I agree which is why I have stopped where I have.
I really dont need or want much more power than I have.

What do I see is, full bolted + aggressive tune + WOT shifting + stock rods = eventual trouble

There is so many variables that saying 350wtq is the limit is very much opinion, you can talk to him, or then have some one at dcr saying the rods look good for 500hp, since most of the failures have been low load and most of those that did werent making 350wtq, i still dont see that weve found a safe limit for the rods yet. Putting numbers out there is one thing but actual failures is another, 350wtq is high 300's if not 400whp on a big turbo so still good numbers.

doesn't this pretty much show that the weird failures had to do with either lack of fuel (higher than stock boost w/o a FP upgrade), or manufacturing issues where the tolerance was out of the given range (pistons seizing in the bore)?

I definitely vote that most blow ups were crankwalk/ flaw rather than too much power imo

The individual I quoted has seen many rods - and he designs and manufactures them. His words are of course opinion but there is some experience behind that. In the end, the material properties and cross sectional area tell you the strength of the rod.

Given a forged rod with our cross sectional area where it necks off, those were his estimates.

There are many factors that will never make this black and white but the more information we have the better off we are.

One thing to remember is that A LOT of rod failures happen at low load - especially when the rod has already been bent or compromised. This does not mean the damage was done at low load.

And his estimates jive exactly with the "fat part of the bell curve" of failures.

And now I'm convinced. Thanks again for delivering well reasoned opinions and now actual facts.

Lex, what do you think of these 2 alternate strategies (for a torque-oriented build, broad torque curve, peak hp depending on size of turbo)

-----------Plan A: Buy insurance
1. replacing the rods and pins only, same bearing sizes (which have different weights, to the whole setup would have to be balanced) and
2. setting the peak torque at more than the stock rods are safe at and less than a consenus estimate of what the pistons are good for
3. Taking care to have no torque spikes whether by design or accident
4. Addressing the ring issue if possible
5. Cer-coat top of piston to keep it in operating range while more heat (=power) is being put through the engine???

That keeps the daily-driver friendly oem pistons and save a few $. Not cheap, but cheaper than the full grenade effect.

-------------Plan B: Deep Pockets, Tight Wallet
Lower performance goals, but might bend the rods
1. Remove stock rods, inspect, and see if their compressive strength can be improved about 15% by some means such as heat/cryo treating. I do not know if that is possible. Also discard rods showing any signs of defect.
1B. If you own/work at/are on great terms with a machine shop: See if there's a stronger OEM rod with dimensions close enough to be subbed in with modifications (thicker rods can be planed down, slightly oversize big ends can be shimmed, etc); then you order custom pistons. That was done in the 'ol days before cheap stroker kits from China.
2. Since the builder knows he's running right up to design limits, pull the bottom end after a period of driving and using what's believed to be "safe" and inspect. Obviously this is not for the average person with a full time job etc, unless that job is building engines!
It may still let go (real world variables) which is why I call this the deep pocket option.
What level of force do the factory piston pins start flexing at


My 2c is that modern engineering methods plus MBAs whipping the engineers allowed/pushed Mazda to cut just a little too much material out of the rod. Maybe an ounce more material was needed for overload capacity given the expected use. It's fine in normal operation, but if the regulator hose slips off or if a car named Speed and marketed to the tuner crowd actually gets an intake and exhaust, maybe an MBC installed ... boom.

All that sounds very complicated.

I would go with:

a) stay under 300 whp
or
b) build the engine properly and go for the power you want.

Lex ---

Say, what (if anything) useful would we learn by making a compression fixture (rod held via bearings as if in engine) and slowly compressing till it bends?

Other than making a 2nd pass with a voodoo doll of Mazda MBAs that is ;-)

just want to touch on the fueling issue a bit as it's directly related to power output...

the new Ferrari 458 is 4.5L DI but NA making 562hp...with 2900psi fuel pressure...

our engines are good enough to make 300hp, not because it can't make more but development might be limited by production cost...

also, the Ferrari have 3 salvage pumps basically removing some of the funky airflow we have in our engines...good for 7wtrq, they say...

I know we're not driving Ferrari's but we can surely learn from more expensively developed DI systems...

You can only do comparison tests this way and you'd need one mother of a press and fixture.

As for your other post.

You can run the stock motor up to a certain point. Many people do and are happy.

The first level of upgrade would be replacing the rods only and head and main bolts. This leaves the stock pistons and needs no machining of the block. You don't need to rebalance anything - just make sure the rods are balanced themselves.

The second level is pistons and rods, all bearings, gaskets ... basically a full rebuild. I suggest doing this on a spare motor and swapping in when you're done.

No, there are no OEM rods that I would put in there from a different car. The big time and money expense is not the aftermarket rods, it's taking the motor out and taking it apart. If it was easy to drop in rods, people would do it as a first mod. $800 is less than a good FMIC kit.

Thats NOT what they are saying.

They are saying stay under 300 ft-lbs of TORQUE. Limit torque in lower RPMs...and let her rip in upper RPMs.

That is not what was said also, lex said he thinks they should be good for 300-350ft-lbs of torque, which is not to say that at 350 they will be at their limit but that is the safe zone for the stock rods from what i understand.

I have a quick question, can you set your psi so you don't spike with a cobb ap? That way I'm not putting too much load on my rods. My car isn't tuned and I don't know if I should save up alittle bit more money and buy some forged rods or get a cobb ap. Sorry to ask this question in this thread but it seems like Lex would be a good person to ask about this

so today i found out that the DI porsches actually get their entire head disassembled and hot tanked everytime they go in for service to remove the reversion deposits on the valves. apparently they cause alot more airflow restriction then just some gunk.

Wtf really?

yep, its a porsche, what you expect haha

In short: Yes.


How? Just read this thread:

http://www.mazdaspeedforums.org/foru...journey-32804/

If a 3-angle valve job can help performance...


You better bet a fucking stalagmite on your valves will hurt it.

Yep, thus why my engine is a meth addict...

lol i was JUST about to pwn you on the whole stalagmite vs stalactite debate but u actually got it right haha

Anyone able to give an outlook on how long it would take to pull the engine from the car, do a nice build like Lex said, (i.e. some pauter rods and arias pistons) and drop the engine back in the car?

Curious to guess at how long I'd be out of a speed6. a week's time?

Sounds simple, but its easier said then done, if its your dd it would not be a smart idea to do it as you will always run into problems, my best suggestion if its your only car is to build a second motor on the side then swap it in

It takes alot of planning to do quickly. Machine shops will always run slower than slow. You have to call those guys every day for a progress report, and eventually they get to your motor. Make sure you have all the parts there and ready to go. Also, have enough cash on hand for unexpected things (like my experience yesterday having to buy a deck plate for $550, wtf?).


I doubt it's possible to do in one week honestly. maybe two at the fastest.

If you have the money, it's easier to just buy a spare motor, build it and then swap the two in a day or so. Then you can sell your stock long/short block and recoup the money.

Thanks for the fast responses guys....... basically, it is my "daily" but I do have another car I can drive around until it's finished up.

The best part is, my shop is actually my best friend LOL. He's a Bimmer Fanatic but he can build and tune a car like nobody's business, lol, so I trust him. He pretty much has everything a full-fledged shop has, minus a lift, and all the tools needed.

Since I actually prefer to work on my car instead of a shop, I was considering hisself and myself performing the work. I was just trying to get a take on a feasible timeline in which said modification could be done.

2 or 3 weeks would be acceptible as well, since I can still drive my other car around, I just didn't want to be out of my MS6 for too long (honest to god I love driving this car :D)

Meth FTW!