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Old 06-23-2016, 07:21 PM   #1
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Default Weakest points in engine?

Hi all.

Curious to know at what levels of power and/or boost components start failing. Ive read time and again that rods will go at c.250bhp in both the 1.6 and 1.8 NA and NB, but I'm more interested in once stronger rods pistons (and potentially crank) have been fitted (crank obviously 1.8). Where are the weaknesses?

Thanks in advance for any input, and apologies if this is a common question by I couldn't find what I was looking for through searching.
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Old 06-23-2016, 07:32 PM   #2
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No one that I can think of (on this site) has tested the limits like that around here, and those that did break stuff broke different things, so the results are inconclusive.

You start breaking things like transmission, axles, etc and 90% of your drivetrain becomes a consumable.
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Old 06-23-2016, 07:49 PM   #3
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No one that I can think of (on this site) has tested the limits like that around here, and those that did break stuff broke different things, so the results are inconclusive.

You start breaking things like transmission, axles, etc and 90% of your drivetrain becomes a consumable.
So you roll the dice and take your chances? I'm not aiming for huge figures, so if those upgrades and the rest of the lump will be safe to 300 then I have no worries. Just wanted to make sure everything is well within tolerance.

Thanks.
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Old 06-23-2016, 07:52 PM   #4
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300 is no problem. we have people at 450-500 with not much more than rods/pistons
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Old 06-23-2016, 07:58 PM   #5
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So you roll the dice and take your chances? I'm not aiming for huge figures, so if those upgrades and the rest of the lump will be safe to 300 then I have no worries. Just wanted to make sure everything is well within tolerance.

Thanks.
Just put a 2jz in yo
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Old 06-23-2016, 08:05 PM   #6
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I daily drove a miata over 30k miles at over 300whp on a stock NA8 bottom end with eagle rods (stock pistons and everything else). My last miata was at ~370whp for about 5k miles before I broke the 6 speed transmission.

Maybe I've just been lucky, but I've never broken anything in the motor other than things that are the direct result of my shoddy mechanic skills.



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Old 06-23-2016, 08:07 PM   #7
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Just put a 2jz in yo
Ha I'd love to but I think the only way to get one in the UK is out a Supra.
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Old 06-23-2016, 08:14 PM   #8
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Just put a 2jz in yo
Quote:
Originally Posted by pdexta View Post
I daily drove a miata over 30k miles at over 300whp on a stock NA8 bottom end with eagle rods (stock pistons and everything else). My last miata was at ~370whp for about 5k miles before I broke the 6 speed transmission.

Maybe I've just been lucky, but I've never broken anything in the motor other than things that are the direct result of my shoddy mechanic skills.



Wow I'd have been watching the bonnet the whole time waiting for something to smash up through it.
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Old 06-23-2016, 08:16 PM   #9
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The only time I let somebody besides me drive my car my cam broke. and I'm only pushing 185whp. No idea how he did it, but nonetheless it was done.
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Old 06-23-2016, 08:19 PM   #10
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I have an expensive motor now, but if it were to break, I'd use FM wiseco pistons, cheap ebay rods, an ATI damper (already have it, so I'd reuse it) and that's it. Boost the nuts off of it. OEM gaskets/seals, stock everything else.

I ran 20+ pounds of boost on a rods-only motor for years, though I did break stock pistons around 350whp (on pump gas, pdextra is on E85). I think a rods only motor would live on E85 at 350whp, pdextra's car is a great example of this.
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Old 06-23-2016, 08:35 PM   #11
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Autocrossers break transmissions and axles, drag racers break axles and differentials, road racers break transmissions and CV joints.
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Old 06-23-2016, 08:39 PM   #12
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...road racers break transmissions and CV joints.
And rear hubs.

--Ian
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Old 06-23-2016, 11:03 PM   #13
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Daily Drivers break speed limits.
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Old 06-24-2016, 10:23 AM   #14
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Daily Drivers break speed limits.
I have seen a street only car strip out 3rd on a 5 speed. He was around 280-290hp to the rear though (on a 1.6!).

Yeah, from what I have seen/read, the motors are good with rods, pistons, damper and an oil pump for well above the power level where you will need to fix everything else in the drive train.
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Old 06-24-2016, 01:08 PM   #15
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Consensus is:
1) Rods will break somewhere in the mid 200s. Where exactly depends on luck, how good of a tune, how much torque you make, etc.
2) There is dispute as to whether pistons are necessary or not. I think they give insurance personally and they're cheap compared to the total cost of a rebuild.
3) Oil pump gears are notorious for not liking big power or high rpm. Might as well upgrade the harmonic damper as well while you're in there.
4) Everything else is capable of holding immense amounts of power.
5) Except the transmission, which will become a wear item past 300whp. Six speed is stronger than the five speed, but neither one of them is going to tolerate more than say 350whp for long especially for sustained track duty.

The real annoying problem you'll eventually run in to is that the miata aftermarket has great resources for fixing every conceivable problem except transmission strength. A bunch of people here have awesome builds... and a couple of spare trannies sitting in the garage for when their OEM one breaks again.
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Old 06-24-2016, 01:27 PM   #16
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Many are keeping their fingers crossed for the hopefully near future T5 conversion setup
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Old 06-24-2016, 03:20 PM   #17
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His website reported being a week away from production... like five or ten years ago. I would love one too but I'm not holding my breath.
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Old 06-24-2016, 03:38 PM   #18
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Im not talking about begi. They are basically extinct.
Im talking about andrew/tse
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Old 06-24-2016, 04:10 PM   #19
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Quote:
Originally Posted by x_25 View Post
I have seen a street only car strip out 3rd on a 5 speed. He was around 280-290hp to the rear though (on a 1.6!).

Yeah, from what I have seen/read, the motors are good with rods, pistons, damper and an oil pump for well above the power level where you will need to fix everything else in the drive train.
Mine is also a daily driver and broke 3rd gear of a 5speed. Virtualdyno tells my something like 275whp and 300wtq(lbft)
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Old 06-24-2016, 07:13 PM   #20
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I'm getting a cryo treated 6 speed, with a few billet bronze parts. I doubt I'll break it soon, but I'm curious how it holds up to frequent racetrack/drag/very hard street driving. I only expect around 200wtq and 260whp.
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