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View Poll Results: How much torque are you putting through you stock rods?
200-225 ft/lbs 22 50.00%
225-250 ft/lbs 13 29.55%
250-275 ft/lbs 3 6.82%
275-300 ft/lbs 1 2.27%
> 300 ft/lbs 1 2.27%
I broke 'em. 4 9.09%
Voters: 44. You may not vote on this poll

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Old 06-09-2009, 05:37 PM   #1
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Default Rods... and Torque

Ok, I'll grant you that if I were in our position reading this, my first inclination would probably be to tell me to use the damn search function. Unfortunately, I'm rather lazy.

I'm looking to gather some statistical data on what kind of torque figures people around here have been able to achieve on the stock rods without breaking anything.

I don't want to hear about how I'd be an idiot not to pick up a set of the M-tuned rods for only $299 during the group buy, or hear about how you're making 950 ft/lbs at idle on your Carrillos.

I also don't want to hear about how you broke your stock rods because you're an idiot and you tried to 18 PSI on a powercard at 15:1 AFR and cracked three pistons in half. On the other hand, if you did kill a rod on an otherwise well-tuned engine that wasn't detonating, that'd be good info so long as you've got a dyno chart to show how much it took to do.
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Old 06-09-2009, 05:52 PM   #2
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Joe, sorry, I can't help you with a dyno sheet unless Jared (leatherface) has one that I don't know about, but I bent an OEM rod (cyl. 1) while starting the car oddly enough. The actual cause is unknown, the cylinder was not hydrolocked or anything out of the ordinary, I think the rod had begun stressing long before, and that particular start was it's last hurrah. I can tell you at least that the setup was a stock '95 motor, older FMII kit with GT2560R, BEGi DGDP, FM exhaust, at 15psi with a solid tune. No detonation to note either. Not really sure what the average HP output of that would be, but hopefully it will give you an idea.

Pics because why not?

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Old 06-09-2009, 06:48 PM   #3
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226 torque. so just barely a D-

these are 2001 stock bottom end rods and pistons. runs like a clock. lost count of miles.
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Old 06-09-2009, 07:07 PM   #4
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240ft/lbs on a stock 95 motor and still holding on, but only ~3000 miles on it so far.
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Old 06-09-2009, 07:08 PM   #5
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Joe, much like 5-speed tranny data or 1.6 rear end data, it really depends on how you drive it. If you daily drive it, run up the occasional onramp, don't overrev, and don't overboost, I think 230-240tq is doable on a long-term basis. If you overrev the motor, track it, and generally beat the **** out of it, you can toast a stock rod at 200tq.

Short, lazy-**** answer: If you want reliability over 220whp, you should probably have forged rods in the motor.
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Old 06-09-2009, 07:13 PM   #6
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but i drive like a jackass! I bark the tires in 2nd or higher almost every time I drive it.
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Old 06-09-2009, 07:21 PM   #7
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Sav- I think it has more to do with accurate, well tuned, ignition timing
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Old 06-09-2009, 07:28 PM   #8
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Detonation plays a big part, but so do revs. If you spend a lot of time at 6500+rpm, the rods won't last as long.
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Old 06-09-2009, 07:29 PM   #9
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Revs will kill rod bolts before it bends a rod.
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Old 06-09-2009, 08:27 PM   #10
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Spec Miatas overrevved to the mid 7k range have been found to have stretched rods. Stretching a rod is the same as coldworking it, which drops its tensile strength and weakens it.
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Old 06-09-2009, 08:29 PM   #11
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Rods are cheap now...
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Old 06-09-2009, 08:46 PM   #12
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Well if we are going to get to nitty gritty. Were these spec miata rods measured before hand and then afterward, or are these stretch measurements based on the book value of length? How much was the supposed stretch?
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Old 06-09-2009, 09:08 PM   #13
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overrevving during a missed shift (>redline) is another potential failure path. puts more strain on the rod than compression.
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Old 06-09-2009, 09:35 PM   #14
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Quote:
Originally Posted by Savington View Post
Spec Miatas overrevved to the mid 7k range have been found to have stretched rods. Stretching a rod is the same as coldworking it, which drops its tensile strength and weakens it.
I over-revved my motor to >8000 once, 2 weeks later one rod popped. 205 ft-lbs.
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Old 06-09-2009, 09:43 PM   #15
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Quote:
Originally Posted by neogenesis2004 View Post
Well if we are going to get to nitty gritty. Were these spec miata rods measured before hand and then afterward, or are these stretch measurements based on the book value of length? How much was the supposed stretch?
I have no idea. Bent rods aren't the only failure mode. Mine just straight up broke during a 3800rpm cruise.
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Old 06-09-2009, 09:45 PM   #16
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Quote:
Originally Posted by Braineack View Post
Rods are cheap now...
Yeah, thanks for that reminder. I had no idea.

Trouble is, I know how things work when I start tearing into engines. If I do have to pull the motor and open it up, it'll go something like this:

Well, while I'm in here I might as well toss in some lower CR forged pistons. So I'll just drop the block off at the machine shop to have it overbored.

Hmm. The machinist said it'd be a few weeks before he could get to my block, so there'd be plenty of time for me to send the head out to Replika Maschinen. Guess while it's there I'd be an idiot not to splurge for oversize valves and the fancy springs.

And you know, I've really been drooling over that absurdflow manifold lately. Of course, I'll need a new turbo to sit on it. And a new downpipe. And I might as well ditch this 2.5" exhaust system for something a bit bigger.

Ooh, can't forget the billet OPG setup. Hey, look! A whole custom-machined high-flow oil pump. What the hell- it's only money.

Wow, glad that finally all done. Motor's back together and in the car, time for a test drive. It'd be a waste not to crank this baby up to 20 PSI or so. (loud noise, followed by quietness.) Huh... What the hell are all these vaguely transmission-shaped bits of metal doing by the side of the road?

I hear the ZF S6-40 is supposed to be pretty strong. We'll just machine off the bellhousing here...
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Old 06-09-2009, 09:53 PM   #17
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Thats what happened with the motor I sold to Tom. Started out as rods and pistons. All said and done I spent almost 5k. The only stock parts on it are the block, oil pan, and the head casting.
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Old 06-09-2009, 10:52 PM   #18
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Old 06-10-2009, 12:27 AM   #19
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Quote:
Originally Posted by Braineack View Post
Rods are cheap now...
Yup.. $299 with ARP 2000 bolts
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Old 06-10-2009, 01:20 AM   #20
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https://www.miataturbo.net/forum/t20544/

Not sure if this is of any help but here it is.
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