Awesome Rod Failure Carnage (dialup beware) - Page 2 - Miata Turbo Forum - Boost cars, acquire cats.

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Old 02-01-2009, 01:34 AM   #21
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Wow, that's impressive carnage! Time to go forged!
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Old 02-01-2009, 01:52 AM   #22
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Wow, that's some serious carnage there. As they say, "If you're gonna go, go big." Good luck w/ the rebuild. Just out of curiosity, how many pounds were you running?
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Old 02-01-2009, 01:53 AM   #23
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All I can say is that if my engine ever blows up, it better be at least as impressive as yours.
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Old 02-01-2009, 02:24 AM   #24
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Quote:
Originally Posted by cardriverx View Post
All I can say is that if my engine ever blows up, it better be at least as impressive as yours.
If I blow it up I don't want some weaksauce crap, I want **** coming through the hood.
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Old 02-01-2009, 02:51 AM   #25
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How much boost / torque were you making?
How did you tune timing?
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Old 02-01-2009, 03:01 AM   #26
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Quote:
If you can make black marks on a straight from the time you turn out of a corner until the braking point of the next turn, then you have enough horsepower.(M. Donohue)
'99 hard top/MS/BEGI-S, GT2560/ 550cc RX7/DIY 18x12x4 FMIC/Tein springs and shocks/Hard Dog M2 with door bars/ACT HD 6-puck
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Old 02-01-2009, 05:12 AM   #27
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#4 cant be reused? Hit it with a wire wheel to smooth things out and it should be fine...

Looks like everything is going well with the build. Some pretty horrible pictures to look at. I just turned over 250 miles on my rebuilt stock internals engine, and hope to see boost soon. Hope mine doesnt end up like that.
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Old 02-01-2009, 10:34 AM   #28
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Boost was (probably) somewhere around 15-16 psi. I was tuned for 14 psi but was using open-loop EBC and it was a cold morning. That means it could have spiked higher.

See attached for my MSQ.
Attached Files
File Type: msq Bent rod map.msq (34.6 KB, 110 views)
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Old 02-01-2009, 04:17 PM   #29
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thats brutal man... all new parts too, it looks like. Should we be advised to stay away from these rods?
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Old 02-01-2009, 04:32 PM   #30
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Quote:
Originally Posted by Endat View Post
Should we be advised to stay away from these rods?
It should be noted that ZX-Tex has a '99, and while I don't think it's ever been conclusively proven in a year long double-blind study conducted by the Rand Corporation, it has long been suspected that the connecting rods used in the NB engines are somewhat weaker than the ones used in the earlier cars.

In this case, the rods that failed were stock. So yeah, avoid stock rods if you run 16 PSI on your NB.


ZX-Tex, a question for you- what's your redline set at? I ask because I'm wondering whether the initial failure mode of the rods was actually a slight plastic deformation (stretching) due to tensile stress, which weakened the rods and predisposed them to failure under compressive load.
edit: Nevermind. I see from your MSQ that it's 7,200 RPM, which seems perfectly reasonable.

Incidentally, I'm with Corky here- I wouldn't attempt to re-use the crank. You're clearly going to be purchasing a complete donor engine so why not work with the (presumably) undamaged crank that it contains?

Last edited by Joe Perez; 02-01-2009 at 04:47 PM.
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Old 02-01-2009, 04:53 PM   #31
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Quote:
Originally Posted by Joe Perez View Post
... it has long been suspected that the connecting rods used in the NB engines are somewhat weaker than the ones used in the earlier cars.
The 99's:

a) make more torque per psi than NA's, due to a better head design and due to VICS

b) have a higher compression ratio

Both factors increase compressive loads on the rods for a given amount of boost. So it may be that the rods are exactly the same as NA rods.
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Old 02-01-2009, 04:55 PM   #32
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Quote:
Originally Posted by ZX-Tex View Post
... 14 psi but was using open-loop EBC and it was a cold morning. That means it could have spiked higher.

See attached for my MSQ.
That is why you detune the map above full boost to be pig-rich and retarded, to protect the engine during overboosting.
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Old 02-01-2009, 04:56 PM   #33
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Quote:
Originally Posted by Endat View Post
thats brutal man... all new parts too, it looks like. Should we be advised to stay away from these rods?
NO the new parts I linked to above are for the motor I am about to build as a result of this failure. The DAMAGED motor is (was) an ALL STOCK INTERNALS '99 with about 90K miles on it.
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Old 02-01-2009, 05:00 PM   #34
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Quote:
Originally Posted by Joe Perez View Post
You're clearly going to be purchasing a complete donor engine so why not work with the (presumably) undamaged crank that it contains?
I assumed Corky was suggesting tongue-in-cheek that I should not reuse the #4 cylinder parts. I had another donor short block that turned out to have a badly damaged crank (spun bearing) so I need another one. I'll have this one checked out closely, which one should do with any used crank regardless. If it is not OK I'll look for another one. Same thing with the head, from which I only need the casting and cams (new valves, springs, etc.)

Last edited by ZX-Tex; 02-01-2009 at 05:16 PM.
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Old 02-01-2009, 05:06 PM   #35
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Quote:
Originally Posted by JasonC SBB View Post
That is why you detune the map above full boost to be pig-rich and retarded, to protect the engine during overboosting.
Agreed. Well I tried to do that, somewhat, just maybe (clearly) not enough. Seems though that one would have to set the table KPa row values precisely to prevent the overly rich condition and/or retarded timing from interpolating into the 'good' cells. Better yet IMO just to have some overboost margin (built motor) and/or do a better job of controlling boost (proper closed-loop EBC).

Either way, if the difference between OK and bang is only 1-2 psi then things are too close to the margin for me for a daily driver.

Plus, for any noobs who might read this, though we are throwing around psi, really the correct way to talk about this is power levels, not boost, since power varies at a given boost level depending on the turbo (and the tune).

Last edited by ZX-Tex; 02-01-2009 at 05:19 PM.
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Old 02-01-2009, 05:55 PM   #36
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The problem may be that the overboosted rows have too much timing.
Oh and that's the advantage of having adjustable MAP breakpoints.
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Old 02-01-2009, 07:26 PM   #37
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Quote:
Originally Posted by JasonC SBB View Post
The problem may be that the overboosted rows have too much timing.
Oh and that's the advantage of having adjustable MAP breakpoints.
Yeah if I understand what you are getting at I agree. Given some dyno time, and a known (desired) boost level, one could basically detune (add fuel, retard timing) the overboosted cells right at the target boost level to maintain the same torque level even if the boost goes over the target level. That would keep the engine stresses constant despite the additional boost. So for example one could set the second or third row (from the top) in the VE and spark table to 200 KPa, and raise the AFR and/or reduce timing (watching EGTs) above that.

Last edited by ZX-Tex; 02-01-2009 at 10:20 PM.
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Old 02-01-2009, 09:45 PM   #38
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How the hell do I have a band aid setup, stock motor, stock tranny, and stock diff and nothing has broken. This is also with racing and 225 tires. Every time I see these threads with bent/mutilated rod pictures I think "I'm never this lucky, I'm next"
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Old 02-01-2009, 11:07 PM   #39
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Quote:
Originally Posted by JasonC SBB View Post
Both factors increase compressive loads on the rods for a given amount of boost. So it may be that the rods are exactly the same as NA rods.
You know, despite the relative ease of doing so, I never bothered to check this out.

And you're correct. In the Mazda parts catalog, the P/N for the '99 and '01-'02 connecting rod assembly is B6S7-11-210E, which is the same number listed for the '94-'97. The 1.6 cars show B6S7-11-210D, but I can't find any info on whether the E rev superseded the D, or whether they're different assemblies.

So that's interesting. While the NBs do have entirely different pistons, the rods are the same.
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Quote:
Originally Posted by ZX-Tex View Post
I assumed Corky was suggesting tongue-in-cheek that I should not reuse the #4 cylinder parts.
He may have been. I just know that if it were my engine, I wouldn't feel very keen about doing a build with nice, shiny H-beam rods, forged pistons, etc., and yet re-using a crankshaft that's had a broken rod flailing around on it, punched a couple of holes through the cast-iron block, and smashed into something with sufficient force to put gouges into the counterweight end.
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Old 02-01-2009, 11:11 PM   #40
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Yeah, that old crank is probably saveable, but I still wouldn't. It could have a spec of twist thrown into it which a machine shop can detect. But if any of the bearing surfaces were damaged, or out of spec, etc, it will need to be turned. Better to find a "perfect" crank that doesn't need to be turned as to keep the current OD of the bearing surfaces.
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