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Old 04-11-2012, 02:22 AM   #1
sdmideas
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Default oem sti rods 2.1l stroker limits

looking into using oem sti rods for a 2.1l stroker and i had a quick question -

what is the limit of the sti rod when used with the lighter 2.0 pistons?

I have seen that many failure reports involve over rev in the 9k plus range...many of these are also with the 2.5 piston though...

whats the consensus? i know theres a handful of variables here but im really interested if someone has some pictures of sti rod failures with 2.0 pistons
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Old 04-11-2012, 07:08 AM   #2
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The question should be, what are your power goals?

I broke a rod with 434wtq. It broke BAD. I'm not saying that those rods aren't tough, I'm just saying you may want to build stronger in the first place so it's less likely that you have issues down the road.
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Old 04-11-2012, 09:47 AM   #3
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The question should not be "what are your power goals" that's been discussed and really isn't a conversation to be had via interwebz. However to avoid this comment the build will be paired with an evo3 16g(absolute power is not the goal)

The question is what are the experienced limits of the sti rod with 2.0l sized pistons.

Since you broke a oem sti rod at 430wtq I have a few ?s for you... What piston was attached to it? What was the weight of that piston? At what rpm did the rod fail? What other components yielded? What fuel/oil do you use? Do you have pictures of the failed rod?


Id like to avoid turning this thread into a discussion of which parts should be used in who's build - theres a million of those already...I'd also like to avoid lettin this degrade into a discussion of 2.0 vs 2.5, 2.35 vs 2.2...

Thanks to all who take the time to read this. I am especially reaching out to those who have a handful of different build platforms under their belts since they are the guys that have most likely disassembled more motors than anyone else on here...you know who you are
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Old 04-11-2012, 01:16 PM   #4
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I didnt mean to start a power discussion, I wasnt sure if you already thought about the issue.

The rods were connected to ej257 wiseco pistons that weigh 371 grams. I had a 10mm oil pump and used 10w30 weight oil. After it snapped, The rod got thrown around and damaged it's piston and cylinder wall. Other than that no other components were damaged and the bearings looked fine.

I had a 7500 rev limit, but the rod broke at ~4000rpm on a WOT pull.

It broke right in the middle of the rod.
I'll post a picture here in a second.
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Old 04-11-2012, 01:25 PM   #5
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Thank you for your very informative response!!! Pics will be the icing on the cake!
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Old 04-11-2012, 03:28 PM   #6
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I want to hear also. I'm doing a 2.1L stroker as well and already have some sti connecting rods. I hope they will work for me.
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Old 04-11-2012, 04:04 PM   #7
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Quote:
Originally Posted by chet.wrb View Post
I want to hear also. I'm doing a 2.1L stroker as well and already have some sti connecting rods. I hope they will work for me.
X2 but mine are the ej255 rods. From my "in depth/at work/on the ****ter" research, they're the same thing.

Now to find a crank to use...
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Old 04-11-2012, 04:28 PM   #8
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Quote:
Originally Posted by sdmideas View Post
The question should not be "what are your power goals"
No, I think that should be the question. We don't need to "reinvent the wheel" so to speak. The torque limits (compression strength) and RPM limits (tension strength) of the STI rod with a 99.5mm piston are more than well documented. With your little turbo on pump gas you should be well within those limits unless you needlessly rev it well out of its efficiency range. Throw in the fact that you have a lighter piston and you have less to worry about on the tension stress end. I'd install ARP rod bolts just to sleep better at night, but that's about it.
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Old 04-11-2012, 05:27 PM   #9
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Quote:
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No, I think that should be the question. We don't need to "reinvent the wheel" so to speak. The torque limits (compression strength) and RPM limits (tension strength) of the STI rod with a 99.5mm piston are more than well documented. With your little turbo on pump gas you should be well within those limits unless you needlessly rev it well out of its efficiency range. Throw in the fact that you have a lighter piston and you have less to worry about on the tension stress end. I'd install ARP rod bolts just to sleep better at night, but that's about it.
to satisfy those who must have a number it will be in the ballpark of 400whp on e85. I understand that there is plenty of information available about the failures of sti piston rod combos. I was trying to see how many who have ACTUALLY built strokers have managed to break their rods.
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Old 04-11-2012, 06:29 PM   #10
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What pistons are you going with? My Mahle stroker 4032 pistons and pins are 105g lighter than the EJ257 piston and pin.

OEM Sti piston: 414g
Mahle 4032 2.12L: 338g (they say 333g in literature, mine actually weigh 338g)
Weight savings from pistons: 76g

OEM Sti wrist pin: 152g
Mahle wrist pin: 123g
Weight savings from pins: 29g

That's almost 20% less which is a significant weight savings IMO.

I'm running Eagle rods in my stroker because I got them for $160 new otherwise I would have gone Sti rods.
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Old 04-11-2012, 06:58 PM   #11
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lol the mahle 4032's are also what im using. stock bore
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Old 04-11-2012, 07:43 PM   #12
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now I know why I got your PM
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Old 04-12-2012, 02:26 PM   #13
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Quote:
Originally Posted by sdmideas View Post
to satisfy those who must have a number it will be in the ballpark of 400whp on e85. I understand that there is plenty of information available about the failures of sti piston rod combos. I was trying to see how many who have ACTUALLY built strokers have managed to break their rods.
I had a Cobb 2.1L YEARS ago, but it also had Cobb rods.

I just didn't see why you would need to find people with a 2.1 that broke a rod when there are about a million 2.5L running the same rod, same crank with a much heavier piston.
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Old 04-12-2012, 02:39 PM   #14
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Yea, the more I analyze the strength of the sti rod, the more I realize that it's plenty strong for a 400hp 2.1L stroker. The only real gains by going aftermarket rods is for weight savings, which for some is more than enough reason to spend the $300-500 for aftermarket rods vs the $100 for good sti rods.

For me.... I'll stick with the STI rods I already have.
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Old 04-12-2012, 02:48 PM   #15
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CKxx.....cuz id like to spin the dam n thing

seriously though it looks like the 2.5 guys snap these when they spin past 9k...id like to be comfy at 8500+, i dont want to sit there all day but id like to have the room.
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Old 04-12-2012, 03:11 PM   #16
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I spin my sti rods with je pistons in my 2.5 to 7500 at least once a day at 440whp and havent had a problem.
mechanical overrev is when they break or bend.
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Old 04-12-2012, 03:52 PM   #17
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Quote:
Originally Posted by sdmideas View Post
CKxx.....cuz id like to spin the dam n thing

seriously though it looks like the 2.5 guys snap these when they spin past 9k...id like to be comfy at 8500+, i dont want to sit there all day but id like to have the room.
I can respect that. I had a 2.35L for a period after the 2.1. I'd honestly do some aftermarket rods if that is the case though, but I'm one for overbuilding something so that it's not something to worry about later.
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Old 07-10-2012, 01:49 PM   #18
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Glad I found this thread! Also doing a 2.1 build and after reading this I can save about $250 on rods!
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Old 07-10-2012, 02:56 PM   #19
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I am also doing a 2.1 build, and for precaution and weight saving, i thought that the extra 250 was worth the money
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Old 07-11-2012, 12:49 AM   #20
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I just built my 2.1 400 is to small of a number, I might get bored with that, need room to mod.
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Old 07-27-2012, 12:36 PM   #21
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^how did it turn out? Break in? Noise? Power? Response?
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Old 11-08-2012, 01:19 PM   #22
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Quote:
Originally Posted by mod maniac View Post
I just built my 2.1 400 is to small of a number, I might get bored with that, need room to mod.
That's awesome.

See for me... I'm thinking of doing a 2.1 stroker and matching it up with my 18g XT. My goals are VERY modest. 300/300.

I drive this car every day. I love my car as it is and it's only got about 205whp right now. 300-325 is more than enough for me and I have zero desire to go higher. I just want it to be able to take thorough beating. I drive the piss out of my cars but I take care of them so I expect them to last. My wrx has 213k on it right now. LOL!
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Old 11-09-2012, 04:19 PM   #23
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My Setup:

2008 Nitrated STi Crank
Mahle 4032s
2008 STi Cams (Hollow)
Sti Rods WITH ARP BOLTS.

This setup makes me feel happy at 350HP/300TQ 8500RPM

oohhhhh yeah and a Twin Scroll VF37....
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Old 12-07-2012, 11:42 PM   #24
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Quote:
Originally Posted by elsuicida View Post
My Setup:

2008 Nitrated STi Crank
Mahle 4032s
2008 STi Cams (Hollow)
Sti Rods WITH ARP BOLTS.

This setup makes me feel happy at 350HP/300TQ 8500RPM

oohhhhh yeah and a Twin Scroll VF37....
Who built and tuned it? Local?
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Old 12-08-2012, 09:34 AM   #25
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speaking from very personal experience with my 2.1L time attack GC8 it is making 450hp on E85 and I have had a couple of BIG failures at big rpm (8500rpm)
hard to tel weather it was rod or bearing in a couple cases but 1 was definately a rod failure and that was using Argo rods.
My car is dry sumped and has all the best internal bits available.
If you want it to last spend a little bit more initially and get the right bits.
Trust me it will work out a LOY cheaper than if you have a failure

Nev
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