Raceboy

944S has 6800 rpm redline from the factory and the rods should be even stronger on 951?

blown 944

One thing to consider is timing at peak torque. I remember that you were working with the ignituib timing in the past, so it may have damaged the rod and bearing. I have seen rods let go due to aggressive timing too early in boost.

ehall

Sorry to hear this, Doug. What's the story with the K27?

Tiger03447

DANG DOUG! that's terrible! I am so sorry for your loss..I know about all the time, sweat, and trouble that you've had...Your story has had me rethink about my rod bolts and nuts..TIME for ARP while my engine is apart I was going to put in new rod nuts anyway but I think I'll do the ARP thing now...Thanks,TIGER 03447 AGAIN. so sorry to hear this..

Dougs951S

Sid, always a good point to consider, but my timing is actually pretty conservative and I'm on E85, I also monitor knock and I wasnt getting any. I can post my timing table up for scrutiny.


I did some more exploring today folks, and I have good news and bad news. The good news is, I didn't blow up my own engine. The failure appears to have nothing to do with my tune. The bad news is, it appears that for guys making some real power on stock rods like I was, they are a ticking time bomb. Turns out, the rod nuts did indeed back out (I think) and I lost the entire big end on rod #1, which took out the whole block. Feast your eyes on the carnage, and tell me what you guys make of this...The entire big end is just gone...Also it turns out now that I have it torn down, the piston did not in fact make an exit at all. The hole in the pan was from the big end taking flight. You can see the hole in the block behind the rod. I do not suspect an overrev has anything to do with this, before the car was megasquirted, it ran a factory redline. After squirting, yes technically the redline is 6800 but it only saw that a few times, the torque is dropping off by then because I'm running a stock intake and the car almost always lived below 6200.





and my timing table





#1 rod bearing ate ****...I don't know what any of this means, experts please chime in and tell me why this exploded while I was in vacuum cruising on the highway, and why it gave me absolutely no warning. I dont want this happening to the next motor. With the crank still in the car, I can't tell if that surface on the journal is just super scored up crank material, or welded on bearing material. I suspect the latter because there isnt a bearing present on the journal, and the bearing shells are somewhere on the road side with the rod big end. Whatever it is, I can't remove it.


By the way if anyone cares, I am still in a 944. When the 951 blew up, I brushed the dust off my N/A that hadn't been driven in 4 years, and I'm pleased to say it did well today on its first voyage out. It will make a fine DD until the 951 is back together.

Thanks everyone.

Raceboy

Most of the rod bolt failures occur during deceleration becase that is when the tensile loads are the highest (no combustion pressure decelerating the piston in TDC).

If the nuts back off, then either the nuts had too little torque applied or they were defective. It's got nothing to do with rod itself, just the matter of rod bolts and nuts.

Dougs951S

I dont know if the nuts backed off or not, if they were not torqued properly, that's on porsche (or just time and fatigue, really) because that bottom end was never opened up. I do not know what happened because the whole rod end is missing. From the bit remaining, it looks like the bolts got sheared off. I was hoping someone could shed some light. I've never seen a rod failure like this ever. I dont know if it was the nuts, a bolt failure, the bearing seizing for whatever reason, the rod just breaking, or something else.

Seeing as how the rod is intact above the big end, I am thinking it's nut/bolt related. However, the marks on the journal/bearing material welded to the journal are making me unsure. It also makes sense that it was a hardware failure since it gave no warning, I would think if I spun a bearing and let it run long enough to weld to the crank and then blow, I would have heard something and had some warning. There was no warning at all...it just let go. I also think I would have heard something if a nut backed off. I personally am currently thinking I broke a rod bolt.

Thom

What was your level of load (or vacuum) when it happened? Are you running the stock camshaft?

V2Rocket

you say the bottom ends never been opened since factory?
i have a feeling you may crack the case open and find cast NA-type rods inside this engine.

forged rods can break but they bend pretty far first, cast will shear off like that much quicker.

refresh951

A while back a Honda oiling engineer did some preliminary analysis on the 944 oiing system and proposed that the system cavitates on the input side. IIRC his preliminary analysis showed cavitation starts right before 6K. This coupled with other factors (Glyco rod bearings, thin oil, wrong oil, heavy internals, oil aeration, bad tunes, etc.) have killed more engines than can be counted. I have no absolute proof other than empirical evidence. This coupled with the fact that if you run the factory turbo intake manifold, there is ABSOLUTELY no reason to run above 6400 (really more like 6K) as power will drop off anyway.

xschop

Heat cycling fatigue coupled with high rpm. Time for some new forged rods and an open-casket burial for that block.

Dougs951S

its an original 86 turbo block. it better have forged rods...

Dougs951S

I maybe 12-14" vacuum in the manifold when it let go, not a stock camshaft. quite a bit hotter. I was really barely on the throttle when it popped. ~2800 rpm.

Dave W.

Sorry to hear the bad news. Is there any discoloration or blueing on the remaining rod?
Good luck on your next engine, it sounds like it's going to be strong!

ibkevin

That sucks to hear, lots of work involved there.

One of the first things I did on my new-to-me '87 was new rod bearings. Good on me because I've kept a challenging pace with 911's, 928's and altitude with no problems.