 RPM a few times.

I only think the rods failed because the piston failed first from what it looks like to me. #3 was definitely collateral damage.

I've already talked to my engine builder friend, about the road to rebuild, and I'm going to build this for my end goals, with aftermarket rods and custom pistons.

[34blazer]

Oh ok. I'm worried about the strength of the rods, even though they are PM, they seem kinda puny to me. Where did you shift at?

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The ring gaps were opened when I had it apart in the summer.

[34blazer]

Nice. Were the rings filed at all or did you leave those alone?

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