Quote:
Originally Posted by swarb
No, I don't want to talk about tunes, I want to talk about your "theory"
Snipped from one of your links-
"What we're thinking is either a severe overheat due to sustained high speed/high boost operation without an oil cooler on pump gas, or possibly too tight of ring gaps from the factory leading to this failure when combined with the high temperature condition."
Cooling issue is not a rod issue, it just caused damage to the rod.
Piston ring gap is not a rod issue.
So explain your theory again? Weak rods because of too much power? or? What evidence do you have to back this up? Because those links BOTH say oil/heat issues.
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Ok now I understand what your saying, I apologize if I was short.
In the link I only was referring to the pictures as a reference my mistake for not saying that. In his failure you can see obvious piston scuffing I would venture to lean toward misgapped rings causing a drag on the cylinder from increased cylinder temps do to boosting or a possible piston pin failure or small end rod bushing failure. I can not say for sure without personally inspecting it myself and measuring everything.
Now with that said I base my findings on all the rods that I have seen that snap off with no piston scuffing. In all the cases that were not catastrophic to the point I could not take the big end off the crank and check the bearing I found all the breakage was in close proximity. There is no sign of oiling or heat being a issue either. I never sent the rod out for a hardness test but from all other indications its weak by design. As you can see they are a basic rod design. Not like a Pauter rod or a H-beam. All in all I would venture to say its the material they are made of is brittle from the manufacturing process of the cracked cap design. Then again they were never designed to be boosted in the fa20 at this compression level. So in closing boosting lets say 20psi in a 12.5 compression motor creates a compression level close to if not over a diesel engine and the rod simply can't take it.
You are running 20 PSI of boost at an altitude of 500 feet. Your motor's static compression is 12.5 :1. At this boost level and altitude your effective compression ratio is 29.41 :1, and without altitude correction your compression ratio would be 29.51 :1.
Boost and Altitude Correction to Compression
You are running 15 PSI of boost at an altitude of 500 feet. Your motor's static compression is 12.5 :1. At this boost level and altitude your effective compression ratio is 25.16 :1, and without altitude correction your compression ratio would be 25.26 :1.
Boost and Altitude Correction to Compression
You are running 10 PSI of boost at an altitude of 500 feet. Your motor's static compression is 12.5 :1. At this boost level and altitude your effective compression ratio is 20.90 :1, and without altitude correction your compression ratio would be 21.00 :1.
No way with these ratios can that rod survive
Now lets do a wrx FA20DIT
Boost and Altitude Correction to Compression
You are running 15.9 PSI of boost at an altitude of 500 feet. Your motor's static compression is 10.6 :1. At this boost level and altitude your effective compression ratio is 21.97 :1, and without altitude correction your compression ratio would be 22.07 :1.
As you can see its a huge difference and the wrx is throwing rods too.
My 1997 Dodge 5.9 Cummins is only 16.3.1 compression and those rods are huge in comparison