Why do our engines blow up?

[SSinstaller]

Originally Posted by djuosnteisn 4drhotrod on 6club blew up a long time ago cause his boost line popped off and he boosted to like 30+ psi with a BT. He's the only other one i know of that has blown from too much boost.

He actually blew up due to ATP's shitty wastegate actuator coupled with his high efficiency L/A intercooler. He was trying to control the boost with his foot until they sent him a lower pressure wastegate actuator. It didn't work out too well for him....

[djuosnteisn]

Hmmmm, hopefully i don't become part of that club, though this morning i fee like i could have...

I've been running a 3071 for about a month now, using the restricted IWG on a stock exh mani. I've had zero creep issues in the warm/hot weather, but this morning it was like 65ish, and creep was bad.

Here's a log:


Granted i'm at 5500ft, but nonetheless, 23+ psi on a 3071 is alot, and my car seemed to love it. Hopefully i'm not tempting fate, but as it stands right now, i believe our engines are pretty damn tough and definitely agree a BT IS safer for our platform.

[SSinstaller]

Your AFR's look safe even with the creep, but you still need to get it taken care of ASAP. Any loss of control is a BIG problem..

[djuosnteisn]

Hahaha, i know. I've got a DCR mani on the way, and first thing i'll do when i get it, is weld on my 38mm tial and a dump pipe. I'm not down with out of control boost.

My point was simply that our motors are not weak at WOT w/ a BT & good tune. If it was sheer power that was killing our motors, i'd have been blown for about 6 hrs already. PT is the killer IMHO.

[devils10]

i heard ouw rods are ridiculosuly weak

[flyrevs2]

Originally Posted by devils10 i heard ouw rods are ridiculosuly weak

I heard a bunch of speculation regarding this but nothing concrete. Cox racing has examined them and feels they will hold 500 hp on a properly tuned motor. He builds lots of 4 cylinder motors with 500+ whp so he should know what he is talking about.

Where did you get your information about the weak rods?

[dphm]

It seems like when the engine blows up it throws a rod so maybe that's where we get info about weak rods. I've seen some pictures of rods snapped in half and read about how its tapered design is a flaw or something. I too would like to know why these engines are blowing up. I'm all paranoid about doing any mods to the car now.

[djuosnteisn]

That's just the thing... the mods aren't the killer. Mod all you want and rest assured your no more likely to blow up than with just a CAI and cat back.

The blow demon doesn't give a rats ass if your modded.

The fact that it's rods means it's likely one or more of the following:

- oiling issue
- heat issue
- over-stressed at such low rpms
- manufacturing flaw

I guess i should rephrase it, it seems like mods on a stock turbo can indeed be deadly, only cause it exaggerates the above possibilities. And a BT alleviates quite a few of them.

[darth vader]

Just cause a rod breaks doesn't mean the rod is weak. There are things NO rod will withstand, like hydrolock, FOD in the chamber or a siezed piston. That's not proof of weak rods; it's just a non-sequitur.

I think our engines blow up often but, not always, because punks can afford this car, beat the shit out of it, mod like they're building a IED and expect 500 horse out of the stock tune.

It's no different than when I was teen to 20-something. We blew shit up, too. I got stories, man, that'd crack you up and would sound eminently familiar to any young person today.

Here's one: My friend's rich-daddy-Supra-owning-douche-buddy raced a Chevette (???) with a 4.3 90* Buick V6 all the way into the mountains and tried so hard to beat this thing he melted down his big-buck 6 cylinder into a slag pile. That was the FIRST GEN Supra with the "cool" digital hockey-stick dash, to put a timeline on it.

[bf360]

Originally Posted by darth vader Just cause a rod breaks doesn't mean the rod is weak. There are things NO rod will withstand, like hydrolock, FOD in the chamber or a siezed piston. That's not proof of weak rods; it's just a non-sequitur. I think our engines blow up often but, not always, because punks can afford this car, beat the shit out of it, mod like they're building a IED and expect 500 horse out of the stock tune. It's no different than when I was teen to 20-something. We blew shit up, too. I got stories, man, that'd crack you up and would sound eminently familiar to any young person today. Here's one: My friend's rich-daddy-Supra-owning-douche-buddy raced a Chevette (???) with a 4.3 90* Buick V6 all the way into the mountains and tried so hard to beat this thing he melted down his big-buck 6 cylinder into a slag pile. That was the FIRST GEN Supra with the "cool" digital hockey-stick dash, to put a timeline on it.

actually most of the people that have higher hp's and have raced the shit out of them havent blown up, ie darksun, chris, whoosh

The stock tune on this car actually isnt fairly bad excpet for the p-t tune and for the top end, but im pretty sure mazda fixed a lot of the p-t problems for the 08.5 and 09

[darth vader]

Well, here's my theory on the majority of the "low rpm blowups". Leaving aside the previous- damage-delayed-let-go possibility, much the same as I stated before but, people romping on the gas pedal alot with ~2K on the clock. That is going to MASSIVELY stress the rotating assembly. This car feels like a V8 with its teeny turbo but, it ain't one and, you can't pull that shyt off and expect no consequences if you persist.

[glocK23]

Originally Posted by darth vader Well, here's my theory on the majority of the "low rpm blowups". Leaving aside the previous- damage-delayed-let-go possibility, much the same as I stated before but, people romping on the gas pedal alot with ~2K on the clock. That is going to MASSIVELY stress the rotating assembly. This car feels like a V8 with its teeny turbo but, it ain't one and, you can't pull that shyt off and expect no consequences if you persist.

Truth.

[steven88]

Originally Posted by darth vader Well, here's my theory on the majority of the "low rpm blowups". Leaving aside the previous- damage-delayed-let-go possibility, much the same as I stated before but, people romping on the gas pedal alot with ~2K on the clock. That is going to MASSIVELY stress the rotating assembly. This car feels like a V8 with its teeny turbo but, it ain't one and, you can't pull that shyt off and expect no consequences if you persist.

would 3k rpms be good enough?

[glocK23]

Safe assurance is basic, don't get full throttle below 3K rpms. Choose your gears wisely. If go light on the throttle if at all below 3000rpms.

That is my method and 24,500 miles on the odo later

[06Speed6]

Actually I am going to say that all of you are wrong, the rods are fine.

The issue is that nearly everyone blows on cyl #3, if it was a rod issue then they would all be blowing about evenly.

Being that it is almost always cyl #3, then we have to look at things that effect that cyl more than others.

The biggest hint was that it is the IM, it was recently put on a flow bench and the difference in flow between the different cylinders is enormous and cyl #3 is the highest flowing... Which also means it will run leaner than the rest.

To back that up, Whoosh/Ron ported his IM himself and probably had more even flow between the cylinders.

[djuosnteisn]

Here are flow bench numbers for the first one they did to the stocker: Stock Manifold: Runner #1: 218 CFM Runner #2: 258 CFM Runner #3: 273 CFM Runner #4: 227 CFM Total CFM: 976 Percentage of imbalance 25.23%

Might as well throw this in for context. This was the most recent flow testing data i'm aware of from JJ's new build in progress.

[FreeFlyFreak]

Originally Posted by djuosnteisn Here are flow bench numbers for the first one they did to the stocker: Stock Manifold: Runner #1: 218 CFM Runner #2: 258 CFM Runner #3: 273 CFM Runner #4: 227 CFM Total CFM: 976 Percentage of imbalance 25.23%

Woah, first time I have seen those numbers, 25% spread, no wonder the stock tune targets 9's for AFR up top

9 AFR leaned by 25% = 12

EDIT: In reality the car will be sensing an average of the cylinders with the O2 sensor, so you can figure the average shown by the wideband has a +/- 12.5% variation between the cylinders.
So a better way to think about it would be, if the wideband AFR shows 10 average for all cylinders at high rpm/cfm, the richest cylinder is around 8.75 and the leanest around 11.42

No wonder the car blows partial throttle, when its targeting at or close to stoic. I would expect the variation between cylinders to be less under lower flows, but even still. Lets say the flow variation at partial throttle is half that, +/-6%, that means @ 14.6 you are 12.77 to 16.69 richest to leanest if my calculations are correct.....

[pidass]

so now the answer to not blowing up is getting a properly flowing IM?

[Matrix311]

Originally Posted by glocK23 Why blame the factory tune? I'm running a full catless downpipe and full cp-e 3" intake/inlet at over 24,000 miles and I haven't had a single problem with the stock intake and fuel pump. None whatsoever.

i'm exactly like this guy. See my mod list in my signature. I've had all these mods installed including beta tunes with the Cobb AP for almost 30,000 miles installed on my car and not a single problem. My fuel pump is just as strong as it needs to be. I can be WOT and it will never dip below 1600psi.

[djthom]

Originally Posted by FreeFlyFreak Woah, first time I have seen those numbers, 25% difference, no wonder the stock tune targets 9's for AFR up top 9 AFR leaned by 25% = 12 EDIT: In reality the car will be sensing an average of the cylinders with the O2 sensor, so you can figure the average shown by the wideband has a +/- 12.5% variation between the cylinders. So a better way to think about it would be, if the wideband AFR shows 10 at high rpm/cfm, the richest cylinder is around 8.75 and the leanest around 11.42 No wonder the car blows partial throttle, when its targeting at or close to stoic. I would expect the variation between cylinders to be less under lower flows, but even still. Lets say the flow variation at partial throttle is half that, +/-6%, that means @ 14.6 you are 12.77 to 16.69 richest to leanest if my calculations are correct.....

so how would we address this?

[802MS3]

What is JJ doing about his IM, doing the porting that whoosh does for people? hopefully we will see some numbers for it.

[FreeFlyFreak]

Originally Posted by djthom so how would we address this?

Well unless you do something with the intake manifold by making it more even flowing, you have no choice but to tune for the leanest cylinder.
Which looking at what was posted is number 3, by 12.5% leaner than the average, at max flow.

So in other words if you assume that you have a cylinder 12.5% leaner than the wideband is showing and tune for that then you should be safe AFR wise in all situations, until a manifold solution is available,

And, by the way, dont take what I say as gospel.
I dont claim to be an expert.
I am just making what seem to me to be logical inferences and assumptions from the manifold flow numbers that were posted by djuosnteisn.

[djuosnteisn]

Originally Posted by opt_ms3 What is JJ doing about his IM, doing the porting that whoosh does for people? hopefully we will see some numbers for it.

Similar to what whoosh has done, but slightly different. I'll let him post the specifics.

Not really a big deal at all, just not my place to divulge his project, haha.

Originally Posted by FreeFlyFreak And, by the way, dont take what I say as gospel. I dont claim to be an expert. I am just making what seem to me to be logical inferences and assumptions from the manifold flow numbers that were posted by djuosnteisn.

Way to point the finger, jerk, hahaha


Just tune for stoich at wot, and you'll be fine (disclaimer: please don't do this)

Or you can be like me and fatten the whole damn map up where needed. I don't have a single 14.6+ in any of my maps, especially around the dreaded 2500rpm.

[subparpunk03]

Originally Posted by opt_ms3 What is JJ doing about his IM, doing the porting that whoosh does for people? hopefully we will see some numbers for it.

I saw his post on another forum... can't remember which one.

IIRC he had his intake manifold ported by MAPerformance, and he has flow numbers for the after-ported head, and they look WAYYY good

*EDIT*
Found it:
http://forum.mazda6club.com/index.php?showtopic=115664

[pidass]

I don't know too much about porting but on the flow numbers after P&P runner #2 and #3 are the same as before just reversed. Either he transcribed it wrong or is it common to lose 20 CFM on a runner after a P&P job?

[djuosnteisn]

I think it's likely they were transposed, but i guess the possibility does exist that he could have disrupted optimal flow with a bad port job. Who knows, that may have even been his intention, though i doubt it.

[DaleNixon]

I never hit the gas hard below 3000RPM. I never got WOT in any gear above 4th unless I'm in the triple digit speeds. I cruise in 3rd gear at speeds below 35mph. I don't shift to 5th until I'm over 50MPH. I don't shift to 6th until I'm over 60MPH.

This driving style and Cobb's 105 stage 1 map seem to make my car extremely happy. To top it all off, I'm getting the best gas mileage I've ever seen now.

[06Speed6]

Originally Posted by FreeFlyFreak No wonder the car blows partial throttle, when its targeting at or close to stoic. I would expect the variation between cylinders to be less under lower flows, but even still. Lets say the flow variation at partial throttle is half that, +/-6%, that means @ 14.6 you are 12.77 to 16.69 richest to leanest if my calculations are correct.....

Yep its pretty scary, the funny part was that no one caught on to how important that is until I brought it up. You can seriously blow your shit up at 16+afr at part throttle. Its the only thing I have seen that really makes good sence as to why we blow part throttle and generally only on cyl #3.

[djuosnteisn]

So this leads back to heat, right? Would the rods be the likely suspect part to fail with 16.xx afr @ PT? Would there be any other indicative signs or things to look for in the failed engines thus far?

[SSinstaller]

Originally Posted by pidass I don't know too much about porting but on the flow numbers after P&P runner #2 and #3 are the same as before just reversed. Either he transcribed it wrong or is it common to lose 20 CFM on a runner after a P&P job?

The big improvement is the amount of variance between the runners... 5% is much better than the OEM 25% flow variance..

[Lex]

Gah, guys don't correlate the % difference in flow to air/fuel ratio. Just because the max flow of cylinder 3 through the IM (you're not even considering the head) is 25% above the lowest, it DOES not mean that you will get a 12.5% variance in AFR.

The amount of air that ends up in the chamber is a lot more difficult to calculate than this.

Easiest way to figure out? Get an EGT probe in each runner of the exhaust manifold. Or if you can afford it an AFR sensor in each runner. I guarantee you won't see the discrepancy of 25%.

[darth vader]

Yep, this is why testing engine parts in isolation on a flow bench and shooting for max CFM doesn't make for good performance on an engine, typically. To do this stuff, you need ALOT of experience and to understand/quantify it, a degree in Fluid Dynamics helps.

I can pretty much guarantee there isn't a 25% flow/volume/w.h.y measure difference cyl-to-cyl in what the running engine's chamber is seeing here, even without a degree in said subject. I have been building engines up for a few decades, though, so, I'll have to trade on that experience.

[djuosnteisn]

Originally Posted by Lex Gah, guys don't correlate the % difference in flow to air/fuel ratio. Just because the max flow of cylinder 3 through the IM (you're not even considering the head) is 25% above the lowest, it DOES not mean that you will get a 12.5% variance in AFR. The amount of air that ends up in the chamber is a lot more difficult to calculate than this. Easiest way to figure out? Get an EGT probe in each runner of the exhaust manifold. Or if you can afford it an AFR sensor in each runner. I guarantee you won't see the discrepancy of 25%.

Probably right, but... The flow variance would be most noticeable at peak torque (max ve), which is right around 2000-2500rpm, and that is where we always get knock. Coincidence?

[FreeFlyFreak]

Originally Posted by Lex Gah, guys don't correlate the % difference in flow to air/fuel ratio. Just because the max flow of cylinder 3 through the IM (you're not even considering the head) is 25% above the lowest, it DOES not mean that you will get a 12.5% variance in AFR. The amount of air that ends up in the chamber is a lot more difficult to calculate than this. Easiest way to figure out? Get an EGT probe in each runner of the exhaust manifold. Or if you can afford it an AFR sensor in each runner. I guarantee you won't see the discrepancy of 25%.

I agree 100% I was just posting an example.
25% is worst case scenario @ max flow. But it is the starting point.

You dont need one in each runner, only in the leanest cylinder. It is what they do in piston aircraft. That way you know the worst case of what is going on.

[Lex]

Originally Posted by FreeFlyFreak I agree 100% I was just posting an example. 25% is worst case scenario @ max flow. But it is the starting point. You dont need one in each runner, only in the leanest cylinder. It is what they do in piston aircraft. That way you know the worst case of what is going on.

You can also run one in the leanest cylinder but then you have no terms of comparison with the other ones.

What pressure was that flow achieved at ?

[FreeFlyFreak]

Originally Posted by Lex What pressure was that flow achieved at ?

Dunno. PM Jumping Jackson

[06Speed6]

Probably the industry standard 28" h2o or ~1psi.

Since we are in the subject of CFM across different parts, the head maxes out around ~200cfm @ .500" lift @ 28" h2o, or probably around 160cfm with the factory cam.

If I remember correctly, the TB will not max out either the IM or the head.

Which brings us to the issue of flow restrictions and VE through the IM. I still think that even though the IM out flows the head by a wide margin, there must be some realised real world flow difference because the IM flow differential is exactly something that could give us a reason why 75% of the blown engines out there blow on the same cyl.

[Trader]

What about the exhaust manifold? The log style manifold on our cars can cause flow disruptions between cylinders as well.

[Lex]

I have seen other cylinders blow - not just #3.

There are many likely causes to "blow". However, if we were always seeing a hole in piston #3 I would agree with your theory as it being dominant.

I think there may be some truth to the oil/fuel/meth ingestion that can be causing some of these "random" broken rods. The IM is likely not designed for wet/liquid flow. This means that liquid can and does pool inside as we've seen with people taking these apart. I would not be surprised if this is part of the issue.

[cpolly69]

Originally Posted by Trader What about the exhaust manifold? The log style manifold on our cars can cause flow disruptions between cylinders as well.

a lot of folks still blow with aftermarket exhaust manis -