What is the main cause of engine failure?

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AutoEuphoria

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'08 CPW Mazdaspeed 3
I'm basically done modifying my car at this point, but I want to keep it running until I can sell it. I've been worried lately hearing all the reports of blown engines, and I'm trying to figure out what I can do to take the chances of that happening down to almost nothing. I know that's hard with a modified car, but I figured there has to be one or two main factors causing these engines to let go.

So is it too much boost? Going WOT at too low of an RPM in higher gears (high load)? High revs? Bad tune?

I have a catless DP and MP, FMIC, CAI+turbo inlet, upgraded CDFP, and a Cobb AP (AFRs in the low 11s at WOT and boost set to 16psi via ATR)

I just want to be able to enjoy this car without worrying it's going to blow up...because at this point I'm through putting money into it and I just want to pay it off as quickly as possible...an engine build would obviously screw that idea up pretty good.

So, what's causing these things to let go? Is it as bad (happen as often) as everyone makes it seem like?
 
If your tune is good than you don't have much to worry about. Just watch your KR and avoid getting on the gas at low rpm's. I think thats why most people end up bending rods (blowing down the road). They get into boost at under 3K rpm which isn't the best idea.
 
Yeah, I've tried to make my tune as conservative as possible, and I definitely have been mindful to not put the car under a lot of load. Thanks for the response, and for clearing up my suspicions
 
I keep hearing the theory about boost under 3k rpm causing a boom and it sounds good, but if your stock I don't see how it would have any effect. If this was the case, then cx-7's would be blowing like crazy, since the same engine is in there, and being a crossover SUV of not insignificant weight, you KNOW they are hitting boost consistently at low rpm.
 
CX-7 had automatic transmission, so they will downshift if applying throttle and load at low RPM. So that could help prove this theory...
But problem is that it seems that CX-7 also have problems (I have no real information on that, only read it here).
 
CX7s are lower HP spec with a smaller turbo and a, let's be generous a, "more mature" crowd of owners. Anything made by man has the faults of man represented in it in some way. Is it possible there are some faulty engines out there? Yup.

However, I go right back to my contention before. We've heard so much bulls*** about what's "wrong" with these engines. You look deeper into individual cases and there's ALOT, and I mean most, that are owner-induced in some critical way.

Let me review *some* of the suspected causes of engine failure over the last year or so:

Pinched rings, PCV induced oil hydrolock, piston siezing, rod fatigue, rod design/quality, not enough WOT pounding, KR, batch-production problems, No tune, Pro tune, Cobb AP issues, Standback issues, fuel injector spray pattern, MAF messups, &c., &c, &c.

Do you really think a Ward's Ten Best engine twice, found in probably millions of Mazdas, that has enough strength to be used as a basis for an endurance racing engine (MZR-R) has this many "design flaws" and hasn't bankrupted the company in Toyota-sized recalls? There's a common element here and...I'm no fanboi but, I don't think it's the engine.

People are such twanks. I'll give you another example. I raced an 88 5.0 Mustang with every power in the book for 13 years on the stock drivetrain. "Everyone" bitched and moaned about the glass T5 I had, how it was "weak", when they were putting out 100+ hp over stock(?!) I mean WTF, no s*** you find stock equipment letting go at that point but that didn't sink in. I ran that stock '88 T5 at the dragstrip, on slicks, with traction aids for that entire period and I sold the car still working perfectly. What I didn't do for that 13 years was flat-foot shift that T5, which was the owner-induced failure mode and, funny, she held up.
 
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Super Unique said:
I keep hearing the theory about boost under 3k rpm causing a boom and it sounds good, but if your stock I don't see how it would have any effect. If this was the case, then cx-7's would be blowing like crazy, since the same engine is in there, and being a crossover SUV of not insignificant weight, you KNOW they are hitting boost consistently at low rpm.
Click to expand...

CX7's have different turbo's designs that move the powerband even lower than the speed3/6. Also as someone mentioned they are auto which prevents hard accel at low rpm.
 
Well, if the "enemy" was load at low rpms, the CX7s weight, it's even more pinner turbo and the fact it's pushing a torque converter fluid coupling around would be blowing these things to smithereens. Autos don't "prevent" hard acceleration at low rpms, quite the opposite, they load up a drivetrain (thus creating boost) alot more than a manual does. Frankly, that's what makes them well-suited to a turbo application, at least in the low-speed acceleration department. You could never run a gear in a stick that can match the multiplication of a torque converter, without running out first before you passed the crosswalk. You can just choose to rev up manual and drop the clutch. Those decisions are out of your hands with an auto.
 
Darth Vader said:
Well, if the "enemy" was load at low rpms, the CX7s weight, it's even more pinner turbo and the fact it's pushing a torque converter fluid coupling around would be blowing these things to smithereens. Autos don't "prevent" hard acceleration at low rpms, quite the opposite, they load up a drivetrain (thus creating boost) alot more than a manual does. Frankly, that's what makes them well-suited to a turbo application, at least in the low-speed acceleration department. You could never run a gear in a stick that can match the multiplication of a torque converter, without running out first before you passed the crosswalk. You can just choose to rev up manual and drop the clutch. Those decisions are out of your hands with an auto.
Click to expand...


The cx7 has less power. A powerband lower in the rpm range. More mature drivers. Aren't modded like speed 3/6's . . .

You don't see many stock speeds blowing either. Its mostly the modded ones with drivers who don't take precautions. Especially when the untuned tq curve is in the perfect spot to bend a rod. It has a spike around 2800-3000 which is right before the turbo starts spooling. So people hit WOT too early and the tq kills their rods. Then they end up blowing later and don't know wtf went wrong.
 
I'm not sure you're actually reading my posts. It's difficult to see how we're saying anything substantively different.

The only difference in our arguments is perhaps you are sure about the mechanical failure mode that's in play at blowup and I'm not convinced the evidence supports that certainty. The blowup failure mode concentration here and elsewhere misses the point. As to root cause, you seem to imply the owners are the problem, same as I do.
 
What they "look like" is not relevant. What they are like is. I've yet to see anyone definitively take these rods and stress-test them to destruction, then match that data with measured forces in the MZR engine.

There's been some home-made attempts at diagnosis but the degree of, let's just say, speculation, is way beyond acceptable for drawing real conclusions.

I'm trying not to be drawn into the (nailbyt) over this. Having a modified car is a risk, no question. I try to minimise the risks by being smart and not pushing the envelope too far. Get greedy, pay for it the hard way, that's what 25+ years of racing and rodding has taught me.
 
Wasn't contradicting what you were saying darth. Just furthering your point.

There is a thread on "other" forums with pics of the MZR rods compared to wrx rods (i think, might have been evo). They weren't inferior.
 
Darth Vader said:
the owner....
Click to expand...

Darth Vader said:
. You look deeper into individual cases and there's ALOT, and I mean most, that are owner-induced in some critical way.
Click to expand...

correct-o-mundo. it's one of those scenarios that's like this: engines that are blown up are modded, but not all modded engines blow up

you're gonna be hard pressed to find a completely stock engine that has had a catestrophic failure like a "blow up". and by mod this includes anything that WAS NOT PART OF THE CAR FROM THE GET-GO.

this point is arguable all day long. someone says that a good tune will prevent failuter. on both ends of the spectrum you will have a car that will have safe AFRs (probably the most significant factor in quick engine failure) but more power puts more stress on the internals anyway. and a car designed and produced from the factory is rarely ever calculated to deal with more power from owner add-ons. i say "rarely" because there are some cases of components that can indeed handle more power. like for instance a GM crankshaft used in many V8 models that is forged and can handle up to 500hp, but put in low hp models because it's cheap to produce one thing

all warranty related issues aside, if you would like to modify your car i suggest using mazdaspeed parts. there's a cai, cbe, suspension, and wheels all offered for this car from mazda. they have been tested and approved by mazda.

that being said the term "pay to play" comes to mind. and if you want to do something the right way the first time you had better have the money to do it. there is only 1 limit to the amount of hp you can have out of any given motor, and that is $$$$$$$$$
 
Gotcha, coyfish, no offense intended or taken.

Yeah, I've seen that thread. Good example of the "speculation" I'm talking about. This rod *looks* thicker here, therefore it must be stronger, type of thinking.

What it's made of, how it's made, how it's used (stroke, piston speed, crankshaft throw, piston weight, &c., &c., &c.) are critically important, making a side-by-each picture comparison invalid.


...and no, it doesn't *look like* detonation is the culprit....You'd be seeing more piston failures or, at least significant damage to the crown and lands, if that was the case.
 
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