Anyone have failure analysis data on oem miata rods?
#5
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What data, exactly, do you want? Except for a very few of us, all we have is personal anecdotes, however well documented.
On that note, from personal experience (the car Laz) - 230 ft/lbs in a heavily tracked environment bends stock rods. I have in my posession said bent rod(s). They will eventually become tap handles.
Now, one might argue that in any engine environment, especially a turbo engine environment, ft/lbs produced of torque is not 100% reliable indicator of cylinder pressures and of force applied to said rod, and one would be correct.
So, 230 ft/lbs when run through stock MSM manifold through stock IHI turbo with upgraded compressor wheel equals ... bent rods.
Greddygalant or Curly can chime in on exhaust sizing, but, really, the manifold and the turbo itself were the major contributing factors to back pressure IMO.
On that note, from personal experience (the car Laz) - 230 ft/lbs in a heavily tracked environment bends stock rods. I have in my posession said bent rod(s). They will eventually become tap handles.
Now, one might argue that in any engine environment, especially a turbo engine environment, ft/lbs produced of torque is not 100% reliable indicator of cylinder pressures and of force applied to said rod, and one would be correct.
So, 230 ft/lbs when run through stock MSM manifold through stock IHI turbo with upgraded compressor wheel equals ... bent rods.
Greddygalant or Curly can chime in on exhaust sizing, but, really, the manifold and the turbo itself were the major contributing factors to back pressure IMO.
#6
Agreed with Mobius, the real answer is "depends".
I've tuned many many miata's at this point, and seen everything from 230wtq bending rods to 270wtq stock rods holding up for over a year with non-stop abuse.
There are eleventy billion variables. In no particular order:
How early does the car make the torque? How does it come on? How is the car used? How much backpressure/restriction is it working with? etc etc etc there's way too much to list.
The latest car I tuned that bent stock rods is sshamrock. No det, and I don't recall if they bent or snapped, but all 4 were banana'd. 250whp and 230wtq on a mustang dyno if I recall (you can look it up, you even posted in that thread). This was a few months ago.
I've tuned many many miata's at this point, and seen everything from 230wtq bending rods to 270wtq stock rods holding up for over a year with non-stop abuse.
There are eleventy billion variables. In no particular order:
How early does the car make the torque? How does it come on? How is the car used? How much backpressure/restriction is it working with? etc etc etc there's way too much to list.
The latest car I tuned that bent stock rods is sshamrock. No det, and I don't recall if they bent or snapped, but all 4 were banana'd. 250whp and 230wtq on a mustang dyno if I recall (you can look it up, you even posted in that thread). This was a few months ago.
Last edited by 18psi; 04-06-2018 at 12:52 AM.
#7
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So we have our (based on my 10 year history here) mt.net axioms: (all based on man usage, track environments)
5 speed dies before usable power is achieved, except for sonofthehill
6 speed is good for 230-250 wtq road race environment. At 300wtq w/hoosiers, gear destruction in almost any gear is virtually guaranteed (see bbundy posts, use google fu)
junkyard vvt 10:1 compression engine is good for lots of turbo race time, at 200whp, if boost is controlled (see rover gets a turbo)
and in general, keep wtq < 200, stock rods survive. And the transmission will survive.
Marcello, what's the goal here? I don't think anybody on this forum has recorded actual cylinder pressures. I don't know how that's possible outside of an OEM environment.
If you want a record of "this rod bent at this wheel torque, given these parameters and usage" then that's a reasonable goal.
5 speed dies before usable power is achieved, except for sonofthehill
6 speed is good for 230-250 wtq road race environment. At 300wtq w/hoosiers, gear destruction in almost any gear is virtually guaranteed (see bbundy posts, use google fu)
junkyard vvt 10:1 compression engine is good for lots of turbo race time, at 200whp, if boost is controlled (see rover gets a turbo)
and in general, keep wtq < 200, stock rods survive. And the transmission will survive.
Marcello, what's the goal here? I don't think anybody on this forum has recorded actual cylinder pressures. I don't know how that's possible outside of an OEM environment.
If you want a record of "this rod bent at this wheel torque, given these parameters and usage" then that's a reasonable goal.
#8
I do a shitload of conversions and I tune them to 210-220 ftlb on a dyno dynamics on shootout, not strapped, chocks only. I have done 100+ and have only a couple of failures in total. I use an 0.86 rear and 3" exhaust on everything and the dyno sheet always has a graph you can lay a straightedge against.
Dann
Dann
#14
If goal is to maximize reliability of a given part under load, minimizing peak loading will improve life.
#16
If anyone has exhaust manifold pressure data and their spark and fuel maps, that bent stock rods we can calculate cylinder pressure. Failing the emap data an accurate turbine map from the maker of the turbo would suffice.
In general if you're in it for big power numbers on stock rods you want to run a big lazy turbo with a ratio of map to emap well over 1, run conservative timing, use e85 and run leaner.
In general if you're in it for big power numbers on stock rods you want to run a big lazy turbo with a ratio of map to emap well over 1, run conservative timing, use e85 and run leaner.
#18
Bending stock rods is directly proportional to peak cylinder pressure. Peak and average are not the same. Leafy described it pretty well on how to keep a stock motor alive. I should drop a stock motor in my car and see what I can get out of it. Just need a VVT motor that's stock and ready for a beating!
#19
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In simple terms, power is directly proportional to average cylinder pressure. More boost means more power, and higher average cylinder pressure. Double the power, you have doubled the average cylinder pressure more or less.
Bending stock rods is directly proportional to peak cylinder pressure. Peak and average are not the same. Leafy described it pretty well on how to keep a stock motor alive. I should drop a stock motor in my car and see what I can get out of it. Just need a VVT motor that's stock and ready for a beating!
Bending stock rods is directly proportional to peak cylinder pressure. Peak and average are not the same. Leafy described it pretty well on how to keep a stock motor alive. I should drop a stock motor in my car and see what I can get out of it. Just need a VVT motor that's stock and ready for a beating!